Transformer & Reactor Commissioning Services

GTR – Utilising Advanced Testing Technology

Commissioning and Maintenance of Power Transformers and Shunt Reactors


Windings Insulation Resistance and Core Limb and Core Clamping Insulation Resistance

This basic insulation resistance test is used to determine the integrity of windings and the condition of windings insulation. Transformer windings are exposed to environmental factors such as dirt, grease, temperature, stress, and vibration which can lead to insulation failure. The test is performed after the initial installation of transformer and as part of the routine maintenance.

Common Electrical Tests

Measurement and Analysis of Short circuit impedance, transformers ratio, vector group, magnetising current, static winding resistance and dynamic winding resistance including analyses of the OLTC switching process.

Results are compared with the manufacturer data and factory test results. Common Electrical Tests are part of routine checks of transformer health and are also used to check the on-load tap changer and the condition of OLTC contacts.


Tan delta

Tan Delta

(Capacitance & Power Factor)

This test is used investigate the condition of the insulation of power transformers bushings. Partial breakdowns between the capacitive layers of bushings can be detected before a major insulation failure.

Oil Sample Tests

As transformer oil is contact with every internal component of a transformer it contains a great deal of diagnostic information.

GTR can assist in conducting laboratory analysis of transformer oil samples to provide an advance warning of developing fault conditions. Standard supervision and maintenance analysis include tests such as dielectric strength, water content, acidity, colour, odour and visible contaminants.

Voltage and Current Transformer

Instrument transformers play a crucial role in protection and control system performance. Reliable operation of protection, control and metering systems can only be achieved with correctly functioning current and voltage transformers. It is therefore essential to assess the performance of all instrument transformers as part of the maintenance routine. Assessments are performed by conducting primary injection tests, insulation resistance measurements of secondary windings, turns ratio, CT excitation and saturation tests, burden impedance checks, winding resistance measurement and polarity tests.

Documentation and Reporting


  • Automated Test Reports from specialised test and commissioning equipment
  • Customised and system specific test documentation
  • Detail report on work completion with test results and further recommendations

The main purpose for all the above routine and maintenance tests and analysis is to detect transformer developing faults before a major failure occurs. In case of a major fault the only system that will isolate the transformer from the network and prevent from further extensive damages is the protection system. GTR specialises in testing and commissioning of protection schemes and protection relays and conducts secondary injections using specialised test equipment with dedicated transformer protection function modules. GTR also performs overall function testing to verify overall system integration, including mechanical trips from transformer protection devices.


  • Installation and refurbishment of protection relays, control devices and instrumentation in generation
  • Secondary injection tests on protection relays and scheme functional checks on protection & control panels
  • Evaluation of site maintenance requirements
  • Preparation of maintenance schedules
  • Equipment specification and purchase
  • Supervision of contactors


Sweep Frequency Response Analysis



Sweep Frequency Response Analysis

SFRA tests are recommended to be performed at the end of the acceptance test at the factory to establish the transformer’s original fingerprint and then again after transportation, and during commissioning. The test generates a unique frequency response, which can be compared with the reference fingerprint. Changes, movement or deformation of internal components lead to changes in this transfer function and can be identified by comparing the plots.


Frequency Response of Stray Losses

Measurement of resistive component of the short-circuit impedances at defined frequency range. By applying FRSL method GTR can identify short-circuits between parallel strands, winding deformations due to forces generated during fault conditions winding fault conditions.

The FRSL measurement is normally carried out during commissioning or acceptance test to establish benchmark results for future maintenance or post fault diagnostics


Dielectric Frequency Response (DFR)

Polarisation Spectrum Measurement


Dielectric Frequency Response

DFR also known as ‘Polarisation Spectrum Measurement’ is used to assess the moisture content of the cellulose insulation located between the primary and secondary winding. This test is normally carried out as part of the maintenance routine to assess insulation conditions. Insulation performance can be affected by paper aging or increased moisture level due to broken seals. This measurement is also used for new transformers to prove the low moisture content after the drying process.

Omicron MPD 600

High-end measuring and analysis

for partial discharges


Partial Discharge

Partial discharge (PD) can cause irreversible damage to power transformer insulation,
long before the insulation actually fails. Even upon detection and analysis, it is
essential to know exactly where insulation defects are located in the transformer.

Test Equipment


  • OMICRON CMC 256/356 – Secondary Injection of protection relays and instrumentation and Transducer Testing
  • OMICRON CPC 100 – Multifunctional Primary Test System (Current, Voltage, Micro Ohm Resistance, etc)
  • OMICRON TESTRANO 600 + TD1 – Common Electrical Tests, Static & Dynamic DC Winding Resistance, Tap Changer, Short-circuit impedance / leakage reactance measurement, Excitation current, Capacitance & Power Factor of the windings and bushings, FRSL.
  • OMICRON CT Analyser – Protection and metering current transformers (Ratio and phase angle, CT excitation and saturation, burden impedance, winding resistance, CT Polarity)
  • OMICRON FRANEO – Sweep Frequency Response Analysis (SFRA)
  • OMICRON DIRANA – Dielectric Frequency Response (DFR) – ‘Polarisation Spectrum Measurement’
  • Buchholz Dry Air Pump – Buchholz relay function test
  • Hart Scientific 7380 Temperature Bath – WI temperature sensors calibration
  • PT100 Simulator – Winding temperature simulator
  • MIT515 5KV Megger – Winding insulation resistance test set
Trouble Shooting and Fault Investigations


  • Partial Discharge Analysis
  • Service values and status checks on in service devices and equipment
  • Post fault investigation and fault records analysis
  • Root Cause Analysis
  • Action plans, solutions recommendation and implementation

Our Services

We are a registered engineering company and supplier of high voltage Commissioning Engineers for power stations, substations, solar energy farms and on/offshore wind farms

GTR specialises in supplying resources to the High Voltage Transmission & Distribution industry from 220V to 400kV.

Design Solutions

Design works in engineering UK & Abroad.

Electric Vehicle Charging Points

GTR & Manpower Connections coming together to form a joint venture in this field

Engineering Resource Solutions

Supplying Resource to the engineering industry in the UK & Abroad.

Equipment Rentals

Hire Latest technology equipment with or without an operator

Generator Protection Solutions

We aim to meet your outage requirements

Renewable Energy Solutions

GTR has completed over 300 G59 Solar connections

SF6 Solutions

Sulfur hexafluoride (SF6)

Transformer & Reactor Commissioning Services

GTR - Utilising Advanced Testing Technology

Transformer & Reactor Installation Services

GTR - Utilising Advanced Testing Technology

Transformer Condition Assessments

GTR - Utilising Advanced Testing Technology

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