Power transformer diagnosis in one day

Power transformer diagnosis in one day

Vol. 5 Issue 1


A team of OMICRON test engineers was assigned to perform a comprehensive condition assessment of a 300 MVA power transformer. The power transformer was intended for sale and, therefore, the operator and the potential customer wanted to receive a clear insight into the current condition of the different transformer components. The expectations were clear: All required tests had to be performed within one day as the power transformer needed to be online again the next day.

Keywords: diagnostic testing, power transformer bundle, common electrical tests


8:00 a.m. – Arriving at the substation

The power transformer was disconnected from the grid in the morning. A smart choice of power transformer test systems was needed to perform all required tests within the short time frame available:

  • The lightweight DIRANA for dielectric response analysis
  • The smart FRANEO 800 for sweep frequency response analysis
  • The three-phase TESTRANO 600 for all common electrical diagnostic tests
  • The accessory CP TD1 for power/dissipation factor testing

Due to their compact design, all the test sets fitted easily into one car without any need for shipping heavy devices in advance or requiring a large van or truck.

The Primary Test Manager (PTM) software was used for convenient operation of all these test devices on site. The PTM software is the ideal support during diagnostic testing and guides its user step by step through the different testing procedures, including detailed wiring diagrams and high levels of automation. It also automatically assesses all obtained test results in accordance with the applicable international IEEE and IEC standards.

8:15 a.m. – Preparation for the first tests

The operator of the power transformer had sent a picture of the asset nameplate prior to testing. It is a 22-year-old, 200 MVA, 220 kV/110 kV power transformer with a star connection on the primary and secondary side. All bushings have a resin-impregnated paper (RIP) insulation.

The transformer and its bushings had already been specified and all test jobs prepared the day before in PTM. This reduced the required offline time of the asset to a minimum and the test engineer was able to start the different test jobs on site immediately.

8:30 a.m. – Initial screening of the power transformer

The operator had taken an oil-sample in advance to acquire a first insight into the transformer and its condition. Based on the sample, a dissolved gas analysis (DGA) was performed. Using DGA means a very broad spectrum of faults in the active part of a power transformer can be detected.