10+ Nagshanti Autocars Interview Questions and Answers

To convert a voltmeter to an ammeter, a shunt resistor is added in parallel to the meter to measure current instead of voltage.

• Add a shunt resistor in parallel to the voltmeter to convert it to an ammeter.

• Calculate the shunt resistor value using Ohm's Law (R = V/I) based on the desired current range.

• Connect the shunt resistor in parallel to the voltmeter with proper polarity.

• Ensure the shunt resistor has a low resistance value to minimize voltage drop and accurate current mea...read more

Synchronous motors require external starting methods due to their design and characteristics.

• Synchronous motors need to be brought up to synchronous speed before they can start operating efficiently.

• Common starting methods include using a pony motor, damper winding, or a frequency converter.

• Synchronous motors are not self-starting because they operate at a fixed speed determined by the frequency of the power supply.

• The rotor of a synchronous motor must be rotating at the same...read more

Series motor shouldn't be started without no load to prevent damage due to high starting current.

• Starting a series motor without a load can result in high starting current which can damage the motor windings.

• Without a load, the motor can run at dangerously high speeds which can also lead to damage.

• The absence of a load can cause the motor to overheat due to lack of cooling.

• Starting a series motor without a load can also cause mechanical stress on the motor components.

• It is im...read more

CT secondary should not be open circuited as it can lead to dangerous high voltage spikes and damage the equipment.

• Open circuiting the CT secondary can lead to dangerous high voltage spikes due to no current flow.

• It can damage the CT and other connected equipment.

• It can also lead to inaccurate measurements and incorrect readings.

• Short circuiting the CT secondary is a safer option to prevent high voltage spikes.

• Proper grounding and connection of the CT secondary is essential f...read more

A single line diagram is a simplified representation of a power system showing the main components and their connections.

• Single line diagrams show the main components of a power system such as generators, transformers, transmission lines, and distribution lines.

• Each component is represented by a simple symbol with lines connecting them to show how they are interconnected.

• For example, a generator is represented by a circle with a line extending from it to a transformer symbol....read more

Most petrol pump stations use LED lighting systems for energy efficiency and cost savings.

• LED lighting systems are commonly used in petrol pump stations

• LED lights provide bright and uniform illumination for safety and security

• LED lights are energy efficient and cost effective, saving on electricity bills

• LED lights have a longer lifespan compared to traditional lighting systems

• Some petrol pump stations may also use solar-powered lighting systems for sustainability

Different types of speed control methods in DC motor include armature voltage control, field flux control, and armature resistance control.

• Armature voltage control: Adjusting the voltage applied to the armature to control speed.

• Field flux control: Changing the field flux to regulate the speed of the motor.

• Armature resistance control: Varying the armature resistance to adjust the speed of the motor.

Arc quenching in SF6 circuit breaker involves the use of sulfur hexafluoride gas to rapidly extinguish the arc.

• SF6 gas is used as the quenching medium due to its high dielectric strength and excellent arc-extinguishing properties.

• When the circuit breaker detects an arc, the SF6 gas is rapidly injected into the arc zone to cool and extinguish it.

• The high thermal conductivity of SF6 helps in quickly dissipating the heat generated by the arc.

• SF6 gas also has a high electronegati...read more

Permanent losses in transformers refer to losses that occur continuously during operation and cannot be recovered.

• Permanent losses include core losses (eddy current and hysteresis losses) and copper losses (due to resistance in windings).

• Core losses are constant and occur even when the transformer is idle.

• Copper losses increase with the load on the transformer.

• Permanent losses result in reduced efficiency and increased heating of the transformer.

• Examples of permanent losses i...read more

Transformer core is laminated to reduce eddy current losses and improve efficiency.

• Laminating the core reduces eddy current losses

• Lamination helps in improving the efficiency of the transformer

• Prevents overheating of the core

• Increases the resistance of the core to magnetic flux

The role of MHO relay is to provide distance protection for power lines by measuring the impedance of the line and tripping the circuit breaker if a fault is detected.

• Provides distance protection for power lines

• Measures impedance of the line

• Trips the circuit breaker if a fault is detected

Buchholz relay is a protective device for oil-filled transformers and reactors, used to detect and prevent internal faults.

• It is a gas and oil-operated relay

• Monitors the gas accumulation in the oil tank

• Triggers an alarm or trips the transformer if gas levels exceed the set limit

• Helps in preventing catastrophic failures in transformers

Distance protection relay is a type of protective relay used in power systems to protect transmission lines from faults.

• Distance protection relay operates based on the impedance seen by the relay from the fault point.

• It measures the distance to the fault by comparing the impedance to a pre-set value.

• It is commonly used in high voltage transmission lines to quickly isolate faults and prevent damage to the system.

• Examples of distance protection relays include impedance relays a...read more

The highest transmission voltage in India is 1200 kV.

• Highest transmission voltage in India is 1200 kV

• This voltage level is used for long-distance transmission of electricity

• It helps in reducing transmission losses and improving efficiency

Armature reaction is the effect of magnetic field produced by armature current on the main magnetic field in a DC machine.

• Armature reaction occurs in DC machines when current flows through the armature winding, creating a magnetic field.

• This magnetic field interacts with the main magnetic field, causing distortion and shifting of the neutral plane.

• Armature reaction affects the commutation process and can lead to sparking at the brushes.

• Compensating windings or interpoles are ...read more

A GIS substation is a high voltage substation that uses gas-insulated switchgear for electrical insulation.

• Uses gas-insulated switchgear for electrical insulation

• Compact design compared to traditional air-insulated substations

• Requires less maintenance

• Provides higher reliability and safety

• Commonly used in urban areas with space constraints

An induction generator is a type of asynchronous generator that produces electrical power by induction.

• Induction generators are commonly used in wind turbines to convert mechanical energy into electrical energy.

• They do not require a separate excitation system like synchronous generators.

• Induction generators operate at a slightly sub-synchronous speed to generate power.

• They are self-starting and do not require external power to initiate generation.

• Induction generators are ofte...read more

Holding current is the minimum current required to keep a device or component in the on state.

• Holding current is essential for maintaining the operation of devices like relays and transistors.

• It ensures that the device remains in the on state even after the triggering current is removed.

• For example, in a relay, holding current is the current needed to keep the relay contacts closed.

• Holding current is typically lower than the operating current of the device.