transformer reliability

8/14/2019 Transformer Reliability

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Tr nsformer Reliability


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300 W. Antelope Road, Medford, OR 97503-1089, Ph. No. 541 826 2

The last ten years have seen growing interest in the evaluation and monitoring of power transformers -

mainly because a vast number of transformers worldwide are fast approaching the end of their effective

operating life. The reliability of the existing units within global distribution networks must thus be assessed

to understand if the transformers are fit for use, or need to be replaced or retrofitted.

Within power systems, transformers form a substantial part of the asset costs; financial pressures today

persuade most utilities to use existing units for as long as possible, as long as overall system reliability is

not at risk. Thus, transformer asset management looks set to play a major part in future planning.

Factors Influencing Power Transformer Reliability

This article focuses on the factors influencing power transformer reliability, which are:

1. Operating Environment

The operating environment is the set of conditions which the transformer will be exposed to

during its service life. This includes weather conditions, location, electrical loading, operating

methods, system parameters and application. Each element that influences the life of the

transformer must be recognized and documented.

National standards like ANSI, NEMA and others address many of these elements and provide

recommendations or standard values wherever applicable; which may be of benefit to the person

or organization responsible for assembling the data.

2. Transformer Specification

The specification of a transformer should describe the function it is to perform and the constraintswhich must be met. It should describe each of the identified operating conditions which affect the

transformer.

3. Transformer Design

Transformer design ensures the operating conditions of the transformer as mentioned in the

specifications are converted to concrete design parameters and into usable information by the

manufacturing organization.

The design engineer must get all the needed information within the specifications, and any

clarification must be obtained from the user or use parameters detailed in the national industrystandards. While manufactures continue to advance the state of the art to meet changing

operating environments, it is still fundamental to the designer that each known environmental

condition be considered and addressed in the design. Any omission could result in decreased

service life and premature failure.


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4. Manufacturing Process

Here the physical product is created from the paper design. The reliability of a transformer when it

completes the manufacturing cycle will differ from the reliability as demonstrated in the design,

due to the variations in the manufacturing process of materials, processes, handling, machines

and personnel.

Reliability will also differ between similar products. Quality techniques are aimed at manufacturing

the product as close as possible to the designed product. To verify the quality and reliability of the

manufactured transformer, two types of tests are performed:

o Compliance Test: The compliance test ensures that the transformer meets the specified

design parameters

o Reliability Test: The reliability test (Including the temperature rise test, induced and

applied potential test, corona test and gas-in-oil analysis) ensures that the product is

manufactured for a long service life.

From the latter test transformers with lesser life are segregated.

5. Installation and Shipment

The time from when the transformer leaves the factory until it is energized by the user is very

crucial. Any mishandling during shipment and installation can lead to failure of the product at an

early stage.

The transformer is typically shipped either by rail or road; and these conditions can sometimes

deteriorate. As a reactive measure, the ride history of the transformer is monitored and recorded.

An impact recorder can provide evidence of rough handling so as to investigate if damage has

been done to the product. An impact recorder is a recording accelerometer which will track either

two or three axis movement. The primary channel records impacts in the horizontal movement,

the second records the vertical movement and the third monitors the transverse or side to side

movement. If rough handling is suspected, immediate documentation should take place for the

benefit of the user and the manufacturer.

Once the transformer is accepted, the unit should be located at its permanent location forinstallation. The steps involved will be clearly written down by each manufacturer in the form of an

instruction book. All items which will come in contact with the oil should be thoroughly cleaned.

And people entering the transformer should not carry any loose items. Insulation resistance tests,

insulation power factor tests, winding ratio and winding resistance tests are performed. These are

the means to ascertain whether changes have occurred during transit.


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6. Transformer Maintenance

Transformer maintenance can be separated into two categories:

o Repair Maintenance: A reactive mode to repair an in-service failure or malfunction. Its

function is to restore the product to its usable condition as fast as possible.

o Scheduled or Preventive Maintenance: The purpose of this is to provide lubrication or

adjustment to components and also to monitor the state of the transformer and its ability

to continue to perform its function. The function of maintenance is to prolong life and thus

the reliability of the transformer.

The need to augment reliability of power systems will only increase. Preventive diagnosis and

maintenance of transformers is thus a crucial activity. Both manufacturers and users must jointly accept

the responsibility of ensuring that transformers are properly specified, designed manufactured, installed

and maintained.

As today's markets insist on higher quality energy supplies, utilities face the challenge of uninterrupted

delivery. This places the burden on the key components of power distribution networks - transformers.

Dedicated solutions are thus necessary to help utilities and power producers to manage equipment more

efficiently.

transformer reliability

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