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Technical Working Groups

Stability of Outflows

Performance Indicator Summary


Performance indicator: Stability of Outflows

Technical Workgroup: Hydropower TWG

Research by: Hydropower TWG

Modeled by: PFEG in the shared vision model with inputs provided by the Power Entities.

Activity represented by this indicator: This PI refers to flows increasing and decreasing from week to week. An example would be to look at monthly outflows. If flows begin the month at 7,000 cms (247,000 cfs) and end the month at 7,500 cms (265,000 cfs) this may look stable. However, if the quarter month flows are: 7,000 cms (247,000 cfs), 7,400 cms (261,000 cfs), 6800 cms (240,000 cfs), 7,500 cms (265,000 cfs) then flows are unstable. This makes planning for maintenance outages, or the ability to meet forecasted demand for generation very difficult.

Link to water levels: Water levels on Lake Ontario determine outflows. Lake Ontario rises and falls in a stable pattern. A regulation plan that is premised on releasing water in relation to the water levels will be relatively stable.

Importance: This PI is a complement of the predictability PI. This refers to the magnitude of fluctuation in outflows from one period to the next. For instance if outflows for four quarter month periods are as follows: 7,500 cms (265,000 cfs), 8,000 cms (283,000 cfs), 7,000 cms (247,000 cfs) and 7,500 cms (265,000 cfs), this gives the false appearance that monthly flows are stable. In fact there is no change from outflows from the first and last period. However the flows fluctuate dramatically from period to period. This impacts outage planning, capacity requirements, and water levels. Even lower flow instabilities are detrimental. They result in loss of efficiency when flows increase, and loss of opportunity for the maintenance, when flows decrease.

This PI is complementary with the Predictability PI. This PI is important for hydropower, but it has importance for other interests as well as mentioned in the PI for flow predictability. Maintenance at the power plants must be performed regularly. Often this requires that several units be removed from service simultaneously. For instance work on a transformer at Moses-Saunders will require a bank of units (4 unit tied together electrically) to be out of service. Power entities try to remove these units when outflows are lower and expect to remain lower. If flows increase unexpected during an outage then generation will be lost by running inefficiently at best and by spilling the water at worst.

Unexpected reductions in outflows will impact the price of electricity in the markets particularly if they occur during high demand periods such as a summer heat wave.

Performance Indicator Metrics: 1958DD performs well for this PI. A comparison of results to 1958DD to plan options would indicate their performance.

Temporal Validity: ongoing

Spatial Validity: n/a

Links with hydrology used to create the PI algorithm: Increasing levels on Lake Ontario should predict increasing outflows and decreasing levels on Lake Ontario should be an indicator that outflows will decrease.

Algorithm: Hydro-Quebec's algorithm is based on the sum of the absolute difference between the plan flow and the 5 weeks moving average of the weekly outflow. That sum is transformed to energy losses by using a loss coefficient of 0.10 MW/m³/s, applied only to flow exceeding 6500 cms (230,000 cfs). This a good approximation for Hydro-Quebec. This algorithm was given to the PFEG for implementation in the Share Vision Model.

The losses at Moses-Saunders would be approximately half of those at HQ. Therefore, it would be appropriate to use the HQ algorithm for Moses-Saunders, but the result would then be halved.

Validation: Calculation of lost generation if flows suddenly increase during periods of unit maintenance.

Documentation and References: Hydropower TWG

Risk and uncertainty assessment: This PI attempts to reduce uncertainty of future outflows. If a regulation plan is selected that directs flows to fluctuate widely and in no predictable pattern then generation will likely be lost. This uncertainty will cause unpredictable water level fluctuations in Lake St. Lawrence and downstream to Montreal. This will have negative impacts on property owners and recreational boaters.



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