Differential Protection Relay

April 21, 2024 Post a Comment

Differential protection relay

The main function of differential relay was to send trip signal to circuit breaker when there is a certain difference current value between primary side and secondary side of the transformer [1].

What is meant by differential protection?

Differential protection is a unit-type protection for a specified zone or piece of equipment. It is based on the fact that it is only in the case of faults internal to the zone that the differential current (difference between input and output currents) will be high.

What does a differential relay switch do?

The differential type relay switch connects the generator to the main bus bar in the electrical system when the generator voltage output exceeds the bus voltage by 0.35 to 0.65 volt. It disconnects the generator when a nominal reverse current flows from the bus to the generator.

What is the difference between overcurrent relay and differential relay?

The overcurrent relays are used for the protection of electrical equipment against fault currents. But this type of relay is not very sensitive as they cannot distinguish between overloads and minor fault conditions. This can be overcome by using differential relays.

How do you adjust a differential relay?

2.2 Procedure for Relay Setting of Transformer Differential Relay MBCH Data Required MVA Rating Voltage ratio Vector group CT ratio on HV Side Winding connection of CT on HV side ICT ratio on HV Side Winding connection of ICT on HV side CT ratio on LV Side Winding connection of CT on LV side Transformer Tap Min -% OLTC

What is differential protection of motor?

Motor overcurrent differential protection measures the current flow into a load and compares it to the current measured on the neutral side of the motor. A current difference is detected as a fault.

Why does a differential relay need biasing?

The purpose of biased differential protection is to detect faults with high selectivity and sensitivity. This means that it can trip with no intentional time delay for faults within its zone of protection, the reason why differential protection is often applied on high value equipment such as transformers.

What is a 59 relay?

59 Overvoltage relay A relay that operates when its input voltage is more than a predetermined value. 60 Voltage or current balance relay A relay that operates on a given difference in voltage, or current input or output, of two circuits.

Why do we use percent differential relay?

It is the advanced form of differential protection relay. The only difference between them is the restraining coil. The percentage differential relay consists restraining coil for overcoming the trouble arising out of differences in the current ratio for the high value of an external short circuit current.

What is differential protection of alternator?

Generator differential protection (87 G) It is unit type protection, covering the stator winding for phase to phase faults due to breakdown of insulation between stator phase windings.

What causes differential trip?

Certain phenomena can cause a substantial differential current to flow, when there is no fault, and these differential currents are generally sufficient to cause a percentage differential relay to trip.

What happens in a differential relay when the saturation is too high?

(1) Saturation of CT magnetic circuit during short circuit condition: Due to these causes the relay may operate even for external faults, the relay may lose its stability for through faults.

Where is differential relay used?

Generally, differential relays are used to protect the equipment against internal faults. Merz price protection scheme is one form of the differential relay which is used to protect the stator winding of Alternator from the internal faults. Differential relay is also used for the protection of transformer winding.

Where is differential protection used?

Differential protection schemes are mainly used for protection against phase-to-phase faults and phase-to-earth faults. The differential protection used for power transformers is based on Merz-Prize circulating current principle. It is generally used for transformers of ratings exceeding 2 MVA.

Can we use differential relay in transmission line?

Current differential relays are used for the protection of electrical equipment such as transformers and generators against internal faults because of their simplicity and sensitivity. Current differential relays are now being used for protection of transmission lines with the development in communication technology.

What is line differential relay?

Line differential relays receive currents from their own terminals and they also receive, via various modes of communication, data about currents at the remote relay.

What is slope in differential relay?

Thus to prevent tripping on through fault we provide a slope so that Differential current increases as the Biasing current increases and Differential protection will operate if the slope exceeds a particular value (which can be set in the Relay).

How is differential protection calculated?

The corresponding LV secondary current referred to the HV side, taking into account the maximum tap position of 15%, is 6.16 A.

Therefore, for a 1A relay, the bias current is: I_B = (7.25 + 6.16) / 2 = 6.7 p.u.
Differential current I₀ = 7.25 – 6.16 = 1.1 p.u.

What is motor protection relay?

Motor protection relay that protects your motor against burnout. Can be used as protection against motor burnout during overload or locked rotor, and offers a wide range of specifications to meet various needs, including protection against overload and phase loss, time lag, quick connect, etc.

Why are differential relays more sensitive than overcurrent relays?

Differential relays are used to protect transformers and generators from local faults. Overcurrent relays depend on excess current for their operation. Differential relays are very sensitive to the faults occurred within the zonee of protection .