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Admittance relay is directional relay.

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Description : Define admittance and state its unit.

Answer : Admittance is defined as the ability of the circuit to carry (admit) alternating current through it.  OR  It is the reciprocal of impedance Z. i.e Admittance Y = 1/Z.  Unit: Its unit is siemen (S) or mho (Ʊ).

Description : In which of the following transmission lines, the value of the Shunt admittance should be approximated to zero ? (A) A 66 kV 35 km long line (B) A 132 kV 200 km long line (C) A 220 kV 300 km long line (D) A 400 kV 500 km long line

Answer : In which of the following transmission lines, the value of the Shunt admittance should be approximated to zero ? (A) A 66 kV 35 km long line (B) A 132 kV 200 km long line (C) A 220 kV 300 km long line (D) A 400 kV 500 km long line

Description : The diagonal elements of a nodal admittance matrix are strengthened by adding :  (A) Shunt capacitors (C) Generators (B) Shunt inductances (D) Resistive loads

Answer : A

Description : Which of the following is the SI unit for admittance? A) Ohm B) Henry C) Farad D) Siemens

Answer : Which of the following is the SI unit for admittance? A) Ohm B) Henry C) Farad D) Siemens

Description : what is the reciprocal of admittance?

Answer : impedance is the reciprocal of admittance.

Description : The purpose of the restraining coil in a biased differential relay is  (A) To reduce CT saturation during fault.  (B) To increase the sensitivity of the relay.  (C) To match the transformation ratio.  (D) To limit the spill current through the relay during heavy external fault.

Answer : d

Description : A relay used for protection of motors against overload is :  (A) Impedance relay (B) Electromagnetic attraction type (C) Thermal relay (D) Buchholz's relay

Answer : A relay used for protection of motors against overload is : Thermal relay

Description : A relay has a rating of 5 A, 2.2 sec IDMT and a relay setting of 125% TMS = 0.6. It is connected to a supply circuit through a C.T. 400/5 ratio. The fault current is 4000 A. The operating current of the relay is

Answer : A relay has a rating of 5 A, 2.2 sec IDMT and a relay setting of 125% TMS = 0.6. It is connected to a supply circuit through a C.T. 400/5 ratio. The fault current is 4000 A. The operating current of the relay is 6.25A

Description : The operating time of instantaneous relay is

Answer : The operating time of instantaneous relay is 0.1 sec

Description : What is the difference between relay and contactor?

Answer : Relay have smaller ratings. Contactor is a high rating relay.

Description : A negative sequence relay is used for protection of  (1) Generator (3) Motor (2) Transformer (4) Long Transmission lines

Answer : A negative sequence relay is used for protection of Generator 

Description : Buchholz relay is  (1) located in the conservator tank  (2) located in the transformer tank itself  (3) connected in the pipe connecting main tank of transformer and conservator  (4) installed in the circuit breaker

Answer : Buchholz relay is connected in the pipe connecting main tank of transformer and conservator 

Description : To prevent mal-operation of differentially connected relay while energizing a transformer, the relay restraining coil is based with  (1) second harmonic current  (2) third harmonic current  (3) fifth harmonic current  (4) seventh harmonic current

Answer : To prevent mal-operation of differentially connected relay while energizing a transformer, the relay restraining coil is based with  second harmonic current 

Description : Reactance relay is normally preferred for protection against

Answer : Reactance relay is normally preferred for protection against earth faults

Description : In the induction type directional over current relay, when a short-circuit occurs in the circuit (A) power flows in reverse direction (B) power flows in normal direction (C) directional power element does not operate (D) over current element is not energized

Answer : In the induction type directional over current relay, when a short-circuit occurs in the circuit power flows in reverse direction

Description : A solid state relay (A) withstands voltage transients (B) does not require auxiliary dc supply (C) provide low burden on CT and P (D) does not provide earth fault protection

Answer : A solid state relay provide low burden on CT and P

Answer : The torque produced in induction type relay (shaded pole structure) is inversely proportional to the square of the current.

Answer : The relay with inverse time characteristic will operate within 5 to 10 sec.

Answer : The under voltage relay can be used for generators, busbars, transformers, motors.

Answer : Reactance relay is preferred for phase fault on short transmission line.

Answer : Induction cup relay is operated due to changes in current, voltage, impedance.

Answer : Interruption of large currents by relay requires arc suppressing blow out coils, wide separation of the opened contacts, high speed opening of contacts.

Answer : Overheating of relay contacts or contact born out is due to slow making and breaking of load circuit contacts, foreign matter on the contact surface, too low contact pressure.

Answer : A differential relay measures the vector difference between two or more similar electrical quantities.

Answer : Burden of a protective relay is the power absorbed by the circuit of relay.

Answer : In order that current should flow without causing excessive heating or voltage drop, the relay contacts should have low contact resistance, be clean and smooth, be of sufficient size and proper shape.

Answer : The relay operating speed depends upon the spring tension, the rate of flux built up, armature core air gap.

Description : How do relay works ?

Answer : Relay working like contact it is noise less 

Description : What is the use of Buchholz relay in transformer?

Answer : This is a transformer that is used to step up and down current. 

Description : What is the difference between a switch and a relay?

Answer : Switch is simply a mechanical contact mechanism and relay is a electromagnetic switch . Switch can be direct mechanically turn on and off but relay can be operated by energising coil .

Description : main parts of Relay

Answer : Coil, plunger, contacts, springs, connecting terminals and enclosure.

Description : What is phase failure relay and how it's work?

Description : Buchholz relay is used as a safety device with respect to which of the following? A) Audio transformers B) Oil filled power transformers C) Air core transformer D) None of these

Answer : Buchholz relay is used as a safety device with respect to which of the following? A) Audio transformers B) Oil filled power transformers C) Air core transformer D) None of these

Description : A reactance relay is (A) Voltage restrained directional relay (B) Directional restrained over-current relay (C) Voltage restrained over current relay (D) Directional restrained over voltage relay

Answer : A reactance relay is Directional restrained over-current relay

Answer : A Buchholz relay can be installed on oil cooled transformers.

Answer : Buchholz's relay gives warning and protection against electrical fault inside the transformer itself.

Description : what is reverse power relay?

Answer : Thereverse powerrelay is a directional protective relay that prevents power from flowing in the reverse direction. Read our article going back ... it all to be up to date. And if you do, read it anyway just to check if youreallydo!

Description : For protection of rotating machines against lightning surges _______ is used.  (1) lightning arrester (2) capacitor (3) combination of lightning arrester and capacitor (4) lightning conductor and arrester

Answer : For protection of rotating machines against lightning surges combination of lightning arrester and capacitor is used. 

Description : With the help of neat diagram, explain operation of static relay.

Answer : Operation of Static Relay: Operation: 1) The solid-state component used are transistors, diodes, resistors, IC s, capacitor etc. The function of comparison and measurement are accomplished by ... ) An auxiliary dc supply is provided for operation of static relay elements as shown in figure.

Description : Describe the construction and Operation of Buchholz relay with neat labeled diagram.

Answer : Construction of Buchholz Relay: It takes the form of a domed vessel placed in the connecting pipe between the main tank and the conservator. The device has two elements. The upper element ... manner that it senses the sudden violent movement of oil/gas from transformer tank to conservator. 

Description : Describe the operation of current differential relay with neat sketch.

Answer : Operation of Current Differential Relay: Figure shows an arrangement of an overcurrent relay connected to operate as a differential relay for alternator protection under fault conditon. ... current flows through relay coil, causing relay to operate for protection of alternator winding.

Description : With a neat sketch, explain the working of Thermal relay.

Answer : Working of Thermal Relay: 1) When the system is in normal operating condition, the heating element carries normal current from CT, this current produces heat = I2Rt. This heat ... of the spring releases which operates relay contacts resulting into providing trip signal to trip circuit.

Description : Define the following terms with respect to protective relays i) Relay time ii) Reset current iii) Plug setting multiplier and iv) Time setting multiplier

Answer : 1) Relay Time: The time interval between occurrence of fault and closure of relay contacts.  2) Reset Current: The value of current below which the relay resets and comes back to ... The adjustment arrangement provided for setting the operation time of relay is known as Time setting multiplier. 

Description : Draw a typical time-current characteristic for IDMT relay. 

Answer : Time-Current Characteristic for IDMT Relay:

Description : Explain operation of balanced beam type relay.

Answer : Balanced Beam Type Relay: Under normal operating condition the current through relay coil is such that the beam is held in the horizontal position by the spring. When the fault occurs on the system the ... becomes greater than pick-up value and beam is attracted to close the trip circuit. 

Description : Explain Buchholz relay with neat labelled diagram.

Answer : Buchholz relay: The relay is located in the path of the oil from transformer tank to conservator. As seen from diagram, the upper mercury switch operates the alarm circuit due to tilting of the ... manner that it senses the sudden violent movement of oil from transformer tank to conservator.

Description : Explain MHO relay in detail.

Answer : MHO Relay: In this relay, poles 1, 2, 3 are energized by a voltage V through polarizing coil to produce flux, the capacitor connected provides phase shift. The left pole 4 is energized by a current which is the ... hence on the ratio (I/V) = Y i.e. admittance, hence called as MHO relay.

Description : Describe over current relay with time-current characteristic.

Answer : Over current relay with time-current characteristics:- 1. Definite time over current relay: Operating time is constant, the relays operates after a predetermined time when the current exceeds the pickup ... of fault current and definite time characteristics at higher values of fault current.

Description : Explain operation of µP based relay with block diagram

Answer : Operation of Microprocessor (µP) based relay: The inputs from the power system through CTs and PTS are received by the analog Input receiver; they are sampled simultaneously or ... compares the dynamic inputs and decides accordingly to generate trip/alarm signal to the output device.

Description : Explain construction and operation of induction type directional over current relay.

Answer : Directional overcurrent relay: Construction: It consists of two units: i) Non-directional Over-current unit ii) Directional power unit The directional unit consists of upper electromagnet ... closes the trip circuit. This operates circuit breaker which isolates the faulty section. 

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