Can Protection CT be used as Metering CT & Vice Versa?

Protection Current Transformer (CT) and Metering CT are two different types of CT as per their requirement and hence design. Therefore, Protection class CT should not be used as Metering CT. Similarly, a Metering Current Transformer should not be used for protection purpose. Let the discuss the reason behind this. Why can’t we use Protection … Read more Can Protection CT be used as Metering CT & Vice Versa?

Resistive Reach Calculation of Distance Relay

Resistive Reach of Distance Relay Characteristics is defined by the fault resistance for which the distance relay characteristics is defined. In MHO type distance relay the major drawback is that resistive reach is defined by the impedance reach and line angle and hence it is not independently settable in the relay. However, it is independently … Read more Resistive Reach Calculation of Distance Relay

A Case Study on LBB Protection Logic

LBB protection is often called CB Failure Protection. As per page Schneider P14x Relay Manual, “Circuit breaker failure protection, monitors the circuit breaker for its opening within a reasonable time in case of fault. If the fault current has not been interrupted following a set time delay from circuit breaker trip initiation, breaker failure protection … Read more A Case Study on LBB Protection Logic

How to Prevent Transformer Trip due to PRD Spurious Actuation?

PRD Spurious actuation is a case in which transformer tripping is initiated by PRD contacts even when transformer is healthy. Ideally PRD is the last line of defense and actuates when the pressure of oil increases beyond the setting value of PRD. But its spurious actuation results in transformer tripping and may lead to power … Read more How to Prevent Transformer Trip due to PRD Spurious Actuation?

High Set 1 (Is-HS1) & High Set 2 (Is-HS2) and Its Calculation

If you ever have seen the setting of Differential Protection of Transformer, you might have noticed two settings shown as Is-HS1 (called High Set 1) and Is-HS2 (called High Set 2). In this post I will be discussing about the significance of these two parameters and its calculation for transformer differential relays. High Set 1(Is-HS1) … Read more High Set 1 (Is-HS1) & High Set 2 (Is-HS2) and Its Calculation

CT Matching Factor in Transformer Differential Protection

CT Matching Factor is basically a multiplication factor by which secondary current of CTs on HV side and LV side is multiplied to make it equal to rated secondary current. This means, if the rated CT secondary current is 1A, then multiplication of CT secondary current by matching factor will give unity. To get this … Read more CT Matching Factor in Transformer Differential Protection

Busbar Protection Scheme Explained

What is Busbar Protection? Busbar protection is a protection scheme meant to protect the busbar from electrical fault.  Various feeders are connected to a busbar through circuit breaker in any of the bus configuration viz. Double Busbar arrangement or one and half breaker scheme. The main purpose of this busbar is to increase the reliability … Read more Busbar Protection Scheme Explained

Difference between Instantaneous and Definite Time Overcurrent Relay

The major difference between Instantaneous and Definite Time Overcurrent Relay lies in their operating time. The former operates instantaneously while the latter one operates after a definite time. Both Instantaneous and Definite Time Overcurrent Relay senses an over current in the circuit and gives tripping command to operate the circuit breaker for isolation of faulty … Read more Difference between Instantaneous and Definite Time Overcurrent Relay

What is a Lock Out Relay / Master Trip Relay?

What is a Lock Out Relay? Lock out relay is an electromechanical relay which latches its output contact. As the name suggests, this relay once operated locks out the circuit. Locking out means that circuit cannot be normalized until and unless this relay is reset. These relay have two types of coils: operating and resetting … Read more What is a Lock Out Relay / Master Trip Relay?