Electricity and Control March 2020

TRANSFORMERS, SUBSTATIONS + CABLES

Complementary tests - Particles (counting and sizing) - Metals-in-oil test - Sediment and sludge

appropriate tests are conducted as and when necessary. If particular problems are detected, further tests may be recommended. There is no fixed rule as to which tests are conducted and when. He says, “We generally find that 80 to 90 per cent of transformers are healthy. However, when we are dealing with the problematic ones, we need to identify the problem and determine the severity of the problem. In extreme cases, we would advise that the transformer is taken out of service and the problem rectified.” Transformer tests The following tests are recommended for a basic fleet assessment, considering potential degradation of the solid insulation of the transformers’ active parts. - Dissolved gas in oil test - Oil quality results including moisture and acidity - Estimated or measured moisture in cellulose - Furans analysis - Dissipation factor (DDF/Tan D) or Power factor (PF) of the main insulation - Specified additives (restricted to inhibited and or passivated oils) - Corrosive sulphur in oil test - Transformer oil temperature (loading profile and cooling efficiency)

- Environmental contaminants - Specialist furanic tests (DP) - Diagnosis of tap changers and diverters test data - Gassing tendency of the oil. On-load tap changer (OLTC) maintenance WearCheck's Transformer Maintenance Division has developed a special OLTC programme to optimise maintenance based on its transformer diagnostic tests. The OLTC assessment offers a number of benefits. - It is a diagnostic programme that does not require equipment outages, thus enabling work management flexibility. - It serves to identify problem OLTCs before failure, to reduce system outages. - It is less intrusive than internal visual inspection. - It is an irreplaceable aid in prioritising main- tenance functions and reduces time-based maintenance and the associated expense. - It enables customers to reduce overall costs of maintenance by being selective. WearCheck supports its customers in spending the maintenance budget where it’s needed; this makes financial sense. Condition-based maintenance is

an effective cost-saving tool as it enables customers to focus their maintenance efforts and investments where evidence shows these are required. □

A failed transformer can have a disastrous impact on the operations which depend on it. A good transformer condition monitoring programme detects potential failure before it occurs.

Gert Nel, Transformer Division Manager at WearCheck.

Electricity + Control

MARCH 2020

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