What is instantaneous over current relay?
An instantaneous over-current relay is an overcurrent relay which has no intentional time delay for operation. It has low operating time and starts operating instantly when the value of current is more than the relay setting.
What is high set instantaneous overcurrent relay?
The high-set instantaneous setting is typically for protecting a transmission line and is set at a margin below the maximum remote terminal fault magnitude so that it does not over-reach and trip for faults outside the line protection zone.
What are the settings involved in overcurrent relay?
The current setting of overcurrent relay is generally ranged from 50 % to 200 %, in steps of 25 %. For earth fault relay it is from 10% to 70% in steps of 10%.
What is instantaneous overcurrent protection?
The instantaneous overcurrent protection threshold sets the level of short-circuit current at which the circuit breaker trips with no intentional time delay. Instantaneous overcurrent protection can be duplicated when dual settings are activated.
What are the limitations of overcurrent relay?
The disadvantage of this type of protection is that it’s difficult to coordinate and requires changes with the addition of load and that the short-circuit fault close to the source may be cleared in a relatively long time in spite of its highest current value.
What is a overcurrent relay used for?
Overcurrent protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults, etc. Overcurrent relays can be used to protect practically any power system elements, i.e. transmission lines, transformers, generators, or motors.
What is TMS in overcurrent relay?
Formally, TMS is. defined as the ratio where, for a given PSM T is the desired relay operating time and Tm is the corresponding operating time at TMS of 1.0. TMS is also referred to as TDS (Time Dial Setting). 15.1 Fundamental Principle of Overcurrent Relays.
What are under current relays?
Relays which operates whenever the current in a circuit drops below a predetermined value.
How are overcurrent relay settings calculated?
Calculation of Over Current Relay Setting:
- Over Load Current (In) = Feeder Load Current X Relay setting = 384 X 125% =480 Amp.
- Required Over Load Relay Plug Setting= Over Load Current (In) / CT Primary Current.
- Required Over Load Relay Plug Setting = 480 / 600 = 0.8.
What is Time dial setting?
The time dial setting adjusts the time delay before the relay operates whenever the fault current reaches a value equal to, or greater than, the relay current setting.
What is TSM in relay?
Time Setting Multiplier (TSM): The arrangement provided for setting the operating time of protective relay from zero sec to maximum permissible time for a specified current setting is known as time setting multiplier. It is the ratio of fault current in relay coil to pick-up current.
What are the features of instantaneous relay?
An Instantaneous Relay is one in which there is no time delay provided intentionally. As the current coil is an inductor, there would be a certain delay to reach the current in the coil to its maximum value. There is also some time required for mechanical movement of the armature in the relay.
Can a 50 relay provide instantaneous overcurrent protection?
A single 50 relay sensing current on a single line would not provide adequate instantaneous overcurrent protection for all three lines. The amount of CT secondary current necessary to activate the 50 relay is called the pickup current.
How is the operating time of an overcurrent relay adjusted?
The operating time of both overcurrent definite-time relays and overcurrent inverse-time relays must be adjusted in such a way that the relay closer to the fault trips before any other protection. This is known as time grading. The difference in operating time of these two relays for the same fault is defined as discrimination margin.
Which is the best definition of Instantaneous overcurrent protection?
Instantaneous overcurrent protection is where a protective relay initiates a breaker trip based on current exceeding a pre-programmed “pickup” value for any length of time. This is the simplest form of overcurrent protection, both in concept and in implementation (relay design).
How are overcurrent relays set for earth fault?
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.