Module 5: Substation overview, Lecture notes of Mechanics

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5|Substation Overview

W E S T E R N E L E C T R I C I T Y C O O R D I N A T I N G C O U N C I L

Course Outline

1. Introduction to WECC
2. Fundamentals of Electricity
3. Power System Overview
4. Principles of Generation
5. Substation Overview
6. Transformers
7. Power Transmission
8. System Protection
9. Principles of System Operation

Purpose of Substations

• In general, a substation is a power system facility that contains power system components such as: - circuit breakers and other switchgear - transformers - reactors - capacitors

• A substation usually includes a control house that contains equipment such as: - protective relays - meters - alarm annunciators - communications equipment

Purpose of Substations

Purpose of Substations

• Outdoor substations have the same equipment as indoor substations but the equipment is located outside where it is exposed to natural elements, rather than in a building. The equipment is usually enclosed within a fence.

Purpose of Substations

Purpose of Substations

• Ground Mat
  • Substations usually include a ground mat. A ground mat is a system of bare conductors, on or below the surface, connected to a ground to provide protection from high voltages.

Purpose of Substations

• Reactive power compensation - Utilities install synchronous condensers, shunt reactors, shunt capacitors, and static VAR compensators at substations to control voltage. - Utilities install series capacitors at substations to reduce line reactance.

Purpose of Substations

Substation Equipment

• In this section we describe the function and operating principles of the following power system components: - Switchgear Equipment - Capacitors - Reactors - Ground Switches - Lightning Arresters - Wave Traps

• Under normal conditions, switchgear equipment enables routine switching operations to occur.
• For example: Switchgear equipment disconnects and isolates a piece of equipment so maintenance work can be performed.
• Under abnormal conditions, switchgear equipment automatically disconnects faulted equipment from the rest of the power system as soon as possible, in order to minimize damage. Under these conditions, switchgear equipment performs a protective function.

Switchgear

• All switchgear operates by pulling apart electric conductors (contacts). As the contacts are drawn apart while power is flowing through the device, an arc forms between the contacts. The arc is drawn out in length as the contacts open. To interrupt current flow, the arc must be extinguished with a dielectric substance, such as air, oil, or sulfur hexafluoride (SF6).

Switchgear

Circuit Breakers

• Circuit breakers disconnect circuits or equipment from the power system. A circuit breaker's primary function is to interrupt current flow under load or fault conditions.
• Circuit breakers rapidly isolate faulted portions of the power system. They also provide a means to carry out routine switching operations, such as disconnecting a device to conduct maintenance.

• To interrupt the current, the circuit breaker must trip. Let's examine the mechanics involved in tripping circuit breakers under fault conditions.
• When a fault occurs, relays sense the fault and initiate the opening of the circuit breakers related to the faulted equipment by energizing the circuit breakers' trip coils. Module 8: System Protection, presents the details on the operation of relays.

Circuit Breaker Operating Principles