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Top Interview Questions on Voltage Transformer
What is the Rated Voltage Factor in voltage transformers, and how is it determined?This is the ratio of the maximum operating voltage to the rated primary voltage of the PT. This factor is to be multiplied with the primary rated voltage to determine the maximum operating voltage of the PT at which the PT can … Read more
Top Interview Questions on HV Lightning Arresters
What is the definition of rated voltage of a lightning arrester?As per IS 3070 the definition of the “rated Voltage of a Lightning Arrester” as given below.The maximum permissible r.m.s. value of power-frequency voltage between line and earth terminal under temporary over-voltage conditions for a duration of 10 seconds as established in the operating duty … Read more
Top Interview Questions and Answers on Power Transformer
What are the short circuit withstand levels for 400kV, 220kV, and 132kV transformers?Ans: 400 kV transformers must withstand 63 kA for 1 second. 220 kV transformers must withstand 50 kA for 1 second and 40 kA for 3 seconds. 132 kV transformers must withstand 40 kA for 1 second and 31.5 kA for 3 seconds. … Read more
Working Principle of a Transformer
A transformer is a static electrical device that transfers electrical energy from one circuit to another through electromagnetic induction, without any physical connection. It works only on AC supply and can step up or step down voltage levels without changing its frequency. The transformer consists of primary and secondary windings wound around a common magnetic … Read more
Working Principle of Digital Tele Protection Coupler
A Digital Tele Protection Coupler (DTPC) is often referred as a Digital Protection Coupler (DPC). It serves as a high-speed, reliable interface for transmitting protection commands between substations over a communication medium (OPGW). Typically it is used for carrier protection of transmission lines. Working Principle First, a protective relay such as a digital distance relay … Read more
Gas Insulated Switchgear (GIS) – An Introduction
A Gas Insulated Substation (GIS) is sometimes also referred to as Gas Insulated Switchgear or Gas Insulated System. Why GIS is the Future of High Voltage Power Systems There are several reasons for preferring a Gas-Insulated System (GIS) over an Air-Insulated System (AIS). Constructional Details of GIS A GIS consists of several key modules, each … Read more
Selective DC Scheme in Breaker Control Circuits
The Selective DC Scheme in circuit breaker control circuits is a specialized design used to enhance reliability and ensure fail-proof operation in power system protection and control. In a Selective DC Scheme, multiple (normally two) DC supplies are taken to ensure that control circuit of CB remains functional even if one of the supplies fails. … Read more
Understanding the Anti-Pumping Scheme in Circuit Breakers
In electrical power systems, circuit breakers play a crucial role in protecting equipment and ensuring the stability of the grid. However, improper operation of breakers can lead to major fault and unsafe conditions. One critical issue in breaker operation is multiple closing attempts before clearing a fault. This can occur due to a continuous closing … Read more
Sweep Frequency Response Analysis (SFRA) – Working Principle
Power transformers are critical to electrical systems, and their failure can lead to major disruptions. Sweep Frequency Response Analysis (SFRA) is a powerful diagnostic tool used to detect mechanical and electrical issues inside a transformer before they cause serious problems. It helps identify winding movement, core displacement, insulation failure, and structural deformations by analyzing how … Read more