EEE Important Short Note for Interview-1


(1) SCADA System.

Supervisory Control and Data Acquisition (SCADA) : The combination of transducers, communication links and data processing systems which provides information to the National Load Dispatch Centre(NLDC) on the operation of the Transmission System and the Generating Units.

(2) Smart Grid

A smart grid puts advanced information and communication technology into electricity generation, delivery and consumption with dynamic pricing, making systems cleaner, safer, and more reliable and efficient into the current electricity grid.

(3) What is substation?

A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse. Main equipments of a substation- Power transformer, Circuit breaker (CB), Instruments transformer ( CT/PT), Lightning arrestor (LA), Disconnection switch (DS), Control panel, Relay panel, Battery and Battery charger.

(4) Power transformer.

A power transformer is an electrical device that varies the amounts of current and voltages flowing through power lines. This means that, a transformer steps up the voltage while reducing the current and vice versa. Both side KVA or MVA is same .

(5) Lighting arrestor.

The lightning arresters provide protection against surges. A lightning arrester is a protective device, which conducts the high voltage surges on the power system to the earth or ground.

(6) Circuit Breaker (CB)

Electrical circuit breaker is a switching device which can be operated manually as well as automatically for controlling and protection of electrical power system respectively. In a Circuit Breaker two contacts called electrode remains closed under normal operating conditions. When fault occurs on any part of the system, the trip coil of the circuit breaker get energized and contacts are separated.

(7) What is instruments transformer (CT/PT)?

Instrument transformers transform high currents and voltages to standardized low and easily measurable values that are isolated from the high voltage system. When used for metering purposes, instrument transformers provide voltage or current signals that are very accurate representations of the transmission line values in both magnitude and phase.

(8) Function of a Power System.

To generate electric energy “economically” and with the “minimum ecological disturbance” and to transfer this energy over transmission lines and distribution networks with the “maximum efficiency” and “reliability” for delivery to consumers at “virtually fixed voltage and frequency” ensuring proper “safety”.

(9) Buchholz Relay

Buchholz relay is a mechanical protection device for monitoring the gas and oil movements in oil immersed transformers. It is used in practically all power transformer with the exception of small distribution transformers. It is located in between transformer tank and conservator. When a slight fault occurs in the transformer, the small bubbles of gas which pass towards the oil conservator tank are trapped in the relay housing, causing oil level in side the casing to fall. If an arc forms, gas accumulation is rapid, and oil flows rapidly into the conservator which is called oil surge. This flow of oil operates a switch (for alarm and shutdown) attached to a vane located in the path of the moving oil.

(10) Pressure Relief Device (PRD) of Transformer

Pressure Relief Device is a safety element of the transformer that employs to prevent heavy damages of the tank in the case of sudden rise of the internal pressure from transformer internal fault. These device has been designed in order to remove the excess pressure in a very short time as soon as the pressure in the tank rises above pre-seted safety limit.

(11) What is relay flag in Substation?

Physical indication that ensures operation of a protective devices (relays) in a substation.

(12) What is a Busbar?

Generally busbar is a good quality conductor used to carry a large amount of current.

(13) Back to Back substation

Back to Back is an interface substation where both Rectifier and Inverter are present for conversion and reconversion of AC and DC transmission.

(14) Directional over-current relay.

try self…..

(15) Reverse Power Relay

A reverse power relay is a directional power relay that is used to monitor/protection the power from a generator running in parallel with another generator or the utility. The function of the reverse power relay is to prevent (send trip signal to CB) a reverse power condition in which power flows from the bus bar into the generator.

(16) SF6 circuit breaker

SF6 circuit breaker in such breaker, that Sulfur Hexa Flouride gas (SF6) is used as the arc quenching medium. Sulfur Hexa Flouride (SF6) gas is an electro-negative gas and it has high electric strength and outstanding arc quenching characteristics. The Sulfur Hexa Flouride (SF6) circuit breakers have been found to be very effective for high voltage system. SF6 breakers are smaller than air-blast breakers.

(17) Transformer Common Test list:

Tan Delta Test
Insulation Test
Ratio Test
Short/Open Ckt test
Magnetic Balance Test
Vector Group test
Percentage Impedance Test
Break down Voltage test (Oil)
Acidity Test (Oil)
Sweep Frequency Response Analysis (SFRA)

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