# UPPCL JE 2016 Electrical question paper with Explained Solution(Evening Shift)

Ques 1. Which of the following batteries does not require trickle charging?

2. Alkaline cell
3. Lead-acid and Alkaline cell both
4. Neither lead-acid nor alkaline cell

In trickle charging, the batteries are given a charge at a very low rate for a long period of time or continuously throughout their service. Trickle charging is used for acid batteries that are stored for relatively long periods.

The current is then adjusted to just counteract local action within the cells so that the voltage and the specific gravity of the electrolyte remain constant. Trickle charging is also used for keeping batteries in peak condition i.e a very low current is continuously passed through the battery and kept it fully charged.

Continuous trickle-charging or constant-current fast charge is not suitable for use with rechargeable alkaline batteries. The alkaline cells are not tolerant of high continuous charge currents and may be damaged if a high current is forced into them after they have reached a partially recharged state.

Ques 2. The voltage limit for AC single-phase induction motor is

1. 3 kV
2. 1.5 kV
3. 250 V
4. 11 kV

AC single-phase induction motor is a small-horsepower motor (upto 5 H.P) that is mainly used for household purposes e.g  Air conditioners and refrigerators, Ceiling fans and blowers, Machine tool drive, Pump drives etc.

Our household supply ranges from 110 V – 220V i.e 110 V in the USA and 220 V in India, therefore, the voltage limit of AC single-phase induction is around 250 Volt.

Ques 3. In a delta connection, line voltage lags behind phase current by

1. 30°
2. 60°
3. 90°
4. 120°

In Δ connection, the line voltage is equal to phase voltage, as each winding is connected between any two lines. Therefore,

VL = Vph

Let the RMS value of the current of the three phases be IB, IR, IY. Let the direction of the currents be as shown in the figure. Since the loads are balanced, all the three currents will be equal in magnitude but will differ in phase by 120°.It is seen from the figure that lR when positive will flow away from the line conductor R. Similarly, IY flows away from the line conductor Y. and IB flow away from the line conductor B.

Now If we consider the line conductor R, then the current IB flows towards it while current IY flows away from it.

Hence in Δ connection, the current in any line is equal to the phasor difference of the current in two phases connected to the line. Thus,

Current in Line R = IR − IB
Current in Line Y = IY − IR
Current in Line B = IB − IY

As the current in line R is the phasor difference between IR and IB, it is obtained by subtracting IB from IR. To do this, phasor IB is reversed as shown in fig. such that (IR – IB) becomes [IR + (-IB)]. From the phasor diagram, it is observed that the two phasors IR and -IB are equal in magnitude and are displaced at 60°. So, the current in line R.

IR − IB = 2Iph cos(60°/2)

= 2Iph cos30° = √3 Iph

Similarly current in Line Y =  IY − IR = √3 Iph

current in Line B = IB − IY = √3 Iph

Thus, in a balanced three-phase delta connection, line current = √3 x phase current. It is also noted the line current IR − IB lags behind the phase current IR by 30°.

Ques 4. The efficiency of Sovonious Windmill is about

1. 5%
2. 15%
3. 25%
4. 35%

Savonius wind turbines are a type of vertical-axis wind turbine (VAWT), used for converting the force of the wind into torque on a rotating shaft. The turbine consists of a number of aerofoils, vertically mounted on a rotating shaft or framework, either ground stationed or tethered in airborne systems.

With a Savonius wind turbine, it does not matter from which direction the wind is blowing, since there will always be more force exerted on whichever cup has its open face into the wind, and this will push the rotor around.

The Savonius turbine is one of the simplest turbines. Aerodynamically, it is a drag-type device, consisting of two or three scoops. The differential drag causes the Savonius turbine to spin. Because they are drag-type devices, Savonius turbines extract much less of the wind’s power than other similarly-sized lift-type turbines which are around 15% of the wind energy hitting the rotor is turned into rotational mechanical energy

Ques 5. With increase in temperature, the resistance of semiconductors:-

1. Increases
2. Decreases
3. Do not change
4. May increase or decrease

The resistance of semiconductor, Insulator, and Electrolyte(silicon, Glass, Varnish etc) decrease with increase in temperature.

At zero temperature, the semiconductor behaves as a perfect insulator.  As the temperature increases, some of the electrons acquire energy and become free for conduction. Hence, conductivity increase and resistance decrease with an increase in temperature.

A semiconductor has a negative temperature coefficient of resistivity therefore with the increase in the temperature the resistance decreases

Ques 6. The ballistic galvanometer is calibrated to measure

1. Current
2. Voltage
3. Resistance
4. Charge

A ballistic galvanometer is used to measure the total quantity of electricity, i.e. charge, displaced by a varying current of short duration such as in the charging and discharging of a capacitor.

Here, maximum deflection or throw is proportional to the total charge which passed through the galvanometer.i.e θ ∝ q

Ques 7. ________ is not a method of high resistance interruption of arc extinction.

1. Blast effect
2. Arc lengthening
3. Arc constraining
4. Arc cooling

Blast effect is low resistance method or Current Zero Method of arc extinction.In this method, the ionized particles in the arc chamber are swept away at zero current points and replaced with the new ones, so these new particles offer high dielectric strength in between the circuit breaker contacts.

Ques 8.  Semiconductor strain gauges depend upon _________ for their action.

1. Piezoelectric effect
2. Piezoresistive effect
3. Hall’s effect
4. Superconductivity

Semiconductor strain gauges depend upon the Piezoresistive effect for their action.

For achieving high sensitivity, a high value of the gauge factor is desirable. A high gauge factor means a relatively higher change in resistance which can be easily measured with a good degree of accuracy. Semiconductor strain gauges are used where a very high gauge factor is required. They have a gauge factor 50 times as high as wire strain gauges. The resistance of the semiconductor changes with the change in applied strain.

Semiconductor strain gauges depend on their action upon the piezo-resistive effect, i.e. change in the value of the resistance due to change in resistivity, unlike metallic gauges where the change in resistance is mainly due to the change in dimension when strained. Semiconductor materials such as germanium and silicon are used as resistive materials.

Ques 9. SCR is a ______ layer ______ junction device.

1. Single, Three
2. Two, Four
3. Three, Four
4. Four, Three

A silicon-controlled rectifier or semiconductor-controlled rectifier is a four-layer and three-junction solid-state current-controlling unidirectional device (i.e. can conduct current only in one direction).

The silicon control rectifier (SCR) consists of four layers of semiconductors, which form NPNP or PNPN structures, having three P-N junctions labeled J1, J2, and J3, and three terminals. Silicon is used as the intrinsic semiconductor, to which the proper dopants are added.

The junctions are either diffused or alloyed (an alloy is a mixed semiconductor or a mixed metal). The anode terminal of an SCR is connected to the p-type material of a PNPN structure, and the cathode terminal is connected to the n-type layer. SCR is connected to the p-type material nearest to the cathode.

Ques 10. Which of the following is not a part of Steam Power Plant?

1. SwitchYard
2. Ash precipitators
3. Draught fan
4. Surge Chamber

Surge tank (or surge chamber) is a device introduced within a hydropower water system having a  long pressure conduit to absorb and neutralize the sudden pressure rise in case of valve closure. The surge tank is located between the almost horizontal or slightly inclined conduit and steeply sloping penstock and is designed as a chamber excavated in the mountain.

For hydroelectric power uses, a surge tank (Surge Chamber) is additional storage space or reservoir fitted between the main storage reservoir and the powerhouse (as close to the power house as possible).

Surge tanks are usually provided in high or medium-head plants when there is a considerable distance between the water source and the power unit, necessitating a long penstock. The main functions of the surge tank are

1. When the load decreases, the water moves backward and gets stored in it.
2. When the load increases, an additional supply of water will be provided by the surge tank. In short, the surge tank mitigates pressure variations due to rapid changes in the velocity of the water.
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