AC Drives

The torque speed curves are completely different between an induction motor and slip ring motor. You need to understand the differences. If you have selected your slip ring motor to limit starting currents you can short out the slip rings and run your motor but the starting torque is reduced unless you use some features on the VFD to boost starting torque.

If you are using it as torque control on a crane then y ...

Variable frequency drive (VFD) will capable of varying the output speed of a motor without the need for mechanical pulleys, thus reducing the number of mechanical components and overall maintenance. But the biggest advantage that a VFD has is the ability to save the user money through its inherit nature to save energy by consuming only the power that's needed.

A VFD will convert its incoming power, fixed voltage and frequency to variable volta ...

Capacitors inside the variable frequency drive (VFD) is mainly used to maintain the DC voltage, this is common thing all are well known about this, but power factor is mainly improved due to the cosine angle between voltage and current are mostly near to each other, however the inductive load produces the reactive power which will directly affect the wave form of input of VFD sine wave when we used additional filter cap ...

VFD derating is a manufacturer requirement when equipment ambient temperature is above 40 C degrees OR when equipment site is above 3000 feet in altitude. It is clear for manufacturers and engineers to avoid temperature derating by having the VFD's ambient temperature not to exceed 40 C degrees. On the other hand, VFD's manufacturers claim on altitude derating is due to thinner air at higher altitude that compromises the heat dissipation from the electronics. Although, it is a real claim, man ...

In general, if you are using variable frequency drives (VFD) where the control mode can be programmed (as most of the modern VFDs), each VFD has its own control philosophy and some parameters to adjust how efficient they follow the specified control mode: Speed control mode (as follower to a speed command); or Torque control mode follower (as follower of a torque command). Basically the parameters to adjust in the VFDs are related to gains in their internal control loops.

I worked ...

The beauty of variable frequency drive (VFD) is that the maintenance is negligible if are well maintained.
Yearly maintenance:
Tighten all nuts and bolts, all terminal blocks, cable/wire connections.
Remove dust everywhere (vacuum cleaner is good). Do not try any kind of solvent.
Check all power supply for correct voltage level.
Replace / clean filters.
GoHz maintenance plan do specify which component to change and when (for example blowers every ...

Situation: Here is my current problem and was wondering if anyone had experience of the following:
Application - 260Kw submersible motors/pumps must be running up to full speed within 5-6 seconds of startup.

My proposal had always been to use a soft start until the pump manufacturer has stated that in order to provide sufficient cooling to the stator windings (using the sea water), it must be at full speed in 5-6 seconds.

I have been in touch with ...

If we define nominal torque, it's generated at the motors peak efficiency point, that being at the apex of rated voltage and Hz. The lower the RPM, the higher the nominal torque, but the higher the current. Then, nominal torque is basically what the motor can generate continuously at the peak efficiency point without overheating. To define using nominal torque at zero speed is better defined as stall torque, and not really applied in high torque startin ...

First make sure the cause of the noise is not mechanical in nature (bearings, misalignment, worn bearings, lose hardware, lubrication, etc., etc.). If the cause is identified as being electrical in nature you can check some of these.

Is the motor rated for VFD service? Although you may be able to use a regular 3 phase AC motor with some VFD's, a regular 3 phase motor is not design to work with VFD's and thus will operate with higher electrical losses than a motor which is rated for ...

All variable frequency drives using power electronics are essentially "frequency choppers". Either the VFD is a current-sourced inverter topology, or a voltage-sourced inverter topology. To obtain the desired output (usually defined as voltage at some specific frequency), the incoming signal gets "chopped" and rectified to produce a DC pulse, which is then inverted back produce a "sample" of a fraction of a sinusoidal waveform.

The sample can v ...

Asynchronous motors are capable of developing significantly higher starting torque than synchronous motors. It has everything to do with the slip. Two pole motors are also an issue at start, due to a significantly lower starting torque capability than 4 or more pole motors.

An encoder of some type is typically used for hoisting applications when the hoist has no mechanical load brake in the gear case. Generally, when we build flux vector hoist controls, we employ 1024 PPR, 24 VDC, ...

An LCI drive is an old and different topology to a VSI AFE drive. The LCI drive has a long history and its advantages and limitations are well understood. It is simple and reliable, but requires careful attention to ac power system issues related to harmonic currents and reactive power. It also demands specially designed motors with low reactance, and must work with harmonic heating and air gap torque harmonics.

LCI drives have low input power factor, 0.5-0.92, especially at lower ...

What the system sees with a "standard" squirrel cage induction motor connected directly to the line is the inductive loading caused by the nature of the magnetic circuits within the machine design. This can result in a reactive power demand that is anywhere from 10 to 30 percent of the real power rating of the machine (e.g. power factor lies between 0.900 and 0.700). It also gets worse (i.e. farther from unity power factor) as the machine ...

Most of the variable frequency drives (VFD) below 600 HP or so are IGBT with Diodes to supply the DC. If only six pulse the harmonics can become a concern if a number of VFDs are used on the same bus. One of the jobs I'm currently trouble shooting has 6x600 HP VFDs all connected to the same power source. This means that my harmonics are added together as there are no filters or phase shifting transformers. I expect the power factor at full load to be arou ...

Most DC drives do not have capacitors to generate reactive current, they draw current from the AC lines only. When the motor is moving slowly with high torque, the drive has to produce full current even though little work is being done. This current has to come directly from the line side. So, even though there is no power factor on the DC side (just high current and low voltage), a demand for reactive power is created on the l ...

Q:
I'm looking for ways to estimate the supply current to variable frequency drive (VFD) when an asynchronous motor is running under different torque and speed outputs.

Motor manufacturers usually provide the rated torque, rated current and rated speed of the motor, but when the motor is not running at the rated conditions, how can one estimate the supply current to the VFD from the actual speed and torque output of the motor?

A: ...

Case:
I am used a 20hp VFD in Hoist application (415v three phase). In this application there is a problem that in the time of starting main motor Drum is Roll back first. So to avoid this Roll back problem it is any possibly to increase the output torque of the VFD by changing the Rotor resistance of motor in VFD motor parameter group. What happen if I increased or decreased rotor resistance in VFD motor parameter group?
...

To answer your first question, regenerative braking in variable frequency drives (VFD), the premise is that whenever a motor is rotating faster than the winding are excited the motor becomes a generator. Regenerative braking means the voltage produced is "placed somewhere else". Often the excess voltage can be absorbed by the IGBTs or the addition of a braking resistor...maybe even placed back on the AC power network. In ...

I have an interesting (yet frustrating) project I am trying to get to function accurately. My customer is a machine tool shop that refurbishes well casing for oil and water drilling. We installed a VFD driven system to move the pipes from area to area. The reason for the VFD is for the high torque start and stop and also the fact that not all the pipes are the same size and weight. The problem I am trying to overcome is when they are driven into the CNC lathes that clean up the threads on the ...

All electrical machines have some amount of dis-symmetry to them, just because they are constructed of individual parts. Sometimes this is in the steel portions (segmental laminations, or unequal airgaps, etc) and sometimes in the winding (unequal resistance paths, different connections and/or lead lengths, lead routing, etc).

As soon as there is a difference in the magnetic path (or the magnetic strength), some amount of voltage will be induced on the motor shaft. The purpose of a ...