Upgrading the Anglo-Scottish Interconnector: commissioning of Longannet static excitation

The original excitation to each alternator was supplied by 400 Hz Permanent Magnet Pilot Exciters, regulated by a single GEC 2VH Automatic Voltage Regulator controlling power to rotating exciters. The open circuit response time of the generators was typically 400/500 msec and overshoot between 15 and 20%. The new excitation system chosen comprised static exciters and a triplex digital AVR with a processing time of 10 msec. Each AVR channel is synchronised to the generator terminal voltage three-phase waveform and can provide a control response to the static exciter of between 5.3 and 8.3 msec. The use of a computer model is outlined and the course of system site tests is summarised