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Ontario - Canada

Series Capacitors for increased power transmission capability of 500 kV intertie in Canada

Hydro One is the largest electricity transmission and distribution company in the province of Ontario, Canada. The Company owns and operates substantially all of Ontario’s electricity transmission system, accounting for approximately 96.6% of Ontario’s transmission capacity.

Hydro One is operating two series capacitors supplied by Hitachi Energy in their 500 kV transmission grid in Ontario, Canada. Each series capacitor is rated at 750 Mvar.

In the 500 kV power transmission system of Ontario, the north-eastern part is connected to the south mainly by two single circuit lines between Hanmer s/s at Sudbury and Essa s/s at Barrie. Without series compensation, the development of new generation in northern Ontario could result in increased power congestion over the lines. The installation of the series capacitors at Nobel s/s at approximately the midpoint of the lines enhances the use of these circuits by increasing the power transmission capability of the lines by at least 30%. The total length of the corridor is approximately 280 km.

TRV control

Special importance was attributed to avoiding any impact (increase) on the transient recovery voltage (TRV) on existing line circuit breakers following breaker operation for any reason, i.e. during normal load flow just as well as for fault clearing anywhere along the lines. Such increase could otherwise be caused by the voltage over the series capacitors when the line breaker is opened. Avoiding this is enabled by means of Hitachi Energy's Fast Protective Device (FPD), allowing very fast bypassing of the series capacitors in conjunction with line breaker opening in the transmission lines carrying the series capacitors. This means the impact of trapped charges in the series capacitors is eliminated, and does not add to the TRV stressing of the circuit breakers.

In fact, studies prior to the project indicated insertion of a series capacitor in the Hanmer to Essa 500 kV line would have exasperated the TRV on the terminal breakers clearing faults on the line. This emphasized the importance of a fast bypassing mechanism for this project and was one of the factors which led to selection of Hitachi Energy as supplier of the series capacitors.

Main data
System voltage: 500 kV
Rated current:
2330 A
Rated reactance: 46 Ω
Rated reactive power: 750 Mvar
Degree of compensation: 50%
MOV rating (middle phase) 70.5 MJ
MOV rating (each outer phase) 46.2 MJ
Ambient temperature range -50ºC to +40ºC