7503 System Voltage Control

This third course in the Transmission System Operation training program develops the principles of voltage control on the transmission network. The material builds upon discussions of power flow fundamentals and transmission line characteristics from the two previous courses. We begin by describing the system's need for reactive power (VARs) and how VARs are generated and/or absorbed by the various components of the power system. Next, it is demonstrated that the flow of VARs has a profound effect on the voltage level (much more so than the flow of Watts). Transmission line MW loading and its effect on VAR requirements and voltage are also examined, as well as the effect of contingencies. Various real-life scenarios are described in which power systems have collapsed from significant off-nominal voltage. Finally, this course discusses a wide array of equipment and methods system operators can use to effectively control transmission voltages to comply with industry standards.

At the completion of this course, you should be able to: Name the two distinct types of power produced at the generators when load is connected, Explain the basic difference in function between Watts and VARs, and why both types of power are necessary to make electrical equipment work, Sketch and compare curves for power in a purely inductive circuit and power in a purely capacitive circuit, Recognize the difference between positive VARs and negative VARs, Name 3 power system components that create a demand for VARs, Name 3 power system components that supply VARs to the system, Describe what it means for some components to 'compensate' for others, Explain how MW and MVARs are produced in an electric generator, Recognize that a change in generator voltage or MVAR supply must come from a change in the unit's DC excitation current, Discuss the function of an Automatic Voltage Regulator (AVR), Predict the response of the AVR to an increase or decrease in MVAR demand on the system, Recognize that it takes a difference in voltage magnitude to drive MVARs through the system, and that the direction of MVAR flow is from high to low voltage, Discuss the function of a synchronous condenser and a static VAR compensator, Explain why a transmission line can be either a MVAR source or a MVAR load, Describe the effect of MVAR flow on voltage drop. Compare to the voltage drop resulting from the flow of MW, Name 3 events that can have a profound effect on MVAR flows and voltage level, Explain what happens to the MVARs required by a transmission line as MW loading is increased, State the significance of a line's surge impedance loading (SIL), Understand why it is important to have adequate MVAR sources located at intermediate points in the network, especially during contingencies, Sketch the voltage profile along a transmission line operating above SIL, with voltage at both ends fixed at 100%. Compare with the voltage profile below and at SIL, Explain why MVAR supply from a line's capacitance drops off sharply at loadings above SIL, Name some typical loading levels for transmission lines in percent of SIL, Sketch a typical transfer limit curve (P vs. V) and explain the significance of the knee of the curve, Explain why line loadings must be restricted to well below the knee of the transfer limit curve, State the industry (NERC) limit for percent voltage change following any single contingency, Give examples of system conditions and events that may lead to voltage collapse. Explain why it is important for system operators to prepare in advance for voltage emergencies, Describe how operators can adjust voltage/MVAR supply at the generating units, Understand why AVR set points must be raised/lowered in unison to effect a net change in voltage/MVAR supply, Sketch a typical generator capability curve and discuss the MW and lagging/leading MVAR limitations, Describe the function and operation of Maximum and Minimum Excitation Limiters on generating units, List some power system components that allow operators to adjust voltage/MVAR supply at locations other than generating plants, Discuss the reactive overload capability of generators, synchronous condensers, and static VAR compensators, Describe some typical applications for shunt reactor and capacitor banks on the transmission system, Explain how a series capacitor can be of assistance in voltage control, Understand the function and operation of Load Tap Changing Transformers (LTCs) in providing voltage correction on the transmission and distribution systems, Discuss the importance of operator actions in implementing voltage control: curtailing economy transfers, bringing on local generation, bringing on reactive sources ahead of the morning load rise, removing lines during light load, etc.

If you are taking this course for NERC credit, the following credits will be reported.

NERC CE HOURS: CE HOURS = 4.00 OPS Topics=4.00 Standards=0.00 Simulation=0.00 EO=4.00