ISMT Mechanical Maintenance Technician Interview Questions and Answers

A circuit breaker is an electrical switch that automatically interrupts the flow of current when it exceeds a certain limit.

• It is used to protect electrical circuits from damage caused by overloading or short circuits.

• It works by detecting the excess current and tripping the switch to break the circuit.

• It can be reset manually or automatically depending on the type of circuit breaker.

• Examples include thermal circuit br...read more

A contactor is an electrical switch used for switching an electrical circuit on or off.

• It is used to control electric motors, lighting, heating, and other electrical loads.

• It consists of a coil, contacts, and an enclosure.

• The coil generates a magnetic field that pulls the contacts together to close the circuit.

• Examples include HVAC systems, elevators, and industrial machinery.

• Contactor ratings are based on the amount o...read more

MCB stands for Miniature Circuit Breaker. It is an electrical switch that automatically shuts off the electrical circuit during an overload or short circuit.

• MCB is a type of circuit breaker that is commonly used in residential and commercial buildings.

• It is designed to protect electrical circuits from damage caused by overloading or short circuits.

• MCBs are available in different current ratings and can be easily replac...read more

A motor is a device that converts electrical energy into mechanical energy to produce motion.

• Motors are used in various applications such as electric vehicles, industrial machinery, and household appliances.

• There are different types of motors such as DC motors, AC motors, stepper motors, and servo motors.

• The basic principle of a motor is the interaction between a magnetic field and an electric current.

• Examples of motor...read more

A current transformer is a device that measures the current flowing in a circuit by producing a proportional current in its secondary winding.

• Consists of a primary winding and a secondary winding

• Primary winding is connected in series with the circuit carrying the current to be measured

• Secondary winding is connected to a measuring instrument or protective relay

• Produces a current in the secondary winding that is proporti...read more

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 a...read more

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 volta...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 5

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

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...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 ...read more