What is low impedance REF protection?

Low-impedance REF protection has low inherent stability against CT saturation for external faults. High-impedance REF protection has high inherent stability against CT saturation for external faults. The operating current of the low-impedance REF protection is not realized by CT connection.

What is low impedance and high impedance 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.

What is difference between high impedance and low impedance?

High impedance circuits are low current and potentially high voltage, whereas low impedance circuits are the opposite (low voltage and potentially high current). Numerical definitions of “high impedance” vary by application.

How does high impedance busbar protection work?

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.

What is the difference between high impedance and low impedance busbar protection?

High impedance is based on Merz-Price circulating current principle. Low impedance is parallel to all current transformers which function to measure the current sum [4] , [13]. Line differential protection is a mechanism of protection in power system, equipped with a communication tool. …

What is high impedance REF protection?

The high- -impedance principle means that the protective relay is connected in series with such a large impedance that even the largest through-fault currents occurring during transient conditions will be prevented from initiating an unwarranted relay operation.

Is low impedance good?

In general, low impedance headphones (which we will hereby define as below 50 ohms) are designed to work properly with portable devices, as they can efficiently reproduce adequate sound quality and volume from a low voltage device.

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.

Why impedance is important?

Why is impedance matching needed? Impedance mismatch can lead to signal reflection and inefficient power transfer. These reflections cause destructive interference, leading to peaks and valleys in the voltage. Impedance matching is therefore important to obtain a desirable VSWR (voltage standing wave ratio).

When high impedance differential relay is used, it is called High Impedance Busbar protection. Similarly, when low impedance differential relay is used, it is called low impedance busbar protection.

How reliable is busbar protection?

Usually, the busbar is left without any protection. They are assumed to be reliable, and if they had any protection, they might mal-operate and end up affecting the whole system. This article covers all the necessary information about busbar protection schemes, the best way to detect faults, and the way they operate.

Why busbar protection is implemented in two zones?

To avoid any spurious actuation, two zones i.e. main zone and check zone scheme are implemented in each of the Zone-1 (for Bus-1) & Zone-2 (for Bus-2) using two different cores of same CT. The wiring and protection scheme is so done that, busbar protection is only actuated when both main zone and check zone relays are operated.

What is high-speed bus protection?

In extensive networks a secure and dependable high-speed bus protection is an essential element to maintain stability and, in the vicinity of large generating units can be instrumental in avoiding shaft damages. The relay presented here is a high-speed low-impedance microprocessor-based current differential relay for power system busbars.