Modelo comparativo zona rural y zona urbana

Usually, the shaded pole principle is employed for hystersis motor. The rotor of this motor is smooth, having high retentively, so that, hystersis loss is high. It has no winding, the rotor poles magnetically locked up with the revolving stator poles of

opposite polarity. However, rotor poles always lag behind stator poles by a small angle ‘α’ and the rotor revolves synchronously.

The mechanical power developed by rotor is given by Pm = Ph (1-S)/ S

Pm = Mech power developed

Ph = Hysteresis loss in rotor and hysteresis torque Th = (9.55 Pm )/NS

2πNS TSh /60 = (Eb Ia - losses) = out power Pm = (Eb Ia - losses)

∴ Tsh = Pm /(2πNS /60) = (60/2π ). (Pm/NS) = (9.55 Pm / Ns)

This hysteresis torque is solely dependent on the area of rotor’s hysteresis loop. Q.60 Write short note about following:-

(i) Power System structure with diagram. (8)

(ii) Wave energy. (4)

(iii) Ocean thermal energy. (4)

Ans: Power System structure with diagram:

Electrical power system can be divided into following regions : • Generating stations

• Transmission systems • Receiving station • Distribution system • Load points

Generating stations:

In all these regions, there are switchgears. Bus bars are connecting bars to which a number of local feeders are connected. Bus bars operate at constant voltage. Besides the bus bars, there are other equipment in the electrical schemes such as circuit breakers, CTs, PTs, etc. These equipments can be installed according to various schemes depending upon requirements.

Equipment in electrical scheme of Transmission system;

The power transformers are installed between two bus bars of different voltage levels. A power transformer is the costliest, heaviest, and most important equipment in substation.

Typical station is distribution system.

In 11 kV distribution system, the cost of elaborate protection may not be justified for protection transformer upto about 500 kVA. The substations are generally unattended. The H.V fuses is the only protection provided on H.V. side.

Receiving system & load points for a medium size industrial work:

The switch gear is installed in the substation of local points, such as industrial works, railway substation, cinema house, large building, foundries etc. The substation has following items:

- Incoming line section - Transformer section

(ii) Wave energy:

The periodic rise and fall of water level of the sea can be used to convert wave energy into electrical energy by moving turbine blades from fall and rise of water waves. In about 24 hrs, there are two high & two low waves/ tides. The rise and fall of wave follow sinusoidal curve.

The world first wave/dual power plant was commissioned at ‘Range’ in France. This plant is of 240 mW capacity. There are three main components of a wave energy power plant as follows:

- The dyke to form basic or basin

- Sluice ways from the basin to sea and vice-versa - Power house

The turbines, electric generators and other auxiliary equipments are the main equipments of power house.

Advantage

- Tidal/wave power has a unique capacity to meet peak power demand effectively when it works in combination with hydropower plant or thermal power

Disadvantage:

- Power transmission cost is high because the tidal/wave power plant are located away from load centre.

(iii) Ocean Thermal energy :

The conversion of solar energy stored as heat in the ocean into electrical energy by making use of the temperature difference between warm surface water and the colder deep water. The operation of OTEC (ocean Thermal energy conversion) plants is based on a well-established physical (Thermo- dynamics) principle. If a heat some is available at a higher temperature and a heat sink at a lower temperature, it is possible in principle to utilize the temperature difference in a machine or prime moves (Turbine) that can convert the part of the heat taken up from sources into mechanical energy and hence into electrical energy.

The solar energy absorption by the water takes place according to Lambert’s law of absorption, which state that each layer of equal thickness absorbs the some fraction of light that passes through it

-dI(x) / dx = kI or I(x) = I0e-kx

Where Io and I(x) are the intensities of radiation at the surface (x=O) and at the distance ‘x’ below the surface, k= extinction coefficient

Requirements:

- Coastal zone land must be available.

- Sea floor must be descended sufficiently rapidly from the shore based plant location. Q.61 What are the factors which are involved in circuit breaker rating. (8)

Ans: Factors involved in circuit breaker rating

The following rated quantities for HV ac circuit breeders

Opening time: interval of time between energizing the shunt trip coil and instant of separation of arcing contact in all poles

Breaking time: it is time between energizing of opening release and the instant of final arc extinction.

Closing time: The time interval between energizing of closing circuit and contact touch with all poles.

Open close time: it is time between separation of arcing contacts all the poles and contact touch in first pole deriving open close operation.

Reclosing time: Time between energizing of shunt trip release and contact toad in all poles.

Close-open time: Time between contact touch in first pole and separation of arcing contact in all poles during close open operation.

The rated characteristics of circuit breaker include rated normal current, rated voltage, rated insulation level, rated transient recovery voltage, rated short circuit breaking current, rated short circuit making current, rated operation sequence etc.

Q.62 Give a list of the factors involved for selecting a factory drive. (8)