Electrical Power System Substation Components

Flashcards for reviewing lecture notes on Electrical Power System Substation Components

Substation

A part of the total electrical system that transforms voltage from one level to another, provides facilities for switching, and provides points where safety devices may be installed to disconnect circuits in the event of trouble.

Lightning Arrester

A device in an electrical power system that protects the insulation and conductors of the system from the damaging effects of lightning.

Station Class Lightning Arrester

Typically used in electrical power stations or substations and other high voltage structures & areas; protects against both lightning and over-voltages where the electrical device has more current in the system than is designed to handle; designed to protect equipment above 20MVA.

Intermediate Class Lightning Arrester

Protects against surges from lightning and over-voltages but are designed to be used in medium voltage equipment areas such as electrical utility stations, substation transformers or other substation equipment; designed to protect equipment in the range of 1 - 20MVA.

Distribution Class Lightning Arrester

Most commonly found in transformers, both dry type and liquid filled; these arresters are found on equipment rated 1000kVA or less.

Current Transformer

Transforms currents from a usually high current value to a value easy to handle for relays and instruments; insulates the metering circuit from the primary high voltage system.

Primary Side (of a Current Transformer)

Where the input power is received or supplied, typically connected to the higher voltage or power side; in current transformers, it's where high-voltage power is delivered.

Secondary Side (of a Current Transformer)

Where the output power is delivered or used, typically connected to the lower voltage or power side; in current transformers, stepped-down current is available, and both current and voltage are reduced.

Potential Transformer

Transforms voltages from a usually high voltage value to a value easy to handle for relays and instruments; insulates the metering circuit from the primary high voltage system.

Disconnect Switch

A mechanical switching device which provides an isolating distance in the open position for safety; allows isolation of apparatus for maintenance, repairs, or adjustments.

Circuit Breaker

A mechanical switching device capable of making, carrying, and breaking currents under normal circuit conditions and also under specified fault conditions such as short circuit.

Gas Insulated Switchgear (GIS)

A type of circuit breaker that uses Sulphur hexafluoride (SF6) gas as the arc quenching medium, commonly used for voltages 110 kV and above.

Oil Circuit Breaker

A circuit breaker that uses oil as a dielectric or insulating medium to extinguish an arc, used to protect medium and high voltage systems. There are two types, Bulk and Minimum oil circuit breakers.

Vacuum Circuit Breaker (VCB)

A circuit breaker that protects medium and high voltage systems where arc quenching takes place in a vacuum medium.

Rated Maximum Voltage (Circuit Breaker)

The highest RMS phase-to-phase voltage for which the circuit breaker is designed.

Rated Power Frequency (Circuit Breaker)

The frequency at which the circuit breaker is designed to operate.

Rated Dry Withstand Voltage (Circuit Breaker)

The RMS voltage that the circuit breaker in new condition is capable of withstanding for 1 minute under specified conditions.

Rated Wet Withstand Voltage (Circuit Breaker)

The RMS voltage that an outdoor circuit breaker or external components in new condition are capable of withstanding for 10s.

Rated Lightning Impulse Withstand Voltage (Circuit Breaker)

The peak value of a standard 1.2 x 50μs wave that a circuit breaker in new condition is capable of withstanding.

Rated Continuous Current (Circuit Breaker)

The current in RMS symmetrical amperes that the circuit breaker is designed to carry continuously.

Rated Interrupting Time (Circuit Breaker)

The maximum permissible interval between the energizing of the trip circuit and the interruption of the current in the main circuit in all poles.

Power Transformer

A transformer which transfers electric energy in any part of the circuit between the generator and the distribution primary circuit.

Indoor Transformer

A transformer which, because of its construction, must be protected from weather.

Outdoor Transformer

A transformer of weather-resistant construction suitable for service without additional protection against weather.

Pole Type Transformer

A transformer suitable for mounting on a pole or similar structure.

Liquid Immersed Transformer

A transformer in which the core and coils are immersed in insulation liquid.

Insulation Dry Type Transformer

A transformer in which the core and coils are in gaseous or dry compound insulation medium.

ONAN Cooling

Oil Natural (thermo-syphon) circulation with Air Naturally circulated for cooling.

ONAF

Oil Natural Air Forced cooling. Forced air-cooling would allow the rating to be increased by a small amount.

OFAF

Forced (pumped) oil circulation and forced (fan) air-cooled radiators.

Off-Load Tap Changer

Taps are for use in transformers that rarely require output voltage adjustments.

On-Load Tap Changer

Taps that require frequent operations as customer or system load fluctuates during the day.

Basic Insulation Level (BIL)

A specific insulation level expressed in kV of the crest value of standard lightning impulse.

Withstand Voltage

The voltage that an electric equipment is capable of withstanding without failure or disruptive discharge when tested under specified conditions.

Routine Test

Test made for quality control by the manufacturer on every device (or representative sample) to verify during production that the product meets the design specifications.

Switchgear

A general term covering switching devices and their combination with associated control, measuring, protective and regulating equipment, also assemblies of such devices and equipment with associated interconnections, accessories, enclosures and supporting structures.

Protection Relay

A relay whose function is to detect defective lines or apparatus or other power system conditions of abnormal or dangerous nature and to initiate appropriate action in the control circuit.

Gas Insulated Switchgear (GIS)

Utilized in locations where space is either too expensive or unavailable, or in places where the surrounding environment requires a protected enclosure from severe weather or surroundings.

Metal-enclosed Switchgear and Controlgear

Switchgear and controlgear with an external metal enclosure intended to be earthed and complete except for external connections