West wide System Model (WSM): Present Challenges, Continued

Improvements & Solution Accuracy

byHongming Zhang, Slavin Kincic

Peak Reliability

1

Agenda

• The WSM Overview and Model Update Process.• Modeling Challenges & Improvements:

– BA-BA boundary modeling consistency with entities.– Critical sub-100-kV network identification and modeling– WBRTF-reconcile modeling discrepancies between WSM

and WECC Basecase.– RAS modeling and monitoring in SCADA and RTCA.– Other WSM modeling improvements.

• SE and RTCA Solutions Quality/Accuracy Metrics.

2

Peak-WSM Overview

• The WSM marks one full Western Interconnection operational model covering BES constituents of 37 BAs and 64 TOPs across US, Canada and Mexico.

• The WSM has provided Peak Reliability (formerly WECC RC) the wide area view for monitoring the system reliability since 01/2009.

• The WSM has been shared with member entities under a universal NDA in multiple data formats e.g. GE/PSLF, PowerWorld, Alstom NETMOM Savecase, CIM/XML files and Access.

3

Main Modeling Facts

• DC Ties with Eastern Interconnections and ERCOT are modeled as equivalent units/loads.

• The WSM was originated to monitor Western BES reliability operation. Typically 92 kV lower network components are not modeled explicitly.

• Till date the WSM is scaled by: • 14,000 Buses/17,000 Branches/8,000 Subs/3,400 units.• 8,200+ Contingencies with 200 RAS/SPS modeled.• 125,000+ ICCP points mapped.

4

SCADA ICCP Statistics5

Model Update Workflow

• The WSM is usually updated for every 4-6 weeks. Each model update cycle consists of six steps:1. Network model update by Alstom ETS 2.0.2. SCADA/ICCP model build by the custom scripting.3. Contingency list update by the custom scripting.4. RAS model update via EMS UI and scripting.5. WSM model integration test, SCADA one-line

displays and PI tags update.6. Database upload in Prod.

6

Model Update Process Diagram7

Lessons Learned 1: BA Boundary Modeling Discrepancy

• SE solution per BA/CO summary NOT match with telemetered BA’s AGC Total signals because of• BA-BA boundary definition errors, typically missing of low

kV tie lines and pseudo ties.• Splitting loads and non-conforming/dynamic loads.• Dynamic generation schedules and Jointly Owned Unit

shares NOT applied to SE solved actual area NI.• Inconsistency between BA’s AGC load calculation and

WSM network load modeling & estimation.• Non-telemetry units and loads e.g. pseudo injections

8

Impact to SE and RTCA solutions

• The discrepancy of network model and SCADA BA total AGC signals resulted in• Invalid SE solution or poor load estimation when some BA

area load measurements are enabled in SE.• BA total Gen/LD/NI values estimated inaccurately.• False Basecase and post-contingency violations due to

bad load estimates in the local pocket.• When a SE snapshot is retrieved into offline tools for next

hours or next day study, PWRFLOW does not solve well while BA submitted load forecast and NI schedules are applied.

9

Lessons Learned 2: Critical Lower kV Network Modeling

• In the wake of Sep11 2011 blackout, Peak initiated the new SOL/IROL methodology, including studies of loss of critical sub-100-kV equipment to the BES.

• False overload/violations/unsolved were found in both basecase and post-contingency solutions due to missing or inaccuracy of lower kV networks. Ex.• SRP contingency SRP1L010 (Miami-Pinal 115Kv) resulted

in 115Kv voltage collapsed to ~83KV. SRP did not agree with RC’s assessment.

• The issue was resolved by modeling SRP 69kV network.

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Mitigation Plan Implemented

• RC took steps to ensure monitoring sub-100-kV facilities that may impact BES.– Performed basic power flow studies on a WECC base case

to identify sub-100-kV facilities that see an increase in flows of 30 MVA or greater due to a 230 kV or higher equipment outage contingency.

– A handful of critical sub-100-kV facilities were identified and submitted to TOP for feedback. Once agreed by TOP, the changes are added to WSM for real-time monitoring.

– Requested TOP to submit their own list of sub-100-kV facilities that should be monitored.

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Screen Critical Sub-100-kV Equipment

COACHELV 92 kV network components fall into the screening list

12

Lessons Learned 3: WBRTF-Reconcile Modeling Discrepancies

• WBRTF was initiated to reconcile discrepancies of the WSM and WECC planning basecase. Such as,– Missing devices and unmapped generating units et al– XFMR Tap Changer modeling (nominal vs off-nominal kV,

located at XFMR From /To side)– 3-winding XFMR (WSM) vs. 2-winding XFMR (Basecase)– Wind farm modeling-how to handle sub-kV step up XF?

• WBRTF is extended to evaluate the WSM against BA/TOP’s EMS/operational model now.

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Wind Farm Detail Modeling14

Load Modeling with Step Down XF

BCS

WSM

• Step downs for load e.g.115kV/12.5 kV

Modeling Challenges: RAS/SPS• WSM-RTCA screens over 8000 contingencies in 5-min

interval. 800+ contingencies are enabled for RAS trigger screening.

• As of May-2014, 196 RAS/SPS records are modeled in the WSM, representing 64% of the master list of the RAS real-time operated in the Western Interconnection.

• 4800 RAS Analog & Status points are modeled in SCADA, and most of them are mapped to SE.

• The software is limited for (1) Nomogram based RAS, modeling; (2) Armed/Trigger status evaluation in next day study case; (3) RAS backfire in case a post-contingency solution is unavailable, etc.

WSM-RAS Modeling Project Summary

• Two engineers have been full time working on RAS project since May 2013.

• By May 2014, 64% RAS in the Master list were modeled.

• Look to finish the rest RAS (except inactive or software limited RAS) project by July 2014

SCADA RAS Points Modeled & Mapped

RAS Monitor, Alarming & Visualization

• Peak RC awareness was obtained through training, real-time RAS measurements, alarming, RAS overview displays, and RTCA solution with RAS modeled

• Each alarm point contains the information to identify the RAS.

• From the alarm page RC can navigate to the RAS Overview page by right click and select “Location Display”.

• Hundreds RAS info are linked to RAS Overview displays.• RAS results are to be visualized into RC Workbook tool.

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WSM-SE & RTCA Solution Accuracy Metrics (2012 vs. 2013)

Statistics Facts: RTNET/SE & RTCA

solutions are being 7X24 watched by RCs and Engineers.

SE valid solution runs reach 99%.

RTCA valid solution runs % is nearly 100%.

Daily average unsolved CTG counts down to 3 in 2013.

Other WSM Improvement Projects

• Model impedance table for all Phase Shifting Transformer (PST) and selected LTC transformers.

• Integrate Phasor angle measurements (PMU) into SE.• HVDC modeling improvements (PDCI & Transbay DC

Poles controllers).• Improve bus voltage limits modeling and bus kV

violations monitoring in SE and RTCA.– Set AVR flags for units and shunt devices properly.– Set shunt switching deviation band to 7% over the

regulated bus voltage target.

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PI based PMU Data Validation Tool

Highlights: Compare Phasor values (30 samples/1s) to known trusted values

ICCP/SE (10s/60s scan rate)• Set allowable deviation

Angle = 2 Deg.Mag = 1% of Nominal KV

• Determine “% Good” (within allowable deviation)

Notes:• SCADA ICCP measurements are

being refreshed in 10s.• PMU voltage measurements are

sent in SCADA at 1s interval.• SE solves for every 60s. The SE

values need be written in SCADA for storing in PI

• At least one of PMU reference angle measurement need be enabled in SE for bus angle synchronization.

= 𝑨𝑨𝑨𝑨𝑨𝑨(𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰/𝑺𝑺𝑺𝑺 − 𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑽𝑰𝑰𝑷𝑷𝑷𝑷) >𝑫𝑫𝑽𝑽𝑫𝑫𝑫𝑫𝑽𝑽𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫 𝑳𝑳𝑫𝑫𝑳𝑳𝑫𝑫𝑫𝑫

The low “Good” % PMU KVA records need be validated and confirmed if they are caused by

• Bad PMU raw signals

• SE solution issues due to topology and/or modeling errors.

• Too tight setting on the threshold of deviation.

EX: Critical PMU Angle Data Validation

5/6/2014 - 5/28/2014Voltage Angle (SE

Compared)Device Within +/- 2 Deg. of SE (%)

SUBSTN.AULT.LN.CRGC_AULT_1345.PMU.KVA 94.23

SUBSTN.HALLEN.LN.HALL_LENZ_1500.PMU.KVA 94.37SUBSTN.HASSYYAM.BUS.900B.PMU.KVA 98.48

SUBSTN.INGLEDOW.LN.CUST_INGL_2500.PMU.KVA 0

SUBSTN.INTMTN.LN.INTE_GOND_1230.PMU.KVA 75.65

SUBSTN.LANGDON.LN.LGDN_JANT_1240.PMU.KVA 52.11SUBSTN.MALIN.BUS.500_NORTH.PMU.KVA 97.20

SUBSTN.MIDPOINT.BUS.MPSN_230B1.PMU.KVA 99.78

SUBSTN.MIGUEL.LN.IVAL_MIGU_1500.PMU.KVA 94.35

SUBSTN.SHRUM.LN.GMS__PCN__1500.PMU.KVA 99.10SUBSTN.WESTMESA.BUS.118.PMU.KVA 20.72

Hongming ZhangManager of Network Applicationshzhang@peakrc.comSlavin Kincic, Power System Engineerskincic@peakrc.com