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

In the plate earthing a pit of about 3 meters depth is dug. The earth electrode used may be a copper plate having a dimension of 60 cm × 60 cm × 3.18 mm. (In the case of the G.I (Galvanized Iron) plate, the dimension is 60 cm × 60 cm × 6.36 mm). After placing the electrode in the pit, layers of charcoal and salt are used to fill the space around it.

The electrode can be connected to a G.I. pipe of 12.7 mm diameter for carrying G.I. earth wire. The pit is covered with an iron plate for periodic check-ups. To increase moisture and dampness a pipe is provided for carrying water.

An induction regulator is used to maintain the constant voltage in the feeder circuit.

Feeder voltage regulators are used extensively to regulate the voltage of each feeder separately to maintain a reasonably constant voltage at the point of utilization. A voltage regulator is used to maintain the voltage of a circuit and is essentially a special application of an autotransformer.

The voltage in the portion o the winding which is added or subtracted in an autotransformer is made variable, so the outgoing voltage may thus be kept approximately at the rated value. These are two types of voltage regulators commonly used, and the principle of operation of both is the same as for the autotransformer.

1. Induction type voltage regulator
2. Step type voltage regulator

In the modern electrical system, step-type voltage regulators have practically replaced induction-type regulators.

Induction type voltage regulator

In induction type voltage regulator the primary winding is a high voltage winding that is connected across (or in shunt with) the circuit to be regulated. The secondary or low-voltage winding is connected in series with the circuit.

The primary (high-voltage) winding is mounted so that it can rotate on the axis of the secondary winding. The voltage induced in the secondary or series winding depends on the position of the primary winding. The high-voltage winding thus can be placed so that the voltage induced in the series winding will add or subtract from the input line voltage.

When the load current is small. the primary will be rotated in one direction, thus lowering or bucking the line voltage. When the load current is larger, the primary will be rotated in the opposite direction, thus boosting it. The reactance of the secondary can cause a large voltage drop during the rotation of the primary. To avoid this drop (or cancel it out), a third coil is added and mounted on the movable core at a right angle to the primary winding and short-circuited on itself. The turning of the primary coil is usually controlled by means of a voltage-sensitive relay (called a contact-making voltmeter connected to the output side of the circuit.

The process of connecting the neutral point of a supply system on the non-current carrying parts of electrical apparatus to the general mass of earth in such a manner that at all times an immediate discharge of electrical energy takes place without danger is called earthing.

In an earthed neutral system, the neutral is earthed either directly or through resistance or reactance depending on the requirement. Thus the system neutral can be grounded effectively or non-effectively. In an effectively grounded system, the neutral is grounded directly and hence it is called solid grounding.

The main advantages of neutral earthing are:

1. The magnitude of transient voltage is small in this system.
2. The static charges which are induced are grounded immediately and are thus prevented from causing any disturbance.
3. As the neutral point is not shifted in this system, thus the voltages of healthy phases remain nearly constant.
4. This system is more reliable and provides safety to personnel and equipment with reduced operational and maintenance costs than the ungrounded system.

Current Chopping in the circuit breaker is defined as a phenomenon in which current is forcibly interrupted before the natural current zero. Current Chopping is mainly observed in Vacuum Circuit breakers and Air Blast Circuit breakers.

For average values of load current, current chopping occurs more frequently in the Air circuit breaker.

In an air blast breaker, a high-velocity jet of air is made to flow through the arcing contacts that extinguish the arc much before natural ac current 0 is reached, the air blast breaker retains the same extinguishing power irrespective of the nature of the fault, consequently, the blast of air sweeps out the ionized particles in between the contacts thereby building the resistance and hence ultimately extinguishing the arc.

MCB (Miniature Circuit Breaker) is an automatically operated electrical switch designed to protect electrical appliances and human beings from electrical shocks and faults.

Advantages of MCB

1. MCB is more sensitive to current than the fuse. It detects any abnormality in the current flow and automatically switches off the electrical circuit.
2. MCB provides a better interface with the help of a knob than a fuse. In case of a fault, the compete handle needs to be taken care of.
3. MCB is reusable and hence has less maintenance and replacement cost. Whereas a fuse needs to be replaced whenever it goes faulty.
4. MCB is arranged for plug-in mounting, is compact, and since it is not repairable, has the advantage of being relatively inexpensive.

Speed of Induction motor is given as

Ns = 120f/P

600 = 120 x 40/P

P = 8

The value of the quantity to be measured should not get altered significantly because of the insertion of the instrument to measure it. Ideally, an ammeter should have zero resistance and a voltmeter infinite resistance to give correct readings.

A voltmeter is connected in parallel with the original circuit. If it draws any current from the main circuit, the actual Potential Difference in the main circuit may not be determined.

Current chooses a path with low resistance, hence the resistance of an ideal Voltmeter must be infinitely high so that no current flows through it and the entire current flows only in the circuit.

Since the conductance are connected in parallel, therefore, its equivalent conductance

i =i G₁ +i G₂ +i G₃

= 2 + 3 + 6 = 11 mho

Since conductance is the inverse of resistance i.e

G = 1/R = 11 = 1/R

R = 1/11 ohm

Uninterruptible power supply (UPS) is a type of power supply system that contains a battery to maintain power to provide power to electronics in the event of a power surge or outage.

• Pin-type insulators are used for the transmission and distribution of electric power at voltages up to 33 kV.
• Beyond operating voltage of 33 kV, the pin-type insulators become too bulky and hence uneconomical.