Definition
Home » Blog » Definition » Variable speed drive Power Factor

Variable speed drive Power Factor

Power factor is a measurement of reactive power. Reactive power is the VA used to establish the magnetic field in a motor. For permanent magnet motor, most time you see pf being unity, which means all VAs are used to generate torque (minus the loss, of course). Under the condition of field weakening operation though, you will see the PM motor gets less than unity pf because some VAs are used to counter the perm magnet field. In induction motor, the pf indicates the portion of VAs used to generate the field comparing to the VAs that generate torque (and loss), which is related to the v/hz in scalar controller or Id in vector control. So under light load condition, you can improve the pf of an induction motor by lowering the field a bit.

The motor power factor does not make a big difference other than giving an idea of loading. In regards to the variable speed drive fixing power factor everyone is mostly correct. A variable speed drive will always show a DPF (Displacement Power Factor) near unity. DPF is what a utility company traditionally monitors and is the measure of lag looking at current and voltage of power at 60hz or fundamental only. The true power factor on a VFD will change with loading etc and includes current and voltage inclusive of harmonics.

Variable speed drive makes assumptions about the motor, and these assumptions affect the relationship the drive controls between voltage applied, frequency and current. For example, a simple volts/Hz drive assumes a motor requires a certain voltage at a certain frequency. In a synchronous or PM motor this parameter can change the PF from lagging (normal) to leading. In an induction motor there is an optimal relationship for a given load. By looking at PF you can adjust the drive parameter to improve the operating PF of the motor. Those who tell you this is set at the factory are quite wrong. The optimum value is established at motor manufacturer, but there are an infinite number of sub-optimal values.

You may also like:

Explaining some premature motor winding failures (multiple manufacturers) on VFD (multiple manufacturers) driven motors in high elevations. Some motors are VPI, all are inverter rated. Voltage varies from ...
Due to current decrement in the Generator during fault conditions the Back-up protection with IDMT relay for a generator in the Electrical protection Scheme becomes complicated. Accordingly, the setting of the ...
If a guarantee is involved with stiff liquidated damages, then lots of testing and certification on each serial numbered unit is likely to be necessary. (not to mention the cost of law suits....). Like the ...
1. Slip energy recovery with the current motor but with dual inverter on rotor side, which may not be too expensive as it is lower power on rotor side and no change in motor. 2. Slip ring motor with shorted ...
Converting a synchronous motor to an induction motor is easily done, to most motors, by shorting the rings, however, you would most likely need to use a properly sized VFD to get the starting torque you need. ...
service VSD blog: A deep observation of automation control industry, especially in AC motor variable speed drive for industrial motor controls.

Hot Tags

Featured

7 months back I was involved in a harmonics evaluation study at Budweiser. This was one of many I've participated in over the past 20 years, basically because in facilities like ... Most of variable speed drives are applying on high temperature fans, kiln head coal mill fans, kiln head surplus fans, raw mill circulating fans and so on. Two production lines ... Variable speed drive application in purification system optimizes the system performance, improves purification effect, reduces power consumption greatly. According to related ... The motor power factor does not make a big difference other than giving an idea of loading. In regards to the variable speed drive fixing power factor everyone is mostly correct. ... A soft starter is a basic device which will ramp up the speed of your motor to full speed over a preset time, easing mechanical stress and also easing the high inrush currents ...

What's New