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MUQADSA IFTIKHAR (09ABELT0290)
ZUNAIB ALI (09ABELT0296)
ENGR. SANIA SAEED
• The purpose of a motor speed control is to take a
signal representing the demanded speed and drive the
motor at that speed.
The speed of dc motor is directly proportional to the supply
voltage, if we reduce the supply voltage from 12V to 6V, the
motor will run at half the speed.
SCR “phase-angle controlled” drive -By changing the firing
angle, variable DC output voltage can be obtained.
Here we are using microcontroller applications. For this we
are using TAP changing and by using this we are setting the
speed of motor.
1. 220 V , 50Hz AC Supply
2. Tap changing Step Down Transformer
3. DC motor
4. Thyristor (SCR)
5. NPN Transistor
6. 5V DC Supply
A tap changer is a device fitted to power
transformers for regulation of the output
voltage to required levels. This is
normally achieved by changing the ratios
of the transformers on the system by
altering the number of turns in one
winding of the appropriate transformer/s.
Tap changers offer variable control to
keep the supply voltage within the limits.
The 2 ½% step can be used on
transformers with automatic tap
Voltage regulation is normally achieved by changing
the ratios of the transformers on the system by altering
the number of turns in one winding of the appropriate
transformer/s. Tap changers offer variable control to
keep the supply voltage within these limits. Tap
changers can be on load or off load. On load tap
changers generally consist of a diverter switch and a
selector switch operating as a unit to effect transfer
current from one voltage tap to the next. Tap changers
can be adjusted to fit the application needs.
To supply a desired voltage to the load.
To counter the voltage drops due to loads.
To counter the input supply voltage changes on load.
Additionally required to perform the task of regulation of
active and reactive power flows.
Some form of impedance is present to
prevent short circuiting of the tapped
A duplicate circuit is provided so that
load current can be carried by one circuit
whilst switching is being carried out on the
Tap point is placed
In star connected winding, near the star point.
In delta connected winding, at the center of the winding.
In autotransformer, between the series and common windings
No-Load Tap Changer (NLTC or
On Load Tap Changer (OLTC
Mechanical tap changers
Thyristor-assisted tap changers
Solid state (thyristor) tap
The DC motor is electric motor that runs on direct current electrically.
DC motor works based on the LORENTZ FORCE.
In DC motor voltage is proportional to speed
Low initial cost
Simple control of motor speed
Reduction of power losses
Voltage profile enhancement
Less heat produce
DC OPERATED DRILL MACHINES.
MOBILE AIR CONDITION FANS.
ELCTRONIC DOOR CONTROLLERS.
ELECTRONIC CHAIRS (beauty parlor etc.)
We have achieved the required speed and thyristor is
a very good device for obtaining the variable DC there
by controlling the motor speed.
This circuit is just a basic circuit for understanding DC
motor speed control. In case of HWR we got zero
voltage in negative half cycle that’s why has power