# Interruption of large currents by relay requires?

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

## Related questions

Description : What is voltage interruption?

Description : Explain following techniques related to energy conservation in transmission and distribution system. (i) By balancing phase currents (ii) Variable technical losses (I2R losses).

Answer : (i) Balancing Phase currents: Proper (healthy balanced) three phase loads always draw equal currents in all lines but single phase loads in the 3 phase 4 wire system or loads connected between two ... . 11) Minimize I2R losses. 12) Balance the load currents. 13) Regulate the system voltages.

Description : The transient currents are associated with the?

Answer : The transient currents are associated with the changes in the stored energy in the inductors and capacitors.

Answer : In a single phase power factor meter the phase difference between the currents in the two pressure coils is exactly 90°.

Answer : For handling greater currents induction wattmeters are used in conjunction with current transformers.

Description : Eddy currents are induced in the pole shoes of a D.C. machine due to?

Answer : Eddy currents are induced in the pole shoes of a D.C. machine due to relative rotation between field and armature.

Description : How eddy currents are generated?

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.

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 : 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 : A large AC generator, supplying power to an infinite bus, has a sudden short-circuit occurring at its terminals. Assuming the prime mover input and the voltage behind the transient reactance to remain constant immediately after the fault, acceleration of the generator rotor is

Answer : A large AC generator, supplying power to an infinite bus, has a sudden short-circuit occurring at its terminals. Assuming the prime mover input and the voltage behind the transient reactance ... , acceleration of the generator rotor is inversely proportional to the moment of inertia of the machine

Answer : A sensitive galvanometer produces large deflection for a small value of current.

Answer : Large capacity generators are invariably hydrogen cooled.

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 : The current zero interruption, in oil and air blast circuit breakers, is achieved by?

Answer : The current zero interruption, in oil and air blast circuit breakers, is achieved by lengthening of the gap, cooling and blast effect.

Description : Ratio relay by using line-to-neutral voltage protect (A) 3-phase faults (B) double line faults (C) double-line-to-ground faults (D) generator bus earth faults

Answer : Large internal faults are protected by merz price percentage differential protection.

Description : Departmentation by time is one of the oldest forms of departmentation, generally used at lower levels of the organization. Which of the following is not an advantage of departmentation ... results in improved coordination and communication (d) It results in a continuous cycle without interruption

Answer : (c) It mostly results in improved coordination and communication

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.

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