Conclusion: reliable post contingency capacitor switching should be feasible to be planned. However, the simulation needs to be repeated as new information becomes available. Errors were found in the submitted load climate zone data for the approved 12HS4 case. Also, in the coming months and years, new information should become available on the load mix and composition at the modeled load objects. The composite load model for power flow purposes will also be improved.

WECC 17HW2 approved case modified to include 3 rd Monroe capacitor Puget Sound area generation displaced with remote generation until voltage stability limit reached for Category C Schultz-Raver1&Schultz-EchoLake 500 contingency Two capacitors switch post-contingency: EchoLake and Monroe V-Q simulation confirms condition is at the voltage stability limit with zero margin Critical voltage is very high at 520-kV

Condition exceeds voltage stability limit if no capacitors switch post contingency V-Q simulation confirms reactive deficit is about two 500-kV capacitor banks

Example load at SCL’s Broad Street in basecase The next slide will show powerflow conversion to distribution equivalent using WECC Composite Load Model, 1 out of 2200 loads converted in Northwest and BCHydro

Load converted from data in the WECC Composite Load Model

500-kV voltage with cut-in settings of capacitors at 490-kV after 30 second delay

Total system load Notice restoration of load began at 32 seconds, but declines after 38 seconds This demonstrates system is beyond the voltage stability limit Load unable to restore even after capacitors switch in

Monroe and Echo Lake capacitors switch in after 80 seconds

Example distribution voltage regulating transformer ratio compared to load voltage at Broad Street Tap ratio increasing means the voltage should be restoring to the deadband Instead, the tap changes are causing the voltage to decline further This is what happens for conditions exceeding the voltage stability limit: the taps change until the maximum tap is reached The two capacitors that switch in at 80 seconds restore some of the voltage, but not enough to get back to the deadband

Not all loads affected by the voltage decline after the outage are in the voltage instability area This load is at Longview and notice how the taps successfully restore the load voltage to the deadband Since this and other more distant loads from the outage are being successfully restored, the effect is actually detrimental to loads in the voltage instability area, because it is loading the transmission back up

Now let’s change the capacitor cut-in settings to match the today’s field settings Those settings have very high voltages and short time delays Notice within seconds after the outage the voltage substantially recovers A later slide will show an Echo Lake capacitor switched in within seconds Later capacitors switch in after the distribution load voltage regulating transformers change taps, which restores load and causes the main grid voltage to decline to the cut-in settings

The system load restores close to the original after about a minute This is an indication the conditions do not exceed the voltage stability limit at that time point Notice before that time how the load begins to successfully restore, but then declines These are intermediate conditions that exceed the voltage stability limit, until capacitors switch in and bring it out of the condition

As expected, capacitors at Echo Lake and Monroe switched in Notice how a capacitor way down at Ostrander switched in A total of three capacitors switched in bring the system out of the voltage instability state

Here is our Broad Street example once again Notice how the tap changes are not increasing the load voltage, but at least the voltage is not decreasing The final Monroe capacitor that switched in brought the voltage within the deadband However, it was a little too much and eventually a tap went the other direction to bring the voltage back down within the deadband

Here is the Poulsbo load Notice how it is in the voltage instability condition until the final capacitor switches in After that final capacitor at Monroe, the tap changes successfully start to raise the load voltage

Now let’s restore the lines to see if there are any overvoltage issues before capacitors switch off Nothing apparent at the 500kV level

However, notice the nearly 1000 MW jump in the load Now that will cause an underfrequency alarm to go off and make operators erroneously think they lost generation The loads are brought back down by the distribution voltage regulating transformers within minutes

Here is our Broad Street example Looks like the overvoltage at the load is not too severe The voltage regulator brings the voltage back down after the 30 second time delay for the tap changing to start