What is Protective Relay and its Types?

What is Protective Relay?

A protecting relay is an automatic electric component designed to experience a circuit breaker while a fault is detected. The first protecting relays were electromagnetic devices, relying on coils operating on moving factors to provide detection of weird operating conditions which include over-current, overvoltage, contrary electricity flow, over-frequency, and under-frequency.

Power structures and their additives want safety from natural dangers in addition to human errors.

Reset Level:

The current or voltage beneath which a relay contact opens and returns to its preceding position.

Operating Time of Relay:

After the pickup degree of actuation amount is exceeded, the relay’s moving mechanism (for example, a rotating disc) begins advanced movement and, in the end, closes the relay contacts on the course of its journey. The time which elapses a number of the right now while actuating quantity exceeds the pickup fee to the right now while the relay contacts near.

Reset Time of Relay:

The time it takes for the actuating amount to fall beneath the reset cost and the relay contacts to go back to their normal position.

Reach of Relay:

A distance relay operates on every occasion the gap seen thru the relay is lots much less than the pre-unique impedance. The actuating impedance with inside the relay is the function of distance in a distance protection relay. This impedance or corresponding distance is known as the acquirer of the relay.

Protective Components

Protective additives have 3 fundamental additives. They are

• Sensors to discover gadget abnormalities

• Relays to offer alerts to prompt safety devices

• Circuit breakers (interrupts) to open (disconnect) the circuits.

In order to carry out its functions properly, the safety system ought to have the following characteristics

  1. Reliability

  2. Selectivity

  3. Speed

  4. Sensitivity

Reliability :

The reliability of the protection device is its capability to carry out upon the prevalence of any fault for which it has become designed to protect. In unique words, the safety gadget ought to carry out whilst it is supposed to and now no longer carry out when it isn’t required.

Selectivity :

Selectivity is the capability of the safety system to encounter a fault, choose out the issue at which the fault took place, and isolate the faulted circuit element by tripping the minimum number of circuit breakers. Selectivity of the protection device is received thru proper coordination of the running currents and time delays of the protective relays.

Speed :

A protected relay ought to function at the desired speed. It have to now no longer be too slow, as this will cause equipment damage, nor have to it’s too rapid/fast, as this will bring about the unwanted operation at some point of temporary faults.

More load is often moved among unique locations at the facility energy system without lack of synchronization the shorter a fault is permitted to stay at the system.

Sensitivity :

It refers to a protecting relay’s capacity to reply reliably, when required, to a failure that consequences with inside the least quantity of short-circuit current passing through it.

Types of Protective Relays

The forms of relay safety are particularly divided in line with their characteristics, good judgment, parameters of motion, and mechanism of motion.

Protection relays may be divided into electromagnetic relays, static relays, and mechanical relays in line with the mechanism of motion. In reality, a relay is not anything greater than an aggregate of 1 or greater open or closed contacts. When actuation parameters are carried out to the relays, all or a few unique contact relays will extrude their state. In the electromagnetic relay, those closings and opening s of the relay contacts are finished with the aid of using the electromagnetic motion of the solenoid.

In mechanical relays, the final and starting of those relay contacts is carried out with the aid of using the mechanical displacement of various tools structures.

Based on Characteristic the safety relay may be labeled as:

• Definite time relays

• Inverse time relays with specific minimal time (IDMT)

• Instantaneous relays.

• IDMT with inst.

• Stepped characteristic.

• Programmed switches.

• Voltage restraint over current relay.

Based on logic the protection relay may be categorized as-

• Differential.

• Unbalance.

• Neutral displacement.

• Directional.

• Restricted earth fault.

• Over fluxing.

• Distance schemes.

• Bus bar protection.

• Reverse power relays.

• Loss of excitation.

• Negative phase sequence relays etc.

Based on the actuating parameters the protection relay may be labeled as-

• Current relays.

• Voltage relays.

• Frequency relays.

• Power relays etc.

Advantages of Protective Relay

  • It continuously monitors the system
  • Improves system performance, reliability, and system stability
  • Minimize risk of fire
  • Provide safety for the system as well as people working on the system.