Classification of relays? and what are the five design criteria required for an efficient protective system

What is a Relay

Relays are small devices that are connected throughout the power system a relay can be considered as an electrical switch which can control a high voltage circuit with a low voltage source. It can detect any within an assigned area, a relay can be called active insurance which can maintain high service continuity and it can limit or prevent the equipment damage.

Classification of relay

A relay can be divided into five functional categories

Protective relays – it can detect defective lines, Apparatus with any damage can be detected these type of relay can initiate or permit switching otherwise it can provide an alarm

Programming relays – these type of relay can be used for reclosing and synchronizing

Regulating relays – these relay will become active when an operating parameter deviates from its predetermined limits, it can function through supplementary equipment so that it can restore the quantity to the prescribed limits

Auxiliary relays - this kind of relay operates in response to the opening and closing of the operating circuit to supplement another relay or device. It includes timers, contact multiplier relays, sealing units, receiver relays, lockout relays, closing relays and trip relays

Monitoring Relays – it verifies the condition of the power system or the protection system it includes fault detectors, alarm units, channel monitoring relays, network phasing, and synchronism verification. It can also monitor power system conditions that don’t involve opening circuit breakers during faults

What are the five design criteria required for an efficient protective system

Reliability – the reliability of the system consists of two elements Dependability and security Dependability is the proper operation in response to the system trouble and security is the ability of the system to avoid misoperation between faults.

Speed – it is the ability of the protective system to operate as quick as possible during the detection of the fault, but it must not do any unwanted operation due to the fast process, it must be able to distinguish between real and counterfeit trouble

Selectivity – By selecting a high-speed relay it can provide better service continuity by reducing the faults and hazards to personnel, the low and high-speed relay can be used to protect the power system both of them have high reliability the protective system must be able to provide maximum service continuity with minimum system disconnection

Economics – it can be described as the maximum protection provided by the protective system at minimum cost

Simplicity – simplicity in a protective relay shows that it has a good design but the simplest relay is not the most economical, in a protective system major economics is possible only in a complex relay system which uses minimum number of circuit breakers, simplicity in a system can cause better reliability because there are only a few elements which can malfunction