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 and 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
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.
Oil Sample Tests
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.
(SFRA)
SFRA tests are recommended to be performed
at the end of the acceptance test at the factory
to establish the transformer’s original
ngerprint and then again after transportation,
and during commissioning. The test generates
a unique frequency response, which can be
compared with the reference ngerprint.
Changes, movement or deformation of internal
components lead to changes in this transfer
function and can be identied by comparing
the plots.
(FRSL)
Measurement of resistive component of the short-circuit impendences at defined frequency range. By applying FRSL method GRT 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 bench mark results for future maintenance or post fault diagnostics.
(DFR)
DFR also known as Polarisation Spctrum Measurment 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 aected 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.
(PD)
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.
Documentation and Reporting
- Automated Test Reports from specialised test and commissioning equipment
- Customized and system specific test documentation
- Detail report on work completion with test results and further recommendations
Maintenance
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 future 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 test 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
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
- MIT515KV Megger – Winding insulation resistance test set
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
Commissioning
GTR specialises in supplying resources to
the High Voltage Transmission &
Distribution industry from 220V to 400kV.
Design Solutions
Design works in engineering UK & Abroad.