Implementation of Automatic Under Voltage Load Shedding Program in Entergy System

Transcription

1 Implementation of Automatic Under Voltage Load Shedding Program in Entergy System Sharma Kolluri, IEEE Fellow Manager, Transmission Planning Entergy Services, Inc. Presentation at i-pcgrid Workshop San Francisco, CA March 26, 2014

2 What is Automatic UVLS Program? (Proposed NERC Definition) An automatic load shedding program consisting of distributed relays and controls used to mitigate the risk of Cascading, voltage instability, voltage collapse, or uncontrolled separation resulting from undervoltage conditions. Centrally-controlled UVLS is excluded because it is consistent with nature of SPSs.

3 New NERC UVLS Standard (Project ) NERC seeks to revise current UVLS standard based on FERC directive Modify PRC to require that integrated and coordinated approach be included in all protection systems SDT decided to consolidate the existing UVLS standards to create a single results based standard The proposed standard is currently posted for informal comments deadline April 16, 2014

4 Overview of Entergy System Over 15,000 miles of transmission lines in four states 1,550 substations 36,000 MW of connected generation 24,000 MW Entergyowned 12,000 MW merchantowned 28,000 MW of load

5 Background on Western Region Western Region load growth: ~ 5.1 % (in past) with high composition of air conditioning load Limited Generation resources: Two Lewis Creek units (260 MW, 150 MVAR each) With generation out of service, line outages can lead to potential voltage collapse - FIDVR A SCADA based UVLS program was commissioned to meet NERC requirements

6 FIDVR Event

7 Western Region One Line Grimes Crockett Lewis Creek Units China - Jacinto Oak Ridge - Tamina New Caney - Hickory

8 PV Curve for Western Region (generation and 230 kv line out) p.u Rivtrin Poco Goslin Cypress Conroe Pelican Road Frontier Dayton Rivtrin Conroe Poco Jacinto Cleveland Huntsville Goslin Lewis Creek Pelican Road Cypress Frontier Lewis Creek

9 Voltage Plot of Woodlands Area Buses 1.0 p.u. 0.9 p.u. Second Block Load Shed First Block Load Shed

10 Existing SCADA Based UVLS Program

11 SCADA Based Load Shed Logic Armed all time 4/8 buses <0.92 pu Drop load One or more Lewis Creek units inservice? OEL at Lewis Creek units 4/8 buses < 0.94 pu Time Delay 3 seconds Monitored Buses: Dayton Bulk 138kV Rivtrin 138kV Conroe 138kV Poco 138kV Jacinto 138kV Cleveland 138 kv Huntsville 138 kv Goslin 138 kv Load Blocks: Block 1: 120 MW Block 2: 100 MW Block 3: 60 MW Reset the Process for next LVSH block The above conditions need to be met for 3 scans to trigger load shedding

12 New Relay Based UVLS Program

13 Relay Based UVLS Program This program will replace existing SCADA based program Load shed decision is based on predicted time to recover above a preset voltage value instead of voltage magnitude SEL-451 relays will be installed at 4 selected 138 kv stations Relays monitor positive-sequence voltage on high side of 138 kv buses Program designed to drop a total of 200 MW load at the 4 stations

14 Program Overview Positive Sequence Voltage is sampled and saved once per cycle Program is enabled when the voltage is below 0.8 p.u. 5 consecutive slopes of voltage recovery (with 2, 4, 6, 8 and 10 cycles durations) is used for predicting voltage recovery time If all 5 consecutive recovery time predictions > predefined set time, Load shed is triggered If recovery time < setting time, no action is taken

15 UVLS Recovery Slope Calculation 1.05 pu 0.8 pu Relay Reset Actual Recovery Slope V2 pu V1 pu 0.3 pu 0.1 sec t1 sec t2 sec 2.1 sec 2 SEC 4.1 sec ARM RELAY 2 SEC TIMER DELAY RECOVER To 0.8 pu Within next 2 sec UV Detected

16 Neg seq block Logic Diagram Voltage in range Zero seq block Receive block from other relay Program Enable Transmits block to other relay Block low side fault Secondary voltage present

17 Voltage in range Logic Diagram(contd) Timer Trip count Preset recover voltage Preset time Clock, 1 pulse / cycle

18 Logic Diagram for Tripping Timer within per defined time range Trip Trip count = 5 Program Enable

19 Lab Simulations

20 Lab Setup

21 PSS/E Simulations Cases

22 Comtrade File

23 Relay Event Report V 1M ag RE Q_M A G V1Mag REQ_MAG TRP CNT V1 0.8 p.u. Trip count TRP CNT D igitals 0-5 PLT01 PSV59 Trip Program enable Relay 210 cycle Relay trip Cycles

24 Relay Event Report 65.0 V1Mag REQ_MAG V 1M ag RE Q_M A G V1 Relay trip 0.8 p.u Cycles

25 SUMMARY Relay based UVLS program is more appropriate for addressing FIDVR phenomena Faster when compared to SCADA based program More localized and independent More intelligent and flexible

26 Questions?