Greetings,
The purpose of this blogpost is saving the basic motor knowledge on here. So in such case when I stuck something or try to refresh my mind, I can look at here, and find what I look for easily.
The info is gathered together from several websites and books.
ELECTROMECHANICAL ENERGY CONVERSION II LAB NOTES
Inverters: These are the devices that converts a DC supply to AC
supply. They can be used in transformers to reach a specified voltage. An
inverter is a complex and expensive circuit compared to a rectifier, which
typically has only a few simple parts.
Rectifiers: It’s the opposite device of
the inverters. These are the devices that converts a AC supply to DC supply.
Can be used in transformers to reach a certain voltage. There is usually a
lower voltage. Radios, television receivers and power tools commonly contain
rectifiers.
The Differences Between Synchronous Motors and Asynchronous(Induction)
Motors
Synchronous Motors: Stator poles rotate at the synchronous speed
(Ns) when fed with a three phase supply. The rotor is fed with a DC supply. It
needs to be rotated at a speed near to the synchronous speed during starting.
If done so, the rotor poles get magnetically coupled with the rotating stator
poles, and thus the rotor starts rotating at the synchronous speed.
· Synchronous motor always runs at a speed equal
to its synchronous speed.
i.e. Actual speed
= Synchronous speed, or N = Ns = 120 f/P
Asynchronous(Induction) Motors: When the stator is fed with two or
three phase AC supply, a rotating magnetic field (RMF) is produced. The
relative speed between stator’s rotating magnetic field and the rotor will
cause an induced current in the rotor conductors. The rotor current gives rise
to the rotor flux. According to the Lenz’s Law, the direction of this induced
current is such that it will tend to oppose the cause of its production, i.e
relative speed between stator’s RMF and the rotor. Thus, the rotor will try to
catch up with the RMF and reduce the relative speed.
· Induction motor always runs at a speed which is
less than the synchronous speed.
i.e. N < Ns
True Power: Power dissipated by a load is referred to as true power. True
power is symbolized by the letter P and is measured in the unit of Watts (W).
Reactive Power: Power merely absorbed and returned in load due to its reactive properties
is referred to as reactive power. Reactive power is symbolized by
the letter Q and is measured in the unit of Volt-Amps-Reactive (VAR).
Apparent Power: Total power in an AC circuit, both dissipated and absorbed/returned is
referred to as apparent power. Apparent power is symbolized by the
letter S and is measured in the unit of Volt-Amps (VA).
These three types
of power are trigonometrically related to one another. In a right triangle,
P = adjacent length,
Q = opposite length, and S = hypotenuse length. The opposite angle is equal to
the circuit’s impedance (Z) phase angle.
Source: electricaleasy.com
