Westinghouse Modules 1C-,5X- Emerson VE-,KJ-
Honeywell TC-,TK- Fanuc motor A0-
Rosemount transmitter 3051- Yokogawa transmitter EJA-
When the three-phase voltage system is applied to an induction
motor, the phase currents are phase-shifted from the phase voltages
in the lagging direction by the power factor angle, φ, which
appears to be close to a value of 30º for the classes of 2-hp and
5- hp motors studied in this thesis, as shown by the phasor diagram
in Fig. 2.6, where V ab , V bc , and V ca are the line-to-line
voltages and V a , Vb , and V c are the phase voltages.
The speed of the magnetic rotating field is the synchronous speed.
For a induction motor with P poles, the synchronous speed is given
in r/min as (2.9).
where, nasyn is the asynchronous speed in r/min, and ns is the slip
speed in r/min. Moreover, the slip speed can also be defined in a
per unit system as the slip, spu, as given in (2.11).
As aforementioned, the synchronous speed of an induction motor
connected to a constant frequency sinusoidal ac power supply
depends on the frequency and number of poles. The number of poles
is an inherent characteristic of an induction motor, which can be
typically two, four, six, or eight, etc. On the other hand, the
asynchronous rotor speed depends not only on the frequency and
number of poles, but also depends of the load torque. Thus, higher
torque results in a higher slip and a slower asynchronous rotor
speed. Accordingly, an induction motor connected to a constant
frequency sinusoidal power supply runs only at one asynchronous
speed and thus provides no means of speed variation/control. In
this case, an induction motor can be run only at a constant speed,
and thus be used in fixed speed applications, such as pumps with
constant flow, fans, air compressors, conveyor belts with constant
speed, mixers, and drills.
