Electricity Asset Management Plan 2019-2029
131
Vector Limited://
Population and Age We have a total of 331 DC systems in service in zone substations, communications sites and a number of distribution substations. The table below provides a view of our DC system population (due to legacy data deficiencies a population age graph is not provided).
No of Autoamp 30 V DC chargers
5
No of Benning 110 V DC chargers
62
No of Century Yuasa DC chargers
1
No of Cordex DC chargers
80
No of Innovative Energies DC chargers
127
No of MHS Technologies DC chargers
7
No of Powernet DC chargers
1
No of Santon DC chargers
28
No of Switchtec DC chargers
1
No of Westhinghouse DC chargers
3
No of unknown brand DC chargers
16
Table 4-26 Key statistics for DC Systems
Condition and Health Vector’s zone substation battery chargers are progressively reaching end-of-life and are now showing an increasing failure rate compounded by limited replacement stock availability. Strategy Vector has standardised and modularised its design for DC systems and the modular designs are in accordance with Vector’s design standard ESE601 DC Systems. Vector’s asset strategy for DC systems is described in strategy report EAA601 Auxiliary Systems. The risk for Vector customers is that without a reliable charger supply the zone substation will fail within the 24-hour capacity of the 110V battery string. To ensure continued reliable provision of DC in zone substations and other sites in which a reliable DC supply is required we have commenced a programme of works to replace certain types of DC chargers. Most of the units that will be replaced are from our ageing fleet of Benning-type chargers and this programme has commenced in RY19. With regard to battery strings, as a general rule DC strings are replaced every 12 years under a rolling replacement programme. Sites will be prioritised by the criticality of connected customers and the age, condition and failure history of the charger. Earthing systems are required to minimise the risk of electric shock, limit earthing system related over-voltages on the network, ensure the operation of protection and carry earth fault currents safely. Earthing is normally specifically designed to meet established performance criteria. Every zone substation has an earth grid, commonly a combination of buried earth conductors, earth rods and the building reinforcing. All asset installations with conductive equipment have their own independent earthing systems. In general, the earthing systems comprise a set or sets of pins (electrodes) driven into the earth connected together via bare copper conductor. Copper is both an excellent electrical conductor and mechanically resistant to in-ground corrosion. The nature of the surrounding soil and surface covering play an integral part in the performance of the earthing system. The effects of local soil resistivity and covering (e.g. metal chip and asphalt) must be included in the overall analysis of earth system performance and are covered by step and touch voltage measurement. Condition and Health The condition and health of earthing systems are essentially determined by visual inspection and testing. Theft of copper earthing conductors has been an ongoing issue for some time. The problem with earthing conductors is that they can be removed without causing an outage and therefore without raising an alarm to the EOC via SCADA. This can present a hazardous situation when there is a fault and the earthing system is no longer able to perform as it is designed – hence a rigorous regime of visual inspection. Some of the earthing arrangements for lightning arresters in our network are sub- 4.7.6 EARTHING SYSTEMS Overview
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