Fan is a device having revolving blades for propelling air. It is run by an electric single phase induction motor.
Components of a Fan
1. Electric motor-stator and rotor-capacitor start and run rated at 230V, 50Hz.
2. Blade- usually made of aluminium sheet, 120 degree normally 3-4 blades.
3. Blade flanges and body cover.
4. Ball bearings.
5. Regulator.
6. Suspension rod.
7. Terminal box.
Circuit diagram of ceiling fan and regulator connection.
Electric fan motor works on the principle of electromagnetic induction and rotating magnetic field. There are two parts in this motor: one is a stator and other is rotor. The stator coil is given single phase AC voltage which produces sinusoidal flux that links with router coil. An emf is induced in the router. According to Lenz's law, the rotor coil current opposes the current that has produced it. Due to this the rotor rotates in similar direction as that of the sinusoidal field. The blades of the fan attached to the rotor axle also rotates and we get flow of cool air.
Working
The essential part of a fan is a single phase induction motor. Stator is a stationary part of induction motor. Stator consists of the running winding and starting winding. The starting winding along with a capacitor in series in connected parallel to the running winding. The main winding and start winding offers inductive reactance and the start winding offers capacitive reactance to the current flow. The currents in each winding are 90 degree out of phase. So the magnetic fields that are generated by them are 90 degree out of phase. The effect is that the two windings act like a two-phase stator and produce the rotating magnetic field when AC current flows through them.
The rotating flux links with the rotor conductors and an emf is induced in the rotor coil. The rotor current starts flowing in the rotor conductor. This current produces its own flux. Now the main flux and the rotor flux produce the desired torque, which is required by the rotor to rotate. When the full speed in obtained a centrifugal device opens the start winding. The motor then runs as a single phase induction motor.
Fan Regulators
Fan regulators regulate the speed of rotation of the fan by controlling the supply voltage. Fan regulators provide a convenient environment for the residents. Fan regulators are of four types:
(a) Resistive regulator
(b) Phase angle controlled regulator
(c) Inductive regulator
(d) Capacitive regulator
(a) Resistive regulator
It works by providing different taps on a wire wound resistor, connected in series with the fan. When we rotate the knob, different amount resistance gets inserted into the circuit. It is cost effective. But there is considerable power loss as heat, through resistance at low speeds. It is also balky. It consumes very high energy, when operating at low speed.
(b) Phase angle controlled regulator
The type of regulators employ active devices such as DIAC and TRIAC. The basic principle is to change the firing angle of the TRIAC in order to change the voltage across the fan. It is a continuous speed control, low power consumption regulator. But the speed control is not linear and it is expensive. It produces a disturbing humming sound.
(c) Inductive type fan regulator
An inductive type fan regulator has a tapping on the winding of the transformer and the inductive resistance is varied to achieve variation in speed. Speed decreases with increase in the number of turns of the inductance coil winding. It is a 2 pole 5 way switch. It has low heat power dissipation. But the power factor is low. It is heavy, bulky and costly.
(d) Capacitive type fan regulator
The voltage across the capacitor, Vc=Q/C
Where Q is the charge on the capacitor and C is the capacitance. As C increases Vc decreases. Thus, the voltage across the fan increases when connected in series with a capacitor in an a.c. circuit. So the speed of the fan can be increased. Thus by employing suitable combinations of capacitors, the fan speed can be regulated.
The advantages of this type of regulator are: energy efficient, no humming sound during operations, speed linear reliability as compared to electronic type regulator.
Types of Fans
1. Ceiling Fans
2. Table Fans-oscillating type
3. Industrial Fans-Pedestal fans for halls
4. Air blower Fan-hair drier, transformer cooling
5. Exhaust Fans- used in labs and book rooms
6. Duct Fans- propeller type, mounted with in a cylindrical duct. Ducted fan propulsion is used in aircraft.
Power consumption by electric fan
A typical 48 inch ceiling fan will use 75 watts.
Regulators can make the fans slower or faster. The overall power consumed will be lower at lower speed, but we do not save as much power as we expect. The power not used by the fan is dissipated in the form of heat in the regulator. Electronic regulators do not get heated up and thus save electricity when the fan is running at lower speeds. These regulators save up to 40% at speed 1 and about 30% at speed 2 compared to electric regulators.
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