L&T Technology Services Senior Electrical Engineer Interview Questions and Answers

We are using IEC 61439 standard for designing the panels and selecting switchgear.

• IEC 61439 is the international standard for low-voltage switchgear and controlgear assemblies

• It provides guidelines for the design, manufacture, and testing of switchgear and controlgear assemblies

• The standard ensures safety, reliability, and performance of the switchgear and controlgear assemblies

• IEC 61439 is widely recognized and accepted in the industry

• Examples of switchgear that comply with ...read more

VFDs control the speed of AC motors by varying the frequency and voltage of the power supplied to the motor.

• VFD stands for Variable Frequency Drive

• Basic components include rectifier, DC bus, inverter, and control system

• Parameters include frequency, voltage, current, and acceleration/deceleration time

• VFDs can improve energy efficiency and reduce wear and tear on motors

• Example: VFDs are commonly used in HVAC systems to control the speed of fans and pumps

Explanation of design calculations for selecting busbar size, switchgear, type-2 coordination, and discrimination study.

• Busbar size selection based on current carrying capacity and voltage drop

• Switchgear selection based on fault level and load current

• Type-2 coordination ensures proper operation of protective devices during a fault

• Discrimination study ensures that only the faulty section of the system is isolated during a fault

• Calculation of short circuit current and fault lev...read more

We use various software depending on the type of electrical component being tested.

• We use simulation software like LTSpice and PSpice for circuit analysis.

• For testing microcontrollers, we use software like Keil and MPLAB.

• For power system analysis, we use software like ETAP and PowerWorld.

• We also use software like LabVIEW and MATLAB for data acquisition and analysis.

2 wire and 4 wire communication are methods used for transmitting data or signals between devices.

• 2 wire communication uses a single pair of wires for both transmitting and receiving data.

• 4 wire communication uses two pairs of wires, one for transmitting and one for receiving data.

• 2 wire communication is commonly used in simple applications like telephone lines.

• 4 wire communication is used in more complex applications like Ethernet networks.

• Examples of 2 wire communication pr...read more

A soft starter panel is an electrical device used to control the starting current of an electric motor.

• It reduces the mechanical stress on the motor during startup.

• It gradually increases the voltage supplied to the motor.

• It can be used to control the speed of the motor.

• It is commonly used in applications where a large amount of power is required to start the motor.

• Examples include pumps, compressors, and conveyor belts.

Control logic of electrical panel involves designing and implementing the logic for controlling various electrical components.

• Designing the logic for controlling electrical components such as motors, pumps, and valves

• Implementing the control logic using programmable logic controllers (PLCs) or other control systems

• Testing and troubleshooting the control logic to ensure proper operation

• Documenting the control logic for future reference and maintenance

• Ensuring compliance with s...read more

VFD is a device used to control the speed of an electric motor. LV panels are used to distribute power to various loads.

• VFD works by adjusting the frequency of the power supplied to the motor, which in turn controls its speed.

• LV panels are designed to distribute power to various loads in a safe and efficient manner.

• Design of LV panels involves selecting appropriate components such as circuit breakers, fuses, and contactors based on the load requirements.

• LV panels also need to...read more