Voltage transformer frequency response. Measuring harmonics in Norwegian 300 kV and 132 kV power systems

Measuring harmonics in high voltage power systems with inductive and in particular capacitive voltage transformers, CVTs, may cause large errors. Test carried out by The Norwegian National Grid Company (Statnett), Bergenshalvoens Kommunale Kraftselskap (BKK) and The Norwegian Electric Power Research Institute (now SINTEF Energy Research) revealed errors from 80% to +1200% (0,2-12 pu) of correct values. Inductive voltage transformers did have a relatively small error up to 29^th harmonic (1450 Hz) while capacitive voltage transformers had large errors at a few hundred Hz. Carrying out calibration tests on voltage transformers and capacitive voltage transformers in particular may correct most of the errors. Still inductive voltage transformers should be preferred for harmonic measurements where possible