Asset Failure. What Next? – Recovery Plans! 120MW Turbo Generator Overflux During AVR Compliance Testing

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Malcolm Ballinger
Asset Manager Electrical
AGL Torrens Island Power Station

During AVR compliance testing in 2015 on a 48 year old 120MW turbo-generator running at full speed no load, an incorrect signal was inadvertently injected into the AVR control system into a non-standard injection point outside of the AVR limiters.  The injection resulted in an uncontrolled response from the AVR which caused the unit voltages to rapidly overshoot their nominal ratings. 

With no overvoltage protection installed on the machine, the unit tripped on Unit Auxiliary Transformer Differential.  The event exposed the generator, step up transformer and unit transformer to voltages in excess of 155%, which was established from multiple sources, such as historian, protection relay data, high speed meters and AVR equipment. 

Given the age of the unit and severity of overshoot the initial fears were that the generator and possibly the transformer were critically damaged and that the unit may not be practical to return to service.  This presentation discusses the process of reviews, risk assessments and electrical testing that were undertaken to form a decision about return to service.  The reviews ranged from published literature, comparison to previous similar events, reference to FAT data and testing, OEM consultation and advice and many other sources. 

Malcolm Ballinger is a Chartered Professional Engineer with fifteen years of experience as an engineering consultant, a site based EPC construction engineer, and as an asset owner.  He holds a 1st class honours degree in Electrical and Electronic Engineering from the University of Canterbury New Zealand.  He has worked in various locations in Australia, the United Kingdom and China.  Malcolm has a broad range of experience in engineering design, construction activities, and plant operation reviews.  Since 2012, as the Asset Manager Electrical at AGL Torrens Island Power Station, Malcolm has been responsible for the safe and reliable operation of all rotating and stationary electrical plant.