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## What is per unit system?

The transformers, loads, motors and other electrical equipment in power systems are all at different voltage levels.To relate the voltage, power and current ratings of these devices the per-unit system is used. In this system voltages, currents, powers, impedances are not measured in ordinary units volt, amperes etc. Instead, a base value of the quantity is introduced and the actual value is divided by that specific value of archive pu values.

Mathematically: Per Unit value = Actual Value / Value of Quantity

## What is a condenser, Explain two types of Condensers used in Steam Power Station?

A condenser is an essential part of Steam Power Station which condenses the steam coming from the turbine. Two types of condensers include the Jet condenser and the surface condenser.
A jet condenser is a comparatively economical method in which the steam is mixed with cooling water.
In surface condenser a bank of horizontal tubes which carry the cooling water. Exhausted steam moves over the surface of tubes. Steam loses its heat to water and condenses. Compared to the jet condenser, this method is expensive initially.

## Explain heating Phenomenon in Power Transformer and How it is Controlled?

Heating is a fatal problem in Power Transformers. It causes burning of the winding. Engineers in Power Industry fight the heat problem by ensuring good design. The core features of the good design involve the reduction of eddy currents. Furthermore, the core and winding of transformers are submerged in oil. Heat from windings and core is transferred to oil. Radiator tubes on outside transformers provide a flow path to transformers heat.

## What is Tariff, Explain Most Common Types of Tariff?

The terms tariff refers to the rate of electrical power (electricity). Most common types of the tariff are:

1. Simple Tariff: Each unit of energy is charged at fixed rate.
2. Flat rate tariff: In this, the consumers are divided into different classes based on the type of load they use.
3. Block rate tariff: The units of energy are divided into different blocks and are charged accordingly. For example consumers using units b/w 1-50 kW are charged at \$0.5, consumers utilising 50-100 kW are charged at \$0.3 and so on.
4. Two part tariff: In this type, two factors are considered for assigning tariff. The first one is maximum demand and the second one is the number of units used.

## Mention the Two Advantages of HVDC Power Transmission?

1. HVDC transmission uses two conductors for power transmission, which is comparatively economic as compared to HVAC power system which uses three conductors.
2. There is no inductance/capacitance associated with HVDC Power and due to this better voltage regulation is achieved at the consumer end.

## What are different types of Phase Faults occurring in Power Systems and which one is most Dangerous?

Different types of phase faults on Power Systems are:

1. L-L: Line to Line Fault
2. L-G: Line to Ground Fault
3. L-L-G: Line to Line to Ground
4. L-L-L: Line to Line to Line

L-L-L is the most dangerous type of phase fault.

## What is Diversity Factor and What valuable Information does it provide?

It is a ratio between the sum of individual maximum demands to the maximum demand on the power station.

Mathematically,

Diversity Factor = Sum of individual maximum demand / Maximum demand at power station

Since D.F is inversely proportional to Maximum demand, greater D.F means lesser maximum demand and a smaller plant capacity. The above all scenario means that if D.F is greater than capital investment on the plant is smaller.

## What is A.C.S.R

The combination of the aluminium conductor with steel results in another conductor whose tensile strength is high as compared to individual aluminium itself. This composite conductor is named as aluminium conductor steel reinforced (A.C.S.R)

## What is Booster Transformer?

A transformer which is used to control the voltage levels of the transmission line at a point that is far away from the main transformer. For that purpose, a special type of transformer is used which is named as Booster transformer.

## Mention the components used at Switch Gear

A switc gear contains circuit breakers, switchbusbarsbars, instrumentation transformers and relays.