By I.A.R. Gray(Senior Consultant-(MSAChem I No 51594)
Oilwatch Transformer Service
INTRODUCTION
Load tap changers (OLTCs) are a crucial element of utility networks, as they must operate in a precise fashion in order to maintain a constant voltage output. This must be achieved regardless of variation on input or load. OLTC’s have been a weak link in many networks as they deteriorate over time due to mechanical problems or contact wear from repeated operation. Erosion of the contacts over time is expected due to the nature of their function. Coking of the contacts causes overheating, which can cause thermal runaway. Regular maintenance is necessary to ensure continued proper functioning.
Oil testing has long been recognized as an important tool for detecting incipient faults in the main tanks of transformers and is being applied to load tap changers. Some of the advantages of oil test are.
- can usually be performed while equipment remains in service.
- can detect a wide range of problems in the early stages.
- can be used to ascertain a reasonable sense of the severity of the problem.
- have been shown to be very cost effective.
This testing is used to provide one of the most important early warning diagnostics for load tap changers and because of its effectiveness is making condition based maintenance a reality.
On-load tap-changers (OLTC) can be divided into two groups according to the type of current limiting
impedance used:
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