Power transformer and cable testing

We have recently purchased VLF and tan delta testing equipment to allow pressure testing and condition assessment of cables with operating voltages up to 33kV.  The tan delta test facility is particularly useful to assess the remaining life of power cables that have been compromised by poor laying and resulting water ingress.  The tan delta assessment provides a health index for the cables and the possibility of just-in-time replacement before the cables fail.  This is particularly useful on renewable energy sites where the cable lengths are very significant and the cost of wholesale cable replacement can be prohibitive.

Power transformers are widely considered the most critical components in electrical transmission and distribution networks.  Due to the aging of transformer fleets in the field, regular diagnostic testing and condition assessment become increasingly relevant.  We have on order an Omicron CPC-100 with associated equipment to allow testing of power transformers.  Measuring a full range of different parameters can be a time and cost intensive job.  In order to perform the different diagnostic tests, multiple devices and a frequent change of test leads are required.  Individual phase measurements and multiple tap changer positions further increase the testing effort and the outage time. An automatic switch box will allow us to perform multiple tests using the same test setup. This not only reduces the rewiring effort but also further reduces overall testing time and increases the safety for the operator. After the testing is complete, the results can be automatically assessed according to international standards or user defined limits, using the Omicron Primary Test Manager database.

Parameters we can measure include:-

• Capacitance and power factor/dissipation factor measurement
• DC winding resistance measurement and OLTC verification
• Transformer turns ratio measurement
• Exciting current measurement
• Short-circuit impedance / leakage reactance measurement
• Frequency response of stray losses measurement
• Demagnetization