How to Repair 110kV and Above Power Transformers?

The overhaul period, content, and technology of 110kV and above power transformers should strictly comply with the power industry standards “Guidelines for Inspection and Maintenance of Power Transformers“, “Guidelines for Operation and Maintenance of On-load Tap Changers” and other regulations.

In order to ensure the overhaul quality of power transformers and ensure that the defects do not recur, please read this article.

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Preparation work before repairing 110kv power transformer

The transformer specialist shall submit an application for overhaul in advance in accordance with regulations, operating conditions, defect diagnosis results, and structural features.

Prepare seals, necessary spare parts for overhaul, such as dry white cloth tape, crepe paper, etc., rain (damp) equipment, etc.

Determine a qualified and experienced maintenance team. In principle, the overhaul work is undertaken by the company’s department or team. Outsourcing maintenance should strictly abide by the “Outsourcing Project Management Regulations”, and it is strictly forbidden to “substituting for management”.

The maintenance plan is prepared by the person in charge of maintenance technology. 

The plan should at least include organizational measures (setting up a command group, construction group, acceptance group, security group, logistics group, and propaganda group when necessary), technical measures (overhaul purpose, overhaul content, process requirements, hoisting equipment requirements and precautions, construction Network diagram, layout diagram, signature form for intermediate acceptance content, registration form for storage of tools and instruments). 

The plan should be reviewed and approved. 

If the plan is prepared by an outsourcing (contracting) maintenance unit, it should be reviewed by the transformer owner unit’s transformer specialist and safety supervision personnel, and approved by the production director (factory manager or chief engineer). 

If it is a deficient overhaul, the plan should be discussed and determined by the transformer factory and your technical team.

Collect weather forecasts and apply for power outages.

High pressure, protection and oil service test before overhaul.

Repair 110kV and Above Power Transformers
Repair 110kV and Above Power Transformers

Precautions for repairing 110kv power transformer

If the overhaul is scheduled for April-September, technicians from the local meteorological department should be invited to the ceiling on the day, or they should keep close contact with the technicians of the local meteorological department to keep abreast of weather changes.

The temperature of the transformer oil before draining should not be lower than the ambient temperature. 

Generally, the temperature of the top oil of the transformer should be 5-10℃ higher than the ambient temperature, and the hot oil circulation method can be used in advance.

The ambient humidity when draining the oil should not be less than 75%. In general, dry air or dry nitrogen should be used to break the vacuum.

After hanging the cover, use qualified transformer oil for cleaning.

Before re-covering, check whether there is any foreign matter left in the transformer body, and the signature form of the intermediate acceptance content should be signed intact.

The auxiliary maintenance project combined with the overhaul of the main transformer should also be signed for intermediate acceptance, especially for concealed projects.

When people enter the transformer body for inspection, ensure that the inside of the transformer body is ventilated, and the oxygen content should be guaranteed to be 18% or more. Take protective measures. 

Pay special attention to safety when using a nitrogen-filled transformer to break the vacuum.

Transformers of 110kV and above should be evacuated and filled with oil.

Precautions after repairing 110kv power transformer

For extended overhauls, such as acetylene exceeding the standard before repair, replacement of part of the main insulation, repair of part of the winding, etc., the 110kV transformer should be subjected to partial discharge tests.

There are no remaining defects, and the test and acceptance are qualified.

The on-load voltage regulating switch is qualified. Check that the oil pillow has no false oil level, and the oil level is normal.

All valves have been opened and closed correctly, and the elevated or dead zone positions have been exhausted many times.

The oil pump of the strong oil circulating transformer has been started for a period of time and exhausted the air. 

When the pump is turned on, the windings on each side of the transformer should be grounded to prevent the safety of the operators from being energized due to the oil flow.

The rest time complies with the regulations.

Non-electricity protection has been set up as required.

Matters needing attention when power transformers work

The neutral point of the transformer has been directly temporarily grounded.

The normally open contact of the pressure release valve of the 500kV transformer has been temporarily tripped.

Before repairing the transformer with multi-point grounding of the iron core, the grounding current of the iron core should be tested after it is put into operation. 

The grounding current should be less than 100mA, and the maximum should not be greater than 300mA.

The number of impacts of the transformer after the winding is replaced is 3 times, and the interval between each time is not less than 15 minutes.

When the on-load voltage regulating switch continuously regulates the voltage step by step, the interval time should not be less than 5 minutes;

Two or more transformers operating in parallel should be operated step by step or synchronously at an interval of no less than 5 minutes each time. 

The purpose is to prevent a large amount of gas from accumulating and causing gas action to trip.

At least one gas chromatographic analysis of oil should be performed within 72 hours after commissioning.

Chromatographic analysis of gas in oil should be carried out within 24 hours after the first full load.

After the deficient overhaul, the transformer should be shortened appropriately according to the situation after the transformer is put into operation.

About Bin Dong

Hello, I am Bin, General manager of Daelim which is a leading transformer manufacturer. If you have problems when you are looking for the equipment, what you need to do is tell us.

Custom 110kv Power Transformer

When you need to find more than just existing transformers, Daelim’s Transformer Service Center can help you design and produce distribution transformers that meet your unique needs.

We have our own factory and a professional team of engineers, which can design and modify application requirements that meet all your conditions.

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