W
The moment of inertia is expressed as Wk2 in terms of pound-feet squared. It is the product, the weight of the object in pounds and the square of the radius of gyration in feet.
If the application is such that the motor is driving through
a pulley or gear so that the driven equipment is operating at a higher or lower
speed than the rotor, it is necessary to calculate the inertia reflected to
the motor shaft. This is an equivalent
Wk2 (reflected to motor shaft = Wk2 based on the speed
(rpm) of the motor.
Wk2
(reflected to motor shaft) = Wk2 (driven equipment) x (driven
equipment rpm)2
(motor rpm)2
The amount of power required to maintain a current of one ampere
at a pressure of one volt. Most motors
are rated in Kwatt equal to 1,000 watts. One horsepower is equal to 746 watts
TYPE I (WPI)
weather-protected machine is an open machine with its ventilating passages so
constructed as to minimize the entrance of rain, snow and airborne particles
to the electric parts. Its ventilating
openings are constructed to prevent the passage of a cylindrical rod ¾ inch
in diameter.
TYPE II (WPII) have, in addition to the enclosure
defined for a Type I weather-protected machine, its ventilating passages at
both intake and discharge so arranged that high velocity air and airborne particles
blown into the machine by storms or high winds can be discharges without entering
the internal ventilating passages leading directly to the electric parts of
the machine itself. The normal path
of the ventilating air which enters the electric parts of the machines are arranged
by baffling or through a separate housing to provide at least three abrupt changes
in direction, non of which shall be less than 90 degrees.
In addition, an area of low velocity no exceeding 600 feet per minute
shall be provided in the intake air path to minimize the possibility of moisture
or dirt being carried into the electric parts of the machine.
A wound rotor induction motor is an induction motor in which
the secondary circuit consists of polyphase winding or coils with terminals
that are either short circuited or closed through suitable circuits. A wound rotor motor is sometimes used when
high breakdown torque and soft start or variable-speed operation are required.
A method for starting a motor at rated voltage but drawing locked rotor current and producing reduced locked rotor torque to provide lower starting torque than a straight delta connection. Once the load and motor have been started, the wiring will switch from the wye connection to a delta connection in which mode it must run and deliver full torque.