One of the major issues for most utilities is ageing assets. Using permanently mounted monitoring can extend asset life and defer replacement costs. It also allows the utility to plan and prioritise maintenance activities.
Traditional preventative maintenance schemes are being replaced by condition based, predictive or reliability centred maintenance strategies. These require a regular flow of condition information from each critical asset in each substation.
As part of the suite of functions available with sub.net the condition of critical assets are recorded. A DC input module (IMDC) and a Hall effect probe (HCT) are required to monitor the tripping battery voltage and current.
Circuit breakers
Every trip and close operation of every breaker at a substation is recorded and analysed. This can be a fault clearance or a test trip from the control room. Any variation of a parameter that falls outside the set limits causes an asset warning to be included in the event report.
The accumulated cleared current and other parameters are used to determine the maintenance periods. The mechanism status and main contact duty information may be sent to an asset management database. The asset condition values are available on the RTU ports.
A portable breaker monitor is available for maintenance crews.
Tripping battery
During a breaker trip and close the battery voltage and current are used to calculate the state of the battery. If this exceeds a set value an asset warning message is added to the event report. Fault types detected include damaged cables, bad connections and faulty battery cells.
sub.net can monitor two batteries with separate DC input modules and battery current sensors.
Transformer
The K factor derived from harmonic currents, load levels and through fault levels can all affect the lifetime of a transformer. These data are all available from sub.net. In addition the oil temperature may also be recorded with the ambient temperature.
The data from permanently mounted DGA sensors can be linked to sub.net and included with the regular trend reports.
Cables
Intermittent breakdown in underground cables (pecking faults) can be detected and reported by sub.net so that they can be repaired before they evolve into permanent faults. In addition the sheath currents can be monitored and any neutral current caused by bad joints or earthing can be reported.
Partial discharge
A multi-bay UHF partial discharge sensor system is available to detect increasing levels of PD activity which may lead to a fault. The PD sensors are linked together and the data recorded and reported by sub.net. The sensors use multiple frequency bands and can discriminate between surface and internal discharges.
Temperature
As well as ambient and transformer temperatures the state of MV connections can be checked using novel wireless temperature sensors. These are fitted to key parts of distribution bays where an increase in differential temperature may indicate an evolving fault with a joint or coupling. The temperature levels are recorded and reported by sub.net.