The synchronous generator when act as a motor that relay is operated. or reverse power relay is acted. mainly it sence thet direction of power flow direction
over current protection relay
current relay are using for over current low state & high state.but potential relay are related to voltage.
ocr-over current relay(senses the over current in the circuits) efr-earth fault relay uvr-under voltage relay
Over Current (Inverse Time) Over current relay function monitors the general balanced overloading and has current/time settings. This is determined by the overall protective discrimination scheme. There advantage over definite time relays is that they can have much shorter tripping times can be obtained without any risk to the protection selection process. These are classified in accordance with there characteristic curves, this indicates the speed of the operation. Based on this they are defined as being inverse, very inverse or extremely inverse. The typical settings for these relays are 0.7-2In (normal or rated generator current) in 1-10 second. Inducing a calibrated test current through the normal load current tests this relay.
due to the extension of loads they are using the relays for protection.........
earth fault relay is also a type of over current relay but the set value of current or relay sensing current is much less than the maximum load current.in over current relay relay sensing current ise than maximum load current mor
over current protection relay
current relay are using for over current low state & high state.but potential relay are related to voltage.
An over current relay will operate when current exceeds its design rating. This application is intended protect loads or circuits from excessive current.
in electrical circuit current will increase specific level (full load current).its call over current
ocr-over current relay(senses the over current in the circuits) efr-earth fault relay uvr-under voltage relay
Instantaneous over current relay, which operates very fast with no intentional time delay and the operating time of these relay can be as low as 0.01sec . These relay operates only when the impedance between the relay and the source zsis very small compared to the impedance to the impedance of the protected section zl .
Over Current (Inverse Time) Over current relay function monitors the general balanced overloading and has current/time settings. This is determined by the overall protective discrimination scheme. There advantage over definite time relays is that they can have much shorter tripping times can be obtained without any risk to the protection selection process. These are classified in accordance with there characteristic curves, this indicates the speed of the operation. Based on this they are defined as being inverse, very inverse or extremely inverse. The typical settings for these relays are 0.7-2In (normal or rated generator current) in 1-10 second. Inducing a calibrated test current through the normal load current tests this relay.
A definite time over-current relay operates like an instantaneous over-current relay coupled with a timer. Once current reaches the pick-up value, it initiates the timing circuit. As long as current stays above this pick-up value, the timer will continue to time. Once the definite time setting is reached, the relay gives trip signal to the circuit breaker.
Earth fault relay and an over current relay Methods to energies an earth fault relay with simulation diagram?
Normally the Over current relay is connected using a suitable CT (Current Transformer). Say the CT ratio is 100/5 Amps. (secondary is normally 5 or 1 amps). 100 Amps in the primary induces 5 amps in secondary which flows through over current relay circuit. Secondary current is proportional to the primary current. To test the OCR , inject the current into relay circuit ranging from 0 to 5 amps in steps (which represents upto full load current on primary). Relay will operate accordingly operate the trip contacts. These relays are normally with a time factor setting as well.
To protect things from getting damaged by overcurrent.