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ADDRESS OF MR. DIMITAR BELELIEV
CHAIRMAN OF THE MANAGING BOARD
Dear Colleagues, Clients and Partners,
Since the day of its establishment in 1948, up to now CENTRALNA
ENERGOREMONTNA BAZA (CERB) plays a key role in the energy re-
pairs’ sector in Bulgaria and the whole Balkan Peninsula. Our huge
experience and priceless human resource, combined with our de-
sire for continuous development and renovation, has ensured a
leading place in our sphere for almost 70 years now.
Today, spreading on 20 000 m2, 150 qualifi ed engineers, tech-
nicians and specialist are working in our company. The fi rm has
a growing list of cooperatives, suppliers and numerous clients in
more than 10 countries. More enterprising than ever, the company
will continue its development, entering new markets and sectors
with confi dence, expecting positive results!
We are the only Bulgarian company for maintenance of the main
equipment in the conventional and unconventional energetics. We
perform major international projects in more than 10 countries, Greece, Macedonia, Kosovo, Bosnia and
Herzegovina to name a few.
In the last couple of years we included new services and installed new equipment, as to be up to
date with the most advanced technologies, for example the distance monitoring of rotating machines
through the system VibroHealth+, which is the company’s own product. We have an own data center
– the fi rst in the energy repair sector, own steel foundry with a capacity of 2500 kg melted steel. We off er
industrial cleaning with dry ice blasting.
CERB EAD owes its success to the solid business model we developed and follow: high standards and
continuous improvement, cooperation with clients and care for their investments, reasonable prices,
communication, and mobility.
Our mission is to transform our experience and capabilities into expansion and use for our clients.
Dimitar Beleliev, M.Sc.
2
Built in tradition and with more than 67 years of experience in the power sector, today our company
is a well know reliable supplier of the following services:
� Diagnostics, repair on site and in house of generators (turbo and hydro) and HV motors and
transformers
� Up-rate of power electrical machines and power transformers
� Redesign and manufacturing of new windings for power transformersand generators
� Diagnostics and repair of on load tap changers
� Mounting, dismounting, failure prevention and repairof circuit breakers, disconnectors and other LV,
MV and HV commutation equipment
� Manufacturing of new distribution and power transformers up to 110 kV
� Manufacturing of current limiting neutral earthing resistors (NER)
� Machining of castings and forgings, including large assembled units. Manufacturing of electricity
conducting fi ttings for power cables and conductors, boiler equipment and non-standard mechanical
structures and equipment
� Vibration analysis and dynamic balancing of turbo and hydro generators, steam turbines, electrical
motors, fans and other rotating mechanisms.
� Control of metals
� Oil sampling and chemical analysis of transformer oil
� Transportation of heavy and oversized cargoes by auto trailers and gooseneck railway wagon
HISTORY
Establishment of
CERB (1948)
Registration of
CERB as JSC (1994)
Privatization of
CERB AD (2001)
Sole owner
company (2010)
Implementation of ISO 9001,
ISO 14001, OHSAS 18001
2002 - 2008
Workshop for
rotating electrical
machines
(1948)
Transformers
Workshop
(1956)
Production of new
transformers
(2005)
Production of NER
(2006)
Transport
department
(1965)
Vocational center
for welders
(1975)
Implementation of
SA 8000:2004
(2012)
Dynamic balancing
and vibration analysis
department
(1975)
Own system for online
vibration monitoring
VibroHealth+
(2014)
3
www.cerb.bg
ROTATING ELECTRICAL MACHINES
CERB performs diagnostics, partial repair, overhaul and rehabilitation of the following types rotating ma-
chines: Hydro generators, Turbo generators, Synchronous and asynchronous motor
Repair services and rehabilitation of generators are provided on site and at the workshops of CERB.
ON SITE REPAIR
Stator
� Test of the stator winding
� Complete or partial dismantling of the winding
� Re-insulating of coils and bars
� Cleaning of stator core and body
� Visual inspection of the core and ELCID test for insulation
faults and overheating
� Partial or full rewinding
� Re-wedging
� Final tests
Rotor
� Rotor dismantling
� Poles mounting and dismounting
� Cleaning and replacing of pole
insulation
� Final tests
ON SITE BALANCING OF ROTORS
THROUGH MOBILE STAND IRD BK140
HPP Kremasta,
Hydrogenator 3
HPP Kakanj,
Bosnia and Herzegovina
Traction engine
Induction motor, 4 MW Albania
Hydrogenerator Rotor, 90 MW Greece
4
Winding
When the repair of the winding is partial, it includes
- restoring of the inter-turn insulation and manufac-
turing of new main insulation and insulation of the
end-winding (overhangs).
The complete repair includes manufacturing of new
winding.
CERB manufactures coils and bars via Resin Rich
technology.
Advantages of using Resin Rich insulation system:
� It has excellent electrical, thermal and mechanical properties
� It is able to resist severe environmental conditions
REPAIR OF GENERATORS IN HOUSE
Stator
� Revision and repair of the stator body
� Checking of the geometric dimensions of the stator
� Re-stacking of the core with re-varnishing of the stator lamellas
� Manufacturing of new core
� Hydraulic pressing of the core
� Testing
Rotor
� Replacing of the insulation of the pole coils
� Restoring of cracks of the pole coils
� Replacement of the pole insulation
� Replacement of the aluminum winding of a short
circuited rings
� Partial repair with welding of cracks in the short
circuited rings
� Replacement of the winding insulation of coiled
rotors
� Manufacturing of new slip rings and brush
carrying devices
� Impregnation
� Tests
REDESIGN & UP-RATE OF GENERATORS
Design, construction andmanufacturing of new windings for generators, redesigned to work with
an increased rated power by 10 % over the existing.
5
www.cerb.bg
MAINTENANCE & OVERHAUL OF HV MOTORS
Maintenance:
� Replacement of bearings, brushes, brush-
carrying devices
� Tightening of leads
� Re-wedging
� Cleaning of the stator core
� Cleaning of the stator body
Partial repair:
� Replacing of coils, insulation, bandage
� Re-insulation of coils
� Replacement of the pole insulation
Overhaul repair:
� Rewinding of the stator
� Rewinding of the rotor
Testing:
� ON Load – only ON SITE
Cleaning with dry ice of turbo generators, hydro generators and motors
During the rehabilitation of generators and repair of motors, CERB performs cleaning of the stators and
rotors via dry ice blasting. The cleaning of the stator’s core, windingand body as well as thebody of the
rotor signifi cantly improves the cooling of the unit. Bearings, bearing bodies, bearing guards, covers and
other metal or insulating parts are also cleaned from varnishes, oils and other dirt which appear during
operation.
CONTACT: Rotating machines workshop - tel.: +359 2 8105 418
6
TRANSFORMERSCERB provides:
� Diagnostics, maintenance and repair on site or in house of power, distribution and special transformers
with rated voltages up to 400 kV
� Manufacturing of new transformers with rated voltages up to 110 kV
� Supply of second hand refurbished power and distribution transformers
Transformer 31,5 MVA; 10,5/110 kV HPP Aleko Autotransformer ZTR267 MVA/400 kV, substation Miziya
Diagnostics
At CERB we strongly believe that prevention is better than cure. That is why, with a view to lower the risk
of unforeseen breakdowns and costly emergency repairs, CERB recommends and off ers to its customers
yearly diagnostics and maintenance of transformers ON SITE
On-line Testing
� Thermo-vision inspection
� Determination of the highest oil temperature
� Noise and Vibrations
� Partial discharges
� Oil sampling and analysis
� Analysis of the cooling system,
� Analysis of control and protection systems
Off line testing
� Measurement of no load loss and current (LV)
� Dielectric tests
� Dissipation factor (tg δ) and capacitance (C)
� Turn Ratio Test (TRT)
� Windings’ resistance with DC
� Short circuit impedance
� Measuring of HV bushings – tgδ and C
� Measuring of the built-in current transformers Thermovision of 5 MVA transformer
7
www.cerb.bg
Repair on site
� Removing of oil leakages from gaskets/weldings
� Repair or replacement of all accessories (bushings, relays,
thermometers, valves, cranes etc.)
� Repair or replacement of the cooling system (radiators,
coolers, fans, pumps, wires, control cabinets)
� Revision with opening of the active part
� Drying of the active part
� Processing of the oil:degassing, cleaning, dehydrating or
replacing with new one
� Restoring of the anti-corrosion and decorative protective
coating
� Testing
Repair in house
Provided an overhaul is required, CERB off ers to its customers to transport the transformer IN HOUSE
where the following services are performed:
� Repair of the core
� Repair of the windings
� Manufacturing of new windings
� Repair of the metal construction (tank, cover, bottom,
conservator, pipelines)
� Restoring of the anti-corrosion and decorative protective
coating
� Repair or replacement of all accessories (bushings, relays,
thermometers, valves, cranes etc.)
� Repair or replacement of the cooling system (radiators,
coolers, fans, pumps, wires, control cabinets)
� Drying of the active part in vacuum furnace
� Processing of the oil: degassing, cleaning, dehydrating
� Testing in HV test room
Generating transformer 170 MVA;
220/13,8 kV
Transformer 40 MVA; 110/6,3 kV
8
Manufacturing of new transformers
CERB manufactures new transformers specially
designed to meet the Customer’s specifi c needs.
Range of products:
� Manufacturing of oil immersed power transform-
ers with rated voltages up to 110 kV.
� Manufacturing of oil immersed distribution
transformers with rated power up to 1600 kVA
and rated voltages up to 35 kV.
� Manufacturing of dry type transformers with
rated power up to 630 kVA and rated voltages up
to 10 kV.
� Manufacturing of special transformers according
to Customer’srequirements (including locomo-
tive, measuring transformers in the range of 10
- 35 kV, earthing transformers).
Power transformer 8 MVA 35/20 (10) kV Transformer 20/0, 4 kV, 630 кVA
Set of power and auto transformers
5 MVA; 6,3kV
Transformers are tested in compliance with requirement of ENBDSIEC 60076 or other standards requested
by the Customer.
Supply or giving under rent refurbished power and distribution transformers
We have on stock refurbished second hand transformers as well as a data base with available transformers
owned by our partners which are not in use.
CONTACT: Transformers workshop - tel.: +359 2 8105 468
9
www.cerb.bg
Manufacturing of Neutral Earthing Resistors (NERs)
Neutral Earthing Resistors (NERs) are used in medium-voltage AC distribution networks to limit the current
that would fl ow through the neutral point of a transformer or generator in the event of an earth fault.
NERs limit fault currents to a value that does not cause any further damage to switchgear, generators or
transformers beyond what has already been caused by the fault itself.
CERB has its own design and manufactures neutral earthing resistors (NERs) up to 35 kV / 300 A, 10 seconds,
in compliance with IEEE 32 and certain customer’s requirements.
Our products are produced from up-to-date materials and construction like:
� Resistant elements – Kanthal A1,D; Alkrothal
� Insulation materials – technical ceramics and fi berglass
� Supporting elements – carbon or stainless steel (shaped or on sheets) coated with protection layer of
suitable paint in compliance with Customer’s requirements
� Accessories – bushings, current transformers, leads boxes
Construction
1. Insulation
� Composed of resistances with porcelain bushings as a separator in-between the elements and to the
corpus
� Composed of resistances with glass fabric-based
laminate as a separator in-between the elements
and to the corpus
2. Type of resistance material: FeCrAl
3. Cooling: air, natural fl ow (AN)
4. Mounting
� Vertical
� Horizontal
Operating conditions:
� Outdoors
� Indoors
10
DIAGNOSTICS AND REPAIR OF
ON LOAD TAP CHANGERSРемонт на стъпални регулатори от следните производители:
� „HIUNDAY HEAVY
INDUSTRIES”- Bulgaria
� “TRO”- Germanyя � “ELIN”- Austria
� “ЗТР” - Ukraine � „MR”- Germany � “ABB”- Switzerland
Diverter switch: taking out the insert from the oil vessel and analysis of the condition of the mechanical
system, spring-energy accumulator contact springs buff ering mechanism and the locking mechanism,
measuring the wear of the contact systems, measuring the resistance of the current-carrying path and the
transition impedance, registering the sequence of operation of the contact systems and analysis of the
obtained results.
Motor drive unit:
� checking the condition of the protective box
� checking the operation of the thermostat and the heater
� checking the operation of the counter
� checking the operation of the end electrical and mechanical
blocking devices
� checking the operation and condition of the controller,
commutator, protective circuit breaker, contactors, control
switches and the plug
� checking the electrical blocking device for manual operation
� functional checks: step by step operation, automatically
crossing the middle positions, completion the initiated
switching operation after restoration of failed supply voltage
Tap selector with a change over selector: registering the
sequence of operation of the contact systems, measuring the
electrical resistance of the current-carrying paths of the on-load
tap-changer and assessment of the condition of the contact
systems without an access to the active part of the transformer,
analysis of the condition of the contact systems
System on-load tap-changer and motor drive unit:
checking of the condition of the upper shield, checking of the
condition of the protective membrane, checking of the condition
and operation of the protective oil fl ow relay, checking of the
condition and operation of the worm gear with a local position
indicator, checking of the condition of the bevel gear, checking
of the condition of the vertical and horizontal driving shafts and
cardan couplers.
CONTACT: Transformers workshop - tel.: +359 2 8105 468
11
www.cerb.bg
HIGH VOLTAGE TEST LABORATORY
CERB EAD off ers continuous control of the repair works’ quality, in conformity with the active Bulgarian
and international standards.
The electric test and measurement laboratory
has both stationary and mobile equipment for
performing the following diagnostic, control and
type tests and measurements:
� Testing of cores with nominal induction and
examination of local overheating
� Measurement of the windings’ resistance
� Measurement of voltage ratio and check of
phase displacement
� Measurement of the insulation resistance of
the windings
� Measurement of the windings’ capacity and
the insulation’s dielectric power factor(tgδ)
� Measurement of no-load loss and current with
decreased and nominal voltage
� Measurement of short-circuit impedance and
load loss
� Measurement of the level of partial discharge
in a “no load” state and when energized
� Diagnostics of the oil-paper insulation
� Testing of the inter-turn insulation of the
windings with induced AC voltage (100 Hz)
� Testing of the main insulation of the windings
with AC voltage with industrial frequency, applied from separate source (the laboratory is supplied with
both a stationary high voltage installation for up to 350 kV and a mobile high voltage installation for up
to 75 kV)
� Diagnostics and tests of On Load Tap Changers
� Sweep frequency response analyses. The FRA method capture a unique fi ngerprint of the transformer.
The measurement gives a direct answer if the mechanical parts of the transformer are unchanged or
not. Deviations indicate geometrical and/or electrical changes within the transformer
� The tests of rotating electrical machines include measuring the index of polarization as well as testing
of the main insulation with direct voltage, recording the leak current and coeffi cient of non-linearity
The laboratory performs functional testing of the facilities’ protection and signal equipment, measurement
of the bushings, etc.
CONTACT: HV Test laboratory - tel.: +359 2 8105 471
12
MACHINE-TOOL WORKSHOPMechanical processing and manufacturing of spare parts� Lathe processing on a horizontal or carrousel turning lathe
� Milling processing, performed on universal milling machines, piano-miller and coordinate boring
machine
� Mechanical processing on a horizontal boring machine
� Slotting operations
� Grinding operations – round and fl at grinding
Bench and welding works� Bending of pipes, manufacturing of heating equipment for steam water heating boilers
� Bench works – cutting-up, bending, perforating, etc.
� Welding of steel constructions, under pressure vessels, pipe stacks, shafts, built-up welding
� Welding of aluminum elements
� Welding of non-ferrous metals, such as bronze, brass, copper, etc.
Complex repair works� Mounting and demounting of bearing connections of rotors and shafts
� Repair works for pumps – repair of operating wheels, guide apparatuses, shafts, corpuses,
manufacturing of spare parts
� Relining and mechanical processing of sliding bearings for electric motors, water and steam turbines,
radial and axial generators
Cast manufacturing � Casts of non-ferrous metals, such as bronze, brass, aluminum – silicon alloy
� Crude iron and steel casts
Manufacturing of current accessories (certifi ed manufacturer)� Manufacturing of current clamps – aluminum, bronze, brass, bi-metal
� Manufacturing of fi ttings for fl at and pipe systems
� Manufacturing of portable earthing devices
13
www.cerb.bg
We have a mobile horizontal-boring
machine
The portable horizontal-boring machinecan
create openings ranging from ∅ 22 mm to
∅ 180 mm with the accuracy and speed of a
stationary machine. These devices are meant
to be used in places where operating with a
conventional boring machines is impossible.
The portable horizontal-boring machinehas a
function to build by welding (overlay) without
change of the layout.
The overlay range is from ∅ 25 mm to
∅ 250 mm.
Remetaling of slip bearings
CERB EAD has the equipment and technology for centrifugal remetaling of slip bearings. The main
advantage is the decreasing of the expenses for the basic material and the time for layering a new
composition. The essence of the process is the removal of the already used-up anti-friction lead-tin
composition and layering of a new one.
CERB has a foundry workshop with a capacity of 2500 kg of melted steel
The foundry workshop off ers casting of all types of carbon steel (St25, St35, St45, etc.) as well as from
chrome-nickel steel.CERB has at its disposal a pattern-shop which enables us to produce castings with our
own patterns or with patterns provided by the Customer.
Manufacturing of spare parts and non-standard equipment for electrical machines
� Impellers for pumps and water turbines – manufacturing of pattern equipment
� Carbon steel casts with weight up to 2 t. Crude iron and bronze casts with weight up to 250 kg
� Manufacturing of boiler equipment – shields, serpentines, steam heaters etc.
CONTACT: Machine-tool workshop - tel.: +359 2 8105 480
14
TRANSPORTCERB is a licensed carrier of heavy and oversized loads with weight up to 130 t by road and 250 t by railway.
Our reliable and effi cient transport service is equipped with haulage trucks “MERCEDES”, trailers “SHOERLE”
and railroad special fl at wagon “MAN” with 20 axles, equipped with board hydraulics for the transportation
of self-carrying loads. The railroad wagon is also designed to transport non-self-carrying loads of up to 200
t of mass, suspending an additional interstitial platform.
The road equipment has an active local control on the trolleys, making it easily maneuverable in narrow
transportation corridors. Not only transformers and electric machines are transported, but also any other
industrial loads.
The loading, unloading and supporting are performed by an experienced rigging team.
CONTACT: Transportation Department - tel.: +359 2 8105 209
15
www.cerb.bg
LABORATORIES AND QUALITY CONTROL UNITS
LABORATORY FOR VIBRATION ANALYSIS AND
DYNAMIC BALANCING� Vibration analysis of hydrogenerators and turbogenerators, steam turbines, motors, fans and other ro-
tating mechanisms supported by rolling or sliding bearings.The methods for vibration analysis applied
by our specialists help to reduce the breakdowns, idle time and the expensive repairs of the equip-
ment.
� Balance of hydrogenerators and turbogenerators, steam turbines, electric motors, fans and other ro-
tating mechanisms on stand or on own supports.The laboratory disposes of three stands for dynamic
balancing of rotors. On а mobile stand make IRD BK 140 are balanced rotors with weight from 3000 kg
up to 100 000 kg.
The dynamic balancing is carried out in conformity with ISO 1940/1.
At customers’ request, CERB balances rotating machines and equipment on own supports.
� Adjustment of the regulation system of steam turbines and determination of the static parameters af-
ter general or preventive repair
VIBROHEALTH+
SYSTEMS FOR REMOTE MONITORING OF THE VIBRATORY CONDITION OF ROTATING MACHINES
Individual systems for monitoring and analyzing the vibrations of rotating machines.
The primary data, coming from the external sensors is transformed in specifi c values and specters, through
software programs, fi lter functions and internal signal processing.
The systems are designed upon a modular principle for maximum fl exibility and ensure high productivity
when performing a wide range of tasks.
VibroHealth+ MAX 1.3
The system is designed in a standardized 19“ standard subrack, 3U, 240 мм.
Technical characteristics:
Central module for connection with the data storage server, through a LANinterface, meant for submitting
information for vibration analysis.
16
VibroHealth+ ECO 1.0
The system is designed in a box, for mounting on a DINbus duct.
Technical characteristics:
Central module with a LANinterface, for submitting information by the sensors, connected to it, about the
vibrations and setting the parameters of the system itself.
Two analogue outputs, as per the 4-20 mA standard, corresponding to the mean square values of the vi-
brations of the bearings and two relay outputs for signalizing when a certain alarm level is exceeded are
placed on the corpus. Separate alarm levels are entered for each sensor.
The LCD display is used for visualization of the data, measured by the system.
Light-diode indicators are foreseen, signalizing for a fault along the grid of each sensor, as well as color
indication for the vibratory condition regarding the machine’s alarm zones.
CONTACT: R&D Department: - tel.: +359 2 8105 400
Visualization module for the mean square value of the bearings’ vibrations, supplied with a relay output,
signalizing when a certain alarm level is exceeded.
Module for measurement of the turns (speed), by a laser sensor.
Module for measuring the linear displacement, by an inductive sensor.
Analogue output module, as per the 4 - 20 mAcurrent signal standard, which is supplied with three relay
outputs, triggered when three separate alarm levels are exceeded.
Bearing vibration measurement modules with two accelerometer sensors.
The basic system has 7 inputs for connecting modules, as it can be expanded to up to 32 modules.
17
www.cerb.bg
CENTER FOR METALS CONTROLThe Center for control of metals at CERB is:
� Accredited by EA “Bulgarian Accreditation Service”, certifi cate № 277ОКС as a control body type “С”
� Certifi ed in compliance with BDS EN ISO 17020:2012
The staff is certifi ed I compliance withBDS EN ISO –9712
The following materials, components or equipment are evaluated:
� Boilers and boiler equipment
� Turbines - shafts, blades, diaphragms, bodies, valves, bolts, and studs
� Generators - rotors, binding nodes
� Vessels under pressure
� Metals and alloys - rolling, pipes and pipe-works, forgings and moldings
� Handling equipment
� Welded couplings and springs
The tests are carried out via following methods:
Non - destructive methods (NDT
� Radiographic controlконтрол
� Ultrasonic control
� Magnetic –particle control
� Liquid penetrant control
� Visual control via Endoscope or Borescope
� Density test
� Chemical analysis
� Thermovision of metals and non-metals
Destructive methods
� Microstructure analysis
� Mechanical tension tes
High temperature tests of creeping and durable strength
Evaluation of the residual life of equipment via software program ALGOR
18
The laboratory disposes also with its own developed methods,
such as:
� Methods for performing all kinds of non-destructive and destructive
control
� Methods of analysis of the shafts of turbine rotors on the side of the axial
channel, where visual inspection by endoscope, ultrasonic control and
measuring of the residual deformation of the shaft are applied
� Methods of non-destructive control on the retaining rings of the rotors of
turbo-generators with hydrogen cooling
� Tests of turbine blades applying ultrasound and vortex-electric crack tests
� Inlet control methods of newly delivered seamless pipes for boiler
equipment at TPPs
PORTABLE LABORATORY FOR METAL ANALYSIS
CERB has a portable deviceBelecCompact Port, which determines the chemical composition
of metals via the optic-emission method - by BELEC, Germany
A specifi c feature of this device is the precise air-conditioned camera with individual photo multipliers
for each element, ensuring high accuracy and repeatability of the measurement results not only of the
stationary but from the portable devices also.
Because of the usage of traditional photo multipliers and not CCD detectors, the device’s separating
capacity for the UV specter elements (C, P, S, Ni, Cu и др.) is considerably higher, so as the accuracy of their
determination is guaranteed.
Belec Compact PortFe has the following
equipment:
� 1 base iron (Fe), completely calibrated
� 300 mm spectrometric camera with individual photo
multiplier detectors for each element
� thermally stabilized spectrometer with
air-conditioned camera
� BelecWIN21 analysis software
� Belec-plug-in system for quick switch of the diff erent
measuring probes
� spark excitation for the argon and air probes
� Basic specifi ed recalibration probes /SUS/ (a set)
� built-in data base with all types of steel as per EN and
GOST standard
Belec Compact Port with the Fe basic model is equipped
with the following 16 measuring channels for the
following elements: Fe – basic, C, Si, Mn, Cu, Al, Cr-I, Cr-II,
Mo, Ni-I, Ni-II, V, Ti, Nb, Co, W.
CONTACT: Control of metals center - tel.: +3592 8105 445
19
www.cerb.bg
CHEMICAL LABORATORYAnalysis of transformer oil is one of the most eff ective methods to control the condition of transformers,
early diagnosis and prevention.
Wishing to off er the full range of analyzes in combination with professional interpretation of results,
evaluation of the condition of transformers and subsequent recommendations, CERB joint eff orts with
the independent laboratory ICLab, Athens, Greece.
The chemical laboratory at CERB is accredited by EA “Bulgarian Accreditation Service”, certifi cate № 225 in
compliance with BDS EN ISO 17025:2006 and scope of registration - Oil sampling and oil analysis, covering
the following properties:
� Appearance
� Density at 20OC (gr/ml)
� Breakdown voltage (kV)
� Water content (mgH2O / kgoil)
� Flash point (OC)
� Acidity (mg KOH/goil)
� Acid and alkali existence
� Dielectric dissipation factor at 90OC (tg δ)
� Interfacial tension (mN/m)
The insulation system of a transformer consists of liquid (transformer oil) and solid (celluloses) insulation.
The monitoring and maintenance of the quality of the oil are extremely important for guaranteeing a
reliable operation of the oil-fi lled electric equipment. For the purposes of evaluation of the liquid insulation’s
condition, numerous analyses are performed, such as: physical-chemical analysis, DGA, analysis of furan
compounds, corrosive sulfur, inhibitors, PCBs, infrared spectrum analysis, etc.
With normal exploitation conditions, the insulation oil preserves its electric and chemical stability. With the
presence of abnormal electrical and thermal infl uences,
the oil may begin to decompose, which leads to gas
formations. The character, quantity and speed of increasing
of separate gasses, found in the oil, are indicators for the
type of developing fault in the equipment. Furthermore,
the discovery of gasses, present in the oil and the correct
interpretation of the results may prevent failures and
costly repairs.
The good condition of the solid insulation is also very im-
portant for the proper exploitation of the transformers.
The furan compounds, dissolved in the oil, are a specifi c
product, achieved with the thermal-chemical deteriora-
tion of the cellulose. These compounds are an indicator
for the stage of insulation aging and a source for indirect
conclusion about the remaining resource.
On the basis of the complex of laboratory analyses of
the transformer oil, the Chemical Laboratory of CERB can
diagnose the developing faults in transformers in a very
early stage, as well as off er specifi c recommendations for
further actions.
CONTACT: Chemical laboratory - tel.: +359 2 8105 478
20
DRY ICE BLASTINGDry ice-blasting is a form of abrasive blasting, where dry ice, the solid form of carbon dioxide, is acceler-
ated in a pressurized air stream and directed at a surface in order to clean it.
Dry ice blasting provides a non-conductive, environmentally responsible cleaning process that allows
equipment to be cleaned in-place, without cool down or disassembly. In addition, the outage time typi-
cally needed for cleaning can be reduced up to 65%.
Cleaning with dry ice blasting during rehabilitation of generators
With time, the ventilation channels of the stator core
gets polluted, limiting the air fl ow, which passes
through the core and decreases its cooling. The
dry ice blasting cleans completely the ventilation
channels as well as the rest of the core.
When a replacement of a stator winding is not
necessary, but the existing one is heavily polluted,
cleaning is recommended, since the presence of
pollution on the surface of the stator windings
leads to worsening of the materials’ insulation
characteristics. In most cases cleaning with diff erent
chemicals is applied, but fi rst – they’re very harmful for a person’s health and secondly – they can damage
the insulation of the stator winding. Dry ice cleaning of the stator windings allows a gentle removal of
pollution in the front parts of the stator winding, without a chance of damaging it. After cleaning of a
heavily polluted winding the increase of the insulation resistance is guaranteed. A considerable advantage
of this technology is that it can be performed on site, without the necessity of demounting of the stator.
CONTACTS: Electrical Rotating Machines workshop - tel.: +359 2 8105 455
APPLICATION
� Generators
� AC/DC Motors
� Rotors
� Stators
� Transformers
� Circuit Breakers
� Switch Gears
� Bushings
KEY BENEFITS
� Reduce catastrophic failure
� Improve megohm readings
� Increase polarization indices
� Improve thermal dissipation
� Reduce outage time for cleaning by 65%
� Eliminate secondary waste
� Clean in-place, no cool down or
disassembly
� Non-conductive
� Non-abrasive
� Environmentally responsiblе
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www.cerb.bg
CENTER FOR VOCATIONAL TRAINING OF WELDERSThe Center is certified by the “National Agency for Vocational Education and Training” – license
№ 200312118.
The Center is a member of the “Bulgarian Welding Society” and a provider of the following
education and training courses:
� Hand operated arc welding
� MIG/MAG
� TIG (GTAW Gas Tungsten Arc Welding)
� Oxy-Acetylene Welding
The certifi cates issued by the training center cover the following levels:
� Seam welder
� Sheet welder
� Pipe welder
The education is in compliance with BDS EN 287-1 standard.
CONTACT - tel.: +359 2 8105 436
1 Lokomotiv Str.
1220 Sofi a, Bulgaria
Tel.: +359 2 8105 454
Fax: +359 2 8327 029
E-mail: [email protected]
www.cerb.bg
CERB’s Center for vocational training of welders
CERB’s Center for vocational training of welders was established by Decree of the Council of Ministers in
1976. So far we have trained over 40,000 welders. The center has good facilities and well-trained teachers.
We prepare welders from all disciplines and all levels. In the training center we perform replacement of old
certifi cates and revalidation of subjects that are expired.
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ELECTRIC CONSTRUCTION Main activities:
� Research, design, construction and commissioning of new energy units
� Repair, retrofi t and maintenance of existing energy units
� Design, construction, repair and maintenance of indoor installations
� Subscription services
� Consultancy services
� Electric construction – outdoor electric supply for middle and low voltage, delivery and mounting of CTS
(Compact Transformer Substations), reformation of existing transformer substations and switchgear,
construction of new built-in switchgear, delivery and mounting of measuring, distribution and other
electric boards.
� Pre-project research of possibilities for connection with the distribution system
� Preparation of projects – idea and operation phase
� Coordination with all authorities for receiving a construction permit
� Construction and commissioning
Off ered services:
� Research
� Design
� Coordination
� Construction supervision
� Construction
� Commissioning
� Maintenance and prophylaxis of switchgear
� Consultant services
� Design, construction and maintenance of indoor electric
installations
� Delivery and mounting of all types of electric boards
� Reactive energy compensation systems
CONTACT - tel.: +359 2 8105439
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www.cerb.bg
CERTIFICATES
To assure high quality and high standards of our services we have implemented:
� Quality Management System – EN ISO 9001:2008
� Health and Safe Labor Management System BSI-OHSAS 18001
� System of Environmental Management EN ISO 14001:2004
� System of Social Responsibility SA 8000:2008
CONTENT
Address of Mr. Dimitar Beleliev, Chairman of the Managing Board 1
History 2
Rotating Electrical Machines 3
Transformers 6
Neutral Earthing Resistors 9
Tap Changers 10
High Voltage Test Laboratory 11
Machine-Tool Workshop 12
Transport 14
Laboratories and Quality Control Units 15
Center for Metals Control 17
Chemical Laboratory 19
Dry Ice Blasting 20
Center for Vocational Training of Welders 21
Electric Construction 22
Certifi cates 23