Electrical Transformers | Switchgear Protective Device | Power Consumption of Appliances and Electrical Apparatus

Electrical transformers changed the way of handling the voltage of electrical power lines. At every street end, we see electrical transformers used for providing a consistent voltage supply.  It is an engineering marvel that shaped the electrical distribution network.

It is an electromagnetic machine, that converts A.C electrical energy from a higher voltage to a lower voltage and vice versa or even equal voltage with the corresponding increase or decrease in the current without any change in frequency.

Working Principle:

Metal usually iron made into a C shape structure, each sheet is laminated to each other forming the square block called the core.  Copper wire is coiled to one of the sides of the core and similarly to its opposite side. The power supply is provided to one of the coiling ends (primary) and to the other (secondary) load is connected.

The voltage supplied to the winded primary coil due to this an alternating flux is generated in the metal core. If N1 and N2 are the numbers of individual windings of the primary and secondary coil respectively. E1 and E2 are the e.m.f of each coil then

E2/E1 =N2/N1

When the secondary is the open circuit, its terminal voltage is the same as induced e.m.f. The primary current is then very small, so that the applied voltage V1, is equal and opposite to the e.m.f induced in the primary coil.

V2/V1 = N2/N1 = K

where K is known as the transformation ratio.
(1) if K> 1, the transformer is known as the step-up transformer.
(2) if K< 1, the transformer is known as the step-down transformer.

The size of fuse wires to be used on the HV side of various sizes of transformers.

The capacity of transformers KVAH.T.Voltage rating, KVSize of T.C fuse wire S.W.GHorn gap length in inches

Note: Above values are approximate and may change as per the region and manufacturer.

Switchgear Protective Device

Switchgear is designed for controlling the electricity supply for domestic and industrial applications with safety actions like tripping over short circuits of electrical devices. Initial models of switchgear are the open type and manually operatable. Simple on and off is done by pulling the lever of the socket linked to the scale-type connector. However, this type of operation is not sufficient for handling high-voltage power transmissions in process industries. New models developed in present days operate automatically and have long-life operation capability to provide safe shutdown of equipment.

Some of the most used switchgear protective devices:

  • Fuse 
  • Switch 
  • Isolator
  • Vacuum 
  • Circuit breaker 
  • Sulphur Hexafluoride (SF6) switchgear 
  • Oil model
  • Air type

Power Consumption of Appliances and Electrical Apparatus

Appliance    Consumption in Watts

Incandescent lamps

   10 upwards
Fluorescent lamps   45 to 60
Clock   2 to 3
Radio   40 to 150
Television   200 to 400
Electric Blanket   150 to 200
Electric razor   8 to 12
Heater   1000 to 3000
Table Fan   30 to 60
Ceiling Fan   60to 100
Air-conditioner room   800 to 1500
Sewing machine   60 to 90
Geyser   3000 to 5000
Refrigerator  150 to 300
Iron (steam or dry)  660 to 1100
Hot plate per burner  660 to 1100
Coffee percolator  500 to 1000
Washing machine  350 to 550

0.25 HP ———> 300 to 400
0.50 HP———-> 450 to 600 value
Over 0.50 HP—-> 950 to 1100

1 pint      280W
1pint       325 to 425W
2pints     450 to 650W
3pints     750 to 1000W
4-8 pints 1000 to 1500W


3lb      250W
4lb275 to 300W 
5 lb350 to 450W
6 lb450 to 500W
7 lb500 to 650W
12 lb600 to 700W
20 lb750 to 850W

6’X3/4″wheel    750W

8’X3/4″wheel    1250W
10’X3/4″wheel    2300W

Hair Drier: 550W

1slice     55W to 550W
3 slice    1750W
5 slice     2500 w

Soldering irons
0.5         60W
1 lb        120W
1.5lb      200W
2 lb        275W
3lb         450W

Immersion Heaters
6″ long    200 to 500W
8″ long    500 to 750W
10″long    800 to 1000W
16″long    1450 to 2000W

14 X 14 X 12 “inside      1500W

12 X 12 X 16 “inside      1750W
14 X 14 X 16 “inside      2000W

Vacuum Cleaner
Domestic       200W
High power    300 to 600W

Formula for time required to boil in minutes = Pints/ Watts * 3850(approx)

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