                 ! "   #  AVOIDANCE OF MV SWITCHGEAR FAILURE CASE STUDIES OF ON-LINE CONDITION MONITORING Cliff Walton and Sarah Carter Matthieu Michel Carl Eastham PPA Energy - UK EDF Energy Networks - UK IPEC - UK cliff.walton@ppaenergy.co.uk Matthieu.Michel@edfenergy.com carl@ipec.co.uk sarah.carter@ppaenergy.co.uk ABSTRACT This paper considers, through a series of practical case studies, the avoidance of major incidents through the targeted use of on-line condition monitoring of MV indoor switchboards. A technique to pin point the location of partial discharge (pd) using time of flight measurement techniques is discussed. INTRODUCTION MV switchboard failures are fortunately rare but a single incident can affect many thousands of customers for prolonged periods and consequently have a major impact on customer interruption statistics as well as on customer and regulatory perception, and pose risks to operational staff. The devastation which can be caused by failure of switchgear is illustrated in figure 1. The financial impact of compensation payments, regulatory penalties and the costs of emergency and remedial works can be considerable. Figure 1 Damage to substation following a catastrophic switchgear failure There was an average of 32 switchgear faults per year affecting the 1150 primary (33 kV and 11 kV) substations on the EDF Energy Networks systems over the past three years (incidents on 2.7% of substations pa). The effect of these faults varied from no interruption in supply to the equivalent of 12 customer years of interruption. EDF Energy Networks have deployed extensive multi- sensor on-line monitoring systems together with web based analysis and alarm tools to monitor the condition of some 60 key substations, comprising over 1000 panels of switchgear with on-line monitoring of both cables and switchgear provided by some 1800 sensors. These include substations in London and the Southern and Eastern areas of the UK, as well as in France. Early warnings from these systems are routinely providing opportunities for timely targeted interventions by field maintenance teams before catastrophic failure. The on-line monitoring system is available through remote web-access displaying the latest and historic pd information, together with a switchboard and circuit criticality assessment. Alarm thresholds can be set to enable SMS text messages to automatically be sent to key staff. This paper details three instances where partial discharge on switchgear has been successfully identified remotely by the on-line monitoring system and looks at recent advances which have been made in the analysis of switchgear partial discharge (pd) to pin point an incipient fault. Switchgear pd pulses are characterised by their fast rise time and narrow shape as illustrated in figure 2. Figure 2 Example of switchgear pd PARTIAL DISCHARGE SENSORS Five types of sensors are deployed at some of the substations. A discussion of the sensors with respect to switchgear pd follows: AA sensors Airborne Acoustic ultrasonic sensors are presently located on some higher risk switchboard panels. AA sensors are very effective at picking up local partial discharge provided there is an air path. Location of the source of the pd using AA sensors and acoustic triangulation techniques have been