10+ Power Grid Corporation of India Interview Questions and Answers

The tan Delta value of electrical equipment should be as low as possible.

• Tan Delta is a measure of the dielectric losses in electrical equipment.

• A low tan Delta value indicates that the equipment has good insulation properties.

• The tan Delta value can be affected by factors such as temperature, moisture, and aging of the equipment.

• For transformers, a typical tan Delta value is around 0.001 or lower.

The ground clearance of a 400KV transmission line varies depending on various factors.

• The ground clearance of a transmission line is the vertical distance between the lowest point of the conductor and the ground.

• The ground clearance is determined based on safety regulations and requirements.

• Factors that influence the ground clearance include terrain, vegetation, and proximity to buildings or roads.

• In hilly areas, the ground clearance may be higher to account for uneven terrai...read more

Transformers are rated in KVA because it represents the apparent power they can handle.

• KVA stands for kilovolt-ampere, which is a unit of apparent power.

• Transformers are designed to handle a certain amount of power, and the KVA rating indicates their capacity.

• The KVA rating takes into account both the voltage and current that the transformer can handle.

• It helps in determining the appropriate size and capacity of the transformer for a given application.

• For example, a transform...read more

The SF6 gas used for Ckt breaker chamber should be maintained at a pressure of around 5-7 bar.

• The SF6 gas in the circuit breaker chamber should be maintained at a specific pressure to ensure proper functioning.

• The recommended pressure for SF6 gas in the circuit breaker chamber is typically between 5 and 7 bar.

• Maintaining the correct pressure helps in extinguishing the arc during circuit interruption.

• Too low or too high pressure can affect the performance and reliability of th...read more

The Basis setting of REF protection for a transformer should be determined based on the transformer's characteristics and the system requirements.

• The basis setting of REF (Restricted Earth Fault) protection for a transformer is typically determined by considering the transformer's winding configuration, impedance, and the system's fault level.

• The setting should be chosen to ensure that the protection operates reliably for internal faults while avoiding unnecessary tripping fo...read more

ACSRinvar conductors are widely used in metro principal cities due to their high strength and low thermal expansion.

• ACSRinvar conductors have a high tensile strength, making them suitable for long-distance transmission lines in metro cities.

• They have a low coefficient of thermal expansion, which helps in reducing sagging of the conductors and maintaining power transmission efficiency.

• The use of ACSRinvar conductors in metro principal cities ensures reliable and uninterrupted ...read more

AIS and GIS substations differ in their construction and insulation methods.

• AIS (Air Insulated Substation) uses air as the insulation medium, while GIS (Gas Insulated Substation) uses SF6 gas.

• AIS substations require larger land areas compared to GIS substations.

• GIS substations are more compact and can be installed in urban areas where space is limited.

• AIS substations are more susceptible to environmental factors like pollution and weather conditions.

• GIS substations offer high...read more

Star-star zero phase shift transformer windings are used to provide a balanced three-phase output with zero phase shift between primary and secondary voltages.

• Star-star zero phase shift transformer windings are commonly used in power distribution systems.

• They are used to supply power to three-phase loads such as motors, generators, and transformers.

• The windings are designed in such a way that the voltages in the primary and secondary sides are in phase with each other.

• This co...read more

Vibration dampers are used with conductors to reduce the risk of fatigue failure and damage caused by wind-induced vibrations.

• Vibration dampers absorb and dissipate the energy generated by wind-induced vibrations in conductors.

• They help to reduce the risk of fatigue failure and damage to the conductor and associated hardware.

• Vibration dampers are typically installed at regular intervals along the length of the conductor.

• They can be in the form of spiral-shaped devices, weight...read more

The main function of LA in a substation is to protect electrical equipment from lightning strikes.

• LA stands for Lightning Arrester.

• It is installed in substations to divert lightning strikes away from sensitive equipment.

• LA provides a low-impedance path for lightning current to flow to the ground.

• It helps in preventing damage to transformers, circuit breakers, and other electrical devices.

• LA operates by ionizing the air around it, creating a conductive path for lightning curre...read more

Various types of conductors include copper, aluminum, and steel.

• Copper: highly conductive, commonly used in electrical wiring

• Aluminum: lighter and cheaper than copper, used in power lines

• Steel: used in overhead transmission lines for strength and durability