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This paper presents a basic method of probabilistic transmission planning used in BC Hydro. The method is based on transmission system reliability evaluation and an overall economic analysis including damage cost due to system unreliability. Four alternatives for the Vancouver South Metro system of BC Hydro have been evaluated using the method. The first one is addition of a 230 kV line, the second one local configuration changes ("cuts and ties") in the 69 kV subsystem, the third one operational manipulation and the fourth one curtailable industrial load management. The third and the fourth alternatives can be considered as non-investment reinforcements. The results indicate that the cut-and-tie alternative in the 69 kv subsystem can provide the same reliability level as the 230 kV line addition but with much lower investment and therefore the initial 230 kV line addition could be deferred by 10 years. This deferral allows a major capital expenditure of $ 26.4 million (1997 $) to be avoided. The studies show that the application of quantitative transmission reliability assessment in power system planning can provide utilities with significant economic benefits.

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This paper presents a Monte Carlo based method for probabilistic risk evaluation of transmission system operation modes. The method focuses on simulations of operation measures which include load transfers, generation pattern changes, network reconfigurations and switching actions. An important characteristic in risk evaluation of transmission system operation modes is noncoherence. This characteristic is also analyzed and explained. Inclusion of dynamic ratings of circuits and a simulation capability over any time length are other two features of the presented method. The probabilistic operation risk evaluation method is an enhancement to and should be combined with traditional system analysis techniques. The proposed method has been applied to BC Hydro's metro system. The case study given in the paper indicates that the lowest risk operation mode can be identified under different operation conditions. This helps perform transmission system operation risk control and partial risk transfer from one area to another or from one kV level to another with a reduced total risk level .