Protective relaying plays an important role in minimizing the faults and also in minimizing the damage in the event of faults. Figure above shows basic connections of circuit breaker control for the opening operation. The protected circuit X is shown by dashed line. ... Current flows from battery in the trip circuit.

What does a protection relay do?

The purpose of the protection relay is to detect a problem, ideally during its initial stage, and to either eliminate or significantly reduce damage to personnel and/or equipment.

What is protective relay How do protective relays work?

A protective relay is a switchgear device that detects the fault and initiates the operation of the circuit breaker to isolate the defective element from the rest of the system. They are compact and self-contained devices which can detect abnormal conditions.

What are the main features of good protective relay?

In order that protective relay system may perform this function satisfactorily, it should have the following qualities :

• Selectivity.
• Speed.
• Sensitivity.
• Reliability.
• Simplicity.
• Economy.

What are the six qualities that a protective relay should possess?

Such an essential qualities of protective relaying are: Reliability, Selectivity and Discrimination, Speed and Time, Sensitivity, Stability, Adequateness, Simplicity and Economy.

Types of Protective Relays and Design Requirements, Part 1a.

35 related questions found

When should a relay be sensitive to operate a protective system?

It is desirable that relay system should be sensitive so that it operates with low values of volt-ampere input. 4. Reliability: It is the ability of the Protective Relay system to operate under the pre-determined conditions.

What type of protective relay is used in induction motor?

Thermal overload relay is commonly used for motor overload protection. Both act to open the motor circuit and therefore to disconnect the motor from the source of supply. HRC fuses provide very rapid short circuit protection.

Why is protection system needed in electrical system?

The objective of power system protection is to isolate a faulty section of electrical power system from rest of the live system so that the rest portion can function satisfactorily without any severe damage due to fault current.

How does a feeder protection relay work?

Relay will monitor Current and Voltage in the feeder line (PT and CT secondary), and from these values, the relay will calculate Impedance value Z. ... I.e., during fault, relay will trip and show the fault parameters like fault current, voltage, reactance, resistance and fault distance on relay screen.

Is relay a protection device?

Protective relay work as a sensing device, it senses the fault, then known its position and finally, it gives the tripping command to the circuit breaker. ... The relay must come into action whenever there is a fault and must not operate if there is no fault. Some relays are used for the protection of the power system.

Which relay is used to protect feeders?

Translay relay:

The translay relay is a differential relay. The arrangement is similar to overcurrent relay, but the secondary winding is not closed on itself. These types of relays are used in the feeder protection and the scheme is called the Translay scheme.

Which relay is preferred for ground fault?

Reactance type relay is very suitable as a ground relay for ground fault because its reach is not affected by fault impedance. Also, used for the protection of short transmission lines.

How does power system protection work?

The objective of a protection scheme is to keep the power system stable by isolating only the components that are under fault, whilst leaving as much of the network as possible still in operation. ... The devices that are used to protect the power systems from faults are called protection devices.

What is protective device in electrical?

A device used to protect equipment,machinery,components and devices,in electrical and electronic circuit,against short circuit,over current and earth fault,is called as protective devices.

What are the requirements of protection?

• The fundamental requirements for a protection system are as follows:

• Reliability:
• Speed:
• The Relay Time :
• The Breaker Time:
• Selectivity:
• Sensitivity:
• Stability:
• Adequacy:

How does motor protection relay work?

Thermal motor protection relays contain three bimetal strips together with a trip mechanism in a housing made of insulating material. The bimetal strips are heated by the motor current, causing them to bend and activating the trip mechanism after a certain travel which depends on the current-setting of the relay.

What is a thermal relay?

A relay that opens or closes contacts with a bending mechanism as a result of the difference in the expansion coefficients of a bimetal, which is heated by the current. The thermal relay switches a magnetic contactor to protect a motor from overload.

What is a motor protection relay?

Motor protection relay that protects your motor against burnout. Can be used as protection against motor burnout during overload or locked rotor, and offers a wide range of specifications to meet various needs, including protection against overload and phase loss, time lag, quick connect, etc.

What is protective relay in power system?

In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. ... Important transmission lines and generators have cubicles dedicated to protection, with many individual electromechanical devices, or one or two microprocessor relays.

What is reliability of the relay?

Reliability means that relay operates only when there is a fault. Unreliable protection system will lead to spurious tripping of circuit breaker. Simplicity – Simplicity increases the reliability. The simpler the system, the greater will be its reliability.

What are the types of protection relays?

Basic classification of protective relays includes:

• Electromagnetic Relays: Armature. Induction cup / induction disc.
• Static Relays: Analog input signals are processed by solid state devices.
• Digital / Numerical Relays: Uses programmable solid state devices based on digital signal processing.

What are the causes of faults in power system?

Causes of Faults

• Overvoltage due to switching surges.
• Severe lightning strokes.
• Aging of conductor.
• Heavy wind, rains, and snowfall.
• Falling trees on the transmission line.
• Excessive internal and external stresses on the conductors.
• High changes in atmospheric temperatures.

Why is a relay used in a circuit?

Relays control one electrical circuit by opening and closing contacts in another circuit. ... Relays are generally used to switch smaller currents in a control circuit and do not usually control power consuming devices except for small motors and Solenoids that draw low amps.

How do you prevent ground faults?

Protection against ground faults is offered by circuit breakers that trip if the flow of electricity suddenly increases, and by a system of grounding wires in the circuits that provide a direct pathway back to ground should current stray outside its established circuit wiring.

What is the most common cause of ground faults?

The usual suspects for ground-faults include worn insulation, conductive dusts, water, or other "soft grounds." Ground faults account for more than 80% of equipment short circuits and in 90% of those cases it is caused by insulation deterioration on wires and cables.