I know for 3 Phase motors rated for 60Hz, it is ok to drop down to 50Hz as long as you make a corresponding drop in Voltage. I do not think this approach works exactly the same with 1 phase motors. Can a 60Hz rated motor rated for 460V operate on a 50Hz system if the voltage is reduced to 400V? Can someone explain the different approaches for using 60Hz rated PSC motors on 50Hz equipment in contrast with 3phase motors? Thanks in advance.
SINGLE PHASE MOTORS AT 50/60HZ
- Thread starter fifty60
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On PSC motors, the same issues apply as in 3 phase motors. Determine the V/Hz ratio of the motor design from the nameplate, apply that ratio to the frequency and come up with the appropriate voltage.
So 460/60Hz rated motor is 7.67V/Hz, multiply 7.67 by 50Hz, 383.5V, then usually +- 10% is OK.
The motor still runs 20% slower though, so don't forget that. Where you can get into trouble on single phase motors then is that if they have a centrifugal switch for starting caps, it will not be working at the same speed point, in fact may not work at all! PSC motors of course don't have a speed switch, so it doesn't affect them.
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It will affect them, but to the extent that the phase shift in the magnetic field will not be the same as it would be for the same value capacitor between 50Hz and 60Hz applied voltage.
But the value of the capacitor is usually not accurate to that same tolerance nor critical to the operation of the motor.
Is this a hypothetical question? And, unless you spec a special transformer where are going to get 400v @50hz?
The motor manufacturer may have the ability to run a design test using their design program to determine how the motor respond to using your parameters.
400V and 50Hz certainly exists in the world. The question is hypothetical to an extent. My problem in understanding is just what does the 50/60Hz mean on a single phase motor? Does it mean that the PSC's capacitor is sized to handle the drop to 50Hz? I know that when wanting to adjust the speed of a single phase motor, you adjust the voltage. Bardac makes (or sells) a VFD that will work for single phase motors, but it is far less common than for 3 phase motors. So if a motor that is rated at 460V and 50/60Hz operation is ran on a supply of 400V and 50Hz, the phase shift and the capacitor will be fine but it will just turn faster. As far as I know most single phase motors for fan applications are VT, so does lowering the voltage lower the torque at a cubed rate instead of linear? What exactly happens to a single phase motor when you lower the voltage? What adjustments do manufacturers make to classify it at 50/60Hz? Why are VFD's so rare for 1phase motors (PSC's and Shaded Pole, I understand why you do not want to drop frequency on single phase motors where the start/run caps are more important) than for 3 phase motors? Thanks in advance again. This forum is a great resource for people who take pride in their work. Thank you.
kwired
Electron manager
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The problem is the governing switch that kicks the starting cap, or the entire aux winding on some smaller hp motors is designed to kick in at a certain speed.
You are finding variable speed drives for submersible well motors more commonly these days. but they eliminate the starting capacitor and potential relay out of the motor circuit and the drive regulates voltage, and frequency of each winding independently to maintain desired motor output. It is not that you can't vary the speed of such motors, but it takes a little more than just putting a drive in the supply conductors like you can with a three phase motor.
I will attempt to sum up my confusion on this matter. If single phase PSC motor had to operate at 400V and 50Hz, would it be better to run a motor that is rated for 460V and 60Hz and then lower the voltage to 400V at 50Hz. Or would a motor that is rated for 50/60Hz at 460V be better to run at 400V and 50Hz. Does the fact that the motor is rated at 50/60Hz mean that you should not lower the voltage to it? To me it is more clear to operate 60Hz rated equipment on 50Hz by maintaining the V/F ratio. I get confused when the motor is rated for 50/60Hz. What is the original V/F ratio on a motor that is 50/60Hz and only 460V? And if so, what happens when you lower the voltage on a 50/60Hz motor that does not happen on a motor that is only rated for 60Hz?
Pretty much anywhere in Europe, many of the countries in the African continent, much of the Middle East, China, Australia .....etc.
I'm sorry, I don't know much about single-phase motors.
Lectricbota
Senior Member
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So you being from the UK does that mean you normally deal with larger equipment so you don't work with single phase that much or that most motors are 3-phase regardless of size.
It isn't a UK thing.
We do use single phase motors here. And probably for much the same applications that you do. Domestic power is almost almost single phase and all domestic appliances run on single phase 230V 50Hz. The motors for fans, washing machines, dryers, refrigerators, power showers etc.
It's just that I don't get involved with them very much - mostly I deal with industrial applications of variable speed drives.
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