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DZS 907-2 : 2015
ISC
Edition1
Draft for Public Comment
Draft Zambian Standard
ELECTRICITY DISTRIBUTION INFRASTRUCTURE
PART 2 - OPERATIONS AND MAINTENANCE GUIDE
ZAMBIA BUREAU OF STANDARDS
This draft standard is for committee
discussion only. It must not be used or
referred to as a Zambian Standard
i
DATE OF PUBLICATION
This Zambian Standard has been published under the authority of the Standards Council of the Zambia Bureau of
Standards on ……………….
ZAMBIA BUREAU OF STANDARDS
The Zambia Bureau of Standards is the Statutory National Standards Body for Zambia established under an Act of
Parliament, the Standards Act, Cap 416 of 1994 of the Laws of Zambia for the preparation and promulgation of
Zambian Standards.
REVISION OF ZAMBIAN STANDARDS
Zambian Standards are revised, when necessary, by the issue of either amendments or of revised editions. It is
important that users of Zambian Standards should ascertain that they are in possession of the latest amendments or
editions.
CONTRACT REQUIREMENTS
A Zambian standard does not purport to include all the necessary provisions of a contract. Users of Zambian standards
are responsible for their correct application.
TECHNICAL COMMITTEE RESPONSIBLE
This Zambian Standard was prepared by the Technical Committee 5/7 on Electricity Distribution Infrastructure upon
which the following organizations were represented:
Copperbelt Energy Corporation (CEC)
Energy Regulation Board
Engineering Institution of Zambia (EIZ)
Kansanshi Mines
Konkola Copper Mines
Lunsemfwa Hydro Power Company (LHPC)
Ministry of Mines, Energy and Water Development - Department of Energy
Rural Electrification Authority (REA)
University of Zambia (UNZA)
Zambia Bureau of Standards
ZESCO Limited
Zambia Bureau of Standards, Email: [email protected] /[email protected]
Lechwe House website: www.zabs.org.zm
Freedom Way South End
P.O. Box 50259, Lusaka
ii
TABLE OF CONTENTS
FOREWORD .................................................................................................................................................v
1. SCOPE ..................................................................................................................................................1
2. NORMATIVE REFERENCES ..........................................................................................................1
3. ABBREVIATIONS AND DEFINITIONS .........................................................................................1
3.1 Abbreviations ............................................................................................................................ 1
3.2 Definitions ................................................................................................................................. 2
4. SAFETY ...............................................................................................................................................3
5. SUBSTATION .....................................................................................................................................3
5.1 General ...................................................................................................................................... 3
5.2 General conditions at substations ........................................................................................... 3
5.3 Transformers ............................................................................................................................ 4
5.3.1. Power/Distribution transformers .................................................................................. 4
5.3.2. Instrument transformers ............................................................................................... 6
5.4 Switchgear ................................................................................................................................. 6
5.4.1 Busbars and associated structures ................................................................................ 6
5.4.2 Circuit Breakers ........................................................................................................... 6
5.4.3 Disconnector/Isolator ................................................................................................... 8
5.4.4 Ring Main Units ........................................................................................................... 8
5.4.5 Feeder Pillars ............................................................................................................... 9
5.5 Capacitor Banks ..................................................................................................................... 12
5.5.1 General ....................................................................................................................... 12
5.5.2 Storage of capacitors .................................................................................................. 13
5.6 Insulating oil requirements .................................................................................................... 14
5.7 Oil Containment Tank ........................................................................................................... 14
5.8 Fire Blast Walls ...................................................................................................................... 14
5.9 Substation yard junction boxes and marshalling kiosks ..................................................... 14
5.10 Control gear ............................................................................................................................ 15
5.11 Batteries and Battery chargers ............................................................................................. 18
5.11.1 Safety ......................................................................................................................... 18
iii
5.11.2 Types and Frequency of Maintenance for Substation Batteries ................................. 18
5.11.3 Failure Modes of the Batteries ................................................................................... 18
5.11.4 Details of Maintenance Activities .............................................................................. 18
5.12 Metering .................................................................................................................................. 19
5.12.1 General ....................................................................................................................... 19
5.12.2 Scheduling and frequency .......................................................................................... 19
5.12.3 Maintenance actions ................................................................................................... 19
5.13 DC supply equipment ............................................................................................................. 20
5.14 Relay rooms............................................................................................................................. 20
5.15 Auxiliary Equipment .............................................................................................................. 21
5.15.1 Substation lighting ..................................................................................................... 21
5.15.2 Emergency lighting .................................................................................................... 21
5.15.3 Security Lighting ....................................................................................................... 21
5.15.4 Fire suppression systems ............................................................................................ 21
5.16 Equipment Earthing............................................................................................................... 21
5.16.1 Inspections ................................................................................................................. 21
6. OVERHEAD DISTRIBUTION ........................................................................................................23
6.1 General Line Maintenance .................................................................................................... 23
6.2 Detailed inspections ................................................................................................................ 23
6.2.1 General ....................................................................................................................... 23
6.2.2 Towers........................................................................................................................ 23
6.2.3 Steel and concrete poles for power lines .................................................................... 24
6.2.4 Wood pole power lines .............................................................................................. 24
6.2.5 Servitudes ................................................................................................................... 24
6.2.6 Foundations (towers) ................................................................................................. 24
6.2.7 Structures ................................................................................................................... 24
6.2.8 Hardware (split pins) .................................................................................................. 24
6.2.9 Conductors ................................................................................................................. 25
6.2.10 Spacers and dampers .................................................................................................. 25
6.2.11 Insulators .................................................................................................................... 25
iv
6.2.12 Pollution ..................................................................................................................... 25
6.2.13 Bird nests ................................................................................................................... 25
6.2.14 Reticulation line equipment ....................................................................................... 25
6.2.15 Earthing ...................................................................................................................... 26
6.2.16 Anti-climbs ................................................................................................................ 26
6.2.17 Wayleave .................................................................................................................... 26
6.2.18 Insulators .................................................................................................................... 29
7. UNDERGROUND DISTRIBUTION ...............................................................................................34
7.1 Cable Route Markers ............................................................................................................. 34
7.2 Cable Take-off Marking Plates ............................................................................................. 34
8. GENERAL MAINTENANCE PRACTICES ..................................................................................34
8.1. Corrective maintenance – Items for immediate action ....................................................... 34
8.2. Preventive maintenance – Scheduled actions ....................................................................... 34
8.3. Infrared scanning ................................................................................................................... 34
8.4. Reporting and recording ........................................................................................................ 35
8.5. Maintenance documentation ................................................................................................. 35
9. APPENDICES ....................................................................................................................................36
v
FOREWORD
The Zambia Bureau of Standards (ZABS) is the Statutory Organization established by an Act of
Parliament. ZABS is responsible for the preparation of national standards through its various
technical committees composed of representation from government departments, the industry,
academia, regulators, consumer associations and non- governmental organizations.
This National standard has been prepared in accordance with the procedures of the ZABS. All
users should ensure that they have the latest edition of this publication as standards are revised
from time to time.
No liability shall attach to ZABS or its Director, employees, servants or agents including
individual experts and members of its technical committees for any personal injury, property
damage or other damages of any nature whatsoever, whether direct or indirect, or for costs
(Including legal fees) and expenses arising out of the publication, use of, or reliance upon this
ZABS publication or any other ZABS publication.
Compliance with a Zambian standard does not of itself confer immunity from legal obligations.
DZS 907-2: 2015 was prepared by the Technical Committee TC 5/7 on Electricity Distribution
1
ZAMBIAN STANDARD
ELECTRICITY DISTRIBUTION INFRASTRUCTURE – Application Guide
Part 2 - Operations and Maintenance Guide
1. SCOPE
This part of DZS 907 provides recommendations and minimum maintenance and operations
requirements for ac distribution networks ranging from three phase 33,000 Volts to 220 Volts ac
single phase.
It is a general guide to good technical practice for safe operation and maintenance of overhead and
underground power distribution networks.
This standard excludes power supply to underground mining power distribution networks and
other zoned and categorized areas.
2. NORMATIVE REFERENCES
The following standards contain provisions which, through reference in this text, constitute
provisions of this part of DZS 907. All standards are subject to revision and since any reference to
a standard is deemed to be a reference to the latest edition of that standard party to agreements
based on this part of DZS 907 are encouraged to take steps to ensure the use of the most recent
editions of the standards indicated below.
Information on currently valid national and international standards can be obtained from Zambia
Bureau of Standards.
IEC 61203:1992 Synthetic organic esters for electrical purposes - Guide for maintenance of
transformer esters in equipment
3. ABBREVIATIONS AND DEFINITIONS
3.1 Abbreviations
EMA Environmental Management Act
NEC Neutral electromagnetic couple
NECR Neutral electromagnetic couple with resistor
NER Neutral earthing resistor
OEM Original Equipment Manufacturer
OLTC On-load Tap Changers
2
PCB Polychlorinated biphenyl
3.2 Definitions
3.2.1 Minor maintenance: (Non-intrusive maintenance and testing philosophy): This involves
the execution of scheduled or preventive maintenance work and may require the RMU to be
taken out of service. Minor maintenance may be time based and/ or operational based. Minor
maintenance may also include the assessment of the condition of the RMU switchgear and its
associated components.
3.2.2 Major maintenance: (overhaul) is work performed with the objective of repairing or
replacing parts which are found to be out of tolerance by inspection, test, examination, or as
required by the manufacturer‘s maintenance manual, in order to restore the component and/ or
the switchgear and controlgear to an acceptable condition(within tolerance).(For example,
contact inspection or replacement
3.2.3 Partial Discharge (PD): is an electrical discharge or spark due to insulation breakdown in
air or in insulation mediums. It emits measurable energy as electromagnetic emission and acoustic
emission, providing clear evidence that an asset is deteriorating in a way that is likely to lead to
failure.
3.2.4 Routine inspection: This involves a visual inspection/ investigation of the principal
features of the RMU without requiring it to be taken out of service. Observations resulting from
inspections may lead to the decision to carry out further maintenance activities.
3
4. SAFETY
Before commencement of any work on any apparatus, ensure all statutory and equipment
manufacturers‘ safety requirements are complied with. For the purposes of this standard refer to
ZS 418: 2013 - Electrical Safety Code: Code of Practice.
A risk assessment shall be carried out in accordance with Occupational Health and Safety Act, and
all work shall be carried out in accordance with approved relevant safety procedures.
5. SUBSTATION
5.1 General
Good design, proper installation, quality assurance, and sound operating and maintenance
programmes provide the basic foundation for the safe and reliable operation of industrial electrical
power system. A plant engineer who is faced with the task of improving the plant‘s electrical
power system performance, however, will likely find that programmes to reduce human error are
most cost-effective than system modifications or additional preventive maintenance.
Notwithstanding the provisions of ZS 907-1;
a). All substations and the major primary plant equipment shall be maintained and kept in
good working conditions;
b). All serious defects that are critical shall be reported immediately in line with internal
reporting procedures and corrective actions taken; and
c). All defects found shall be noted and reported in line with internal reporting
procedures;
5.2 General conditions at substations
All fences and gates shall be properly secured, in a good state of repair, in good mechanical
condition and they shall be properly earthed, (refer to ZS 418 and provisions of earthing in ZS 907
-1). Gates shall be locked at all times. Removable gates shall be chain locked.
a). All statutory notices and signs shall be clearly displayed (see ZS 418).
b). All buildings, doors, windows and paintwork shall be in a good condition .refer to ZS 907-
1
c). All substation yards (including the firebreak) shall be free of weeds and clear of loose
wires, debris and unused equipment.
d). All telephones and radios shall be in working order and emergency telephone numbers
shall be displayed next to the telephone.
e). All trench covers shall be in place and free of damage;
f). All trench exits shall be barricaded;
g). Yards shall be free of silt and water pooling after rain;
h). Floodlighting shall be checked to ensure that all lights are working. If fitted with day/night
switches, the functioning of the day/night switch shall also be checked.
i). Stand-by generators shall be run-up in accordance with manufacturer`s recommendations
and laid down procedures.
j). Access roads shall be properly maintained.
4
k). Any excessive audible noise i.e. transformer vibration or arcing of substation equipment
shall be reported in line with internal reporting procedures
l). The substation yard shall be maintained with a layer of 35mm stone size with a depth of at
least 100mm and that is clear of weeds, sand and debris.
m). Check the foundations for deterioration of the base concrete and for any settling, loose
anchor bolts or loose levelling shims. In no case shall this settlement cause tension on any
bushing, bus-bar support or cable connection;
n). Check all metal work for corrosion or rust.
5.3 Transformers
5.3.1. Power/Distribution transformers
5.3.1.1. Condition monitoring
5.3.1.1.1 Visual inspection
Visual inspection shall be carried out on a routine basis. Any defects found shall be recorded and
reported in accordance with internal company procedures.
The following actions shall be taken and records thereof shall be kept:
a). Check all bushings for chips, cracks or broken sheds;
b). Check pollution levels on bushings;
c). Check for any insulating oil leaks;
d). Check oil levels in all conservators, tap changers, diverters and bushings (taking into
consideration the effect of ambient temperature). Maximum and minimum levels shall be
clearly marked on all gauge glasses;
e). Ensure that all gauge glasses are clean and legible;
f). Check silica gel, the colour change should not exceed 1/3 of the length of the breather from
the bottom upwards;
g). Ensure that all breather oil baths are filled to the correct level and free of water and dust;
h). Check all explosion vent diaphragms for cracks, visible oil or other damage. The
diaphragms shall not be painted.
i). Check surge arrestors for cracked or broken porcelain, signs of flashover (e.g. soot around
seals on porcelain), and broken or punctured vents;
j). Ensure that diverters surge relief valves are in the ‗service‘ position;
k). Check whether the tap changer mechanism box door seal is intact;
l). Check whether the tap changer mechanism heaters are working;
m). Record all tap change operations using OLTC counters;
n). Record maximum winding and oil temperatures and also the temperatures indicated at the
time of reading. Minimum and maximum pointers shall be reset shall also be noted;
o). Check tap change mechanism boxes for cleanliness and for any general or obvious defects;
p). Ensure that all off-load tap changer switches are locked in position;
q). Check whether seals on all auxiliary connection boxes and temperature gauge housings are
in order;
r). Listen for any audible discharges;
s). Check whether the radiators are warm at the bottom indicating satisfactory operation;
5
t). Check whether radiator cooling fans are clear of obstructions and ensure that all valves are
open. (A colder fin will indicate insufficient oil circulation normally caused by a half-
closed valve. This can be detected by use of thermal imaging);
u). Check all cooling fans and oil pumps for correct operation;
v). Check whether all tertiary connections are correctly shrouded and insulated;
w). Ensure that valves on fins of transformers are in the open position;
x). Check whether the operating labels are securely mounted and legible from the operating
point;
y). Check whether the earth straps are in good condition and effectively connected;
z). Ensure that the oil catchment area is clear of all stones and free of any debris and water;
and
aa). Check for corrosion and paint of all metal work.
Annex A is an example of the record or checklist for routine inspection of power transformers.
5.3.1.1.2 Transformer Oil sampling
Oil samples shall be taken in accordance with ASTM D117-10. Oil samples shall also be taken
after any significant/abnormal system event, which might have stressed the transformer.
For an optimised oil sampling frequency ,an oil sampling plan may be derived in accordance with
ASTM D117-10
Routine oil samples shall be taken to an accredited laboratory for analysis. Portable oil
analysis/testing units may be used to test the transformer oil following an abnormal system event.
5.3.1.1.3 Transformer Infra-Red scanning
Refer to clause 8.3
5.3.1.2. Transformer Corrective maintenance-Items for immediate action
If there are any faults or damage or if faulty items need to be replaced during an inspection and the
repairs can be effected with the equipment in service, immediate action shall be taken. The
following are examples of such actions:
a). All oil levels that are close to or below the minimum level shall be corrected in all
conservators, tap changers, diverters and bushings (taking into consideration the effect of
ambient temperature);
b). If silica gel colour change is 1/3 of the length of the breather from the bottom upwards, it
shall be replaced;
c). if silica gel is changing colour from the top ,reseal the breather/breather pipe mating
surface and performadielectricstrengthtestontheoilassoonaspossibletoidentify any possible
ingress and degradation of the insulation medium;
d). Repair or replace defective tap changer mechanism box door seal;
e). Repair or replace faulty mechanism heaters
f). Repair or replace damaged seals on all auxiliary connection boxes and temperature gauge
housings;
g). Clean the breather oil bath and fill to the correct level with transformer insulating oil.
6
Where multi breathers are fitted ensure that a common oil bath is fitted;
h). Clear radiator-cooling fins of any obstructions and open all valves;
i). Faulty cooling fans, oil pumps and flow indicators shall be repaired or replaced.
j). If worn out, refit the operating labels so as to be legible from the operating point.
k). Replace earth straps that are not in good condition and reconnect those that are not
effectively connected; and
l). Clear the oil catchment area of all stones and free it of any debris and water
5.3.2. Instrument transformers
5.3.2.1 Cleaning of Instrument Transformers
When a CT or VT is taken out of service for maintenance purposes, ensure that any dirt or oil that
has collected on the CT or VT is cleaned off. Steam cleaning or high pressure cleaning might be
necessary.
An anti-pollution medium shall be applied in accordance with internal company procedures.
5.3.2.2 Oil leaks on Instrument Transformers
If oil leaks are present on a CT or VT, the CT or VT shall be replaced or repaired in accordance
with the manufacturer‘s recommendations.
5.4 Switchgear
5.4.1 Busbars and associated structures
An inspection of busbars and associated structures shall cover the following: a). Inspect all busbars and associated structures for discoloration (indicative of overheating),
galvanic corrosion, deformation, buckling or cracking. Where any of the above occurs, it
shall be immediately rectified;
b). All insulator discs shall be checked for chipped, cracked or broken sheds;
c). Check all connections for loose, missing or damaged bolts;
d). Busbar labelling shall be legible and correctly installed;
e). Structure earthing shall be intact and properly connected;
f). Check for bird nests and remove;
g). Equipment that should be locked shall be locked;
h). Ensure that all barricading are in place where appropriate.
5.4.2 Circuit Breakers
5.4.2.1 Condition monitoring
5.4.2.1.1 Visual inspections
Inspections shall be carried out on all circuit-breakers and oil-immersed isolators to check for
abnormal conditions on the equipment.
The condition and cyclo-meter readings of the equipment shall be recorded on appropriate
checklists..
7
5.4.2.1.2 Monitoring of insulating oil
Circuit-breaker oil shall be changed in accordance with maintenance requirements as as specified
in the manufacturer's manual.
Oil shall be handled in accordance with ASTM D117-10.
5.4.2.1.3 Circuit-breaker fault operations
The duty cycle of fault operations shall be monitored to determine when a maintenance
intervention is required.
The action limit (10 operations at rated fault current on SF6 circuit breaker and 1 operation for oil
circuit-breaker) at which a maintenance intervention is required shall be determined by the
following formulas:
SF6 circuit-breakers:
ts=(I1/I2)2× ns
Where; ts is the action limit for SF6circuit-breaker;
I1 is the kilo-ampere rated current of the switchgear;
I2 is the busbar fault current level in kilo-ampere; and
ns the OEM specified number of trips at maximum kilo-ampere rating but which is taken as
being 10 in the absence of an OEM specification.
For oil filled circuit-breakers:
to= (I1/I2)2× no
where;
ts is the action limit for oil filled circuit breaker;
I1 is the kilo ampere rated current of the switchgear; I2 is the busbar fault current level in kilo
ampere; and
no is the OEM specified number of trips at maximum kilo ampere rating but which is taken as
being 3 in the absence of an OEM specification.
5.4.2.2 Corrective maintenance–Items for immediate action
If there are any faults or damage or if faulty items need to be replaced during an inspection and the
repairs can be effected with the equipment in service, immediate action shall be taken. The
following are examples of such actions:
a). Repair or replace mechanism box door seal;
b). Refit the operating labels so as to be legible from the operating point;
c). Ensure that the earth straps are effectively connected and in good condition;
d). Replace mechanism door handles or hinges; and,
8
e). Reset and record of panel alarms.
5.4.3 Disconnector/Isolator
Overhauls on all isolators shall be carried out in accordance with the manufacturer‘s
specifications, as local conditions dictate or after a period not exceeding ten years from the date of
the first commissioning or the last Overhaul.
Maintenance tasks shall be carried out by specialist personnel only and shall be in accordance with
approved, relevant maintenance work instructions.
5.4.4 Ring Main Units
Several assessment techniques and diagnostic tests exist to assess the condition of these assets.
These key techniques and tests are described in this clause.
When considering the techniques described here, it will be important to note that for the
RMU, SANS 1874 requires a 30-year maintenance-free period. The use of intrusive tests and
RMU switchgear internal condition assessment techniques is therefore only required once the
RMU has reached its 30-year age. This statement is only applicable to the new generation of SF6
RMUs and special consideration needs to be given to older-generation oil-insulated RMUs.
a). Visual inspection
This equipment lends itself to visual inspections because key components are visible and
accessible. Visual inspections can detect the SF6 gas pressure or oil level, external
contamination, corrosion, evidence of overheating, misalignment, plus cracks and leaks on
bushings, support insulators, tanks, enclosures, drives, linkages and fittings. Visual inspection
can also verify the condition of gaskets and seals as well as the degree of contact erosion/wear on
de-energized equipment, such as vacuum breakers. Internal conditions, control components, and
mechanism cabinets can be inspected visually as well. Visual inspection serves as a start to
condition assessment, but must be supplemented by detailed reviews of maintenance and test
records.
b). Time or travel testing
This test shall not be mandatory due to the requirement of a long outage to remove the cable
terminations, perform the test and redo/replace the cable terminations. This test will purely be
used as and when required, based on on-site conditions.
This testing measures velocity, close and trip times, plus wipe and rebound. It offers a way to
evaluate a circuit-breaker‘s mechanical condition and helps to ensure that mechanism/linkage
performance meets the manufacturer‘s specifications.
c). Contact resistance testing
This test shall not be mandatory due to the requirement of a long outage to remove the cable
terminations, perform the test and redo/replace the cable terminations. This test will purely be
used as and when required, based on on-site conditions.
This test involves determining resistance in the main current-carrying circuit by taking
9
measurements across each interrupter head with the breaker closed. Resistance measurements
outside of predetermined values require further investigation.
In addition to static tests, dynamic tests during circuit-breaker operation enable one to see
where main and arcing contacts touch. Dynamic testing provides useful information when
extended arcing contact fingers exist.
d). Over-voltage test
This test shall not be mandatory due to the requirement of a long outage to remove the cable
terminations, perform the test and redo/replace the cable terminations. This test will purely be
used as and when required, based on on-site conditions.
This over-voltage test measures the insulation medium dielectric strength. This test can be done
for the circuit-breakers and/ or busbars.
e). Stored energy test (spring recharge time)
This test shall not be mandatory due to the requirement of a long outage to remove the cable
terminations, perform the test and redo/replace the cable terminations. This test will purely be
used as and when required based on on-site conditions.
This test helps detect poor motor, pump, compressor and other operational conditions. It
involves measuring recharge times or pressure drops during operation.
f). Insulation testing
This test shall not be mandatory for new-generation RMUs, due to access limitations to the
SF6 insulation medium. This test will purely be used as and when required, based on on-site
conditions.
The older-generation oil-insulated RMUs will, however, require a mandatory insulation
breakdown strength test and moisture content test.
g). Historic failure performance
This is used to identify the historic failure performance of the free-standing RMU or system
component, and to assist in identifying specific failure trends.
h). Online partial discharge testing
Online PD testing is only used for testing cable terminations or compartments easily accessible
by the test equipment.
5.4.5 Feeder Pillars
5.4.5.1 Inspection and Maintenance
5.4.5.1.1. General Maintenance
This section is to be used as guide to the maintenance of low voltage feeder pillars. It should be
read in conjunction with IEC 60947.
10
BS 6423: 1983, the British standard code of practice for the maintenance of electrical
switchgear and controlgear for voltages up to and including 650V, which sets out
recommendations for safe conditions during maintenance work and guidelines for maintenance
procedures.
It is assumed throughout that the precautions necessary to render the apparatus safe to work on,
including the isolation of normally live parts as required, have been taken..
5.4.5.1.2. Frequency of Maintenance
5.4.5.1.2.1. Different environments, loadings, types of load and frequency of operation will
affect the maintenance requirements of isolators, and boards, so that the following
recommendations are for guidance only. They are based on equipment installed
outdoors where the atmospheric conditions of the site are reasonably clean and the
equipment is not subjected to excessive pollution, such as occur in some industrial
areas, and employed on normal distribution duties.
It is recommended that the following intervals are considered but may be reduced to
cater for any adverse conditions. Operational experience will determine how much
more or less attention particular installations require.
5.4.5.1.2.2. In the case of units supplying bulk consumers, it may be possible to schedule
substation outages with the customers own maintenance programmes. Where a
number and variety of consumers are served by an installation, however, an
escalating programme as follows is suggested.
5.4.5.1.2.3. Routine Inspection, essentially visual and involving no operations or system outages,
should be undertaken as frequently as possible and in any case at least once every 12
months. For specific details see 5.4.5.1.3.
5.4.5.1.2.4. Examination and Service, should be undertaken at least every five years, during
which:
i). Disconnectors are opened for examination and lubrication.
This involves an outage of the whole equipment. For specific details see
5.4.5.1.4.
ii). Enclosures, exterior and accessible interior parts are cleaned.
This does not involve an outage of the whole equipment.
Where interrupting the supply could cause major problems, the period between
services may be extended, but extreme caution and very careful inspection
between services is recommended.
5.4.5.1.2.5. Disconnector Replacement, involves making the whole low voltage assembly dead,
and can usefully be combined with transformer and/or medium voltage
switchgear maintenance. .
5.4.5.1.2.6. General Overhaul involves making the whole low voltage assembly dead and
partially dismantling it to give access to the busbar and connection supports and
other normally inaccessible components. Such an overhaul need only be undertaken
11
when indicated by inspection, servicing or testing, or every fifteen years, whichever
is the sooner.
5.4.5.1.3. Routine Inspection
5.4.5.1.3.1 Check that the substation area is clean and well-ventilated and that external
ventilation grilles are clear. Clear any rubbish, provided that this does not involve
interfering with the equipment.
5.4.5.1.3.2 On opening the enclosure doors, listen for any sizzling noise due to electrical
discharge or rattling of loose components; sniff for any unusual smell which may
indicate an electrical discharge or overheating; have a general look round.
5.4.5.1.3.3 As far as is reasonable practicable, look for signs of corrosion, damaged
external insulation, loose earth connections and any other visible signs of
abnormality.
5.4.5.1.3.4 Check as applicable, that any operating handle, locking off devices, or other
equipment which should be there are present, accessible and in good conditions.
5.4.5.1.3.5 Look at the closed disconnector links for signs of overheating or damaged insulation.
5.4.5.1.4. Examination and Service of Disconnectors
5.4.5.1.4.1 MAKE THE TRANSFORMER DEAD FROM THE PRIMARY SIDE.
Operate the disconnectors to the OPEN and then INSPECTION position. Ensure
ALL back feeds are isolated.
5.4.5.1.4.2 Clean any hardened or discoloured grease from the disconnector contacts using a
suitable solvent, such as one based on electronics grade trichloroethane. Silver
plating on the contacts may be tarnished black. This is not serious, but may be
cleaned up using silver polish.
A small amount of pitting is not significant, but if there are signs of serious damage
due to overheating the complete single phase disconnector should be replaced.
Regrease the contacts with appropriate grease before returning the disconnector to
the OPEN and then the CLOSED position.
5.4.5.1.4.3 Check the contact pressure of the closed disconnector to the manufacturers
recommended pressure.
NOTE: This must not be done with the supply live.
Repeat for all phases of the disconnector.
5.4.5.1.5. Examination and Service of Enclosure
5.4.5.1.5.1 Clean any loose dirt from the equipment exterior and accessible parts of the interior.
5.4.5.1.5.2 Cotton waste or cleaning cloths having loose fibres, loose particles or metallic
threads shall not be used.
5.4.5.1.5.3 Brushes or blower nozzles contaminated with metallic material shall not be used
12
5.4.5.1.5.4 Tools, loose parts and metal filings shall be not left in the compartment.
5.4.5.1.6. General Overhaul
5.4.5.1.6.1 MAKE THE TRANSFORMER DEAD FROM THE PRIMARY SIDE.
5.4.5.1.6.2 Ensure ALL other supplies are isolated.
5.4.5.1.6.3 Carry out all the inspection, servicing and overhaul procedures as described in 2.3
and 2.4. Carry out the procedures in 2.9 as required.
5.4.5.1.6.4 Unfasten and remove any front covers/screens as described in the instructions
supplied with the equipment, as necessary for access.
5.4.5.1.6.5 Clean and inspect all insulation, looking for burning, cracks or other defects. Replace
as necessary.
5.4.5.1.6.6 Clean all busbars, risers, droppers and other copper work. Check their fastenings for
tightness. Examine the busbars and other copper work supports. Check all main
and secondary earth connections for continuity and tightness of fastenings.
5.4.5.1.6.7 Inspect the cable tails for overheating of connections or discolouration.
5.4.5.1.6.8 Clean and clear any dirt or rubbish.
5.4.5.1.6.9 Check that external ventilation grilles are clear.
5.4.5.1.6.10 with all fuses removed and/or MCCBs switched OFF/, close the incoming
disconnectors to connect the busbars and connections to the low voltage windings of
the (still unenergised) transformer. Remove the neutral earth link between the earth
bar and neutral busbar. Test the resistance between phases and phase to earth.
5.4.5.1.6.11 Values will vary between different equipment depending upon the content and site
location. Values in excess of 20 megohms can be expected, but values above 1
megohm are acceptable.
5.4.5.1.6.12 Comparison of recorded insulation values, where available, will indicate any
deterioration in the insulation.
5.4.5.1.6.13 Refit all covers and make alive.
5.4.5.1.7. Post Fault Maintenance
5.4.5.1.7.1 If a fuse blows/ MCCB trips due to an overload or a fault, the cause of the tripping
should be identified and the problem rectified. If possible, check the cable
terminations for signs of loosened contacts or damaged insulation and examine the
MCCB for obvious signs of damage. Indications of light emissions of soot from the
MCCB arc chutes are normal.
5.5 Capacitor Banks
5.5.1 General
13
Capacitor bank inspection and maintenance shall be carried out in accordance with manufacturer`s
recommendations and shall cover at least the following;
Inspections shall be carried out on all capacitors and SVCs to check for abnormal conditions on
the equipment. The conditions of the equipment shall be recorded.
WARNING: Do not enter a capacitor bank enclosure when the capacitor bank is live. Ensure the capacitor bank is
discharged and earthed
Inspect and record the following:
a). Ensure interlocks to entry are in good working condition;
b). Externally fused capacitors shall be inspected for blown fuses;
c). Insulators shall be inspected for chips, cracks or broken sheds.
d). Capacitor cans shall be checked for insulating fluid leaks;
e). The fence and gate shall be checked to ensure that they are properly secured, in a good
state of repair, free of rust, effectively earthed and the gate locked at all times;
f). All notices and labels shall be securely fixed and legible;
g). Earth straps shall be in a good condition and shall be effectively connected; and
h). An earthing procedure for each specific unit shall be available at each site for earthing
purposes.
i). The labelling on the bank shall be in accordance with the procedure.
j). Check pollution levels on the insulators;
k). Check for any insulating oil leaks on the capacitor cans and balancing CT;
l). Check the oil level on the current transformer (where applicable);
m). Check for any visible hot connections on connection studs, balancing CT ;
n). Check whether all the cans on the capacitor banks are numbered;
o). Ensure that all working earth application points are marked or numbered;
p). Check whether the connection box of the balancing current transformers is closed/sealed;
q). Check whether the zero potential earth conductor (where applicable)is effectively
connected;
r). Listen for unusual sounds being emitted by the capacitors;
s). Check whether the capacitors are clear of dirt and debris;
t). Check whether the live chamber is free of weeds;
u). Check the capacitor cans, structures, balancing current transformer and discharging
reactors for bird nests; and
v). Check the capacitor cans‘ nameplate for PCB presence. Should the insulating oil contain
PCB, all the affected cans shall be labelled as such, only the approved service provider
shall discard the PCB containing cans whenever they are being discarded.
w). Check the integrity of the surge arrestors
5.5.2 Storage of capacitors
Special considerations shall be taken as per manufacturer`s recommendations and the
requirements of the Zambia Environmental Management Agency (ZEMA).
14
5.6 Insulating oil requirements
Insulating oil used for topping up substation equipment shall comply with requirements of
IEC60296 (mineral oil) or IEC 61203(synthetic oil) and spillages shall be removed as per
environmental statutory requirements. The approved service provider shall be the only one
permitted to discard the oil. Where deviations from the standards have been observed corrective
measures shall be taken.
NOTE: The mineral and synthetic oil should not be mixed in operations.
5.7 Oil Containment Tank
All oil containment tanks shall be kept free of stones, debris, oil and water and shall comply with
the ZEMA
5.8 Fire Blast Walls
Where ever fire blast walls exist they shall be maintained in good order in accordance with the
ZEMA
5.9 Substation yard junction boxes and marshalling kiosks
a). Junction box/marshalling kiosks inspections shall be included in routine substation yard
inspections.
b). The frequency of all routine inspections shall be determined by the manufacturer`s
recommendations and internal company maintenance procedures.
c). All junction boxes/marshalling kiosks and terminal connections shall be kept free of dust
and spider webs.
d). The door seals shall be inspected for deterioration and replaced if necessary.
e). Metal junction boxes/marshalling kiosks shall be checked for rust and, where necessary, a
rust remover shall be used and an approved paint shall be applied to the affected area.
f). Unused cable gland holes shall be blanked off to prevent moisture and dust collecting in
the box.
g). Latching arrangements shall be checked, and adjusted if necessary, to ensure that the door
makes a good seal when closed.
h). Door latching arrangements, door hinges and locks shall be checked and oiled regularly.
i). Water drain holes at the bottom of the door lip shall be checked to ensure that they are
clear.
j). Each junction box/marshalling kiosks shall be labelled to identify the panel with which it is
associated.
k). All Local-off-remote (LOR) switches shall be in the ―remote‖ position during normal
operation.
l). Harnesses shall be tidy and secure and checked to ensure that there are no loose
terminations.
m). Access into the junction box/marshalling kiosks shall only be through the doors. All other
n). apertures shall be sealed. Vents shall be insect proof and vermin proof.
o). All unused cores shall be combined together and earthed.
p). Any heater and socket outlet shall be inspected and tested for functionality.
q). DC equipment/accessories shall be inspected and tested for functionality.
15
5.10 Control gear
5.10.1 Protective relays and ancillary equipment
5.10.1.1 General examination
Protection devices should be subjected to careful examination (before or after operational or
functional testing) for defects or signs of deterioration which may affect reliability. Equipment
shall be treated with care and, where appropriate, anti-static bands shall be used and measures
shall be taken to prevent any foreign matter from entering the relay boxes and associated
equipment. Depending on the generation (phase 1, phase 2, and so on) of the protection
equipment, ensure that the relay movement is free, the magnet gap and induction disc are clean,
gear teeth mesh smoothly, contacts are clean and have an adequate ―wipe‖. During the
examination of the protection devices, the following should be checked:
a). Ensure that make-and-break contacts operate in the correct sequence with respect to each
other;
b). Ensure that contacts are in the ―make‖ position when multiplier settings are at zero;
c). Ensure resetting times are as specified;
d). Ensure flag mechanisms operate freely and in correct sequence with associated contacts;
e). Ensure external reset and trip knobs operate correctly with covers in place;
f). Ensure that relay cover glass panel and seals provide an effective seal;
g). Check for signs of overheating and corrosion;
h). Ensure that current transformer shorting and d.c. isolating contacts in withdrawal cases are
i). Clean and operate correctly; and
j). Check that hand, electrical or latched reset devices operate correctly.
5.10.1.2 Operational or functional tests on individual protection devices
Test every protection device to ensure compliance with operational and functional requirements.
Where applicable, ensure comprehensive verification of all self-diagnostic functions. Verify that
all levels, times and characteristics are within specified limits. Table 5-1 below lists the
recommended protection specific tests.
Table 5-1: Protection specific tests
Item Description
IDMTL, DTL and
instantaneous
protections
Verify the pick-up and drop-off current levels and the time to output contact
operation at setting.
Verify the IDMTL operation characteristic at (as minimum) three PSM
points, of which at least one PSM point should reflect the maximum system
fault level condition. Verify that the pick-up/drop-off ratio and disc reset
times (for electromechanical IDMTL relays) are within specified limits.
Take extra care when verification tests are being performed especially at
high current levels
Thermal overload
relays
Verify the operation of the thermal elements by injecting appropriate
currents according to the supplier‘s specification. Verify the characteristic
for ―cold start‖ and ―hot‖ operating conditions.
Voltage operated
protections
Verify the voltage levels for pick up and drop off and the time to output
contact operation at setting.
16
Verify that the pick-up and drop-off ratio are within specification as the
appropriate standard limits.
Voltage
transformer failure
Verify phase failure to the specification setting by lowering one phase at a
time until the relay drops out.
Directional
protection
Verify the IDMTL and DTL characteristics as applicable.
Verify the pick-up and drop-off levels of the polarizing quantity at setting.
Verify the directionality of the protection by applying polarizing and
operating quantities of appropriate polarity, having regard to the protection
characteristic angle.
Determine the two perimeter angles where restraint is initiated
Distance protection Use power system information, automated test equipment and suitable
supporting software(where applicable) to verify protection operation for one
phase fault and one earth fault per zone at reaches of 90 % and 110 % of
reach respectively.
Verify the operation of the zone timers and ancillary functions (power swing
blocking VT fuse fail line, check, current reversal guard, weak in feed,
circuit breaker ―echo‖.)
Where communication assisted tripping is employed, verify that a
permissive or transfer instruction at any one end is received at the opposite
end‘s appropriate scheme terminals.
Verify the full scheme by doing functional testing as may be appropriate.
Automatic voltage
control (tap
changer AVR)
Verify the voltage setting by secondary injection and a variation of the
control voltage by a margin in excess of the bandwidth setting.
Verify the bandwidth setting and verify that the tap changer operation is
blocked for under voltages or overvoltages (or both), as may be appropriate.
Verify the functionality of alarming or operation, based on circulating
current as a variable
Feeder differential
unit protection
Verify the operational setting of all operational quantities by secondary
injection.
Verify the integrity of the communication link and ensure appropriate
scheme operation for different instruction sets (e.g. reclose or inter trip.)
Verify that the pilot supervisory circuitry is operational (where appropriate.)
Feeder phase
comparison unit
protection
Verify the pick-up and drop-off levels of all starter and guard functions and
the associated chronological resetting of functions.
Follow/use manufacturer instructions to verify the operating current level as
appropriate.
Execute a communication channel test
Under frequency
load shedding
Verify each load shedding frequency stage and time delays by secondary
frequency injection testing.
High impedance
busbar/ restricted
earth fault
protection
Verify the primary setting current protected for, by ensuring secondary
current injection from one of the current transformer terminals is within the
specified sensitivity as required by the setting philosophy. Apply the
stability voltage to the relay branch and verify that the currents in the
scheme (i.e. summated CT excitation currents, Metrosil current, shunt
resistor current, CT open circuit relay current and high impedance relay
current) all correspond to the distribution as set for
Verify the characteristic current of the non-linear device to be within
parameters at one voltage point.
Verify the CT open circuit detection and annunciation (where applicable).
Low impedance Verify the primary setting current protected for, by ensuring secondary
17
busbar zone
protection
injection from one of the CT‘s terminals is within the specified sensitivity as
required by the setting philosophy.
Verify the CT open circuit detection and annunciation, if applicable.
Verify the operating/total current bias characteristic and the operating
current at zero bias.
Current block
busbar protection
Verify the margin of current detection to be at least 25 % of the
blocking/feeder measurement.
Verify the busbar strip timer setting.
Transformer biased
differential
protection
Verify the operating/through fault current bias characteristic and the
operating current at zero bias.
Verify the operation of the harmonic restraint functions.
Verify the operation of differential high set by applying the harmonic
restraint and injecting50 Hz currents of a value exceeding the differential
high set setting through the operating winding.
Buchholz
protection
Verify the operation of the Buchholz gas accumulation detection and the
surge detection modes respectively by injecting a known volume of nitrogen
and a surge at suitable minimum pressures
Temperature
indicators
Verify the transformer temperature indicators against a standard
thermometer at acceptable intervals over the instrument operating range.
Carry out a further check on the winding temperature indicator to ensure that
the winding temperature increment obtained, when the appropriate current
specified by the transformer manufacturer is injected into the indicator
heater circuit, agrees with the commissioning results.
Check all oil circulating pumps and air fans that are controlled by these
indicators, to be functionally operational at the given setting levels.
Motor protection
Verify the single-phase and unbalance protection function and timers.
Verify the operation of overload protection by injecting balanced positive
phase sequence quantities in accordance with the protection overload
philosophy.
Insulation
resistance test
Apply the insulation resistance test using an electronic (or brushless) tester
at 500 V to grouped d.c. circuits and grouped a.c. circuits. If the readings so
derived are < 75 MΩ, test circuits individually until source of problem is
located
5.10.1.3 Examination of miscellaneous protective equipment
Examine all protective equipment and components mounted on protective panels or cubicles,
switchgear, isolators, transformers, current or voltage transformers (or both), and carefully
scrutinize them for signs of failure or deterioration in reliability. The equipment and components
examined are listed in Table 5-2.
Table 5-2: List of protective equipment and components
Item Description
Control/selector switches and push
buttons
Verify smooth operation.
Check for signs of broken terminals, cracked cells.
Verify the tightness of clamping devices (terminal strips,
nuts)
Indicator lamps Verify that indicator lamps operate correctly and ensure
that they are of the correct colour
Measurement instruments, Verify the transducer output values and accuracy with
18
indications and transducers secondary injection.
Verify the accuracy of the indications and ensure that
scaling is suitable
Isolating links and terminals Verify the isolating link setting and contact sequence as
given in the relevant setting sheet.
Check on tightness of terminal lug nuts and that terminal
cabling numbers are in place and as given in schematic
drawings.
Check condition of auxiliary box cover and seals
Test blocks
Verify the pressure of the contact springs and that no
terminal studs are broken.
Verify that the shorting strips in current test blocks are
operational
5.11 Batteries and Battery chargers
5.11.1 Safety
a). Preparation of equipment for maintenance must comply with Safety Regulations.
b). Personal Protective Equipment (PPE) should cover the potential hazards.
c). Eye wash should be readily available
d). There should be adequate ventilation to ensure clearing of hydrogen from battery rooms
e). There shall be no use of naked flames in battery rooms.
5.11.2 Types and Frequency of Maintenance for Substation Batteries
Only Inspections and Tests shall be carried out on the batteries. This is maintenance activity to
establish the condition and serviceability of the batteries and when their replacement is due. This
type of maintenance shall be done annually.
5.11.3 Failure Modes of the Batteries
The systems and components indicated below need to be inspected and tested in order to ensure
continued reliable operation of the batteries.
a). Deterioration of internal cell capacity
b). Deterioration of bolted current-carrying components between the cells
c). Increase in cell impedance.
d). Change in electrolyte level and specific gravity in the cells due to evaporation
e). Failure to charge due to charger connection problems
5.11.4 Details of Maintenance Activities
The tests and checks detailed below provide the barest minimum standard to which maintenance
should be carried out. Maintenance activities are expected to take into account prudent practices
and should be done to the highest quality and standard.
Other work instructions to govern the works are to be found in the relevant maintenance
procedures.
Table 5-3: Battery maintenance
19
No
Tests / Checks
Frequency
1 Ensure the cell terminals are clean. Monthly
2 Record the charging voltage and current. Monthly
3 Test and record the voltage and specific gravity (were necessary) for each
cell. Monthly
4 Record the ambient temperature Monthly
5 Record the temperatures of the cells. Monthly
6 Switch off battery charger and allow the battery to supply the load for a
period of 30 – 60 minutes. Record
a. The battery voltage at start
b. The battery voltage at the end
c. The discharge current
Bi-annual
7 Apply industrial Vaseline to all battery connection points after inspection /
cleaning. Clean off the old Vaseline were necessary
During
maintenance
when there is
need
8 Check level of electrolyte and top up with distilled water as required Monthly
9 Observe the condition of the cell interior to note condition of the plates
(formation of lead sulphate and segment deposits)
Monthly
10 Carry out cell impedance and strap resistance measurements Annually
11 Check condition of the battery stand Monthly
5.12 Metering
5.12.1 General
Routine inspection maintenance consists of actions that focus on the verification of the external
general correctness of selected subsystems of the total metering system.
5.12.2 Scheduling and frequency
Routine inspection maintenance consists of non-intrusive investigative actions that can be
executed on the basis of one substation at a time or one customer type at a time, as required.
5.12.3 Maintenance actions
5.12.3.1 Implementation
Maintenance actions shall be implemented by doing the tests in 5.12.3.2 to 5.12.3.9.
5.12.3.2 Instrument transformer functional tests
20
The following shall apply:
a). voltage instrument transformer functional test;
b). current instrument transformer functional tests;
c). summation CT functional checks;
d). cabling connection checks.
5.12.3.3 Meter panel functional tests
The following shall apply:
a). battery tests (where fitted);
b). meter accuracy checks;
c). meter dial to recorder register verification.
5.12.3.4 Phasor test
Verify correctness of the meter installation by comparing a phasor diagram.
5.12.3.5 Measurement functional tests
Test the integrity of transducers.
5.12.3.6 Time accuracy tests
Synchronize time on all recorders and meters, where applicable, to align with real time.
5.12.3.7 Meter/equipment sealing
Ensure that all equipment seals are intact.
5.13 Auto-reclosers/ Sectionalizers
Carry out Functional tests as per manufacturers recommendations
5.14 DC supply equipment
All DC supply equipment shall be maintained in accordance with the section on Batteries and
chargers.
5.15 Relay rooms
In a control room:
a). All panels shall be correctly labelled at the front and back (where the panel is accessible on
both sides);
b). All panels shall be clean and free of dust
c). All vermin proof shall be kept in good condition;
d). All indication lamps shall be in working order;
e). All meters (ammeters, voltmeters, etc.) and recorders shall be in a good working condition;
f). All panel-blanking plates shall be fitted where required;
g). Key boxes, where fitted, shall be kept locked or sealed;
21
h). The latest revision of the substation diagram shall be displayed at all times;
i). All energy meters shall be checked for proper functioning;
j). All protection relays shall be checked, and those that could have operated shall be logged
and only reset once reported in line with internal company reporting procedures. ;
k). The substation logbook shall be in place;
l). Panels opened at the back shall be barricaded; and
m). Control panel labelling shall be permanent, adhesive plastics strips labels shall not be used.
n). Check whether the capacitor bank is balanced on the protection panel;
o). Check the status of alarms and flags;
p). Door lights and DC emergency lights shall be in a good working condition.
5.16 Auxiliary Equipment
5.15.1 Substation lighting
Ensure all perimeter lighting is in good working order.
5.15.2 Emergency lighting
Ensure all emergency lighting are in good working order.
5.15.3 Security Lighting
Ensure all security lighting are in good working order.
5.15.4 Fire suppression systems
Ensure all fire suppression systems are in good working order and ensure validity of the
gas/powder cylinders.
5.17 Equipment Earthing
5.16.1 Inspections
5.16.1.1 Visual inspections
Inspections shall be carried out on equipment earthing to check for abnormal conditions. The
conditions of the earthing and the readings taken on the equipment earthing shall be
recorded. .
As part of the routine substation inspection, the following shall be done and any structure with a
cut off, missing earth tail shall be treated as live:
a). The earthing conductor shall be checked to ensure that it is firmly connected and in place;
b). Metal structures, particularly fences at ground level, shall be checked for corrosion;
c). Check shall be carried out for evidence of loose or otherwise faulty connections; and
d). Check shall be carried out for stolen or missing earth tails.
5.16.1.2 Detailed inspections
An annual inspection of the items listed below shall be carried out as an ongoing exercise:
a). Copper earth tails —earth tails shall be checked for corrosion on an annual basis. The
layer of crushed stone and about 100 mm of soil shall be removed to allow inspection and
22
the copper shall be checked for pitting;
b). Copper alternative earth tails — all non-copper earth tails shall be checked annually as
severe corrosion is likely. The stone and soil shall be excavated down to below the
alternative conductor to the copper joint and the conductor shall be checked for pitting;
c). Copper tails cemented — a continuity test between structures shall be performed in the
case of a substation where copper earth tails are cemented.
d). A checklist/check-sheet shall be completed on completion of the detailed inspection.
5.16.1.3 Removal of pitted earth tails
Where a section of copper earth tail is found to be badly pitted, this section shall be replaced. To
carry out replacement:
a). bond the new section of copper to each end of the pitted section; and
b). cut away the pitted section and send it for material analysis, along with a relevant soil
sample
Carry out the soil sampling as follows:
a). An appropriate amount of soil shall be collected;
b). The sample shall be taken from the same depth as which the earthing is buried and within
one metre from the affected section of earthing;
c). If the backfill is different from the natural soil of the area, ensure that the sample is taken
from the backfill;
d). The soil sample shall be placed in a sealed plastic container; and,
e). The soil sample shall be sent for material analysis together with an indication of where the
sample came from, including the name and telephone number of the contact person.
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6. OVERHEAD DISTRIBUTION
6.1 General Line Maintenance
Visual and physical inspections of overhead power lines shall be carried out at the minimum
frequencies given in annex B. All inspections shall be properly reported for further action, if
necessary. The check sheet shown in annexes C and D are examples of the type of report or check
sheet system that can be implemented.
Inspections shall be carried out in order to identify defects on overhead power lines such as the
following:
a). broken insulators and arresters;
b). pollution;
c). dampers and spacers adrift or faulty;
d). erosion;
e). discoloration and corrosion of conductors;
f). damaged conductors;
g). incorrect clearance from ground or trees;
h). clearances from other services;
i). activities below power lines, for example, building;
j). worn hardware and damaged structures, switchgear or transformers;
k). damaged, rusted or corroded switchgear on the line;
l). security of fibre optic cables strung on the lines;
m). security of earthing straps on steel structures, poles and street furniture associated with the
distribution network; and
n). Anti-climbing devices.
6.2 Detailed inspections
6.2.1 General
Detailed hands-on inspections shall be carried out at the frequencies specified in table E.1 of
Annex E using a pre-determined checklist similar to the sheet illustrated in the examples in
annexes C and D. Inspections shall cover at least the items given in 6.2.4 to 6.2.16. All other hardware items shall be checked for signs of wear and replaced, where necessary. 6.2.2 Towers
The following should be inspected: a). all hardware for signs of wear;
b). all components (especially at the coast or in polluted areas) for corrosion;
c). depending on the length of the overhead line and taking its environment into
consideration, a sample number of structures should be selected and the interface between
conductor and clamp, or spacer, or damper inspected for damage; and
d). depending on the number of structures, a sample number of structures should be selected
and the earth connections to the general mass of ground tested.
24
6.2.3 Steel and concrete poles for power lines
The following should be inspected on steel and concrete poles: a). all hardware for signs of wear;
b). all components (especially at the coast or in polluted areas) for corrosion;
c). paint work and condition of the foundation;
d). pole numbering, and
e). all bolts, dampers, connectors, etc.
6.2.4 Wood pole power lines
The following shall be checked on wood poles: a). a pole-by-pole check of the condition of each pole (including partial excavation and a
check for degradation as recommended in annex B, or as determined by experience in
suspect areas);
b). a visual inspection shall be performed on all wood pole lines in accordance with
the recommendations in annex E.
6.2.5 Servitudes
The supply authority‘s rights with regard to servitudes and the approach to the control and cutting
of trees and bushes within these servitudes shall apply.
Servitude roads necessary for the patrol and maintenance of lines shall be maintained so that they
are useable at all times.
All servitude gates shall be kept locked unless otherwise agreed upon with the landowner who
shall indemnify the supply authority. Gates shall only be installed with the permission of the
landowner and the supply authority shall maintain them in good order. This specifically includes
any earth straps that bond the gates and posts.
Encroachment on the supply authority‘s servitudes of new buildings, extensions, tennis courts,
swimming pools and barns, shall be reported immediately, especially if the servitudes are located
below the lines, or inside the stipulated safety clearance.
6.2.6 Foundations (towers)
Foundations or capping shall be cleared of soil, and shall be repaired if found to be damaged.
Erosion at tower legs shall be repaired to prevent recurrence, and a suitable anti-corrosive
coating shall be applied to the tower legs where they enter the concrete.
6.2.7 Structures
No tower or pole shall be climbed if it is mechanically or electrically unsafe to do so. Damaged
anti- climbing devices shall be repaired. All loose bolts and nuts shall be re-tightened, punched
and painted with an anti-corrosive paint. Damaged and faded warning, circuit and phase labels
shall be replaced.
6.2.8 Hardware (split pins)
All split pins shall be checked to ensure that they are of the correct type, that they are undamaged
and correctly fitted. They shall be replaced, as required, by a stainless steel split pin.
25
There shall be a check for missing nuts and also for loose nuts that can chafe through split pins,
ultimately resulting in the line coming adrift from the support structure.
6.2.9 Conductors
Armouring and ferrules shall be checked and replaced with approved types where damage has
been caused to the conductor. Discolouring, flash marks and any other damage shall be recorded
and repaired, where applicable.
Only approved joints shall be used for repairs
Recommendations on conductor repairs are listed in Annex F.
6.2.10 Spacers and dampers
Spacers shall be checked and replaced, if necessary. Loose or shifted dampers shall be re-
positioned and re-tightened. Damaged dampers shall be replaced by approved dampers of the
correct conductor diameter.
6.2.11 Insulators
6.2.11.1 Damaged insulators
Damaged or flashed-over insulators shall be replaced. If a glass or porcelain insulator has to be
replaced, the remaining insulators on the string shall be cleaned to the same degree of cleanliness
as that of the ―new‖ disc inserted, or the entire string shall be replaced.
6.2.11.2 Live replacement of insulators
Where the expertise exists in a supply authority, the replacement of insulators by live-work
methods shall be the first option.
6.2.11.3 Earth wire insulators
Where fitted, the inspection of earth wire insulators shall form part of the inspections carried out.
The arc gaps shall be checked during such inspections.
6.2.11.4 Stay wire insulators
Where fitted, stay wire insulators shall be checked for cracks or damages.
6.2.12 Pollution
The type of pollution found during inspections shall be recorded. A pollution philosophy should
be included in the strategy document.
6.2.13 Bird nests
Bird nests shall not be removed from structures unless the possibility exists that a flashover can
occur. All structures where bird nests are found shall be identified and reported. A photo of the
nest should be taken, if possible, to identify the type of bird. The trees shall be trimmed back
without damaging the nests if the nests do not encroach on the proximity of the conductors.
6.2.14 Reticulation line equipment
Spark-gap protection is NOT recommended on transformers or other items of equipment where
26
surge arresters are installed. However, if a gap setting is required, see Table 6-2.
All insulators should be inspected at least in accordance with Annex D and E.
Pole-mounted re-closers and sectionalisers shall at least be inspected in accordance with
individual utilities‘ procedures.
6.2.15 Earthing
6.2.15.1 Sub-transmission line
It shall be ensured that earth straps are in place and examined for damage. Connections shall be
checked for tightness.
Table 6-1: Spark-gap settings
1 2 3 4 5 6
Nominal
system
voltage
kV
Recommended
gap
Single gap
mm
Recommended gap
Duplex total
mm
Negative
lightning
impulse,
flashover voltage
at sea level
kV
AC (Pk) flashover
voltage at
2 000 m
Single gap kV
AC (Pk) flashover
voltage at
2 000 m
Duplex gap kV
2.2 21 a 34 22
3.3 26 a 38 26
6.6 52 40 64 45 42
11 74 56 81 56 56
22 a 104 128 90
33 a 160 170 117
a Not recommended.
The tower footing earth resistance of every tenth tower shall be measured as part of the detailed
power line inspection and recorded using an approved system. Where the tower earth enters the
ground, the ground shall be excavated to a depth of 150 mm, the tower earth checked for corrosion
and rectified, where necessary. The results shall be compared with those of the ―hand- over‖ test
results and more extensive investigations shall be carried out if significant variations or
deterioration are found.
6.2.15.2 Medium-voltage equipment
Equipment earthing shall be visually inspected and replaced if missing. Where equipment has
individual earthing there shall be a programme for the testing of pole-mounted transformers and
switchgear earthing resistances, and comparisons shall be made with the ―handover‖ test results.
6.2.16 Anti-climbs
Anti-climbing devices shall be checked for physical damage or corrosion. Damaged anticlimbing
devices shall be repaired or replaced as required.
6.2.17 Wayleave
27
6.2.17.1 General Requirements of Wayleave Maintenance
The electrical network owner or its appointed agent (s) shall:
a). Read and understand the provisions of the relevant environmental management plans.
b). Keep to the existing Wayleave access roads and tracks and within the Wayleave area and
not deviate from the same unless where such access dictates so.
c). Keep all gates locked and leave property owners‘ gates closed or as agreed to in writing
and shall not interfere with the property owners‘ normal or routine activities unless such
maintenance or access demands so.
d). Get all necessary permits in advance for services and general requirements to carry out
vegetation removal and other Wayleave and transmission line maintenance.
e). Keep the environment appropriately neat and apply appropriate management practices.
f). Ensure that there is no disturbance or picking up or removal of unauthorized gems,
artefacts, firewood or any such items.
6.2.17.2 Procedures for Bush Clearing
Bush clearing and Wayleave maintenance play an important role in the delivery of reliable power.
Therefore, the network owner must have basic procedures for bush clearing in both new and
existing electric power infrastructure in order to comply with these standards. The network owner
shall also ensure that all works carried out by its appointed agents conform to these standards.
6.2.17.3 Wayleave Clearing Requirements
The following general requirements shall therefore be observed in all Wayleave clearing or
maintenance activities:-
6.2.17.4 General Guiding Principle
No tree or structure shall be allowed to grow or be erected to a height such that it endangers the
line should it fall under natural conditions or be cut/ brought down. Therefore, vegetation, trees,
bushes and structures should be cleared to ensure the safe mechanical and electrical operation of
the line in accordance with these guidelines.
The Transmission line maintenance crews must look for potentially dangerous situations in the
Wayleave. Swimming pools, buildings, irrigation equipment, wire fences and tall trees can all be
dangerous when too close to power lines.
6.2.17.5 Vegetation Removal Standard
All vegetation cutting or maintenance shall be restricted to the minimum Wayleave size and
allowed growth height provided. For all Wayleaves, the maximum vegetation growth height
allowed outside the boundaries shall be such that if any tree were to fall, it would not impact the
transmission line. Under the power lines the maximum allowable vegetation growth shall be 0.5m.
6.2.17.6 Vegetation Control
Vegetation growing under transmission lines shall be controlled in order to prevent it from
encroaching on the minimum safety clearances of the power lines so as to prevent any hazard to
nearest inhabited dwelling or place of activity.
28
6.2.17.3.1 Vegetation Removal in Forests and Protected Areas
All bush clearings that are to take place within national forests or protected areas shall conform to
the laid down cutting procedures in the Forest Act or Zambia Wildlife Authority (ZAWA) Act and
as stipulated in the general code of practice under these guidelines.
6.2.17.3.2 Wayleave Access
In all Wayleave contracts or agreements, the network owner and/or its appointed contractor (s) has
the right to enter or be found on the property where any line or such infrastructure is located, at
any time whether to perform work on the section of the line traversing the property, or to gain
access to any adjacent areas within the property. The network owner shall however, exercise due
diligence in its attempts to notify the property owner or any such relevant authority of any
intention to enter the property to cut trees and other vegetation and shall endeavor to obtain
consent to the proposed work. All staff assigned to carry out such work shall have valid means of
identification.
In farm areas where ranching or access is by way of gates, in order to assist with access, the
network owner or its contractor (s) shall access such areas through appropriate gates or may erect
such gates as may be necessary, in consultation with the property owners. Under no circumstances
shall access be gained by cutting or ―dropping‖ fences. All such access shall be to the satisfaction
of the land owners.
All various native tree species that are protected by law shall only be cut under the guidance of a
qualified national or approved private forester. The said officer shall determine whether a tree
species is protected or not, under the Forest Act or any such relevant local knowledge and such
trees and bushes that do not grow high enough to cause interference with the line or cause a fire
hazard, shall not be cut down or trimmed.
6.2.17.3.3 Use of Herbicides
The use of herbicides shall be discouraged and where permitted, restricted to areas where
mechanical vegetation removal is not feasible. Any such herbicides shall be targeted at specific
grass species and not tree nor shrubs or bush species. The herbicides shall conform to the Pests
and Toxic Substances Regulations and administered in accordance to the provisions and
requirements of the regulations. All such relevant records of herbicide type, application rates, and
dates of application, staff involved and general weather conditions shall be kept by the network
owner.
6.2.17.3.4 Vegetation in River Approaches and Erosion Sensitive Areas
In areas where power lines traverse sensitive areas such as deep valleys with steep slopes or
approaches to river banks, or in areas where access by vehicle is not possible, or in legally
protected areas, vegetation shall not be cleared provided that the vegetation poses no threat to the
operation and reliability of the line and meet the minimum safety clearances for all line voltage
levels.
In order to avoid, prevent, or reduce soil erosion, minimal amount of vegetation shall be
maintained at all times in steep slopes. If soil erosion is induced in the Wayleave as a direct result
of an act or omission by the land owner, contractor, user or the network owner, corrective
29
measures such as planting of vertiva grass, shall be implemented. Re-vegetation of disturbed areas
shall be restricted to visibly disturbed or scalped areas only.
All approaches to rivers, watercourses and other water bodies shall be kept clear of felled trees,
bush cuttings and debris. Where possible, the integrity of riverbanks shall be maintained by
placing pylons or such infrastructure at least 10m away from the banks on both sides. In areas
where lines traverse waterlogged areas, appropriate construction methods shall be implemented
and any subsequent vegetation management should not induce soil erosion.
6.2.17.3.5 General Considerations in Wayleave Maintenance
Lines, especially high voltage lines tend to disfigure the landscape hence the need to take into
consideration aesthetic beauty of the surroundings at points such as where the line crosses a
railway line, major road, river, dense bush or woodland. In areas where the line run parallel or
along a road, a screen of vegetation should be left between the road and the line wherever
practicable.
In areas where some shrubs, trees, grass, natural features and topsoil, are not removed, these shall
be protected from damage during operations and only be disturbed where it is inevitable and for
access purposes only.
All vegetation removed from the Wayleave shall be surrendered to the local communities, land
owners and where such offer is not accepted, vegetation shall be disposed of appropriately.
6.2.17.3.6 Control of Danger by Safe Clearances
Electricity travels on high-voltage power lines high above the ground. However, electricity, like
water, seeks the most direct path to the ground through nearby objects. Just like lightning, electric
current in a high-voltage power line may seek to reach the ground by arcing, to a tall-growing tree
and other conducting objects in the vicinity. To avoid arcing, an electric utility shall maintain
prescribed safe distances between its power lines and tree limbs as well as other conducting
objects.
Clearances between power lines and other objects, including trees, must allow for line sag. During
warm weather or when the line is carrying heavy electrical loads, it heats up and stretches. This
makes the line longer and it sags closer to the ground or objects underneath it. Because the amount
of sag varies with electrical load, weather and line composition, a safe clearance distance in winter
may not provide the same safety on the warmest summer days. Thus, to maintain a safe distance
between the line and anything that can conduct electricity, an electric utility maintains a clear zone
on all sides, above and below its power lines.
Tall growing trees or other tall objects that could fall into a power line must be removed. Heavy
winds can blow branches into power lines and additional weight from snow and ice (where
applicable) can bend or break branches, bringing them close enough to cause a flashover.
NOTE: Refer to the Wayleave Code of Practice for more information
6.2.18 Insulators
6.2.18.1 Safety
A risk assessment shall be carried out in accordance with local risk assessment procedures.
30
All work shall be carried out in accordance with approved relevant safety procedures and, all
environmental hazards shall be removed in accordance with the individual utility‘s policy.
6.2.18.2 Insulator pollution types
For the pollution types mentioned below, flashover occurs mainly at 50 Hz and at
service voltage (Un-Umax). A switching impulse may be a factor but this would be very
rare. Remedial action to prevent such flashover will depend mainly on the mode of pollution.
These pollution types are further discussed in details in annex B. The following are two main forms of insulator pollution that can lead to flashover: a). pre-deposited pollution; and
b). instantaneous pollution
6.2.18.3 Insulator maintenance procedures
Insulator maintenance i.e. cleaning, washing, coating or replacement shall be carried out in
accordance with individual utility‘s procedures. 6.2.18.4 Condition monitoring
To monitor the condition of the insulators the following shall be done using binoculars, infra-
red scanner, acoustic detectors etc.: Visual inspections shall be carried out on all insulators to check for abnormal conditions on the
equipment. The conditions of the equipment shall be recorded on the approved checksheets or
feedback templates provided with job plans or cards. The check sheets or feedback templates
shall be handed over to the works co-ordinator for equipment history data capturing. The following are examples of conditions that shall be checked on the insulators when
inspections are carried out: a). pollution build up;
b). tracking, chipped or broken sheds (maximum of 20% is allowed) and cracks;
c). corrosion on the pin of cap-and-pin of disc insulators;
d). birds‘ droppings on the insulator surfaces; and
e). Dry band formation: The rise in temperature due to leakage currents results in further
drying of the pollution layer and arc continue to extend along the insulator, bridging
more and more of its surface. This in turn decreases the resistance in series with the arc.
Ultimately, the insulator will be completely bridged and a line to earth fault occurs
(flashover). The pollutant does not usually pose a problem when dry but when the
pollution layer on the surface becomes wetted, the insulator could flashover (usually
occurs on hydrophilic insulators).
6.2.18.5 Condition based maintenance
6.2.18.5.1 General
All defects shall be analysed and correlated on an ongoing basis so that maintenance outages
can be scheduled on time.
31
Prior to a scheduled outage all defects shall be identified using condition monitoring to
ensure that the correct equipment, material and personnel are available on site.
6.2.18.5.2 Corrective maintenance - items for immediate actions
If there are any faults or damages or if faulty items need to be replaced during inspections and the
repairs can be effected with the equipment in service, immediate action shall be taken.
6.2.18.5.3 Preventive maintenance
6.2.18.5.3.1 Scheduled actions
a). All routine maintenance shall be carried out according to the prescribed period
specified in the manufacturer‘s manual or as dictated by local conditions.
b). All defects shall be analysed and correlated on a monthly basis in order that maintenance
outages can be timeously scheduled. Prior to a scheduled outage, all defects shall be
identified to ensure that the correct equipment, material and personnel are available on site.
c). All scheduled work shall be carried out in accordance with the requirements of the specific
job plans or cards and the relevant maintenance instructions or code of practice.
d). All maintenance tasks shall be carried out by, at minimum, trained personnel and in
accordance with the approved maintenance procedures.
e). All solvents, lubricants, pastes or grease that are used when performing
maintenance shall be as specified in manufacturer's manuals or approved maintenance
instructions.
6.2.18.5.3.2 Insulator maintenance options and precautions
a). When insulators cannot be readily replaced, for example, insulators that support
apparatus, a solution involving the longest maintenance-free interval shall be
considered, for example, installing creepage extenders together with silicone rubber
coating.
b). Shed extenders shall not be applied to insulators without coating the entire assembly,
due to differing surface characteristics, which can create electric field distortions.
c). Where the pollution is the ‗instantaneous type‘ (refer to clause 3 in annex B), washing
or cleaning will not be effective in preventing flashover.
d). Where the ambient, pre-deposited pollution is the bulky, high non-soluble deposit
density (NSDD) type, greasing of the insulators shall not be undertaken as the layer will
become quickly overloaded or saturated with contaminants and have an adverse effect on
the performance of the insulator.
e). Non-ceramic insulators shall not be greased; greasing will lead to severe material
erosion.
f). High-pressure spray washing shall only be undertaken in accordance with the
manufacturer‘s recommendations.
g). Coating or greasing of overhead line insulators is not an economically viable option.
h). When assessing line performance it shall be remembered that bird generated flashovers
could be a factor, and as such cleaning or replacing the insulators could then be the
wrong remedy.
i). Where a bird streamer mechanism is identified, no insulator treatment will be
effective. The only solution shall be to prevent birds from perching on critical parts of
the structure.
32
NOTE Point (i) above is specific to lines and is not an issue in substations.
j). All products used shall be utility approved type.
k). Insulators shall not be greased in areas with strong winds and large amounts of particles
(sand) that will be trapped in the grease.
6.2.18.5.3.3 Possible insulator pollution origin or cause
The appearance of dirt, or lack thereof, on the surface of insulators is not a good indicator of
potential pollution problems. For example, layers of non-conductive sand may present no threat.
However, SO2 produced from a near by plant, which when combined with moisture forms a
highly conductive acidic mist and can precipitate flashover but leaves no evidence of
contamination on the insulators involved.
NOTE Flashovers or faults on lines might not necessarily be an insulation problem. A careful
investigation shall be undertaken to determine the cause. This action will avoid unnecessary re-insulation
and associated costs. The following indicators shall be used to guide field personnel in diagnosing insulator pollution
problems:
a). line insulator flashovers that cannot be attributed to other causes such as lightning, fires
etc.;
b). insulator flashovers history;
c). insulator flashovers occurring during periods of rain, fog, mist or high humidity;
d). flashovers occurring during the early morning;
e). Partial discharges are visible on the insulator surfaces during wetting by rain, fog, mist
and high humidity. These discharges might not necessarily lead to a flashover but do
give an indication of pollution build-up which could eventually lead to a flashover;
f). flashover or discharges are evident at particular times of the year;
g). corrosion of the pin of cap-and-pin disc insulators;
h). the insulator is near a potential source of pollution for example, the coast or a chemical
plant;
i). the insulators are covered with old, whitened layers of grease;
j). erosion of the glass around the base of the pin on glass disc insulators; and
k). evidence of erosion of the surface of polymer or resin insulators.
6.2.18.5.3.4 Guideline for insulator maintenance periods
a). Insulator maintenance period depends on the level of pollution in the area and the creepage
distance of the insulator in question; i.e. an insulator of creepage 25 mm/kV in a high
pollution area will need more regular attention than an insulator with a creepage of 31
mm/kV.
b). Table 1 describes the period required between washing and greasing of insulators for the
different pollution levels and for different insulator creepage. When determining the
maintenance period required it is important to determine the pollution severity of the area
as described in annex A and then find the insulator creepage of the insulators in question.
c). The periods between maintenance intervals can be determined by using information from
point (b)
d). above. The number in the table represents the number of months between maintenance
33
intervals.
Table 6-2: Number of months between maintenance intervals
1 2 3 4 5 6 7 8 9
Washing Greasing
Insulator creepage in mm/kV 10 20 25 31 16 20 25 31
Light pollution N N N N N N N N
Medium pollution 24 N N N 24 N N N
Heavy pollution 2** 12 24 N 2** 12 24 N
Very heavy pollution **** 2** 12 24 **** 2** 12 24
NOTE 1 N = No washing or greasing is required.
NOTE 2 **** = Insulator is under creepage limits and should be replaced with an insulator of higher
creepage.
NOTE 3 ** = Insulator is under creepage limits and it is recommended that the insulator be replaced
with an insulator of higher creepage.
6.2.18.5.3.5 Bird guard or perching guard
a). It has been established that bird streamers are one of the causes of line insulator
flashovers.
b). In the case of point a) above, suitable prevention in the form of bird guard can be
considered.
6.2.18.5.3.6 New lines
New constructed lines (using ceramic insulators) shall comply with individual utility
specifications with regard to the specific creepages.
6.2.18.6 Maintenance documentation
The equipment identification information (make, serial number, type etc.) on the maintenance
document or the equivalent shall be compared with equipment nameplate on site at each
inspection. Any change in the information shall be noted and returned to the maintenance service
provider via the work co-ordinator who shall update the information in the maintenance system.
All faults, repairs and replacements effected during inspections and maintenance work shall be
recorded
6.2.18.7 Insulator pollution remedial action chart
A decision tree diagram or insulator pollution remedial action chart (see annex A) was developed
to be used as a quick reference to the selection of the most appropriate action.
The flow chart is self-explanatory and it guides the user to a list of possible technically acceptable
solutions. The user can then decide on the best action to be taken by referring to the maintenance
34
intervals, risks and costs tabled in the insulator pollution remedial action chart.
7. UNDERGROUND DISTRIBUTION
7.1 Cable Route Markers
Cable route markers shall be inspected annually and replaced if damaged, missing or unclear
7.2 Cable Take-off Marking Plates
Cable Take-off marking plates shall be inspected annually and replaced if damaged, missing or
unclear
8. GENERAL MAINTENANCE PRACTICES
8.1. Corrective maintenance – Items for immediate action
If there are any faults or damage or if faulty items need to be replaced during inspections and the
repairs can be effected with the equipment in service, immediate action shall be taken. The
following are examples of such actions:
a). replace the protection panel indicator bulbs;
b). reset and note any protection alarms;
c). replace any damaged labels;
d). replace faulty meters;
e). replace print-out paper;
f). repair or replace connection box door seals;
g). ensure that earth straps are in good condition and effectively connected;
h). seal spare or unused cable entry holes on connection boxes or auxiliary connection boxes.
i). replace missing bolts or nuts; and
j). re-tighten loose connection-bolts and nuts.
8.2. Preventive maintenance – Scheduled actions
a). All routine maintenance shall be carried at the intervals specified in the relevant
manufacturer‘s manual or as dictated by local conditions.
b). All defects shall be analysed and correlated on a monthly basis in order that maintenance
outages can be timeously scheduled.
c). All scheduled work shall be supervised by company certified personnel in accordance with
the relevant approved maintenance instructions.
d). All solvents, lubricants, pastes or greases that are used when performing maintenance shall
be as specified in manufacturer's manuals or in approved maintenance instructions.
e). The conditions of the equipment shall be recorded.
8.3. Infrared scanning
a). Infrared scanning shall be carried out in accordance with internal company procedures.
b). Any defects found shall be recorded and managed in terms of the internal company
maintenance procedures
35
8.4. Reporting and recording
a). All substations shall have a log book and inspection checklist. All work done by any
person who performs any type of maintenance at the substation shall be recorded.
8.5. Maintenance documentation
a). A work order with the applicable job description and approved maintenance instruction
shall be issued before any work is carried out. The feedback required for each specific job
shall be stipulated on the job description.
b). The equipment identification information (make, serial number, type etc.) on the work
order shall be compared with the equipment nameplate on site at each inspection. Any
change in the information shall be noted and returned to the maintenance service
provider in accordance with internal company procedures and the information shall be
updated in the maintenance system.
c). All faults, repairs and replacements effected during inspections and maintenance work
shall be recorded on feedback forms or checklists and returned to the relevant staff that
shall capture the information for maintenance planning and for equipment history.
36
9. APPENDICES
Annex A: Record list for routine inspections of power transformers
Substation: …………………………………. Date: ……………………………..……………….
Panel/Bay: …………………. Make: …………………………….. Serial No: …………………
S/N TASK REMARKS
1 Check and record ambient temperature
Check and record oil temperature and maximum
Check and record winding temperatures and maximums
(reset max. indicator)
2 Check and record present loading HV
Check and record maximum loading HV (reset max.
indicator)
3 Check and record main tank conservator oil level
Check and record Diverter Conservator oil level
Check and record bushing oil levels
Check and record auxiliary equipment oil level/s
4 Check and record percentage of silica gel pink
Check and record oil pot levels
5 Check, test-run and record condition of the cooling fans
Check, test-run and record condition of oil pumps
6
Check and record all on-load tap change operation
counters (do not reset)
7
List of all defects from the inspection checklist
DONE BY (PRINT NAME) ___________________________ SIGNATURE __________________
ACCEPTED BY (SUPERVISOR) _________________________________
37
Annex B: Recommended Visual Inspections
(Informative)
Table B.1 give guidelines for the various visual inspections to be carried out on sub-transmission and
distribution overhead power line networks.
Table B.1 - Recommended Visual Inspections
1 2 3
Frequency of
Inspection
Equipment Task
Annually Auto-recloser Switches Test SEF batteries and replace, if
necessary
Annually Conductors (Including joints) Check:
-Condition
-Line conductor tension and line sagging
-Debris etc. on the line
-Joints
Annually Insulators Check:
-For damage e.g. chipping, cracks
-Pin fixing
-Conductor binding
-For rust on Hardware (detailed)
-For flashovers
-For incorrect and missing insulators
Annually Poles Check:
-Alignment
-For damage, e.g. rot, cracks, rust
-Numbering
-For soil erosion, under mining
-Vandalism
-For being water logged
-Planting depth
Annually Cross-arm Check:
-Position, alignment on the pole
-Condition, e.g. rot, cracks, rust
-Mounting bracket condition
-Rust on hardware
-Support straps
-General hardware line conditions
Annually Swan Necks (if installed) Check:
-For rust
-Position and damage
Annually Stay assemblies Check:
-Damage/condition
-Tension
-Insulators, where fitted
-Stay cover/guard
-Corrosion
-Stay rod
Annually Anti-climbing devices (where
applicable)
Check damage/condition
Annually Vibration Dampers ( Where Check:
38
fitted) -Position
-Condition
Annually Expulsion fuses Check:
-Insulator condition
- Signs of tracking or symptoms of
electrical damage
-Loose connections/crackling
Annually
Surge arrestors Check:
-Insulators
-Connections
-Mounting brackets
Annually Air break switches Check:
-Insulator condition
-Contact leads
-Earth bonding conductor
-For loose connections
-Mechanism stability (detailed)
-For rust on hardware
-Operating handle mechanism for
damage or luck of lubrication (detailed)
-Condition of padlock, i.e. missing, ease
of operation and damage (detailed)
-Jumper condition and clearance
-Labelling, naming
Annually Auto-reclose switches Check:-
-Insulators
-Jumper condition and clearance
-Paintwork
- Oil leaks
-Oil levels,
-Earthing/ bonding
- Anti- climbing devices
-Access
-Mounting bracket condition
-Control box (where applicable) e.g.
mounting
-Labelling, naming
Annually Sectionalizers Check:
-Insulators
-Jumper condition and clearance
-Paintwork
-For oil leaks
-Oil, levels
-Earthing, bonding
-Anti-climbing device
-Access
-Mounting bracket condition
-Control box (where applicable), e.g.
mounting
-Labelling, naming
39
Annually Transformers Check:
-Insulators
-Jumper condition and clearance
-Paintwork
-For oil leaks
-Meter box (where applicable), e.g.
mounting
-Labelling, naming
Annually Network and equipment
accessibility
Check:
- Tree and shrub growth
- Servitude condition
- Vehicle access
- Encroachments (buildings, etc.)
- Access gate condition and security
Annually Tower and mast structural steel Check for corrosion on:
-Legs,
- Beams,
- Cross-arm(s),
- Footings
- Plates and bolts
- Loose, damaged or missing components
Check:
- Earth straps
- Erosion
- Flooding or water logging
Annually Earthing Check if:
- Test results are satisfactory
- Earth straps are in place and their
condition
Annually Stays and guys Check for:
- Corrosion
- Tension
- Guy grip, pre-formed end
- Stranding
- Stay guard
- Stay insulator
40
Annex C
(Informative)
Example of the detailed visual power line inspections
1 2 3 4 5
Lattice Tower
Tower number
or column
Self-
supporting
Guyed tower Tower sections Inspected by: Date: Remarks A. Tower or mast
– Structural
steel
Corrosion:
- Steel members
- Beam
- Cross-arm(s)
- Footings
- Plates/Bolts
A.1 Galvanizing: 1. Is there a reddish/whitish
discoloration?
2. Are there whole members or only
portions showing rust?
3. Does the metal appear to be corroded
away?
4. Is there rust streaking off the bolts?
5. Does the galvanizing appear to be
sandblasted?
A.2 Foundations:
6. Is there any subsiding at the
foundation?
7. Is there any erosion at the footing?
8. Is any erosion getting close to the
tower?
9. Is the concrete 150 mm above ground
level? 10. Is there any sand or soil over the concrete
foundation?
11. Are there any hairline cracks on the
footing or benching?
A.3 Members:
12. Look for loose members, if you see none,
hit the structure with a rubber mallet or similar
and listen for bolt ringing
13. Are there missing members?
14. Are the bottom members bent or
damaged?
15. Are there any loose step bolts?
16. Paint: Is the paint blistering?
17. Is the paint peeling?
1.
41
Annex D
(Informative)
Example of detailed power line inspection checklist
1 2 3 4 5
Lattice Tower
Tower number or
column
Self-supporting Guyed tower
Tower sections Inspected by: Date: Remarks A. Earthing
- Adequate
- Test results
1. Is it bolted tightly?
2. Is the bolt rusting?
3. Remove the soil where the earth strap
enters the ground - is the metal corroding?
1.
2.
3.
B. Stays/guys
- Corrosion
- Tension
- Grip
- Strand
1. Is the guy/cross head housing or U-bolt
rusting?
2. Is there visible slip between guy wire and
performed rods?
3. Are the tamper guards in place?
4. Examine cut guy end - are strands all the
same lengths?
5. Is bitumen still present - is there rust?
6. Does the guy wire appear to be slack?
Note if the wind is blowing as leeward slack
- Tension on a wire dynamometer: 22
dia>3,5 ton, 24 dia > 4,3 ton, 28 dia > 6 ton,
32 dia > 7,5 ton
1.
2.
3.
4.
5.
6.
7.
C. Insulators
- Clean
- Damaged
- Clips missing
1. Are the insulators dirty?
2. Is it a bird‘s dirt?
3. Is it pollution?
1.
2.
3.
C. Insulators
(continued) 4. Are insulators broken?
5. Insert number of broken insulators per
string and position
6. Is there faulting on insulators?
7. Are there any security clips missing?
8. Is there wasting at pins or stems?
9. Is there discoloration of hardware?
10. Insulator type
Tick the appropriate block at 10
-Porcelain ( A )
- Glass ( B )
- Cycloaliphatic ( C )
- Composites ( D )
4.
5.
6.
7.
8.
9.
10.
A B C D
D. Conductors and
earth wire
- Condition
- Spacers
1. Check suspension clamp for wear.
2. Is the damper/spacer distorted?
3. Is there any loose wire or bird caging?
4. Is there any bulging of the wire?
1. 2. 3. 4.
42
- Dampers
- Jumpers
- Joints
5. Is there white powder on the conductor?
6. Does the conductor appear to be wearing?
7. Are there burn marks on the conductor?
8. Is the bundle twisted?
9. Is the hardware wearing? (use binoculars)
10. Is conductor pulling/slipping out from
the armour grip suspension clamps?
11. Look for heat discoloration on ends of
midspan joints and strain clamps, dampers,
etc.
12. Is there a railway line within ± 800 m?
13. Is there insulation on the earth wires?
14. Are there loose bolts on the clamps?
15. Is the Crosby clamp in place on the
jumper?
16. Have the dampers moved along the
span?
17. Is there damage due to armour rods?
5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
E. General
- Identification
- Servitude
- Anti-climbing
- Tree clearance
- Gate locks
- Access
1. Is the tower numbered?
2. Is the number peeling?
3. Is the number clear?
4. Is the anti-climbing device damaged?
5. Is the anti-climbing device obstruction free?
6. Is the service road obstruction free?
7. Are there access road wash-a-ways?
8. Is the retaining wall damaged?
9. Are there any trees growing towards the
phases that could get too close to the line?
10. Are all locks in place?
11. Is there any damage to the gates?
12. Is the access difficult, is a helicopter
required, are new roads appearing, are quarries
appearing? (Use remarks column)
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
43
Annex E
(Informative)
Recommended Intervals for inspections
All the visual inspections tasks done yearly, which are not part of the ten-yearly maintenance, shall also be
carried out when ten-yearly maintenance is executed.
Table E.1 — Intervals for inspections
1 2 3
Frequency of
inspection
Equipment Task
Ten-yearly Poles Check:
- Pole base for rot
- Damage to pole
- Pole top for rot.
- Whether wire binding is intact (also
yearly)
- Whether earth down leads are intact (if
installed) (also yearly)
Ten-yearly Cross- Arms Check:
- Condition and alignment
- Rot
- Whether earth bonding is sound
- Whether pole mountings are secure
- Support straps for stability
- General hardware condition
Ten-yearly Transformers Check:
- That all connections are tight
- Insulators for damage
- Pole mountings
- For rust on tank and hardware
- LV circuit-breaker for safe operation
- That earth bonding is complete - For oil
leaks
- Earth resistance (measurements of earth
mat and earth electrode)
- Meter boxes, e.g. condition of the meter
box and the meter
- Labelling and naming
Ten- yearly Air break switches Check:
- Insulators
- All connections
- Jumper condition or clearance, or both
- Contact condition
- Contact alignment
- Operating mechanism for ease of
operation
- Lubrication, if necessary
- Padlock condition and ease of
operation.
- Unit operation
- Labelling and naming
Ten-yearly Connections Check:
- For corrosion
- Security of clamps
44
- For grease, if necessary
Ten-yearly Cross- Arms Check:
- Whether mounted secure on pole
- For rust on and damage to hardware
- For rot
- Earth bonding for soundness
- Support straps for stability
Ten-yearly Swan necks (where installed) Check:
- For rust and damage
- Earth bonding for soundness
Ten-yearly Conductors Check:
- Condition, e.g. corrosion, discoloration
- Line conductor tension and line sagging
Ten-yearly Tower or mast of structural steel Check for corrosion on:
- legs;
- beams,
- cross-arm(s);
- footings; and
- plates or bolts
Check for
- loose, damaged, or missing components;
- earth straps
- erosion;
- flooding or water logging; and
- tower footing resistance
Ten-yearly Earthing Check:
-if test results are satisfactory
- Earth straps are in place or in good
condition
Ten-yearly Stays, guys Check for:
- corrosion;
- tension;
- guy grip or pre-formed end;
- stranding;
- stay guard;
- stay insulator; and
- hazardous condition of stay wires
Ten-yearly Insulators Check for:
- pollution;
- missing clips or split pins;
- damage, e.g. chipping, cracks;
- rust on hardware (detailed);
- flashovers; - incorrect or missing
insulators;
- condition of conductor ties or binding;
- pin mounting or fixing
45
Annex F
(Informative)
Conductor Repairs
F.1 Pre-formed repair rods should be installed if no more than one strand is broken or nicked deeper than
one third of the strand diameter, or when a number of strands are reduced in area not exceeding the area of
one strand. Not more than two sets of pre-formed repair rods shall be installed on any one conductor in any
given span.
F.2 Compression-type repair sleeves (see F.3) should be installed if not more than one third of the outer
strands of the conductor are damaged over a length not exceeding 100 mm or not more than two strands are
broken in the outer layer of the conductor and the area of any other damaged strand is not reduced by more
than 25 %.
F.3 Compression-type repair sleeves should not be installed on one conductor in a given span if it already
contains a conductor splice, conductor dead-end, or another compression-type repair sleeve.
F.4 Damage to the steel strands or aluminium strands exceeding the stated limits for repair sleeves should be
cut out and spliced by means of a mid-span joint.
