Principles and Philosophy of Protective Relaying

7/27/2019 Principles and Philosophy of Protective Relaying

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PRINCIPLES AND PHILOSOPHY

OF PROTECTIVE RELAYING

P1-COURSE PRESENTATION

BYENGR.W.A ASONMWONRIRI


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PERSONAL INFORMATION

NAME: Engr. Wilfred Amen Asonmwonriri (MNSE)

DATE OF BIRTH: September 1970

Married

Protection Engineer

FORMAL EDUCATION

M.ENG(POWER AND MACHINES)

B.ENG(ELECTRICAL AND ELECTRONICS)

PROFESSIONAL AND TECHNICAL EDUCATION

Travelling waves systems: QUALITROL

Power System Engineer ing:Power System Training Institute: - New Delhi

Protective Relay Testing using Omicron Test set :OMICRON

Conditi on-Based evaluation of power transformer:HIVOTEC-UNILAG

Reyrol le Protective Relays ApplicationsREYROLLE

Power system traini ng methods(Israel Electricity Training School. Tel-Aviv)


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PRINCIPLES AND PHILOSOPHY OF

RELAYING PROTECTION

The electric power system is designed to generateand supply energy to meet the demands of theusers on a continuous basis.

It comprises of many diverse equipment that arevery expensive

The whole system must be kept in operationcontinually without major breakdown so as toprevent severe disruption to the normal routinesof modern society


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To keep the power system in operation

continually adequate protection must be

provided.

Protective relays detect abnormalities or faults

and eliminate such abnormalities by isolating

the smallest portion of the system.


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Faults on transmission line

possible causes Lightning

Switching

Pollution Salt storms

Growing trees

Bush fires Damage or sabotage

The most often!


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RELAYS

Relays are the devices, which monitor the conditions of acircuit/device and give instructions to isolate it underunhealthy conditions.

The conditions of a circuit or equipment are monitoredfrom the electric power system parameters, the most basicof which are voltage, current, frequency and power.

The power system parameters have predetermined values

under healthy conditions.

. Any shift from this normal behaviour therefore, could bethe result of a fault condition.


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PRIMARY AND SECONDARY RELAYS

PrimaryRelays are the first line of defense in thesystem. They are generally high-speed relays. Theprimary relay scheme is designed to remove

minimum equipment from service. Secondary Relays also called backup relays are

intentionally delayed in their operation so as togive the primary relays a chance to operate first.

The backup relays scheme is independent of theprimary relay scheme and operates if the primaryrelay scheme fails to operate.


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ELECTRICAL POWER SYSTEM DEVICE

NUMBERS AND FUNCTIONS

1 Master Element

2 Time Delay Starting or Closing Relay

3 Checking or Interlocking Relay

4 Master Contactor

5 Stopping device

6 Starting Circuit breaker

7 Anode Circuit breaker

8 Control Power Disconnecting Device


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9 Reversing Device

10 Unit Sequence Switch

11 RESERVED FOR FUTURE APPLICATION

12 Over Speed device

13 Synchronous Speed device

14 Under Speed device

15 Speed or frequency matching device


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16 RESERVED FOR FUTURE APPLICATION

17 Shunting or Discharge switch

18 Accelerating or Decelerating device

19 Starting to Running Transition Contactor

20 Electrically Operated Valve

21 Distance Relay

22 Equalizer Circuit breaker


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23 Temperature Control device

25 Synchronizing or Synchronism Check device

26 Apparatus Thermal device

27 Under Voltage relay .

28 Flame Detector .

31 Separate Excitation device

32 Directional Power relay


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37 Undercurrent or under power relay

40 Field relay

50 Instantaneous over current or rate of rise relay

51 A.C. Time Over current relay

52 A.C. Circuit breaker

55 Power Factor Relay

81 Frequency Relay


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59 Over voltage Relay

63 Pressure switch

64 Ground Protection Relay

65 Governor

67 A.C Direction or Over-current Relay

79 A.C. Reclosing relay


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Power system protection is realized byprotecting the different primary equipmentthat variously constitute the power system.

A faulted component needs to be isolatedfrom the entire grid as quickly as possible to

prevent the fault from spreading to otherparts of the grid and to prevent damage toequipment and personnel.


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Main purposes of protective relays

To ensure uninterrupted power supply.

To reduce equipment damage.

To maintain quality of service.

To guarantee safety of life and property.

To ensure operation of equipment at peakefficiency.


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ATTRIBUTES OF PROTECTIVE RELAYING

(a) Sensitivity

A relay must be sensitive to the least fault

conditions for which it has been configured.

(b) Reliability

It must be relied upon at all times to respondto any fault by relaying signals that will cause

the faulty part to be isolated.


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(c) Selectivity

The relay must be able to discriminate between

faults and abnormal conditions.

(d) Simple

For a relay to be effectively used, itsconstruction and operation has to be simple in

nature.


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(e) Speed of Operation

To be able to prevent damage to the associatedequipment the relay is protecting, it must act

fast before the damage is done.

(f) Cost

The relay should not be so expensive as tooutweigh the benefit of using it to protect theassociated equipment.


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CATEGORIES OF FAULTS

Single phase to ground fault

Double phase to ground fault

Three phase to ground fault

Phase to phase fault

Three phase fault.

The commonest, in occurrence, of the above faultconditions, is the single phase to ground faultwhich is about 70%.


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Protective relaying was introduced in practice asearly as the first power systems were invented tomake sure that faults are detected and damagedor faulted components are taken out of service

quickly.

Faults occur randomly and may be associated

with any component of the power system.

The longer the fault duration, the larger is theextent of damage.


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EFECTS OF FAULTS IN A POWER

SYSTEM

Over heating

Over voltage (surge)

Over load

Fire disaster Unbalanced loading

Loss of synchronism

For the faults and abnormal conditions enumeratedabove protective relays are designed to isolate andreduce damage to the system equipment.


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RELAY PERFORMANCE

Performance of relays can be classified as:

Correct

Incorrect

Inconclusive.

Incorrect Operation

This can be due to the following factors:

Incorrect Relay Setting

Personnel Error

Equipment Malfunction


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Incorrect tripping may be either failure to trip or falsetripping.

Failure to trip can be caused by faulty associated

instrument transformer, circuit breakers, control cablesand wiring and station batteries.

Inconclusive Operation

This is the last resort when no evidence is availableeither for a correct or incorrect operation. Quite often,this is a personal involvement.


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RELAY OPERATING TIME

Relays can be classified in terms of their operatingtimes as follows:

High Speed Relays - operate in less than three (3) cycles Slow speed relays - operate in three (3) cycles or more

Time delay relays - have built in time delay facility toallow co-ordination with other relays within the power

system. Instantaneous relays - have no deliberate time delay

facility. They operate instantaneously.


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BASIC COMPONENTS OF A

PROTECTION SYSTEM CURRENT TRANSFORMERS

VOLTAGE TRANSFORMERS

CAPACITOR VOLTAGE TRANSFORMERS

CIRCUIT BREAKERS

RELAYS

CONTACTORS

DC BATERRY BANKS


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EQUIVALENT CIRCUIT OF A CVT


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BASIC COMPONENTS OF LINE

PROTECTION

PROTECTION

EQUIPMENT

TRIP

COIL

TELE

COM

DC SYSTEM

FAULT

VOLTAGE

TRANSFORMER

CURRENT

TRANSFORMER

CIRCUIT BREAKER


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ZONES OF PROTECTION

For effective protection of the system with

minimum part disconnected during fault,

protection zones are mapped out.

Motor Protection Zone

Generator Protection Zone

Transformer Protection Zone

Bus bar Protection Zone

Lines Protection Zone


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Zones of Protection

To limit the extent of the power system that is disconnected when

a fault occurs, protection is arranged in zones

Zones of protection should overlap, so that no part of the power

system is left unprotected

Location of the CT connection to the protection usually defines

the zone

Unit type protections have clear zones reach e.g Diff. Relay, REF

relay


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RELAY OPERATING TIME

Relays can be classified in terms of theiroperating times as follows:

High Speed Relays - operate in less than three (3)cycles

Slow speed relays - operate in three (3) cycles ormore

Time delay relays - have built in time delayfacility to allow co-ordination with other relayswithin the power system.

Instantaneous relays - have no deliberate timedelay facility. They operate instantaneously.


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DEVICES PERFORMING MORE THAN

ONE FUNCTION

If one device performs two relatively important functions in an

equipment so that it is desirable to identify both of these functions,

this may be done by using a double device function such as: 50/51 -

An over-current relay with an instantaneous element and an inverse

element.


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SUFFIXNUMBERS

If two or more devices with the same function number and suffix letter (if

used) are present in the same equipment then these are distinguished as

follows 52x-1, 52x-2, 52x-3 etc

SUFFIX LETTERS

Suffix letters are used with device numbers for various purposes. The

meaning of each suffix letter or combination of letters should be clearly

indicated in the legend on the drawings or publications accompanying the

equipment.Example: 52 TC Tripping coil of the breaker


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COMMONLY USED LETTERS

R - Raising relay or for remote operation

L - Lowering relay or for local operation

O - Opening relay or contactor

C - Closing relay or contactor

CS - Control Switch

CC - Closing Coil TC - Trip Coil PB - Push Button

G - Generator T - Transformer L - Line F - Feeder etc


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REPRESENTATION OF DEVICE

CONTACTS

There are almost in all electrical devices,

particularly in circuit breakers and relays, a set

of contacts which are normally open and

another set of contacts which are normallyclosed.

When the device operates, the contact

position reverses. Those normally openbecome closed and vice versa.


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CARRER GUIDE FOR YOUNG

PROTECTION ENGINEERS

The protection engineer is saddled with ensuringthe reliability and stability of the power system.

As a protection engineer you are an electricalengineer with specialisation in power systemsand protection systems.

It is obviously a great field as it forces you to fullyunderstand the technical aspects of the powerindustry.


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The major challenges facing the young

protection engineers

Bridging the gap between schooling and thereal world as most engineering students arebombarded with abstractions without ideas of

the big picture let alone a sense of the valueof work they will be doing.

Entry level position and qualification isanother challenge as the protection engineer

requires a solid foundation in electric powersystems to be successful.


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A deep understanding of the operation of all theelements of the power system is required as onecannot protect an equipment which operation hedoes not know.

He requires a solid understanding of manytechnical features of the power systemincluding:machine design parameters,bus

configuration, trip circuits, symmetricalcomponents,fault currents, unbalanced powerflow and much more


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For an early success in the protection

engineering career the young engineer should

undergo the following:

He should be made to pass through training

courses that are tailored specifically for

protective relaying.


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He should place himself on a continousprofessional development program by accessingpower system references and training materialswhich include textbooks,relay manuals, standards

and technical papers.

He should place himself on a continousprofessional development program by accessing

power system references and training materialswhich include textbooks,relay manuals, standardsand technical papers.


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The young engineer needs to develop good

hands-on-the job skills with ability to stay on

the job untill he gets result.


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The young engineer should be passionate

about his work as he requires the positive

mental attitude that goes with love for work

to succeed.

He needs to be quick and able to learn new

things all the time


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He needs a mentor for guidance as he

progresses in his career.

He needs to develop or join an existing

professional network or peer group in the

industry.


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This is quite a lot to ask of any one person but the

professional and psychological reward can be very

great.I cannot imagine a better field to begin a

power engineering career than protective relayingas the challenges it provides are endless and the

learning process a life- long one.

Documents

Principles and Philosophy of Protective Relaying