Some specially designed motors meant for use with VFDs are designed to operate at higher than normal speeds at frequencies above 60 hertz.
Increasing frequency above 60 hertz makes the motor run faster than normal and creates two primary concerns:
1. Was the motor or the load it drives designed to operate at these increased speeds?
Many motors and devices were not mechanically balanced to operate at increased speeds and will create vibration, mechanical and safety problems.
2. VFDs are not capable of increasing voltage so as frequency increases above 60 hertz, the torque produced starts to decrease.
In order to maintain a constant horsepower output to drive our load, if speed is increased, torque must decrease.
Bottom line - if you're looking at a steady load torque requirement (4.5 HP at 25 rpm on the output shaft of the gearbox, for example), then a 4 pole 5 HP squirrel cage induction will be your best bet. If the load is varying (either by varying speed or by power requirement), you may find another type and/or size of machine will be better suited to your needs.
It is possible to reduce the speed if a 3 phase motor is used with VFD and ultimately reduce the load but the mechanics and desired mixing may then be affected. The best way to change is either replaces the motor with the correct horsepower/kW, use a different ratio gearbox or change mixing impeller.
Standard Squirrel cage induction motor with VFD is used for infinite speed variation for spindle application. However it must be remembered that Motor can be used from 10% of rated speed onward for better cooling. Motor will deliver constant torque/variable HP up to rated speed and constant HP/variable reducing torque above rated speed. Motor speed above rated speed is limited by bearing design of motor.
That's the reason to minimize the cable's section, because it not, the Earth Fault Current should be enough to trip the protection installed at the head of this circuit, so, the Software will choose the necessary section to have an Earth Fault Current bigger than the setting of "Magnetic Protection or Short-time Protection".
When you use DC Injection Braking, once you initiate the braking, you are usually committed until it stops. Only then would you be able to start back up again. With a VFD and dynamic braking, you always have control over the motor speed and would easily be able to start back up in the middle of a stopping sequence if needed.
An induction motor (sq - cage) driven by VVVF/ VFD system is ideal replacement for slip-ring induction motor. However, the torque requirement / duty cycle of the crusher motor at various stages is important and the VVVF /VFD drive should be able to control the torque / duty cycle exactly through precise programming. Other method may be to retain slip-ring motor and control the slip ring current by employing thyristor (DC) convertor.
The Motor will be either IC 416 or IC 616 or IC 666. In these types of cooling, external fan is not mounted on the motor shaft and totally independent, which is designed to remove the heat / losses from the motor at reduce speed. Normally during low speed motor fan which mounted on motor shaft is not sufficient to remove the complete heat so this external mounted fan removes the heat from the motor.
I am currently producing a surface mount permanent magnet motor for the oil and gas application in Canada. Since China is controlling the NdFeB magnet and the price of the magnet has gone up 5 times since a year ago, I have to look into induction motor to fill my customer's need. Since this motor is VFD driven, the poor power factor will be an issue between the variable frequency drive and the motor that will not affect the line.
If you can design the stator and rotor magnetic paths such that there is no dynamic saturation under normal operating conditions (i.e., if something is saturated, it remains saturated as long as the power is on) and the laminations are skewed, it should be at least as quiet as a SPM. Depending on what type of load you're talking about, the control can be speed-sensorless (very simple for a fan or centrifugal pump/compressor, up to observer-based sensorless field orientation for a piston pump/compressor). IMs are also very robust to high temperatures.
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