Question

Answer the following:

1. Name four ways by which electricity is used for heating with brief explanation of the heating mechanism in each case.

2. Explain briefly:

a. The means of thyristor conduction.

b. How it is used to control the speed of a dc motor?

3. What is distributed generation?

4. List any four advantages of distributed generation?

5. Distinguish between (a) uninterrupted, (b) emergency and (c) standby power and list one example each of load situation they would be employed in.

Answer 1

1) Electric Heating is a process in which Electrical energy is converted to Heat energy.

4 ways electricity is used for heating include:

a) DOMESTIC ELECTRICAL UNDERFLOOR HEATING: An electric underfloor heating system has heating cables embedded in the floor. Current flows through the conductive heating material. The heated cables warm the flooring by direct conduction and will switch off once it reaches the temperature set by the floor thermostat.

b) HEAT PUMP: A heat pump uses an electrically driven compressor to operate a refrigeration cycle. It extracts heat energy from outdoor air and moves that heat to the space to be warmed.

c) IMMERSION HEATER: It is a water heater used for domestic or industrial purposes. An immersion heater has an electrical resistance heating element encased in a tube and directly placed in the water to be heated.

d) CONVECTION HEATERS: Here, the heating element heats the air in contact with it by Thermal conduction i.e,the microscopic collisions of particles and movement of electrons within the body. Hot air being less dense than cool air  rises due to buoyancy. This sets up a convection current of hot air that rises from the heater and heats up the surrounding space.

2) a) A Thyristor is a semi-conductor device with 4 layers of alternating p- and n- type materials.

There are 2 designs and their respective means of conduction is given below:

In a three-lead Thyristor, conducting begins when the gate receives a current trigger. The small current on its Gate lead controls the larger current of the Anode to Cathode path.

In a two-lead Thyristor, the conduction begins when the potential difference between the Anode and Cathode is sufficiently large (breakdown voltage).

b) Controlling the speed of a motor means accelerating the motor, running the motor at desired speed under varying load torque conditions, decelerating or braking the motor to reduce the speed.

A 3 phase fully controlled thyristor bridge working as rectifier can produce varying DC voltages by phase angle control of the thyristors. If we add an additional bridge in parallel (anti-parallel configuration), the second bridge can act as an inverter, also by phase angle control , can feed energy from DC armature voltage back to the supply AC system, thereby braking the motor.

Thus , by using required type and number of thyristor bridges and suitable digital or analog controllers, it is possible to control the speed of a DC motor to meet practically all types of load or process requirements.

3) Distributed generation refers to a variety of technologies that generate electricity at or near where it will be used, such as solar panels. They typically use renewable energy sources such as hydro, biomass, biogas, solar power, wind power etc.

4) The advantages of Distributed generation includes:

a) It can be used to generate electricity at homes and businesses using renewable energy resources such as solar and wind.

b) It harnesses energy that might otherwise be wasted.

c) It reduces or eliminates the “line loss” (wasted energy) that happens during transmission and distribution in the electricity delivery system.

d) Distributed Generation systems are decentralized, modular, and more flexible technologies.

5) a) Uninterrupted Power refers to the power delivered to a load when the input power source or mains power fails.

Load : Computers, Data centers etc.

b) Emergency Power refers to the power used or taken by a public authority to meet the exigencies of a particular emergency (as of war or disaster).

Load: Hospitals, Scientific Laboratories, Power plants etc.

c) Stand-by Power refers to the electric power consumed by electronic and electrical appliances while they are switched off or in standby mode.

Load : Remote Controls, Mobile phones etc.