Wk2 (MOMENT OF INERTIA)
The moment of inertia is expressed as Wk2or WR2in terms of pound-feet squared. It is the product of 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 motor, it is necessary to calculate the inertia “reflected to the motor shaft,” that is, an equivalent Wk2(reflected to motor shaft) = Wk2 based on the rpm of the motor.
Wk2(reflected to motor shaft) = Wk2(driven equipment) x
|(driven equipment 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 and having its ventilating openings so constructed as to prevent the passage of a cylindrical rod 3/4 inch in diameter.
Type II (WPII) shall have, in addition to the enclosure defined for a Type 1 weather-protected machine, its ventilating passages at both intake and discharge so arranged that high-velocity air and airborne particles are blown into the machine by storms or high winds can be discharged 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 shall be so arranged by baffling or separate housing as to provide at least three abrupt changes in direction, none of which shall be less than 90ƒ. In addition, an area of low velocity not 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.
WOUND ROTOR INDUCTION MOTOR
A wound rotor induction motor is an induction motor in which the secondary circuit consists of polyphase winding or coils whose terminals are either short-circuited or closed through suitable circuits. A wound rotor motor is sometimes used when a high breakdown torque and a soft start or variable speed are required.
A method of starting a motor at rated voltage but drawing locked rotor current and producing reduced stocked rotor torque but it provides 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.