Where are over current relays used?

Where are over current relays used?

Only The operating time of the relay is very less (time of pickup and contact closing). These type of over current relay is normally implemented where the high speed tripping is required. The relay protects the system from earth fault and also used for protecting the system from circulating current.

Why distance relay preferred over overcurrent relay?

Distance relays are preferred to overcurrent reIays because they are not nearly so much affected by changes in short-circuit-current magnitude as overcurrent relays are, and, hence, are much less affected by changes in generating capacity and in system configuration.

What is the purpose of overcurrent protection?

Overcurrent protection devices include circuit breakers and fuses. Overcurrent protection devices are meant to protect against the potentially dangerous effects of overcurrents, such as an overload current or a short-circuit current, which creates a fault current.

What are the disadvantages of over current protection?

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.

Why is distance protection necessary?

Distance protection is comparatively simple to apply and it can be fast in operation for faults located along most of a protected circuit. It can also provide both primary and remote back-up functions in a single scheme. It can easily be adapted to create a unit protection scheme when applied with a signalling channel.

What are the principles of over current relays?

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.

What is the difference between an over current relay and current differential relay?

♥ The operating coil of over current relay is connected across the CT secondary circuit. ♥ This differential relay compares the current at the two ends of the alternator winding.

What are the advantages of distance protection?

Selective and dependable tripping for line faults without the need for a pilot channel, as well as simple time coordination of distance relays across the system, are great advantages of distance protection.

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 does over current protection work?

An overcurrent protection device protects the circuit by opening the device when the current reaches a value that will cause an excessive or dangerous temperature rise in conductors. Most overcurrent protection devices respond to both, short-circuit or ground-fault current values as well as overload conditions.

What is working principle of distance relay?

The major principle of distance relay is it functions depending on the distance of fault in the transmission line. Its operation depends on the impedance between the point of fault and the point where the relay is installed. The impedance at that particular point becomes the operating quantity for the relay.

What are the three zones of protection?

As the figure above shows, there is a zone of protection covering from each feeder breaker (Blue dotted lines), a zone covering each low-side bus, a zone covering each transformer (Green dotted lines), a zone covering each high-side bus and a zone covering each incoming transmission Line (Yellow Dotted lines).

Why are over current relays used in electrical systems?

Over-current protection protects electrical power systems against excessive currents which are caused by short circuits, ground faults, etc. Over-current relays can be used to protect practically any power system elements, i.e. transmission lines, transformers, generators, or motors.

When to use an overcurrent relay for overload protection?

The overcurrent relay can be used as overload (thermal) protection when protects the resistive loads, etc., however, for motor loads, the overcurrent relay cannot serve as overload protection Overload relays usually have a longer time setting than the overcurrent relays. 1. Instantaneous Overcurrent relay (Define Current)

How does the inverse time of an overcurrent relay work?

Ideal inverse time characteristics cannot be achieved, in an overcurrent relay. As the current in the system increases, the secondary current of the current transformer is increased proportionally.

When does an overcurrent relay close the contacts?

The relay has no intentional time delay for operation. The contacts of the relay are closed instantly when the current inside the relay rises beyond the operational value. The time interval between the instant pick-up value and the closing contacts of the relay is very less.