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. Hydro Québec Maine New Brunswick 28,083 MW all-time summer peak demand set on August 2, 2006. Vermont Eversource Energy 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. New York New Hampshire Massachusetts Connecticut Rohde Island
Eversource Energy 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 Eversource Eastern MA NSTAR LCC: majority of Greater Boston area, Southeastern MA area. 20% of ISO-NE load. Connecticut Massachusetts Eversource East
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 Boundaries Contingency Definitions 230 kv boundary 345 kv boundary 115 kv boundary NSTAR LCC Control Area
Contingency Definitions Contingency Categories 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) 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
Contingency Definitions Network Condition and Contingency Priority 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. 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
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 ratings (thermal MVA) are primary determined by: Cable and duct/pipe characteristics External heat sources and heat dissipations Most important parameters: air and earth ambient temperature heating from closest cables oil circulating and cooling through Heat Exchangers. When you hear Heat Exchanger. think Ratings. When you hear Cable Trip. think Ratings. Season Companion Cable Status Cable Rating Heat Exchanger Status
Contingency Definitions Dynamic Ratings of Cables Oil Pressurization and Circulation Pump Plant Cable A Heat Exchanger Stop Joint Cable B
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
Contingency Definitions Dynamic Ratings of Cables Implementation Cable A Cable A PS1 HX A Cable A PS2 HX B Cable B Cable B PS1 Cable B PS2 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.
Contingency Definitions Dynamic Ratings of Cables Example 1 Cable A Cable A PS1 HX A Cable A PS2 HX B Cable B Cable B PS1 Cable B PS2 Cable A O/S: Post-Contingent loading is measured against Cable B PS1 (Companion Cable O/S, HX OFF)
Contingency Definitions Dynamic Ratings of Cables Example 2 Cable A Cable A PS1 HX A Cable A PS2 HX B Cable B Cable B PS1 Cable B PS2 HX A & B OFF: 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 PRE-CONTIGENCT POST-CONTIGENCT ACTIONS 2 H or 30 MIN Operator Actions at Pre- and Post- Contingent 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)
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 postcontingent 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 postcontingency MVA or kv values.
Display Layout on Multiple Screens Alarms NSTAR internal alarms CB Open/Close External, ICCP SE, RTCA Alarms Dashboards, Tabular SE, RTCA Dashboard SE, RTCA Tabular Apps sequence Flow Chart (or EMS Health) Area Diagrams Caps/Reactors, LTCs Station voltages Transmission overview Study Mode Apps DPF, STCA Station one-lines Other off-line Apps Area loads Area generators
Real-Time Contingency Analysis 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.
RTCA Enhancements New Tabular with Integrated Functionalities Contingencies not converging RTCA Results for Lines RTCA Results for Transformers RTCA Voltage Results for Buses
RTCA Enhancements Immediate Visual Image Percentage base LTE exceedance Bar chart: simple and useful! Color configurable Percentage base selectable Devices approaching SOLs included Coloring and bar length meaningful STE exceedance
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 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. Attention: post-contingency STE violation for 30 min.
RTCA Enhancements Alarm Acknowledgement Unacknowledged Contingency Ack. Alarms Acknowledged 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. Unacknowledged Contingency Acknowledged Contingency
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).
RTCA Enhancements A Wrap-up 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 Another enhancement: include RTCA result to SE tabular to provide a combined view of SE and RTCA results
Validation and Actions for 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 precontingency 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
Summary 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.
Thank you for your attention! Q & A