Transformer Maintenance Inspection | MBT

Why maintenance of the transformer is required? 

A transformer is the most essential and expensive piece of equipment in a power substation. Therefore, to achieve optimum performance and increase product life, it is best to conduct periodic maintenance checks on your machines.

Table of Contents

1. Purpose and forms of transformer maintenance

2. Monthly Periodic Transformer Maintenance Check

3. Daily Basis Maintenance and Checking

4. Basic annual transformer maintenance schedule

5. Transformer maintenance on a half-year basis

6. Maintenance of Current Transformer

7. Annual maintenance of voltage transformers or capacitor voltage transformers


1. Purpose and forms of transformer maintenance

a. Purpose of transformer maintenance

The primary purpose of transformer maintenance is to ensure that the transformer and accessories' internal and external components are kept in good condition, "fit for the purpose" and can operate safely anytime. Equally important is to maintain a historical record of the transformer condition.

b. Transformer maintenance forms

Power transformers require a variety of routine maintenance tasks, including measuring and testing different transformer parameters. There are two primary forms of transformer maintenance. We perform one group periodically (called preventive maintenance) and the second on an exceptional basis (i.e., on-demand).


Transformer Maintenance

2. Monthly Periodic Transformer Maintenance Check

- The oil level in the oil cap must be checked monthly so as not to fall below a fixed limit, and thus damage caused by it is avoided.


- Keep the breathing holes in the silica gel breathing tube clean to ensure proper breathing operations.


- If your power transformer has oil fill bushes, make sure that the oil is filled correctly.


If necessary, the oil will be filled into the bushing to the correct level. Oil filling is performed in the shutdown condition.

3. Daily Basis Maintenance and Checking

- Read the MOG (Magnetic Oil Meter) of the main tank and storage tank.


- The color of the silica gel in the breath.


- Oil leaks from any point of the transformer.


In the event of an unsatisfactory oil level in the MOG, the oil must be filled into the transformer, and the whole transformer tank must be checked for oil leaks. If an oil leak is found, take the necessary action to seal the leak. If the silica gel becomes slightly pink, it should be replaced.

4. Basic annual transformer maintenance schedule

- The automatic, remote, and manual function of the cooling system mean that oil pumps, air fans, and other equipment join the transformer cooling system and the control circuit. They will be examined over a one-year period. In case of malfunction, investigate the control circuit and the physical condition of the pump and fan.


- All transformer bushings must be cleaned with a soft cotton cloth annually. During the cleaning of the bushing should be checked for cracks.


- The oil status of OLTC will be checked annually. Therefore, the oil sample will be taken from the drain valve of the diverging tank, and this collected oil sample will be tested for dielectric strength (BDV) and humidity (PPM). If the BDV is low, and the PPM for the moisture is higher than the recommended value, the oil inside the OLTC needs to be replaced or filtered.


- Mechanical inspection of Buchholz relays to be carried out every year.


- All containers must be cleaned from the inside at least once a year. All lights, space heaters are checked to see if they are working correctly. If not, you must take maintenance action. All the terminal connections of control and relay wiring to be checked a tighten at least once in a year.


- All relays, alarms, and control switches together with their circuits, in the R&C (Control Panel and Relays) and RTCC (Remote Tap Change Control Panel) panels, should be cleaned with substance proper cleaning.


- Pockets for OTI, WTI (Oil temperature indicator & coil temperature indicator) on the transformer's top cover to be checked, and if the oil is needed.

- The proper function of the Pressure Release Device and Buchholz relay must be checked annually. Therefore, the devices above' trip contacts and alarm contacts are shortened by a small piece of wire and observe if the related relays in the remote control panel are working correctly.


- The transformer's insulation resistance and polarity index shall be checked with a megger operated with a 5 kV battery.


- The ground connection's resistance value and the rizer must be measured annually with a clamp on the earth resistance meter.


- DGA or dissolved gas analysis of transformer oil should be performed annually for 132 kV transformers, once in 2 years for transformers below 132 kV, for two years for transformers on a 132 kV transformer.

Action to be taken once every two years:

  • The OTI and WTI calibration must be done once every two years.
  • Tan & delta; The measurement of the transformer bushings shall also be carried out once every two year

5. Transformer maintenance on a half-year basis

Your power transformer needs to be tested every six months for IFT, DDA, flash point, sludge content, acidity, water content, dielectric strength, and transformer oil resistance.

6. Maintenance of Current Transformer

Current transformers are an essential part of any equipment installed in a power transformer station to protect and measure electricity.

  • The insulation strength of the CT must be checked annually. In the process of measuring insulation resistance, it must be remembered that there are two insulation levels in current transformers. The insulation level of the primary CT is relatively high, as it must withstand the system voltage. But the secondary CT's has a low insulation level in general of 1.1 kV. Therefore, primary to secondary and primary to the earth of current transformers are measured in 2.5 or 5 kV meggers. But this high voltage megger cannot be used for secondary measurements since the insulation level is relatively low from the design's economic point of view. Therefore, the secondary insulation is measured in 500 V megger. Thus, the primary terminal to the earth, the primary terminal to the secondary measuring core, and the primary terminal to the protective secondary core are measured in 2.5 or 5 kV meggers.
  • Thermo vision scanning of primary terminals and top dome of a live CT should be performed at least once in a year. This scan can be done with the help of the Infrared Thermal Surveillance Camera.
  •  All CT secondary connections in CT secondary box and CT junction box must be checked, cleaned, and tightened annually to ensure the lowest possible CT secondary resistance path. Also, make sure that the CT junction box is cleaned correctly.


Products of MBT Transformer


7. Annual maintenance of voltage transformers or capacitor voltage transformers

  • The porcelain cover must be cleaned with cotton clothing.
  • The spark gap assembly will be checked annually. Remove the movable part of the spark gap when assembling, clean the braes electrode with sandpaper, and fix it back in place.
  • High-frequency grounding point should be visually checked annually in case the issue is not used for PLCC.
  • Thermal vision cameras are used to check any hot spots in capacitor stacks to ensure professional rectifying action.
  • Terminal connections PT junction box consists of ground connections tested for tightness once a year. Besides, the PT junction box must also be properly cleaned once a year.
  •  The condition of all gasket joints should also be visually checked and replaced if damaged seals are found.

Although your power transformer may continue to function smoothly, continuous failure of the electric vents and even minimal maintenance can speed up the failure avoidance of transformers. To avoid this, contact our experts at MBT Transformer by +84913 006 538 or email: [email protected] for a free consultation and support and receive the most preferential quotation.

(+84) 0913.006.538
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