Electricity Asset Management Plan 2019-2029
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Vector Limited://
Figure 4-38 Age Profile for Protection Relays
Condition and Health The population of numeric relays is relatively new and we have not experienced any systemic failures. The electromechanical relay population is reliable but the relays in this population that provides differential protection functions are at the mercy of an ageing and failing Copper pilot network. Strategy Vector’s asset strategy for protection systems is described in strategy EAA801 Protection Systems. The power system is continually becoming more complex and this commensurate with higher expectations from customers to have a network with improved reliability and higher resilience has prompted Vector to invest in protection systems with advanced analytic and advanced protection functions. This programme commenced in the late nineties and is continuing. Many of our OH lines share 33 kV subtransmission circuits with 11 kV distribution circuits and this has led to erroneous tripping because of mutual coupling for faults in the distribution lines with a commensurate risk to SAIDI and service levels. We have embarked on a programme of works to install numeric differential protection together with fibre optic communications channels to improve reliability and resilience. To improve SAIDI we are also embarking with a programme to replace electro-mechanical feeder protection relays with numerical relays on rural feeders to achieve fast clearance for switching onto faults, implement broken conductor alarming, improve our ability to have distance to fault information and to provide historical summaries and trends. Numeric relays are also more granular in their pickup settings and fault response timing. Power transformers are a vital part of the electrical distribution network, but they are also large and expensive assets usually without spares readily available and with a very long lead time for replacement. As result of this, monitoring and diagnostic technologies focused on power transformers, are essential to provide a means to monitor transformers, predict failures, and proactively manage their performance. Transformer management systems(TMS) have migrated over time from various discrete electro-mechanical relays performing specialised functions such as voltage regulation and thermal protection to modern numerical relays that provide all the functionality in one device, e.g. voltage regulation on variable tap transformers, monitoring of key health conditions, monitor and control cooling systems and fans, and provide condition alarms and trips with advanced control, reporting and analysing functions. Population and Age Around 52% of TMS on power transformers have been replaced with modern numerical systems. Due to legacy issues, the age-related data for TMS especially in the Northern network is not reliable and hence an age profile graph is not included. 4.7.2 TRANSFORMER MANAGEMENT SYSTEMS Overview
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