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 KVA | H.T.Voltage rating, KV | Size of T.C fuse wire S.W.G | Horn gap length in inches |
| 3000 | 66 | 21 | 20 |
| 2500 | 66 | 21 | 20 |
| 2000 | 66 | 21 | 20 |
| 1750 | ” | 22 | 20 |
| 1500 | ” | 22 | 20 |
| 1250 | ” | 23 | 20 |
| 1000 | ” | 26 | 20 |
| 750 | ” | 28 | 20 |
| 500 | 22 | 32 | 20 |
| 250 | 22 | 23 | 10 |
| 500 | 11 | 20 | 8 |
| 250 | 11 | 23 | 8 |
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 |
Motors:
0.25 HP ———> 300 to 400
0.50 HP———-> 450 to 600 value
Over 0.50 HP—-> 950 to 1100
APPROXIMATE POWER CONSUMPTION OF ELECTRICAL APPARATUS:
Kettles:
1 pint 280W
1pint 325 to 425W
2pints 450 to 650W
3pints 750 to 1000W
4-8 pints 1000 to 1500W
Iron:
| 3lb | 250W |
| 4lb | 275 to 300W |
| 5 lb | 350 to 450W |
| 6 lb | 450 to 500W |
| 7 lb | 500 to 650W |
| 12 lb | 600 to 700W |
| 20 lb | 750 to 850W |
Grinding:
6’X3/4″wheel 750W
8’X3/4″wheel 1250W
10’X3/4″wheel 2300W
Hair Drier: 550W
Toaster:
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
Ovens
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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