1. Voltage Control Brad Calhoun Consultant, Sr. Trainer Spring 2016

2. Introduction Voltage control in an electrical power system is important for proper operation of electrical power equipment, to prevent damage such as overheating of generators and motors, to reduce transmission losses, and to maintain the ability of the system to withstand and prevent voltage collapse. In general terms, decreasing reactive power causes voltage to fall while increasing it causes voltage to rise. A voltage collapse occurs when the system try's to serve much more load than the voltage can support. 2

3. PUBLIC 3 Objectives Identify the coordination of efforts between TOPs and QSEs necessary to maintain the voltage profile within established limits ensuring reliable operations. Given a list of reactive and voltage control devices, identify each as a dynamic or static device and state its purpose in maintaining an adequate supply of reactive reserve. Identify the NERC Reliability Standards, ERCOT Protocols, and ERCOT Guides requirements governing activities that ensure an adequate supply of reactive reserves ensuring reliable operations.

4. Dynamic Reactive Reserves Generators are the only true sources of reactive power 4

5. PUBLIC 5 Dynamic Reactive Reserves Static reactive devices will be managed to ensure that adequate dynamic reactive reserves are maintained at all times. Nodal Operating Guides 2.7.2 Maintaining Voltage Profile ERCOT, in coordination with TSPs, shall deploy static Reactive Power Resources as required to continuously maintain dynamic reactive reserves from QSEs, both leading and lagging, adequate to meet ERCOT System requirements. 3.15.1 ERCOT Responsibilities Related to Voltage Support Each TSP, under ERCOT’s direction, is responsible for monitoring and ensuring that all Generation Resources required to provide VSS dynamic reactive sources in a local area are deployed in approximate proportion to their respective installed Reactive Power capability requirements. 6.5.7.7 Voltage Support Service

6. PUBLIC 6 Automatic Voltage Regulator

7. PUBLIC 7 Automatic Voltage Regulator Dynamic reactive device The automatic voltage regulator (AVR) senses the voltage level at the generator terminals via a potential transformer (PT). If the measured voltage is lower than the set point, the AVR will cause the excitation system to increase the DC excitation current. This DC current is applied to the generator's rotor field winding. If the voltage measured is higher than the set point, the excitation system will lower the DC excitation current applied to the field winding.

8. PUBLIC 8 Synchronous Condenser

9. PUBLIC 9 Synchronous Condenser Dynamic reactive device A synchronous condenser is very similar to a synchronous generator with the exception that it is not capable of producing any active power. It produces only reactive power. Synchronous condensers do not need a prime mover (steam or water turbine) as they are operated like a motor. The power system supplies the active power to turn the rotor. An excitation system is used to control the amount of MVAR produced by the synchronous condenser.

10. PUBLIC 10 Static VAR Compensators

11. PUBLIC 11 Static VAR Compensators Dynamic reactive device A power quality device, which employs power electronics to control the reactive power flow of the system where it is connected. As a result, it is able to provide fast-acting reactive power compensation on electrical systems. In other words, static VAR compensators have their output adjusted to exchange inductive or capacitive current in order to control a power system variable such as the bus voltage. Flexible AC Transmission Systems (FACTS) improve transmission quality and efficiency of power transmission by supplying inductive or reactive power to the grid.

12. Static Reactive Reserves Extending the range of dynamic reactive resource response 12

13. PUBLIC 13 Capacitors

14. PUBLIC 14 Capacitors Static reactive device Capacitors are defined as two conductors separated by an insulating medium. These devices store, and later return, electrical energy to the system. Since capacitors store reactive power, they may be viewed as sources of reactive power. Capacitors can be connected to the power system in either a shunt or a series connection. Shunt capacitors are used to supply reactive power to the system. Series capacitors are used to reduce the impedance of the path in which they are inserted.

15. PUBLIC 15 Correcting the Power Factor

16. PUBLIC 16 Capacitor Application Restores dynamic reactive reserves –Coordinate with resources Unloads transmission facilities Location of Capacitors

17. PUBLIC 17 Reactors

18. PUBLIC 18 Reactors Static reactive device a coil or other component that provides inductive reactance in a circuit. Reactors can be viewed as absorbers or sinks of reactive power. Reactors can be connected to the power system in either a shunt or a series connection. Shunt reactors are used to absorb reactive power from the system. Series reactors are used to increase the reactance of the path in which they are inserted.

19. PUBLIC 19 Transmission Lines

20. PUBLIC 20 Transmission Lines Surge Impedance Level (SIL) Ferranti Rise Line Switching

21. PUBLIC 21 CREZ Reactive Compensation Requirements (cover wind output from 1979MW to 12036MW from CREZ) –Nine 345kV 50% series compensated lines –~1400MVAr dynamic reactive devices –~900MVAr shunt capacitor –~3000MVAr shunt reactor

22. Coordination of Efforts Reliable Operations 22

23. PUBLIC 23 Participation Each TSP, under ERCOT’s direction, is responsible for monitoring and ensuring that all Generation Resources required to provide VSS dynamic reactive sources in a local area are deployed in approximate proportion to their respective installed Reactive Power capability requirements. 6.5.7.7 Voltage Support Service Power Factor

24. PUBLIC 24 Voltage Profile ERCOT in coordination with the Transmission Service Providers (TSPs) shall establish and update, as necessary, the ERCOT System Voltage Profile for all Electrical Buses used for Voltage Support in the ERCOT System and shall post all Voltage Profiles on the Market Information System (MIS) Secure Area. ERCOT may temporarily modify its requirements based on current system conditions. 3.15 Voltage Support

25. PUBLIC 25 TSP versus QSE/GO lingo barrier Boost or Buck Lead or Lag Positive or Negative Voltage Set Point Keep it Simple –Dispatch Instructions Raise the voltage by XXX volts Lower the voltage by XXX volts

26. PUBLIC 26 Benefits of Healthy Voltage Profile Reduces transmission lo $$ es Improves system security Reduces system loading –MVA –Transformer

27. Regulatory Requirements The Rules of the Road 27

28. PUBLIC 28 Voltage Ride-Through Generation Resources must be designed and generation voltage relays must be set to remain connected to the transmission system during the following operating conditions: –Generator terminal voltage deviations exceed 5% but are within 10% of the rated design voltage and persist for less than ten seconds; –Generator volts per hertz conditions are less than 116% of generator rated design voltage and frequency and last for less than 1.5 seconds; –A transmission system fault (three-phase, single-phase or phase-to- phase), but not a generator bus fault, is cleared by the protection scheme coordinated between the Generation Entity and the Transmission Service Provider (TSP) on any line connected to the generator’s transmission interconnect bus, provided such lines are not connected to induction generators described in paragraph (9) of Protocol Section 3.15, Voltage Support;

29. PUBLIC 29 NERC PRC Standards PRC-025-1— Generator Relay Loadability – –During the recoverable phase of a disturbance, the disturbance may exhibit a “voltage disturbance” behavior pattern, where system voltage may be widely depressed and may fluctuate. –To prevent unnecessary tripping of generators during a system disturbance for conditions that do not pose a risk of damage to the associated equipment –Apply settings that are in accordance with PRC-025-1 – Attachment 1: Relay Settings, on each load-responsive protective relay while maintaining reliable fault protection.

30. PUBLIC 30 NERC VAR Standards VAR-001-4 — Voltage and Reactive Control –R1. …specify a system voltage schedule –R2. …schedule sufficient reactive resources –R3. …operate or direct the operation –R4. …specify the criteria that will exempt generators –R5. …specify a voltage or Reactive Power schedule –R6, …necessary step-up transformer tap changes and the implementation schedule

31. PUBLIC 31 NERC VAR Standards VAR-002-4 Generator Operation for Maintaining Network Voltage Schedules –R1. …operate each generator in the automatic voltage control mode –R2. …maintain the generator voltage or Reactive Power schedule –R3. …notify its status change on the AVR, power system stabilizer, or alternative voltage controlling device –R4. …notify its change in reactive capability –R5. …provide tap settings, fixed tap ranges, and impedance data –R6. …ensure that transformer tap positions are changed according to the specifications

32. PUBLIC 32 ERCOT Guides in order to prevent one Entity from being a burden to another The operation of all Reactive Power devices under the control of a TO or a Qualified Scheduling Entity (QSE) will be coordinated under the direction of ERCOT to maintain transmission voltage levels within normal limits and post-contingency voltages within post contingency limits. Static reactive devices will be managed to ensure that adequate dynamic reactive reserves are maintained at all times. the response (within the operating Reactive Power capability of the Generation Resource) must be sufficient to initiate response in no more than one minute and return the measurement within the required range in no more than five minutes within 2% of the voltage profile

33. PUBLIC 33 Summary Healthy Voltage Profile Coordinated Effort Active Participation Communication

34. PUBLIC 34 Resources NERC Reliability Standards ERCOT Protocols Nodal Operating Guides Siemens USA Electrical Engineering Portal All About Circuits How Stuff Works