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.

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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)

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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.

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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.

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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

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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: info@cerb.bg

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

23

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