What are the various time current characteristics available for an overcurrent relay?
The operating time of an overcurrent relay can be moved up (made slower) by adjusting the ‘time dial setting’. The lowest time dial setting (fastest operating time) is generally 0.5 and the slowest is 10. Operates when current exceeds its pick-up value. Operating time depends on the magnitude of current.
What is a time overcurrent relay?
A definite time over-current (DTOC) relay is a relay that operates after a definite period of time once the current exceeds the pickup value. Hence, this relay has current setting range as well as time setting range.
Why the time current characteristics are known as IDMT characteristics?
(4.6) known as IDMT. The time-current characteristic is inverse over some range and then after saturation assumes the definite time form. In order to make the relay operate at a constant value of minimum trip current for any TMS, graded holes are cut in the disc or a disc with spiral cut edge is used.
What are the operations of definite time overcurrent relay?
Definite Time Over Current Relay This relay is created by applying intentional time delay after crossing pick up the value of the current. A definite time overcurrent relay can be adjusted to issue a trip output at an exact amount of time after it picks up. Thus, it has a time setting adjustment and pickup adjustment.
What are the applications of over current relay?
Application: Definite time over current relay is used as:
- Back up protection of distance relay of transmission line with time delay.
- Back up protection to differential relay of power transformer with time delay.
- Main protection to outgoing feeders and bus couplers with adjustable time delay setting.
What is the application of relay?
Applications of Electromechanical Relay The typical applications of electromechanical relays include motor control, automotive applications such as an electrical fuel pump, industrial applications where control of high voltages and currents is intended, controlling large power loads, and so on.
What are the causes of over current?
Possible causes for overcurrent include short circuits, excessive load, incorrect design, an arc fault, or a ground fault. Fuses, circuit breakers, and current limiters are commonly used overcurrent protection (OCP) mechanisms to control the risks.
How can we prevent over current?
10.7. Overcurrent protection devices such as fuses, breakers, and others limit the current to the proper rate and disconnect short circuits. The type of overcurrent protection system used and the maximum current passing through the circuit components determine the size of the overcurrent protection system.
How does definite time over current relay work?
Definite Time Over Current Relay This relay is created by applying intentional time delay after crossing pick up the value of the current . A definite time overcurrent relay can be adjusted to issue a trip output at an exact amount of time after it picks up. Thus, it has a time setting adjustment and pickup adjustment.
How does time inverse over current relay work?
Inverse-Time Overcurrent Relay. The relay operates only when the magnitude of their operating current is inversely proportional to the magnitude of the energize quantities . The operating time of relay decreases with the increases in the current. The operation of the relay depends on the magnitude of the current.
What is the function for over current relay?
Relays by functions Overcurrent relay. An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. Distance relay. Current differential protection scheme. Directional relay. Synchronism check.
What is setting over current relay?
Setting overcurrent relays involves selecting the parameters that define the required time/current characteristic of both the time-delay and instantaneous units. This process has to be carried out twice, once for the phase relays and then repeated for the earth-fault relays.