VFDs can be used not only to slow down a motor, but also to drive it beyond its rated speed (overspeed) by increasing the VFD output frequency above 60 Hz. Some HVAC equipment manufacturers overspeed a motor to allow for fan and motor combinations that really shouldn’t have been allowed in the first place.
How slow can you run a motor on a VFD?
Generally speaking, TEFC motors are not designed to operate at less than a 4:1 speed range, while some manufacturers make a 10:1 or 20:1 range motor. Most often, operating the motor slower than this requires an auxiliary cooling system. This threshold can be higher depending on the torque the motor is providing.
Can an electric motor overspeed?
Average 2 pole industrial motors can safely exceed its base speed by 25%. Many manufacturers balance their 2 pole and 4 pole rotors to the same speed – 25% over the 2 pole base speed. A 2 pole motor may therefore operate up to 125% over base speed before reaching its balance limit.
How much can you overspeed a motor with a VFD?
Motors generally have to withstand 10 % overspeed. But it in no way means many motors cannot withstand much higher over speeds.
Do you need a special motor for a VFD?
Output voltages are available for VFDs to match almost any existing motor voltage. However, very few, if any, VFDs have a direct 13,800-volt output for very high-voltage motors. For these cases, using a step-up transformer on the output of the VFD is often necessary to match the motor voltage.
What is a VFD rated motor?
VFDs vary the speed of the pump to optimize system control, usually by lowering the speed below the baseline frequency. … As a result, define the pump operating speed range to ensure the motor is not overloaded at increased speed and the motor is able to withstand decreased cooling at lower speeds.
What is the danger of running a VFD drive too slow on a motor?
An inverter duty motor can deal with the higher voltage spikes produced by VFDs also can run at very slow speeds without overheating. The general purpose motor don´t, it can overheat if it is running too slowly, so bearings and insulation will be damaged.
How do you know if a motor is inverter duty?
Motor insulation systems that are rated for inverter use will be specified on the motor nameplate (or a sticker). These systems should have wire rated for a minimum of 1600 volt spikes, F or H class insulation, and will be processed with 100% sold resin in a vacuum pressure impregnation (VPI) system.
What happens if you overspeed a motor?
Operating motors at an overspeed frequency they are not capable of sustaining can result in a shortened life expectancy, or even motor break up. Among the motor features that must be considered when running at overspeed: • Motor rating: o Many general duty motors are not rated to handle overspeed operation.
What is the maximum rpm of an electric motor?
In this case, unless external limitations are applied, the maximum torque is achieved at low RPM. For example, the AC motor found in the Tesla Roadster (2008) produces near constant maximum torque from 0 to about 6000 RPM, while maximum power occurs at about 10000 RPM, long after torque begins to drop off.
Can you run a motor above 60Hz?
Traditionally, maximum motor speed has been 60Hz for motors controlled by VFDs. Sometimes, it is necessary to have a higher upper frequency limit. Danfoss VFDs can run at output frequencies higher than 60Hz.