14 replies to this topic

[chaterpilar]

We use lot of 3 phase VFD in our process but a new requirement for single phase (220 volts) motor 1.5 HP has come up for speed control. The load is a Fan.

Which drives/make would you suggest for this application?

regards,

Chaterpilar

[CJC_PE]

There are many small VFDs that are designed for single phase input power and provide three phase output. In addition to the ones that are designed for single phase input, many others will operate successfully on single phase input if they are rated for about twice the HP of the connected motor. The exact derating required may be published in the drive manual or spec sheet. The best thing to do is to use one of these and replace the single phase motor with a three phase motor.

If replacing the motor is difficult, there are VFDs that will operate single phase motors but only if they are the permanent split capacitor or shaded-pole type of motor. See http://www.anaconsys...ext/opti_1.html.

[chaterpilar]

Thanks CJC for the inputs

chaterpilar

[marke]

Speed control of songle phase motors is not usually a particularly good idea except in special cases.
Firstly, most motors have a start winding which is swiched out by a speed sensitive switch as the motor approaches full speed. If you operate at reduced speed, the start winding will remain in circuit and damage will resuolt.
Secondly, inverter systems normally operate with a high frequency switching arrangment. If a capacitor is in the circuit, the currents and voltages around the capacitor will be incorrect due to the non sinusoidal voltage. Commonly, you will have a capacitor failure.
Thirdly. In order to operate, the single phase winding uses a start winding that is physically displaced from the run winding to give a displaced rotating field. This must be driven by a displaced waveform in order to work. In normal operation, this electrical displacemnt is achieved by the use of a capacitor or high resistance winding or similar. The electrical displacement is frequency dependant.

It is possible to build an inverter that produces two outputs, one to drive the run winding and a second that produces a quadrature output to drive the start winding. This assumes that the motor and inverter are comp[letely compatible, and at the end of the day, a three phase motor and threephase output inverter is going to give a better result at a lower price.
Hence, the standard operation is to use a single phase input, three phase output inverter with a three phase motor of the corect voltage rating.

Another option worth looking at, a fan as a quatratic load curve and provided that the motor used has a high resistance rotor, the speed can be controlled by varying the voltage applied to the stator. NB This can only be done on high resistance rotor motors, not standard motors.
If is quite common for motors built intl fan systems (an integral fan motor assembly) to have high resistance rotors so that they can be speed controlled. The manufacturer will specify if this can be done or not. If the motor is a standard motor that has been fitted to a fan, then it can not be done.

Best regards,

[chaterpilar]

Thanks Marke for your valuable inputs...i have decided to change the single phase motor with a 3 phase motor and use drive which has single phase input and 3 phase output.

Regards,

Chaterpilar

[marke]

Definitely the way to go!!

Best regards,

[AB2005]

Thanks Marke for your valuable inputs...i have decided to change the single phase motor with a 3 phase motor and use drive which has single phase input and 3 phase output.

Regards,

Chaterpilar

Hi Chaterpilar,

Why you haven’t decided to use a 3phase VFD? Is there any problem for three phase supply availability? I think three phase input/output VFD is the more compatible than using a VFD with single phase input and three phase put.

[marke]

AB2005

There is nothing wrong with a single phase input three phase output VSD.
The difference is that the single phase input uses a single phase rectifier and the three phase input uses a three phase rectifier.
The DC output of the three phase rectifier is higher than the single phase rectifier and the ripple current through the capacitors is much higher on the single phase rectifier. Provided the capacitors are selected for the ripple current, there should be no other issues other than the output voltage is lower in the single phase input VSD.

If you are on the 400V 50Hz system, a single phase input inverter gives 230 volt three phase output and the three phase input gives 400 volt output.
Small motors are typically delta connected for 230 volt and star connected for 400volt, so there is generally no issue getting 230V three phase motors in the 50 Hz world.

Best regards,

[AB2005]

Dear Marke,

Thanks for correction.
I think the price of single phase VFD may be higher than three phase VFD

[jraef]

AB2005,
Up to 3HP (2.2kW) that is not the case. In fact there are some brands, such as the Teco FM50 / Motortronics ME-2 that no longer even offer a 3 phase input on 1HP and under. It saves them space by using a smaller IPM. But at 5HP (3.7kW) and up, it will indeed cost more because you need to buy a VFD twice the rating of the motor in order to accommodate the 1 phase input.

[marke]

Hello AB2005

I agree with jraef, on our local market, the small single phase input VSDs are definitely much cheaper and more common than the three phase input ones.

Best regards,

[kens]

Hi All, the only real disadvantage that I see with the single phase in VSD is the single phase current can be fairly high. However if we are talking ~ 1-2kW it is not so important, I seem to remember talk of a 7.5kW 1-3 phase VSD from one of the manufacturers?
Kens

[AB2005]

Thanks to all.

[jraef]

Hi All, the only real disadvantage that I see with the single phase in VSD is the single phase current can be fairly high. However if we are talking ~ 1-2kW it is not so important, I seem to remember talk of a 7.5kW 1-3 phase VSD from one of the manufacturers?
Kens

AC Tech, the US division of Lenze, has a 5HP (3.7kW) VFD capable of 1 phase in - 3 phase out with no derating, but as far as I know, they are the only ones that go that high. If you know their pricing system well, you will also see that this drive is essentially the same price as their 7.5HP (5.5kW) 3 phase only version, so it is likely that they are one and the same, just marketed differently. You can almost do that with other brands as well. A 5HP 230V motor will draw 15.2FLA, so to use a 1 phase input, the input current (x1.732) is going to be 26.3A. Most 7.5HP 230V VFDs are rated from 24A to 26A, so it isn't much of a stretch to squeeze from 1 - 9% more out of them. AC Tech was probably just smarter about their marketing when they did their ratings.

[chaterpilar]

AB,

The machine runs on a single phase supply and hence the decision to use single phase input VFD.

Thanks LMP team for your valuable inputs.

Chaterpilar