Electrical Interview questions and answers

1) What output power you will get from an ideal transformer and why?

An perfect transformer has no losses such as hysteresis loss, eddy current loss, and so on. As a result, an ideal transformer's output power is exactly equal to its input power. As a result, 100% efficiency.

2) What is transformer efficiency & all-day efficiency? What is the condition form maximum efficiency?

Transformer Efficiency: The transformer's efficiency is calculated by dividing the output power by the input power. Some of the input power is squandered in internal processing.

losses of the transformer.

Output Power / Input Power = Efficiency

All Day Efficiency:

All-day efficiency is defined as the ratio of energy delivered in Kilo Watt-Hour (kWh) to energy input in kWh of the transformer over a 24-hour period.

all_day = kWh output / kWh input

Condition for Maximum Efficiency:

The copper loss must equal the iron loss, which is the sum of hysteresis and eddy current losses.

Cu Loss = Iron Loss

Wcu = Wi

3) Why the current transformer’s secondary should not be open when there is current flowing in its primary?

On the secondary side, the current transformer is essentially a step-up transformer that increases the voltage while decreasing the current.When the secondary is open, the primary current becomes the magnetizing current, generating an extremely high secondary voltage that might damage the insulation and endanger personnel.

4) What will happen if DC supply is given to the primary of the Transformer?

Transformers have a high inductance and a low resistance. There is no inductance in a DC supply, therefore only resistance acts in the electrical circuit. As a result, a large electrical current will flow through the transformer's primary side. As a result, the coil and insulation will burn out.

5) What exactly is the distinction between an ammeter and a voltmeter?

Ammeter is a low resistance indicating instrument while the voltmeter is high resistance one.

6) Why should an ammeter have such a low resistance?

The ammeter connected in series with the circuit carrying the current under measurement must have a very low resistance so that the voltage drop across the ammeter and the power absorbed by the circuit are as low as possible.

7) Why should a voltmeter be of very high resistance?

Voltmeter, which is connected in parallel with the circuit across which the voltage is to be measured, must be of very high resistance so that the current flowing through The voltmeter and power consumed by the circuit are as low as feasible.

8) How can an ammeter be changed in to a voltmeter?

An ammeter with a low range can be transformed into a voltmeter by connecting it in series with a high resistance, providing the current through the series combination is within the ammeter's range when connected across the voltage under measurement.

9) What do you understand by the term ‘burden’ of a CT?

When the CT is supplying the instrument with its maximum rated current on the secondary side, the product of voltage and current is known as rated burden and is stated in volt-amperes.

10) What Is Skin Effect?

The current density of alternating current going through a conductor is very high near the surface and very low near the center of its cross-section area. This is known as the skin effect, and it is exactly proportional to frequency. As a result, stranded conductors are employed in power transmission.

 

11) How to reduce Skin Effect?

The methods of reducing skin effects are:

To lessen the skin effect, an ACSR bundled conductor is employed.

Using a cable material with a lower magnetic permeability.

The conductor's size is being reduced.

Increasing voltage by decreasing current, which reduces the skin effect in the same conductor.

 

13) What is Ferranti Effect?

The Ferranti effect occurs when the voltage at the receiving end of a transmission line is greater than the voltage at the sending end. This type of impact is caused primarily by a low load or an open circuit at the receiving end. The key properties of lines with a length of 240km or more are capacitance and inductance. The capacitance on such transmission lines is not concentrated at certain spots. It is evenly spread along the entire length of the line.

When a voltage is provided to the transmitting end, the current drawn by the line's capacitance exceeds the current connected with the load. As a result, at little or low load, the voltage at the receiving end is quite high in comparison to the constant voltage at the sending end.

14) How can we reduce Ferranti Effect?

Ferranti effect can be reduced:

By installing shunt compensation devices at receiving end. A shunt reactor linked in parallel with the transmission line serves as the compensation mechanism. It lowers the voltage by absorbing reactive power.

Running the transmission line with higher load. I.e if you have two line both carries 5 % load in each side means, we can switch of the one transmission line and the remaining load can be diverted in to another one.

15) What is Proximity Effect?

When high alternating voltage is applied to conductors, currents are not equally distributed across the cross-section area of the conductor. This is known as the proximity effect. The proximity effect causes the perceived resistance of the conductor to increase due to the presence of additional conductors conducting current in its vicinity.

16) How can we reduce Proximity Effect?

We can reduce proximity effect by:

Reducing the size of the conductor

Expanding  the space between the two conductors. Dummies, for example, are used in cable manufacture to shorten the distance between conductors.

We can lessen the proximity impact by decreasing the frequency and increasing the voltage. It is virtually impossible.

However, the frequency of the alternating current cannot be adjusted. However, we can increase the voltage further.

 

17) What is a system?

When a set of connected elements performs a given function, the group of elements is said to create a system. A system is also the interconnection of numerous components for a specific activity. Consider the automobile.

18) What is control system?

The Control System is any collection of mechanical or electronic components that maintains, regulates, or commands the behavior of the system via a control loop. It might range from a simple control device to a huge industrial control device used to control processes or machines.

19) What are the types of Control System? Explain.

There are two types of Control System-

1. Open loop control system.

2. Closed loop control system.

The term "open-loop control system" refers to a system in which the control action is independent of the desired output signal.

Examples include an automatic washing machine and an immersion rod.

A closed-loop control system is one in which control action is dependent on the desired output. 

Examples include an automatic iron, a servo voltage stabilizer, and an air conditioner.

20) What are the benefits and drawbacks of an open-loop system?

Advantages of the open-loop control system

o Open loop systems are simple.

o These are economical.

o Maintenance is minimal and straightforward.

Disadvantages of the open-loop control system

o Open loop systems are inaccurate.

o These systems are not reliable.

o These are slow.

o Optimization is not possible.

21) What are the advantages of Closed-Loop System?

Advantages of closed-loop systems

o Closed loop systems are more dependable.

o Closed loop systems are faster.

o Many variables can be handled simultaneously.

o Optimization is possible.

Disadvantages of closed-loop systems

o Closed loop systems are expensive.

o Maintenance is difficult.

o Installation is difficult for these systems.