Electricity + Control January 2018

DRIVES, MOTORS + SWITCHGEAR

D IVE , MOTORS + SWITCHGEAR

This transfer deficit must be recuperated by a comeback load during the off-peak hours in order for the successful load shift interven- tion to be realised. In order to determine the necessary operational procedure to realise a sufficient comeback load during the off-peak periods, the system characteristics must also be determined. The RPS test was thus conducted to determine these characteristics. The data accumulated during the RPS test was used to develop Figure 5 . The graph plots the total High Lift pump station power against its total outflow, as the VSD speed is increased. Each line represents a different combination of running pump sets.

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10,4 MW

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9,4 MW

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3,5 m3/s

Station Power [MW] Power [MW] 0 25,0 20,0 15,0 10,0 5,0

1,3 1,6 1,9 2,2 2,5 2,8 3,1 3,4 3,7 4 4,3 4,6 4,9 5,2 5,5 5,8

Flow [m 3 /s]

1 Set 2 Sets 3 Sets

Figure 5: High-lift pump station power versus flow.

When looking at the red lines on the above graph, it is clear that for a required flow of 3,5 m 3 /s it is better to operate with two pumps at a higher RPM, than three pumps running at a lower RPM. This re- sults in about 1 MW of power saved. It is thus preferable to run the High Lift pump station's pumps at the combination with the lowest curve. So for the flow range of 2,5 m 3 /s to 4,5 m 3 /s, it is better to run two pump lines. This was considered during the process of cal- culating the best load shift scenario for a standard operational day. The knowledge gained from the above tests allowed for the development of an optimised control philosophy to be implement- ed on Pump Station A. The optimised control was first simulated before implementation to determined its viability. In Figure 6 the current profile is compared to the optimised weekday and week- end profiles. Further calculations show that the optimised control results in a daily average saving of 5 3 MW for weekdays on Pump Station A, which includes the High Lift and Low Lift pump stations.

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OptimisedWeekday Profile Baseline Profile Weekend Profile

Figure 6: Simulated power profiles for Pump Station A.