Innovative Real-Time Contingency

Analysis Enhancements for

Transmission Operations

Xiaodong Liu

Trevor W. Tessin

Richard A. Flynn

2016 IEEE PES General Meeting, Boston

July 17-21, 2016

Outline

Eversource East Service Area (NSTAR LCC) and EMS System

Contingency Definitions and Dynamic Ratings of Cables

Real-time Contingency Analysis Enhancements

– Interfaces

– Alarming

– Alarm acknowledgement Process

Validations and Actions for Contingency Analysis Results

Summary

ISO-NE

8,500 miles of HV transmission lines

with 13 interconnections

to New York and Eastern Canada.

400 generators in the region with

31,000 MW of generating capacity.

28,083 MW all-time summer peak

demand set on August 2, 2006.

New

Brunswick

Hydro

Québec

New

York

New England’s largest energy

delivery company.

More than 3.6 million electric

and natural gas customers in

3 states: Connecticut,

Massachusetts and New

Hampshire.

Eversource Energy New Hampshire

Massachusetts

Connecticut Rohde

Island

Vermont

Maine

Electric service territory includes

500 towns and covers 13,217

square miles.

3 Transmission Control Centers

and 3 Backups. 5 Distribution

Control Centers: 1 in NH, 1 in CT, 3

in MA.

New Hampshire

Massachusetts

Connecticut

Eversource East

NSTAR LCC: majority of

Greater Boston area,

Southeastern MA area.

20% of ISO-NE load.

Eversource Eastern MA

Eversource Energy

NSTAR LCC’s EMS

Applications: SE, RTCA, DPF, STCA, OPF, VVS (Voltage/Var Scheduler),

CRA (Contingency Remedial Actions)

EMS Model:

– 3,000 buses (15,500 connectivity nodes)

– 920 substations

– 1,800 lines

– 1,400 transformers

– 520 generators

– 22,000 telemetries

Internal Network: 125 substations, modeled down to 13 kV and 24 kV

sub-transmission buses and devices, 25% of 22,000 telemetries

SE runs every 2 min, RTCA runs every 3 min in average

Contingency Definitions

345 kV

boundary

115 kV

boundary

230 kV

boundary

NSTAR LCC Control

Area

Co

nti

ng

en

cy B

ou

nd

ari

es

Contingency Definitions Contingency Categories

Priority

• Loss of Line 3

• Loss of Generator 3

• Loss of Bus section 2

• Loss of Shunt 3

• Loss of Transformer 3

1

• Loss of Single breaker 3

• Loss of HVDC poles 3

• Stuck Breaker 2 (IROL)

1

• Loss of Double-Circuit-Tower 2 (IROL)

1

• N-1-1 1

• Loss of Heat Exchanger 3

11 Categories (950 contingencies):

– Contingencies that are “covered”

by other contingencies are NOT

included in CA scope.

– Based on actual relay protection

scheme (CB open/close)

Some Special Handlings:

– Load Transfer (ABR, Manual)

– SPS (Special Protection System)

– SEECO (Transmission

Sectionalizing)

– “Sequence of event” model – SVC

– Dynamic ratings of PTCs (Pipe

Type Cables)

Contingency Definitions Network Condition and Contingency Priority

Priority Normal System

Condition Emergency System

Condition

3 Every RTCA run Every RTCA run

2 Every RTCA run x1 hour

1 x1 hour x1 hour

Normal System Conditions: a wide range of contingencies are

respected among other requirements in order to promote the highest level

of transmission reliability.

Emergency System Conditions: a lower level of reliability is permitted to

increase operational flexibility, whereby a less stringent set of

contingencies is required to be respected.

Contingency Definitions Dynamic Ratings of Cables – Overview

Underground Transmission Cables in NSTAR LCC (Greater Boston)

area:

– 300 miles of 345 kV (100 mi.) and 115 kV (200 mi.) cables

– Oldest cable dated back to 70 years ago.

Cable Types: HPFF (240 mi.), HPGF, LPFF/MPFF, XLPE, EPR, LLPE

Cable Rating

Season

Companion Cable Status

Heat Exchanger

Status

When you hear Heat Exchanger…. think Ratings.

When you hear Cable Trip…. think Ratings.

– Most important parameters:

air and earth ambient temperature

heating from closest cables

oil circulating and cooling through Heat

Exchangers.

Cable ratings (thermal MVA) are primary determined by:

– Cable and duct/pipe characteristics

– External heat sources and heat dissipations

Contingency Definitions Dynamic Ratings of Cables – Oil Pressurization and Circulation

Cable A

Cable B

Heat Exchanger

Pump Plant

Stop Joint

Contingency Definitions Dynamic Ratings of Cables – Special Handling

6 sets of rating for each cable:

– Summer: 4 sets (companion cable I/S or O/S, HX ON/OFF)

– Winter: 2 sets (companion cable I/S or O/S, HX OFF)

– Applied to SCADA, SE and DPF.

– Rating change is alarmed (along with pump/HX status, backup

pump start, oil pressure, temperature, flow rate, oil tank level).

Problem in contingency analysis:

– Topology based rating at post-contingency

– HX contingencies: cable ratings most limiting

Solution:

– Addition of pseudo-cables

– HXs explicitly modeled

– Alternative solution: RAS customization at ISO-NE

HX B HX A

Contingency Definitions Dynamic Ratings of Cables – Implementation

Each cable is equipped with two pseudo cables – one is assigned the rating

of companion cable O/S, the other is assigned the rating of HX OFF.

Cable A

Cable A – PS1

Cable B

Cable B – PS1

Cable A – PS2

Cable B – PS2

HX B HX A

Contingency Definitions Dynamic Ratings of Cables – Example 1

Cable A O/S:

Cable A

Cable A – PS1

Cable B

Cable B – PS1

Cable A – PS2

Cable B – PS2

Post-Contingent loading is measured against Cable B – PS1

(Companion Cable O/S, HX OFF)

HX B HX A

Contingency Definitions Dynamic Ratings of Cables – Example 2

HX A & B OFF:

Cable A

Cable A – PS1

Cable B

Cable B – PS1

Cable A – PS2

Cable B – PS2

Post-Contingent loadings are measured against Cable A –

PS2 and Cable B – PS2.

Contingency Definitions Dynamic Ratings of Cables – Implementation

Pseudo cables are “behind the scene” components:

– Correct cable ratings are automatically assigned for Contingency

Analysis purposes only (RTCA, STCA).

– Not displayed in any oneline diagrams

– Not utilized in SE

– Not utilized in DPF

– Not utilized when applying a contingency to a study basecase (an

enhancement)

HX contingencies, affecting >115 kV cable ratings, are included in

contingency analysis scope.

EMS cable model, contingency definitions and EMS displays are

maintained using scripts.

Real-Time Contingency Analysis

Why RTCA:

– Situational awareness (N-x) and operational reliability

– Pre- and Post-contingency action plans are to be developed

– Pre-contingency actions need to be executed

– Pre- and Post- contingent actions must be completed in a timely

fashion

NERC TOP-001: Each Transmission Operator shall initiate its Operating

Plan to mitigate a SOL exceedance identified as part of its Real-time

monitoring or Real-time Assessment.

The Operating Plan provides the times within which these actions must

be taken (pre & post-contingent).

Real-Time Contingency Analysis

Operator Actions

at Pre- and Post-

Contingent

POST-CONTIGENCT ACTIONS PRE-CONTIGENCT

ISO-NE OP-19

Timer for STE exceedance:

5 min

Timer for LTE exceedance:

15 min

Timer for OPL exceedance:

One load cycle

(12 H in Summer, 4 H in

Winter)

2 H or 30 MIN

Real-Time Contingency Analysis

Operator Actions

for RTCA results

Timer for SOL exceedance:

2 H

Timer for IROL exceedance:

30 min

Real-Time Contingency Analysis

Displaying RTCA Results (3 types of traditional displays):

– Active Alarm browser

Real-time alarm messages when SOLs are exceeded post-

contingent

– Contingency Summary Dashboard

# of screened-in/screened-out, # of SOL exceedances (MVA or kV),

# of diverged cases, # of contingencies causing generator loss or

load loss, # of contingencies causing islanding …

– Spreadsheet view of detailed RTCA results

List of contingencies, overloaded devices, pre- and post-

contingency MVA or kV values.

NSTAR internal alarms

CB Open/Close

External, ICCP

SE, RTCA Alarms

Display Layout on Multiple Screens

Alarms

SE, RTCA Dashboard

SE, RTCA Tabular

Apps sequence Flow Chart

(or EMS Health)

Caps/Reactors, LTCs

Station voltages

Transmission overview

Area loads

Area generators

DPF, STCA

Station one-lines

Other off-line Apps

Dashboards, Tabular

Area Diagrams Study Mode Apps

EMS tools were not adequate for Situational Awareness due to:

– Lack of immediate visual image of RTCA SOL exceedances

– Lack of audible RTCA alarms announcing severity of limit

exceedance

– Lack of “time duration” RTCA alarms for contingencies continuously

causing limit exceedances

– Lack of indications of elements approaching limits in the RTCA

results tabular

Enhancements developed in-house to address the above issues.

Real-Time Contingency Analysis

RTCA Enhancements New Tabular with Integrated Functionalities

RTCA Results for Lines

RTCA Voltage Results for Buses

Contingencies not converging

RTCA Results for Transformers

RTCA Enhancements Immediate Visual Image

Percentage base

STE exceedance

LTE exceedance

Bar chart: simple and useful!

Color configurable

Percentage base selectable

Devices approaching SOLs

included

Coloring and bar length meaningful

RTCA Enhancements Time Stamp and Time Duration

Time or Minutes Toggle time format

New column to show time of

occurrence or time duration of

continuous SOL (LTE/STE only)

exceedance

Time duration counting up and

refreshing every second.

RTCA Enhancements Voice Alarming

“Attention: post-contingency STE violation for 30 min.”

“Attention: post-contingency diverges.” Mute voice alarming

Voice alarming the severity and the

time duration of LTE/STE

exceedances.

Alarming at the time of new LTE or

STE exceedance (T=0), T+15 min,

T+30 min, T+60 min, T+90 min and

finally at T+120 min.

Immediate recognition of RTCA

alarms and promote OP compliance.

Voice alarming can be muted.

RTCA Enhancements Alarm Acknowledgement

Ack. Alarms

Acknowledged

Contingency

Acknowledged

Contingency

Unacknowledged

Contingency

Unacknowledged

Contingency

Acknowledge selected contingencies

(LTE/STE exceedance only) on the

tabular

Confirmation needed

Mute Ack.

Consistent SCADA and RTCA Alarm

Response process.

One time Ack. or Automatic Ack.

RTCA Enhancements Alarm Acknowledgement

Two types of Ack.

– One-time Ack.:

Valid only for this time of occurrence of SOL exceedance.

– Automatic Ack.:

Valid for a user defined time duration (or even permanent).

Default time to operator shift turnover (i.e. 5:30 pm at the same day or

5:30 am at next day)

Auto ack. unwanted or unnecessary RTCA voice alarms to avoid

excessive alarming (e.g. for distribution transformers, external lines,

and low priority contingencies).

Problems:

Lack of immediate visual image for RTCA SOL exceedances

– SOLVED. Coloring of contingencies and bar charts.

Lack of audible RTCA alarms announcing severity of limit exceedance

– SOLVED. Voice alarming.

Lack of “time duration” RTCA alarms for contingencies continuously

causing limit exceedances

– SOLVED. Time stamping contingencies.

Lack of a list of elements approaching the limits in the RTCA result

tabular

– SOLVED. Configurable based on user preference

In addition, new acknowledgement process is developed to respond

RTCA alarms.

RTCA Enhancements A Wrap-up

RTCA Enhancements A Wrap-up

Another enhancement: include RTCA result to SE tabular to provide a

combined view of SE and RTCA results

Identify SOL, IROL and time allowed based on OP/OG

– Time allowed in current state (120 min or 30 min)

– Time within which an action plan must be developed and pre-

contingency action must be taken

Verify real-time SE solution

– Large mismatch, incorrect or failed telemetries, wrong limits, rejected

measurements, low voltages.

Validate CA solution in study mode

– Assume the accuracy of CA adheres to the accuracy of SE

– Confidence level: 5% for MVA, 1% for kV

Validation and Actions for RTCA Results

Communicate with ISO-NE and neighboring LCC

– Discrepancies not uncommon

Improper modeling incl. regulations, sub-transmission model, circuit

parameters or ratings. Software issues.

– Respect most conservative solution

Develop mitigation plan

– Move PAR taps, switch Caps/Rs & circuits, apply enhanced limits,

request unit Mvar adjustment, seek unit re-dispatch by ISO, shed

loads.

Execute the plan as applicable

– Within the required time frame upon validation of RTCA

Log event in TOA (Transmission Outage Application) DB. Phone

communications are recorded.

Acknowledge related alarms incl. voice alarms

Validation and Actions for RTCA Results

Dynamic ratings of NSTAR cables are implemented by special

handling of PTCs and HXs in EMS model and RTCA.

Important enhancements on RTCA application,

– Colored bar charts

– Contingency coloring

– Limit approaching monitor

– Voice alarming

– Alarm acknowledgement and auto acknowledgement,

– All developed to promote better alarming and situational

awareness.

These improvements provide NSTAR’s system operators with much

more adequate tools for managing and responding to RTCA results

in compliance with mandatory OP and NERC Standards.

Summary

Thank you for your attention!

Q & A