What is a 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 stabilizing resistor?

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 the use of Metrosil 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?

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. Hope you enjoyed this post.

What is nonlinear resistor?

Non-linear resistors are those types of resistors where the electric current flowing through it changes with the exchange in applied voltage or temperature and does not change according to Ohm’s law.

What is the difference between low impedance and high impedance?

A low impedance microphone will lower the impedance of the entire line connected to it. Similarly, if you connect a high impedance microphone, you will have a higher impedance line all the way from the microphone to the mixer. This can become a problem as the length of the cable increases.

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 low impedance and high impedance relay?

High impedance differential protection The basic principle of the high impedance protection is the same as the low impedance principal, it sums up all currents measured by the CT’s surrounding the bus. The biggest difference is how the high impedance principle handles the problem of CT saturation on external faults.

Why is busbar protection needed?

To maintain system stability, the primary objective of busbar protection is to limit damage and remove busbar faults before back-up line protection. A low impedance differential system used to have a relatively long operation time.

What is the purpose of restricted earth fault relay?

The earth fault relay must be very sensitive for sensing the fault. The relay is designed for sensing the fault current which is 15% more than that of the rated winding current. Such settings protect a restricted portion of the winding. Hence the name restricted earth fault protection.

What is ref protection in transformer?

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.

How does REF protection work?

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 do we need metrosil non linear resistors?

Metrosil non-linear resistors are manufactured from a semi-conducting material based on silicon carbide, which has the distinctive property that its electrical resistance depends on the applied voltage. This enables them to act as an electrical ‘safety valve’ to protect equipment and insulation from the effects of overvoltages.

What is the purpose of the metrosil circuit?

Purpose of Metrosil: It is Voltage Limiting Non-Linear Resistor. Non-Linear resistors are connected in parallel with the relay circuit to limit the peak voltage developed across the high impedance components during internal faults to a safe level below the insulation level of the current transformers, relay and interconnecting leads.

Why are metrosils used in high impedance relays?

In some applications of high impedance relays, a non-linear Metrosil resistor is required to limit the current transformer (CT) secondary voltage to a safe level during maximum internal fault conditions. M&I Materials Limited supply a wide variety of Metrosils designed for the protection of high impedance relays.

Why are metrosil varistors used in power stations?

Metrosil provides surge protection to the largest power stations and electrical infrastructure projects in the world. Metrosil offers a wide range of high voltage silicon carbide varistors that typically provide high energy surge protection for large-scale electrical equipment.