What is Metrosil resistor 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.
What is nonlinear resistor?
Non-Linear 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. There are several types of non-linear resistors, but the most commonly used are mentioned below.
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 a high impedance relay?
High-Impedance Bus Differential Relay Operation. The high-impedance input is created by an internal impedance, typically resistive, of 2000 ohms or higher. A sensitive current element in series with the high-impedance element is calibrated in volts based on the voltage drop across the internal impedance.
Why is restricted earth fault needed?
So, complete earth fault protection is not possible with differential relay. That is why you need a restricted earth fault relay with sensitive settings like 5%. Without REF, faults in the transformer star secondary winding need to be detected on the primary of the transformer by the reflected current.
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.
How can you tell if resistance is linear or not?
A graph of current vs. voltage, also called an I-V curve, will immediately tell you the difference between linear and nonlinear resistance. A component with linear resistance will have an I-V curve that is actually a straight line. In contrast, a component with nonlinear resistance will have a nonlinear I-V curve.
How do you calculate Stabilising 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 the difference between low impedance and high impedance relay?
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.
What is the difference between restricted earth fault and earth fault?
Earth fault protection setting range starts from 5% or even lower unlike that of phase overcurrent protection. Restricted earth fault relays are typically used to protect a three-phase winding that is connected in wye (star) when the neutral point is connected to earth outside the zone of protection.
What is a metrosil resistor?
Our strong heritage means that ‘Metrosil’ is often used as a generic term for a non-linear resistor. As a major power house in the 20th century, Metropolitan-Vickers was renowned for its industrial electrical equipment, which included generators, steam turbines, switchgear, transformers, electronics and railway traction equipment.
What is a metrosil varistor?
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 types of relay metrosils are available?
Our Relay Metrosils are available as single disc, two disc or three disc assemblies. The Metrosil chosen depends on the relay setting voltage and the maximum secondary internal fault current. Relays attached to Current Transformers with 1A rated Secondary Output
How do I contact metrosil technologies?
TECHNICAL ENQUIRIES Tel: +44 (0)161 864 5462 e-mail: [email protected] SALES ENQUIRIES Tel: +44 (0)161 864 5456 e-mail: [email protected]