Repair of transformers

  • Working out the design and technological documentation;
  • Technical supervising and performance by ZTZ-Service specialists of the preventive and remedial repair and life extension of transformers;
  • Selection, adaptation, modification, restoration and tests of oil-filled HV bushings, LTC, cooling and breathing systems;
  • Development and performance of a series of works on the transformer oil characteristics rehabilitation;
  • Organization and performance of the repair works by ZTZ-Service Co. specialists and (or) by subcontractors.

There is a documented experience in repair and reconstruction of over 2000 large transformers and shunt reactors including::

  • In-field works on 110-750 kV transformers providing a special protection of the insulation;
  • Restoration after the bushings and LTC failures;
  • In-field windings replacement;
  • Transformers and shunt reactors life extension;
  • In-field drying out of the extremely wet insulation;
  • Degeneration and desludging of insulation using special regenerative oils.

Diagnostics of transformers

Diagnostics and maintance:

  • Assessment of the equipment good condition;
  • Determination of the defect type, cause and danger;
  • Determination of the repair necessity and scope, drafting the defects and failures card;
  • Technical following up of the equipment operation in presence of the defect symptoms;
  • Determination of the equipment wearing level and technical condition for the purpose of its life extension;
  • Working out the recommendations in respect to improvement of the operational conditions.

Base of the expert activity:

  • Accumulated during more than 35 years and continuously expanding database on operation, technical condition, failure types, etc. including information about more than 5000 power transformers;
  • High-skilled specialists having a great practical experience in the field of research, design, system investigation of the failures, tests and repair;
  • Updated diagnostic instruments and special laboratory equipment with wide use of the computer technique;
  • Multi-step diagnostics and functional test methods developed by ZTZ-Service Co. specialists, definition of the probable defects image via diagnostic characteristics;
  • Continuous research in the field of development and implementation of new test and diagnostics methods;
  • Standards and methodical materials MEI, CIGRE, IEEE, ASTM, Doble, extensive foreign information concerning methods of the early diagnostics and their practical application.

Methods used in ZTZ-Service Co. allow:

  • To determine the probable defects in the certain operational conditions, to assess the margin of safety and weak points in the design;
  • To detect the insulation moisture level basing on the results of Water Heat Run Test and temperature dependence of the insulation features;
  • To evaluate the insulation and oil spaces contamination level basing on the data of the insulation features temperature dependence and oil special analysis including the particles disperse analysis;
  • To determine overheating of the current-conducting joints on the base of measuring the contact transient resistances, dissolved gases and degradation products analysis;
  • To determine value and level of the windings deformation basing on the calcula-tion of the possible deformation, change of the short-circuit and capacitance parameters;
  • To detect the presence of overheating and discharges in electromagnetic system basing on the special analysis of the dissolved gases, electromagnetic character-istics and vibroacoustic measurements taking into account the design particular features;
  • To evaluate the insulation overheating presence and its aging level basing on the analysis of the dissolved gases, furanic components and insulation polymerization degree in the specially determined zones;
  • To determine presence and type of the local defect in the bushing core, oil contamination and aging level in the bushing and sediment presence on the porcelain internal surface through insulation characteristics temperature changes and im-balance current on the adjusted transformer in operation;
  • To determine the oil aging level and its residual resource.


Material testing laboratory

When we perform the test of the transformer oil sample in our Laboratory, we answer the main questions about the transformer condition:

  • How did the oil electric insulation characteristics change?
  • How did the oil age during the transformer operation?
  • Are developing the electric, thermal and mechanical defects, the additional equipment defects?

We assess the transformer insulation condition: moistening, contamination, aging degree of cellulose insulation.

As a rule, the oil tests are performed in accordance with international standards, but if necessary, they can be performed according to the Customer's national standards.

The Lab is certified in the Ukrainian certification system.

3000 analyses per year are fulfilled in the Lab.

The Lab possesses information concerning practically all transformer oils manufactured presently all over the world.

In-field testing laboratory

The main task of in-field testing laboratory is obtaining of the objective and reliable information regarding insulation, electromagnetic and mechanical systems of the power and instrument transformers and shunt reactors with the aim of assessment of their technical condition.

The Lab is certified in the Ukrainian certification system.

The works fulfilled by the lab are a part of complex investigation and diagnostics of the transformer equipment.

To perform the measurements the high-productive, accurate and interference-stable testing devices and measurement systems are used:

  • Insulation analyzer M4000 by "Doble", USA;
  • Apparatus by Bruel&Kjeir, Denmark;
  • High-voltage devices and measurement systems by Haefely Trench (+Tettex);
  • Measurement devices by AVO International;
  • Special purpose instruments.

To assess the transformer equipment condition the following methods and procedures are used:

  • Measurement of dielectric characteristics and their temperature dependence for evaluation of the insulation water content and contamination;
  • Measurement of the partial discharges intensity by wide-band and tight-band methods, partial discharge source localization by acoustic method;
  • Measurement of no-load and short-circuit characteristics, acoustic and vibration parameters for assessment of the electromagnetic system condition;
  • Thermovision control - determination of the dynamic condition of the transformer windings and magnetic system;
  • Determination of the contact joints condition and unity of the winding parallel con-ductors;
  • Definition of the transformation and winding connection group factors;
  • Determination of the cooling system condition;
  • Assessment of high-voltage bushings condition;
  • Determination of the voltage regulating devices condition;
  • Determination of dielectric characteristics of current transformers under operating voltage.

Installation of transformers

  • Technical supervising of installation and commissioning of all voltage classes transformer equipment;
  • Organization and performing the installation and tests using our own staff and (or) winning over to other specialized companies;
  • Technical support, tests and checks during warranty period.

We have over 40-years documented experience in installation and commissioning of over 5500 transformers rated 100 MVA and above including:

  • over 300 transformers rated 750 kV;
  • 1150 kV ± 750 kV transformers;
  • in all climate zones from Tropics to Arctic;
  • in mountainous regions;
  • in all regions of the former Soviet Union;
  • in Argentina, Bangladesh, Bulgaria, Canada, China, Croatia, Cuba, Czech Republic, Egypt, Germany, Greece, India, Iran, Iraq, Kuwait, Mexico, Mongolia, Morocco, Nigeria, Northern Korea, Pakistan, Peru, Poland, Romania, Slovakia, Sri-Lanka, Syria, Turkey, USA, Vietnam, Yugoslavia.


ZTZ-Service Co. is a developer of::

  • Guidelines for transportation, storage, installation and commissioning of 110-750 kV transformers;
  • Technical specifications for technological equipment of the oil and insulation processing;
  • Insulation drying out and moisture protection technologies.

We have documented experience in development and implementation of the follow-ing technologies:

  • How to fulfill installation and adjusting in the minimum technological terms;
  • How to prepare (sample, dry, refine and degas) the oil at minimum cost;
  • How to check and restore the transformer after a difficult transportation;
  • How to restore the transformer after ling-term storage in disassembled condition;
  • How to dry, clean, degas and impregnate the insulation.


Technique and technology of refurbishment and life extension. For this purpose ZTZ-Service Co. performs as follows:

  • Investigates in details the technical condition, evaluates the construction physical and moral wearing;
  • Eliminates the detected and potential defects;
  • Restores the electrical strength resources by the way of drying out, purification, special regeneration and reconstruction
  • Decreases the aging rate aging by means of sealing, cooling improvement, oil re-conditioning;
  • Decreases the operational expenses for cooling and maintenance;
  • Implements the effective protection against failure, for prevention of the blast and fire hazard, protection for on-line monitoring sensors;
  • Decreases the operation influence;
  • Fulfills a complex of preliminary, intermediate and post-repair tests with functional inspection of the equipment;
  • Performs the full-range technical following-up of the future operation.