What is Metrosil used for?

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 is Metrosil value calculated?

Setting Voltage Vs = IF (2* RL + RCT)/CT RATIO = 26000 (2*0.2 + 4.04)/1600 = 72.15 Volts. Variable resistor of 0-1 kOhms to be provided. During maximum primary fault current, if the peak voltage developed across the relay should not exceed 1.5 kV, then metrosil is required to suppress the same.

How do you calculate stabilizing resistor?

Rstb= Vs = IF(RCT + 2RL) / Iswhen looping of CT is done at Panel or near Relay end. Thus during through fault, for the worst condition of CT saturation, the current through the Relay coil will not be enough to cross setting value of Is and thus will not operate.

What is ref protection in transformer?

Restricted earth fault (REF) protection is a sensitive way to protect a zone between two measuring points against earth faults.

How do you test a varistor?

Touch one meter probe to the free varistor lead and the other probe to the connected lead. Read the resistance on the meter. If it reads nearly infinite resistance, the varistor is still good. If it reads very low resistance, the varistor is blown.

Why are stabilizer resistors used?

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.

What is high impedance busbar protection?

High impedance protection system is a simple technique which requires that all CTs used in the protection scheme have relatively high knee point voltage, similar magnetizing characteristic and the same ratio. These CTs shall be installed in all ends of the protected object.

Why ref protection is required?

REF is restricted between certain zone. REF is implemented to detect earth fault in the zone from secondary winding to secondary CTs. As illustrated in figure, if earth fault occurs within range of the protected zone; it shall be detected. But if earth fault occurs outside the zone, same shall not be detected.

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 a Stabilising 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.

What is the difference between 51g and 51N relay?

50 and 51 are types of overcurrent relays (relays driven by a current transformer). Type 50 is an “instantaneous off” relay, whereas type 51 has an inbuilt time delay. The N, G, etc depicts not what the relay is, but how it is wired up.