VFDs

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 ...

Over speeding the motor with a variable frequency drive will depend a lot on the existing load on the motor. If it is a fan load and you are currently at 100% of NP rating, you have no head room left to play with. If you have a roll spinning lightly loaded you will have much more head room. In some applications we run 240vac motors on a 480vac VFD and over speed from 60 Hz rated to 90 Hz- and develop 1.5 x the HP at rated torque. If you have a 480vac ...

How can I control through the VFD Torque for a motor as I have a pump motor of 110 KW of rated current 200A controlled by Soft Starter and during the actual operation it consumed only 65 KW with 98A so I want to change this motor with another one lower in KW with VFD to control at the new motor Torque, so how to do that?
If the new motor is large enough to provide the load requirements then reducing the motor size will not affect performance. It is the load that dictates torque required ...

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 ...

Question: How can I control through the VFD Torque for a motor as I have a pump motor of 110 KW of rated current 200 A controlled by Soft Starter and during the actual operation it consumed only 65 KW with 98 A, so I want to change this motor with another one lower in KW with VFD to control at the new motor Torque, so could you help me how can I do that?

Answer: If the new motor is large enough to provide the load requirements then reducing the motor ...

VFD and IMO are not going to be competitors in the same market. The benefits of VFD are various depending on the intended use. Bigger the motor (from kW to MW), bigger the benefit. They can act as soft starters therefore reducing the stress caused to the motor during the startup. With the VFD you do not go above nominal current (if you do not want).

VFD for fan and pump applications will considerably increase efficiency of the system as reducing 10% the top speed, the power absorbe ...

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 starti ...

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 ...

We are looking at an approx 90% + efficiency rating using asynchronous motors with the proper VFD's. With using regen instead of dynamic braking resistors, both in deceleration in traversal motions and in the overhauling effect of the load to the motor in lowering mode, the energy generated by the motor is channeled back to the line source, instead of being dissipated away as heat.


However, ...

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 ...

Failure to balance the V/Hz ratio with 400V/50Hz motors in the US, to accommodate for the widely varying voltage levels in all of the sectional grids across the country results in significant starting torque and HP losses. Variable Frequency Drives (VFDs) capable of full motor voltage/Hz/RPM/FLA levels are the very best option for use of these motor types.

The overall power grid across the US was created over 100 years ago, and though it has of course been expanded across the enti ...

For a hoist application
1) You can make a sensorless VFD (variable frequency drive) work on a Hoist however... If an encoder is not used and the VFD doesn't properly sense that there is a problem (it might be a rare occurrence but I've seen it), you could potentially drop the load. It only takes once to seriously damage equipment, hurt someone or worse.


2) With an encoder, and proper br ...

If the induction motor was really hot and you had a premature insulation failure, probably you had an overheating problem. The main reasons for this situation are:

* The voltage waveform created by the variable frequency drive (VFD) has high frequency harmonics that will cause an increase of temperature inside the motor. If your VFD-PWM has no filter outputs and the cable connection VFD-Motor is long, you can easily get a premature insulation ...

I find that due to the fact that the variable frequency drive (VFD) rectifies the AC to a DC bus, the power factor drawn from the supply is near unity but has harmonics. Harmonic kill the power factor correction capacitors. You need to install harmonic filters to take out these unwanted inputs. GTOs used to power the electronics generally fail open circuit. If your VFD has a ramp down to stop you need to program in a fast stop. All safety devices like E- ...

A variable frequency drive (VFD) will improve the system power factor to which it is connected, primarily because the motor reactive current is supplied by the DC bus, rather than the supply system. This will only improve the displacement power factor. Modern VFDs with AFE draw almost sinusoidal current from the supply, so power factor on the source side can be controlled up to unity and the generated harmonics are ...

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 ...

I do not understand how Power Factor can be affected with typical DC drives, as power factor only exist in AC system when the current wave is either leading or lagging the voltage wave. For DC drives, since phase angles do not exist, why would power factor be affected? This is also my understanding on why power factor is not affected on the line side of variable frequency drive (VFD), as AC voltage is first converted into the DC link vol ...

I had an oil filled motor start capacitor blow once. What I think happened was when someone replaced it, rather than putting it back in its holder, they duct taped it to the side of the squirrel cage motor that it was starting. They started the motor up and walked away. The motor was a continuous duty motor so it wasn't turned off for a long time. One day, someone shut it off to do some servicing. They notice ...

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. I ...