System Ratings, Limits and Real-Time Monitoring. Presented to: Operating Committee April 21, 2016

Transcription

1 System Ratings, Limits and Real-Time Monitoring Presented to: Operating Committee April 21, 2016

2 Thermal Facility Ratings In New England Summer ratings (April 1 to October 31) Winter ratings (November 1 to March 31) Thermal capacity ratings for transmission facilities ISO-NE procedure OP-16 ISO-NE database NX-9 Normal and Emergency ratings are applied Normal continuous 24 hour rating *Long Time Emergency (LTE) 12 hour summer and 4 hour winter load cycle ratings Short Time Emergency (STE) 15 minute rating Drastic Action Limit (DAL) 5 minute rating *The use of these ratings requires the pre-contingent circuit loading to be at or below the Normal rating and that the circuit loading be returned to or below the Normal rating after the daily load cycle 2 2

3 Voltage Limits Voltage limits required with NERC standard changes Full implementation in summer of 2015 No seasonal limit changes for voltage Transmission owners supply limits based on their equipment ratings Voltage limits for transmission facilities ISO-NE procedures OP-19 and M/LCC-15 M/LCC-15, attachment H lists LCC operating area limits M/LCC-15, attachment E lists all exceptions Normal and Emergency limits are applied, high and low Normal Voltage Limit (NORMVL) continuous limit Long Time Emergency Voltage Limit (LTEVL ) minimum of 30 minute limit Short Time Emergency Voltage Limit (STEVL) 15 minute limit Drastic Action Limit Voltage Limit (DALVL) 5 minute limit 3 3

4 4 4 Voltage Limits (M/LCC-15H)

5 Transmission Voltage Limits Used in Operations Operation at voltages and time durations outside of the shaded area may result in an SOL exceedance 5 5

6 6 6 SCADA Transmission Voltage Alarms

7 7 7 SCADA Subtransmission Voltage Alarms

8 Transmission Voltage Limits Used in Planning Company Other New England Utilities National Grid VELCO kv Level Pre Contingency Post Contingency Pre Switching Post Switching High Voltage Low Voltage High Voltage Low Voltage High Voltage Low Voltage Subtransmission 34.5 kv, 46 kv and 69 kv limits 0.95 pu to 1.05 pu pre-contingency 0.90 pu to 1.1 pu post-contingency What is the post-contingency pre switching low voltage limit? What is the lowest voltage allowed at the customer service meter? 8 8

9 Real Time Monitoring Real-Time Contingency Analysis (RTCA) is a predictive tool required for Transmission Operators Uses a power-flow model ingesting real time data In the VELCO control room RTCA runs every 5 minutes RTCA application outages 521 transmission and subtransmission contingencies (element outages) within VT and with our neighboring utilities Ranks thermal and voltage limit violations by severity for the Operators to monitor The Operator must know the risk to the system at all times with this application, have mitigation plans and if necessary take pre-contingency actions to prevent a transmission limit violation 9 9

10 Real Time Monitoring Both VELCO and ISO-NE monitor the VELCO transmission system and run RTCA Both VELCO and ISO-NE have what NERC requires, a wide-area view within our geographic areas VELCO has better detail of the VT system in the EMS model ISO-NE looks to VELCO for ensuring local area reliability ISO-NE Transmission Operating Guides (TOGs) are used for monitoring interface limits Studies performed by ISO-NE and VELCO determine the thermal, voltage and stability operating interface limits for the VT and NE areas 10 10

11 Real Time Monitoring The PSSE load-flow model used by ISO-NE for studies completely models the VT subtransmission system and distribution loads ISO-NE ensures that for all transmission system contingencies, the area customer loads and transfers can be supported, i.e. both thermal loading and voltage The looped VT subtransmission system is critical to supporting load and is impacted by the overlying transmission system VELCO has the responsibility to monitor the subtransmission that ISO-NE does not fully model or monitor in their SCADA/EMS 11 11

12 System Models and Ratings The VT subtransmission system is completely represented in the regional power flow PSSE models Annual update process includes review of the subtransmission system Topology changes provided at least one month prior to change Needed for EMS modeling, Operations awareness, Engineering and Planning studies Modeling data is needed for the following Lines Transformers Shunt capacitor banks Generators Others, such as overload protection schemes 12 12

13 Modeling Data Data responsibilities GMP, VEC, BED, Swanton, WEC, Stowe, VPPSA Existing process Send all updates to DUSYSTEM GMP-North consistently using process 13 13

14 Thermal Circuit Ratings (GMP-North) Covers 34.5kV system Includes other utilities, e.g. Morrisville and Hardwick 14 14

15 Thermal Circuit Ratings (GMP-South) We follow table based on conductor rating Could there be a more limiting element? 15 15

16 Thermal Circuit Ratings (VELCO) Publish 1 st and 2 nd limiting elements Device legend to define limiting elements 16 16

17 Recent Operating Events Several operating events in recent months regarding system thermal ratings used in real-time operation February 3 rd, loss of VELCO K22 line with the K21 open for maintenance Morrisville #3 to GMPR-Johnson B kV circuit was operated up to 111% above its winter limit of 37.5MVA for 22 minutes Ambiguity with the VELCO and GMP control centers on the winter rating Morrisville #3 to VELCO-Stowe kV circuit operated up to 85% of rating The line conductor sagged making contact with the underbuilt lower voltage distribution 17 17

18 Recent Operating Events March 22 nd, VELCO F206 Granite to Comerford line out of service for maintenance The GMP Websterville to McIndoes 3311 line approached overload at 17.9 MVA winter rating 3311 limiting element, Websterville substation switch The 3311 was opened by SCADA control Opening of the 3311 line as a pre-planned option added more load on the NGRID Comerford to GMP Marshfield 3316 line Ambiguity between the VELCO and GMP control centers on the 3316 winter ratings, caused three area generators (Dodge Falls, Ryegate, and McIndoes) to be reduced 3316 limiting element, WEC Danville Tap switch Replacement of the Websterville switch has been postponed with the intention to upgrade with rebuild of the substation 18 18

19 19 19 Geographical Area

20 20 20 GMP Area One-line

21 Survey of VT Control Centers BED have max alarm limits in SCADA and unclear on seasonal changes GMP-N have a list used in the control room, hope to have SCADA upgrade include limits in SCADA and update for Winter and Summer GMP-S have alarm limits in SCADA, however they are very conservative and when in alarm the Operators refer to the list in the control room to verify. No seasonal limit changes being made Swanton no SCADA indications, the reclosers control (limit) line loading. Rely on experience for operating. VEC mainly rely on Engineering, no list in the control room 21 21

22 Possible Solutions Develop a common VT thermal circuit database for subtransmission and specific distribution (e.g. BED 13.8kV) VELCO would be responsible for administration We need consistency in rating methodology In the interim, send all updates to DUSYSTEM DATA@VELCO.COM Make priority for looped subtransmission that can more easily be overloaded Publish common ratings in each control center for real time operation Will require a revision and update process For control centers with SCADA monitoring, apply seasonal limits with alarm set-points Provide training to the VT operators on rating methodologies, contingencies, limit exceedance resolution 22 22

23 23 23 Questions?