What is the function of overcurrent relay?
Overcurrent Relay Purpose and Ratings. A relay that operates or picks up when it’s current exceeds a predetermined value (setting value) is called Overcurrent Relay. Overcurrent protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults, etc.
What are the functions of protective relay?
The function of protective relaying is to cause the prompt removal from service of any element of a power system when it suffers a short circuit, or when it starts to operate in any abnormal manner that might cause damage or otherwise interfere with the effective operation of the rest of the system.
What are the characteristics of overcurrent relay?
a) Instantaneous Over-current Relay:
- Operates in a definite time when current exceeds its Pick-up value.
- Its operation criterion is only current magnitude.
- Operating time is constant.
- There is no intentional time delay.
What are the types of overcurrent?
The three major categories or types of overcurrent are overload, short-circuit, and ground-fault.
What is PSM and TSM?
Plug setting multiplier (PSM). Time setting multiplier (TSM).
What is instantaneous overcurrent relay?
Instantaneous overcurrent relays are used close to the source where the fault current level is very high and a small delay in sending trip signal can cause big damage to the protected equipment. Instantaneous characteristic curve is shown in the Figure 2 A.
What is main function of relay?
Relays are electric switches that use electromagnetism to convert small electrical stimuli into larger currents. These conversions occur when electrical inputs activate electromagnets to either form or break existing circuits.
What is relay principle?
Relay works on the principle of electromagnetic induction. When the electromagnet is applied with some current, it induces a magnetic field around it.
What is TSM in relay?
Time Setting Multiplier (TSM): The time setting multiplier is nothing but an adjusting or speeds up the tripping mechanism of the relay (it is called as the dial). The dial is nothing but a rotating disc, which rotates when the fault current in the relay coil reaches the pickup current.
What is 50 and 50N protection?
50/51 and 50/51N relays. Overcurrent relays are the most commonly-used protective relay type. Time-overcurrent relays are available with various timing characteristics to coordinate with other protective devices and to protect specific equipment.
What is overcurrent in electrical circuit?
An overcurrent is a condition which exists in an electrical circuit when the normal load current is exceeded. The two basic forms of an overcurrent are overloads and short circuits. Fuses and circuits breakers primary role in a circuit is to protect personnel and equipment when dangerous overcurrents do happen.
What is TMS in overcurrent relay?
Time Multiplier Setting used to change the value of operation of the relay. If it is more the relay will take more time to operate and vice versa. Changing the position of TMS setting, changes the distance between the contact of the rotating disk and the coil.
What are the drawbacks of overcurrent relay?
– Time Graded Overcurrent Protection. The line or feeder is divided into number of sections. – Current Graded Overcurrent Protection. The drawback of time graded system is that relay near the source operates at last and the fault current level is high near the source. – Pilot Wire Protection. It uses differential protection principle i.e.
What is the function for over current relay?
Instantaneous Over Current Relay. Construction and working principle of instantaneous over current relay is quite simple.
How does Instantaneous overcurrent relay work?
Instantaneous Over Current Relay. Construction and working principle of instantaneous over current relay is quite simple. Here generally a magnetic core is wound by a current coil. A piece of iron is so fitted by hinge support and restraining spring in the relay, that when there is not sufficient current in the coil, the NO contacts remain open.
Why are overload relays used in circuit breakers?
Motor overload.