# Electrical Engineering Interview Questions: UPSC ESE Preparation

## 1). What is transformer oil and its uses?

Transformer oil is a specially refined mineral oil used to both insulate and cool the transformers. It avoids arcing, cools the transformer and protects the core and coil with the aid of transformer oil.

## 2). What is sludge and moisture in transformer oil, and how does it enter there?

In transformer oil, sludge is the oxidized product, and moisture can infiltrate the transformer due to leakage or condensation, or insulation aging. Both have the same negative impact in that they both reduce the dielectric properties of the oil and results in transformer failure.

## 3). How can sludge and moisture be removed from transformer oil?

Oil impacts such as sludge and moisture can be separated out in an oil filtration system, vacuum dehydrator or degassing process that will serve to purify the oil and replenish its dielectric strength.

## 4). How can we create a vacuum within a transformer tank?

Vacuum is made inside the transformer tank through vacuum pumps that remove air and moisture, and make the transformer free from gases that may lead to the failure of the insulation.

## 5). How is heat dissipation managed in a transformer, and what are the cooling systems used?

Overheating is always avoided in transformers through oil circulation, radiators, fans and other cooling systems such as ONAN (Oil Natural Air Natural) where oil and air cool the transformer and OFAF (Oil Forced Air Forced) where forced oil and air cool the transformer.

## 6). What do you know about controllers?

There are usually responsible for controlling and supervising other system characteristics with an aim of achieving stability and functionality. These are applied in automation and control, to counter act for disturbances and keep achieving a preferable response.

## 7). Plot the response of a 2nd order underdamped system.

In a 2nd order underdamped system the response normally oscillates in a damped manner and these oscillations asymptotically decay to the steady state response. In the plot of the signal, it would be clearly seen that it has a sinusoidal waveform with a diminishing envelope.

## 8). What is gain and phase margin in stability analysis?

Gain margin shows how much gain can be increased before system goes unstable and phase margin shows how much phase can be decreased before the system goes unstable. Both are essential in synchronizing a firm’s control system.

## 9). What is Lyapunov Stability?

Lyapunov Stability is a concept in control theory that is used to examine stability of equilibria in nonlinear dynamics systems. In other words, a system is said to be Lyapunov stable if small disturbances lead to its return to the state of equilibrium.

## 10). What is MPPT (Maximum Power Point Tracking)?

MPPT is one of the strategies applied on solar inverters in order to extract maximum power from the photovoltaic (PV) system; the operating point of the system is adjusted so as to correspond always to the maximum power point of the solar cell IV curve.

## 11). How do we work with MPPT?

MPPTs are incorporated in a solar charge controller or inverter, which is used to control load or operate in tracking of solar panel voltage and current to the maximum power level.

## 12). What is the Maximum Power Transfer Theorem?

The Maximum Power Transfer Theorem explains that the maximum amount of power is delivered through a source to the load when the differential impedance of the latter corresponds to the impedance of the former.

## 13). What is the irradiation and temperature dependency of a solar cell?

A solar cell’s output is proportional to the irradiation but is inversely proportional to the temperature of the solar cell. Higher irradiance raises the present output and reduces voltage with temperature, which determines efficiency.

## 14). What is the efficiency of a solar cell?

The efficiency of a solar cell is defined by the ratio of electrical power output to the incident solar power, where the result is said in percent. They differ based on the type of the materials used in the construction and the conditions in which it is used.

## 15). How do you convert solar input into electrical input for efficiency calculations?

Solar input is defined as incident solar power or irradiance in watts per square meter and is initially converted to electrical output then divided with the total solar input energy drawn to find the efficiency.

Calculation

The efficiency (η) is given by the formula:

η = (Pout / Pin) x 100%

Where:

So, Overall Efficiency Formula is:

Where

E - Irradiance (in W/m²)

A - Area of the solar cell (in m²)