Guide for Installation of Oil-Immersed Transformers (10 MVA and Larger, 69-287 kV Rating)
|Publication Date:||1 January 1980|
Scope and Introduction
The recommendations presented in this guide primarily apply to new large oil-immersed power transformers with high-voltage windings rated 69-287 kV inclusive. However, appropriate sections of the guide may be applied to lower voltage transformers when similar conditions and similar transformer construction exist, and may also be used in servicing older transformers which have been opened for maintenance or repair work.
Increasing application of larger capacity high-voltage transformers with reduced insulation has brought forth the parallel need for increasing care during installation and service. To maintain dielectric strength of the insulation it is essential to avoid moisture and entrapped air or gas bubbles. Since oil is an essential portion of the insulation structure, oil quality and care in handling are extremely important.
Large-power transformers are usually shipped without oil to reduce weight. To prevent entrance of moisture during transit the tank is filled with dry gas (usually nitrogen) under pressure. Generally, the user must conform to the minimum recommendations by the manufacturer of the transformer.
NOTE: In some cases, these transformers are oil filled when received, in which case the instructions relative to initial oil filling may be disregarded. It will not be necessary to drain this oil from the transformer except as required for inspection and repair, unless the original filling by the manufacturer was not done by the vacuum method.
At the installation site all reasonable precautions should be exercised to avoid exposure of insulation to moisture. It should be the aim of the user to put a new transformer into service in a condition at least as good as when it left the factory. Prior to starting installation of the transformer, a detailed procedure for handling, inspecting, assembling, vacuum treating, and testing the transformer should be developed and agreement between all parties concerned should be obtained.
To best ensure a long trouble-free life, it is recommended that all transformers in this class be filled with a high-grade transformer oil under as high a vacuum as conditions permit, but not less than the value specified by the manufacturer.