Standard overcurrent relays are not recommended for backup protection of a generator. The backup relay must be capable of detecting the minimum generator fault current.
What is backup protection relay?
Definition of backup relay
: a secondary relay to protect a power system against faults in the event of failure of the primary relay to function as desired.
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.
Which relay can not be used with DC quantities?
Electromagnetic induction relays operate on the principle of the induction motor and are widely used for protective relaying purposes involving a.c. quantities. They are not used with dc quantities owing to the principle of operation.
What is used for protection in relay?
The DMH type relay provides high speed biased differential protection for two or three winding transformers. The relay is immune to high inrush current and has a high degree of stability against through faults. … Secondly with tapped interposing transformers for use with standard line current transformers of any ratio.
What is primary relay and backup relay?
[wp_ad_camp_1] Refer above scheme, here the relays C, D, G and H are primary relays while A, B, I and J are the backup relays. Normally backup relays trips the circuit breaker, if primary relay fails. So if the primary relay E fails to trip, then backup relays A and B get tripped.
What is an impedance relay?
An impedance relay is a voltage restrained overcurrent relay. The relay measures impedance up to the point of fault and gives tripping command if this impedance is less than the relay setting Z.
What is MHO relay?
Mho relay is a voltage restrained directional relay. Important Points: Reactance relay is suitable for the protection of a short transmission line because its operation is independent of arc resistance. The relay which is selected for a long transmission line should be less affected due to power swings.
What type of relays we usually use for a backup?
2. Backup protection. Consider the backup relaying employed for the transmission line section EF as shown in the Fig. ,The relays C, D, G and H are primary relays while A, B, I and J are the backup relays. The backup relaying often provides primary protection when the primary relays are out of service for repairs.
Which relay is used for motor protection?
To protect against motor damage, we mustensure that this condition is not reached, hence we must trip the motor before the overload limit (service factor) is reached. The relay most commonly used for this purpose is the induction disc relay.
What is Flag relay?
The Flag Relay is constituted by an electromagnet which drives two changeover contacts and optical signalling at three positions with three colours which, in turn, drives two changeover contacts. … This relay is ideally suited for any environmental condition. A large number of flag relays can be assembled in banks.
What are the three types of relays?
The three main types of relays are electromechanical, solid-state, and reed.
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.
What is non directional relay?
Non Directional relay: When there is fault in power system, power flows through fault. Non directional relays operate irrespective of direction of flow of current. For example, breaker at generator end. If there is fault on generator secondary relay has to operate to open GT breaker.
How many types of protection are there?
There are two types of overload protection: instantaneous overcurrent (IOC) and time overcurrent (TOC). Instantaneous overcurrent requires that the current exceeds a predetermined level for the circuit breaker to operate. Time overcurrent protection operates based on a current vs time curve.
What is directional relay?
A directional relay responds to fault current flowing in a particular direction; the directional feature is achieved by incorporating a directional unit as shown in the figure. The main flux is split into two fluxes displaced in time and space with the help of a shaded ring.