10+ Interview Questions and Answers

Composite error and ratio error are two types of errors in current transformers.

• Composite error is the combination of ratio error and phase angle error in a current transformer.

• Ratio error is the difference between the actual turns ratio and the specified turns ratio of a current transformer.

• Phase angle error is the angular difference between the primary and secondary currents of a current transformer.

• Composite error and ratio error affect the accuracy of current measurement ...read more

Power transformers are used in transmission systems to step up or down voltage, while distribution transformers are used in distribution systems to step down voltage.

• Power transformers are used in high voltage transmission systems to step up or down voltage for long distance transmission.

• Distribution transformers are used in low voltage distribution systems to step down voltage for local distribution.

• Power transformers have higher voltage ratings and power capacities than dis...read more

Buchholz relay is used to protect transformers from faults by detecting gas and oil flow abnormalities.

• Buchholz relay is installed in the pipe connecting the transformer tank and conservator tank.

• It operates based on the principle that faults in the transformer generate gases and cause oil flow disturbances.

• When gas or oil flow abnormalities occur, the relay trips and sends a signal to the control panel to isolate the transformer.

• It provides protection against faults such as ...read more

A single line diagram of a distribution system is required with proper specifications.

• The diagram should show the flow of power from the source to the load

• It should include all components such as transformers, switchgear, and cables

• The specifications should include voltage levels, power ratings, and protection devices

• The diagram should follow standard symbols and conventions

• Example: A 11 kV distribution system with a 500 kVA transformer and 630 A circuit breaker

Dewpoint test is done in transformer to check the moisture content in the insulation oil.

• Moisture in insulation oil can cause breakdown of transformer insulation

• Dewpoint test helps to determine the moisture content in the oil

• It is a preventive maintenance measure to avoid transformer failure

• The test involves cooling a mirror until dew forms on it, and measuring the temperature at which dew forms

Minimum insulation resistance value for HT motor.

• HT motor insulation resistance should be at least 1 Mega Ohm

• Insulation resistance should be measured regularly to ensure safety

• Factors like temperature and humidity can affect insulation resistance

An AC drive circuit diagram controls the speed of an AC motor by varying the frequency and voltage of the power supplied to it.

• An AC drive consists of a rectifier, DC link, inverter, and control circuitry.

• The rectifier converts AC power to DC power, which is stored in the DC link.

• The inverter converts the DC power back to AC power with variable frequency and voltage.

• The control circuitry adjusts the frequency and voltage of the output to control the motor speed.

• Examples of AC...read more

The minimum insulation resistance value for a Lt Motor.

• The minimum insulation resistance value for a Lt Motor is typically 1 Megaohm.

• This value is important to ensure the motor is properly insulated and protected from electrical faults.

• Insulation resistance can be measured using a megohmmeter.

• Factors that can affect insulation resistance include temperature, humidity, and contamination.

• Regular testing of insulation resistance is important for preventative maintenance and safe...read more

Transformer parts include core, windings, insulation, tap changer, and cooling system.

• Core: magnetic material that provides a path for the magnetic flux

• Windings: conductors that carry the electrical current

• Insulation: material that separates the windings and core to prevent short circuits

• Tap changer: device that adjusts the number of turns in the windings to regulate voltage

• Cooling system: dissipates heat generated by the transformer

• Examples: bushings, conservator, breather, ...read more