SSC JE 2014 Electrical question paper with solution(Evening-shift)

• Damper windings are windings that are wound to the rotor poles of the machine (winding it similar to that of an induction machine) which help in two ways.
• We all know that a synchronous machine is not self-starting. Thus providing damper windings help synchronous machines to act as an induction motor ( only at starting). Which helps the machine to self-start.
• We all know that hunting is a persistent phenomenon when it comes to synchronous machines.
• We can reduce hunting to a great extent by damping it. They don’t let the motor to oscillate abruptly, they damp the oscillations thus increasing the stability of the machine.

Smooth Cylindrical Type or Non-Salient Pole alternator rotor is used for steam-driven alternator i.e turbo alternator which runs at very high speed.Since the steam turbine runs at a very high speed, therefore, they required fewer poles hence the diameter of the rotor is small, and the axial or rotor length is large.

The series reactor are high impedance electrical components used in alternating-current power systems for protection against excessively large currents under short-circuit or transient conditions; it consists of coils of heavy insulated cable either cast in concrete columns or supported in rigid frames and mounted on insulators. It is also known as the current-limiting reactor.

Power cables are mainly used for power transmission and distribution purposes. An electric power distribution system is the final stage in the delivery of electric power; it carries electricity From the transmission system to individual consumers.

Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage with the use of step-down transformers. Power distribution by cable is generally adopted for line lengths less than 10 km.

Leakage resistance is inversely proportional to the length therefore

R ∝ 1/L

and R₁/R₂ = L₂/L₁

= R₂ = R₁l₁/l₂

R2 = 1 x50/100 = 0.5Ω

The volume of the conductor is Inversely proportional to the square of Voltage ( Vol ∝1/V²).

so if the voltage is increased by n times then the volume is reduced to

Volume = 1/n²

Load factor = Unit generated/(Maximum Demands x hours)

24 × 100/(2 × 24) = 50%

The top of the cable is called a guard wire or earth wire (ground wire)  used mainly to protect lines from lightning. If in case of lightning strikes then it carries the excessive current inrush to the ground.

Its radius is much smaller than the actual transmission wire because the resistance is inversely proportional to the area of the cross-section and as the cross-section decreases the resistance increases.

The increased resistance of earth wire is able to withstand a high inrush of current caused due to lightning and it will safely guide this inrush into the ground.

EARTH CONTINUITY CONDUCTOR (ECC)

A third conductor with line and neutral in a mains distribution system, bonded to earth, provided for connection to any metal component not in the electrical circuit for safety purposes.

The earth continuity conductor connects an electrical system to the earth so that when there is a fault in the circuit the current can travel safely to the earth without shocking someone. The earth electrode is a metal rod that connects the earth continuity conductor to the ground so that the current has a safe path to the ground through a good conductor

Advantages of PVC Insulation

• PVC insulation has a thin layer hence it has a smaller diameter of cables which makes it possible to carry more wires in the conduit of a given size, unlike VIR or CTS wires.
• PVC insulation has better insulating qualities
• PVC insulation provides better flexibility for the cables
• PVC insulation is not affected by chemicals