Hongming Zhang EMS Applications Manager, PEAK RC

Peak V&R R-T Voltage Security Assessment (VSA) Tool Validation

9/9/2014, JSIS

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• Peak-ROSE project deliverables. • ROSE VSA scenarios validation strategy. • Testing, observations and investigations. • RAS modeling work by VB scripts. • Next steps.

Agenda

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• Peak Reliability is implementing real-time assessment and monitoring for two identified IROLs i.e. San Diego Gas & Electric (SDGE) import and Northwest Washington (NW-Wash) transfer.

• These IROLs are voltage stability constrained. • Monitoring the IROLs by real-time ROSE VSA tool

is a critical task to be accomplished by end of 2014.

ROSE Project Deliverables in 2014

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• Among 18 scenarios defined in ROSE, Peak team now focus on validating IROL related scenarios:

• For SDGE Import IROLs, Peak collaborate with CISO to validate ROSE results against Bigwood’s. o ROSE VSA results are to be stored in PI

• For NW-Wash IROL, Peak rely on third-party tools i.e. VSAT and PowerWord for off-line validation.

ROSE VSA Limits Validation Strategy

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• Primary and backup POM servers are configured differently for real-time VSA Limits validation: o Both servers receive identical SE snapshots o Cap switching is set differently on two POM servers o RAS are not enabled for testing

• Use offline POM to reproduce problematic VSA Limits and report the issues to V&R.

• Work with V&R for software fix and solution tuning.

Validation Workflow

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Trend VSA Limits (NW-Wash) from PI

Investigate why VSA Limits changed dramatically?

Sept 2/3 SDGE Summer Import VSA Limits

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SUBSTN.WECCROSE.SCENAR.SUM_SDGE_LIM.MEA.MW SUBSTN.SYSTEM.PATH.SDGEIS_MW.MEA.MW9/3/2014 2:00:00 PM9/2/2014 3:00:00 PM 23.00 hours

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SDGE Summer Import Actual Flow

SDGE Summer Import VSA Limit Margin

(Sept 2, 3:00 PM to Sept 3, 2:00 PM)

Strong Correlation between actual Flow and VSA Limits Margin

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• SDGE VSA Limits are expanded by 15% or higher for SDGE import while Cap switching is enabled.

• NW-Wash VSA Limits vary while Cap switching is enabled for (N-1) CTG, compared to no Cap switching or Cap switching for (N-0) CTG. o What causes the big change of VSA limits?

• VSA Limits solve higher when a smaller step size is applied to solve NW-Wash scenario.

Observations of Real-time VSA Limits

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VSA Limits (with vs. w/o Cap Switching)

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• (N-1) Cap switching incurs numerical instability? • P-V curves depends on whether constant P/Q load

characteristics holds once P-V curves reach 0.8 p.u bus voltage.

• Auto switch to voltage dependent load model at 0.8 p.u. reduces the loads and interface flows, as well as re-shapes P-V curves sharply on a heavily shunt compensated network such as NW-Wash.

What NW-Wash P-V Curves Indicate?

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Case 1: Cap Switching Disabled

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Case 2: (N-1) Cap Switching Allowed

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Case 3: (N-0) Cap Switching Allowed

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• Excessive Cap switching under (N-1) is observed at a collapse approximation point i.e. 16 shunts switching and 38 generators reaching their reactive power limit (Qmax) at the last transfer step.

• Unlikely switch in so many Caps once by operators. • How to solve (N-1) mode massive Cap switching?

o POM Solution parameters tuning (work around) o Smart logic & robust logic against numerical instability

Cause, Effect and Resolution

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• Allowing (N-1) Cap switching is a common practice in industry i.e. assuming system operators shall switch in shunts manually as needed.

• Cap switching in basecase will typically result in a higher transfer capability

• However, as approaching the nose of the PV curve, each transfer step starts to cause large changes in voltage, which in turn cause Caps to switch in excessively. Thereby dynamic step size is desired.

Cause, Effect and Resolution (Cont)

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Case 4: (N-0) Cap Switching & Smaller Step Size Applied

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• Enabling AVR regulation of small shunt banks @ a sensitive location/station could raise VSA limits considerably. For example, o Massachu Cap banks (~30 Mvar in total) is set AVR off:

NW-WASH VSA limit = 4631 (MW) o Massachu Cap banks (35 Mvar in total) is set AVR on:

NW-WASH VSA limit = 4811 (MW) (N-0 Cap switching) • Which Cap banks shall be set AVR flag on under

pre-contingency, and /or post-contingency?

Impact of Shunt AVR Flag Setting

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• RAS in ROSE is model by VB scripts separately, Not imported from WSM-RTCA RAS database

• Using VB scripts for RAS modeling offers additional flexibility: o However, without GUI support, it requires RAS operation

expertise and VB coding skill to add or update RAS correctly in ROSE, sort of challenging for engineer.

• One RAS is likely modeled for multi-VSA scenarios. • It’s desired to separate specific RAS scripts from

individual scenarios for less maintenance & coding efficiency.

Efficient Scripting for ROSE-RAS Model

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[Continued]

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• Keep validating ROSE VSA Limits and sign off test. • Model all RAS related to IROLs scenarios and

validate their impact to VSA Limits. • Deliver user guide and training modules to SOEs. • Work with V&R to develop smart logic against

numerical instability.

Next Steps

Hongming Zhang, hzhang@peakrc.com