What is the use of stabilizing resistor in ref protection?

Typically, a stabilising resistor is needed when residually connected current transformers are used to measure the earth-fault (residual) current. The purpose of the stabilising resistor is to prevent the relay from operating due to saturation of the current transformers during motor start-up.

Why Metrosil is used in ref protection?

Metrosil is used to limit the peak voltage developed by the current transformer (CT) under internal fault conditions to a value below the insulation level of the CT, relay and interconnecting leads.

How do you calculate stabilizing resistor in ref protection?

This reduction of the fault CT nominal ratio results in a “false” differential relay current that may operate the instantaneous overcurrent relay. The wort condition will be when a CT gets completely saturated. Thus we need to make Relay insensitive for through fault. To do this we use Stabilizing Resistor.

Is stabilizer a resistor?

What is a stabilizing resistor? As the name suggests, a resistor is used to increase the stability of the circuit, and a stabilizing resistor is a set of a resistor is connected in series with the current transformer’s secondary terminal.

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How does REF protection work?

Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer. In this scheme, the CT secondary of each phase of an electrical power transformer are connected together as shown in the figure.

What is Metrosil resistor?

Metrosil offers a wide range of high energy silicon carbide varistors. These non-linear resistors provide surge protection for prestigious infrastructural projects. Our brand name is so well known, it is often used as a generic term for a varistor.

What is meant by high impedance?

Hi-Z (or High-Z or high impedance) refers to an output signal state in which the signal is not being driven. The signal is left open, so that another output pin (e.g. elsewhere on a bus) can drive the signal or the signal level can be determined by a passive device (typically, a pull-up resistor).

Why ref is used in transformer?

Fault detection is confined to the zone between the two CTs hence the name ‘Restricted Earth Fault’. REF protection is fast and can isolate winding faults extremely quickly, thereby limiting damage and consequent repair costs. If CTs are located on the transformer terminals only the winding is protected.

Why we use restricted earth fault relay?

Restricted earth fault (REF) protection is a sensitive way to protect a zone between two measuring points against earth faults. … The CT secondaries are wired to cancel each other’s currents during through faults and to drive all secondary current to the relay when the fault is inside the protected zone.

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What is ref and SEF protection?

It is backup protection for restricted earth fault (REF) relay. It operates the CB when REF is failed to trip the circuit, Heavy earth fault outside of the REF protective Zone, and all other earth faults. Simply we can say, it is standby protection for all other earth faults.

What is the purpose of stabilizer?

The main function of a stabilizer is to make the output voltage that feeds the equipment’s connected to it as much as possible equivalent to the ideal electrical power supply, ensuring that the oscillations in electrical power are offset, and its output maintain a stable value.

What is stabilizer used for?


Sub – Category Model Capacity in VA
Stabilizers for Refrigerators VGSJW 50 500
VEW 50 500
VEB 50 500
VG 100 1000

How do stabilizers work?

This transformer is connected in such a way that the secondary output is added to the primary supply voltage. In case of low voltage condition, the electronic circuit in the stabilizer switches corresponding relay such that this added supply (incoming supply + transformer secondary output) is applied to the load.

What is SEF relay?

A system of earth fault protection in which the fault current is limited by design to a low value which generally requires amplification in order to operate an earth fault relay.

What is difference between 51N and 51G?

Quote: As for 51N and 51G, the way modern relay manuals proposes, 51G actually measures the current in neutral using a CT (residual CTs), where as 51N is where current in neutral is calculated by vector sum of the 3 phase over currents by the relay.

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What is SBEF relay?

SBEF is standby earth fault protection. It is backup protection in case of uncleared faults out on the network, or earth faults outside the REF zone.