Technical library

This case study has been generously supplied by the Hitachi Energy Service group in Sweden. A 22 MVA, 10.5 kV/276 V (voltage regulation from 336 to 216 V), Diii furnace transformer, operating in heavy use for many years at a steel melting plant in Europe was subjected to a complete series of tests after a sudden failure during operation. The service contractor evaluated the electrical and dielectric condition of this transformer. During service, this type of transformer has its secondary winding connected externally in a Delta configuration through a high current bridge.

A 1978 vintage, 20 MVA, 69/13.09 kV, Dyn1 transformer, operating for a major North American utility, was taken out of service to repair a pump in the cooling system. The technical maintenance team completed the required repairs and conducted a complete protocol of routine commissioning tests, including a 10 kV line frequency (LF) power factor (PF) test.

A new transformer was tested in the field using Megger’s DELTA4000. This is what was found...

Pinpointing concealed problems inside a resistive-type OLTC before physical inspection - the application of true DRM.A maintenance team at the Electric Power Transmission Network in the City of Karbala performed routine electrical tests on a transformer including: winding resistance measurements (WRM), transformer turns ratio (TTR), short circuit impedance (SCI), excitation current, and line-frequency power factor (a.k.a. dissipation factor or tan delta). This case study looks into their investigations and their results.  

The subject 69 kV bushings are installed on a 10 MVA, 69/13.09 kV Dyn1 two-winding transformer. After completing on-load tap changer (OLTC) maintenance on this 1969-vintage transformer, the utility owner followed with electrical tests.

Electrical maintenance departments are often faced with the challenge of performing different tests on instrument transformers according to official standards and within a limited shutdown time. This is made even more difficult when multiple instruments are needed to perform all the required tests.

Reducing the risk of failure on high voltage instrument transformers in the transmission system using the application of narrowband dielectric frequency response (NB DFR) on HV CVTs.

The Power Grid Corporation of India Limited (PGCIL) is an Indian state-owned company headquartered in Gurugram (North India) engaged mainly in Trans-mission  of  Power  and  transmits  about  50%  of  the  total  power  generated  in  India  on  its  transmission  network.  The  company  owns  and  operates  about  1,61,790  circuit  kms  of  transmission  lines  at  800/765 kV,  400 kV,  220 kV  &  132 kV EHVAC and +500 kV HVDC levels and 248 sub-stations. Also, it has the transformation capacity of about 396 825 MVA as of 30th November 2019.