A national Grid Network is a network of cable that connects all the power stations in a country to transmit electricity to the consumers throughout the nation.

The advantages of the National Grid Network

1. Reduces power lost during transmission. The potential difference is increased before transmission. This can reduce the current and hence reduces the energy lost during transmission.
2. Electricity supply is more stable and reliable. This ensures a continuous supply of electrical energy to the whole country.
3. Electric current can be distributed to different users according to the voltage requirement. Transformer is used to step down the voltage to certain level according to the needs of the consumers.
4. Maintenance and repair work can be done at anytime. This is because any power stations can be shut down without affecting users in other areas.

 

 

Problems Involving Electricity Transmission.

1. Power Loss During Transmission. 
2. The high voltage transmission cable is very dangerous. 
3. The cost of the cables are high. 
4. Charge leakage may happen between cables and earth. 
5. Pylons may be struck by lightning. 
6. Pylons and cables may be struck by light aircraft.

 

1. The heating effect of current in a coil.

Power is lost as heat I₂R whereby I is the current flowing through the coil and R is the resistance of the coil

Methods to increase the efficiency
Use thick copper wires of low resistance. Use coolant to decrease the temperature of the transformer.

2. Heating effect of induced eddy currents

In the iron core. When the magnetic field in the iron core fluctuates, eddy currents are generated in the iron core.

Methods to increase the efficiency
Use a laminated iron core whereby each layer is insulated with enamel paint to prevent the flow of eddy currents. The high resistance between layers of the iron core decrease the prevalence of eddy currents and heat.

3. Magnetization of the Iron Core.

The energy used in the magnetization and de-magnetization of the iron core each time current changes its direction is known as hysterisis. This energy is lost as heat which subsequently heats up the iron core.

Methods to increase the efficiency
Use a soft iron core that is easily magnetized and de-magnetized.

4. Flux leakage.

Some of the induced magnetic flux from the primary coil is not transmitted to the secondary coil, therefore the e.m.f in the secondary coil is decreased.
The secondary coil(windings) are intertwined tightly with the primary coils. The iron core should form a closed loop.

Methods to increase the efficiency
The secondary coil (windings) is intertwined tightly with the primary coils. The iron core should form a closed loop.

 

Calculation of Current Change

Ideal Transformer

Non-ideal transformer

V_p = input (primary) potential difference
V_s = output (secondary) potential difference
I_p = input (primary) current
I_s = output (secondary) current

 

 

There are 2 types of transformer, namely

1. the step up transformer
2. the step down transformer

Step-up Transformer

1. A step-up transformer is one where the e.m.f. in the secondary coil is greater than the e.m.f. in the primary coil. It is used to increases the potential difference.
2. The number of windings in the secondary winding is greater than the number of windings in the primary coil.
3. The current in the primary coil is greater than the current in the secondary coil.