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

Peripheral speed refers to the actual linear speed of a tooth or point of the circumference of an alternator when it is revolving under power. Peripheral speed is thus the product of the circumference of the alternator and the number of revolutions per minute.

The peripheral speed of the alternator

Ps = π × D × RPM

The peripheral speed depends on the speed as well as the diameter of the rotor. So to reduce the peripheral speed of the alternator the diameter of the rotor should be decreased.

Micro hydro is a type of hydroelectric power that typically produces from 5 kW to 100 kW of electricity using the natural flow of water. Installations below 5 kW are called pico hydro. These installations can provide power to an isolated home or small community, or are sometimes connected to electric power networks.

There are three main types of hydroelectric generation

1. Run-of-river plants with pondage
2. Run-of-river plants without pondage
3. Storage type plants

(1). Run-off river power plants without Pondage: Some hydroelectric power plants are located in a place where water is taken from the river directly. These plants are called run-off river power plants without pondage. Such plants use water only as and when available. In such plants, there is no control on the flow of water. During high flow, water is wasted and during the lean flow period, the plant capacity is very low.

(2) Run-off river power plants with pondage: The usefulness of run-off river power plants is increased by pondage. Pondage refers to the storage at the plant to take care of hour-to-hour fluctuations of the load. Pondage increases the firm capacity of the station, provided the floods do not raise the tail race water level, thus reducing the effective water head and plant output. Such plants can serve as base load or peak load plants depending on the stream flow.

(3) Storage power plants: Most hydroelectric plants belong to this category. When water is stored in a big reservoir behind a dam, it is possible to control the flow of water and use it most effectively. Storage increases the firm capacity of the plant and it can be used efficiently throughout the year. Such a plant can be used as a base load or as a peak load plant as per requirement. It can also be used on any portion of the load curve in a grid system.

Pumped storage plants generate electricity mainly at peak demand periods. During off-peak periods when electricity prices are low, these plants pump the water from the low ground back into the reservoir at the high ground. Therefore, they act as both generators and load at different times of the day. Hydroelectric power plants have fast

Vulcanization or vulcanization is a chemical process for converting natural rubber or related polymers into more durable materials by the addition of sulfur or other equivalent accelerators.

We vulcanize rubber to improve the quality of rubber to resistance to friction, solvents, durability, etc., and to make it stable at all temperatures. Rubber is vulcanized with sulfur. With the addition of 1 to 5 percent of sulfur, we get soft rubber and when we add about 30 percent of sulfur, we get a very hard variety of Rubber.

Differential Compound motor

• In the differential compound, motor two field windings i.e shunt and series windings oppose each other.
• This causes a reduction in flux and a consequent decrease in torque.

Flat-plate collectors are the most common solar collectors for use in solar water-heating systems in homes and in solar space heating. A typical flat-plate collector is a metal box with a glass or plastic cover (called glazing) on top and a dark-colored absorber plate on the bottom. The sides and bottom of the collector are usually insulated to minimize heat loss.

For a solar water heater, the efficiency of a flat plate collectors is 40 – 70 %. For solar drier the efficiency of flat plate collector is 30 – 50%

Starting torque if 3 phase induction motor is given as

Where ns = synchronous speed in r.p.s i.e Ns/60

V = Rotor voltage

R₂ = Rotor resistance

X₂ = Rotor Reactance

∴ T_st ∝ V²

So starting torque of a 3-phase induction motor is directly proportional to V²

Linear variable differential transformer (LVDT) is one of the most popular variable inductance transducers used in many industrial applications like measurement of force, weight, pressure, and acceleration.

A thermocouple is used to measure the variation in the temperature.

The transformer Ratio is given as

 

Reciprocal of turn ratio

1/K = N2/N1 = 1/11

The ratio of current in the secondary to primary is from above eqn will be 1/11

Ohm’s law of constant proportionality state that for a given conductor the ratio of voltage to current is constant i.e if the temperature, area, the length did not change the resulting current is directly proportional to the variation in the applied voltage. Hence the graph between voltage and current is linear.(e.g Silver, aluminum copper, iron, etc)