I’ve noticed an increase in requests for operating stock U.S. rotary electric (motor) vibrators that are wound for 460/3/60 power overseas where the power is often 380/3/50. The answer to the question is yes and there are two options available.
First, is the realization that you can operate a 460/3/60 vibrator using 380/3/50 power. My understanding is that the reason it works is due to de-rating the higher voltage 60 Hz motor since 50 Hz power rotates the eccentric weights at a lower RPM (rotations per minute) by a factor of 50/60. For example, an 1800 RPM vibrator would run at 50/60 x 1800 = 1500 RPM.
This same logic can also be applied to the voltage. So, a 460 volt motor would be de-rated to 383 volts by multiplying the 60 Hz voltage by the same factor of 50/60. Therefore, due to 50Hz input, a 60Hz vibrator will accept 380 volts ± 10% without jeopardizing the motor.
However, it is very important to recognize that since the eccentric weights are rotating at a lower RPM, the force output will be reduced by roughly 30%. The exact amount of reduction is the square of the factor provided above for determining the lower RPM of the vibrator due to 50 Hz.
For example, if the maximum centrifugal force at 60 Hz is 1,000 lbs, you need to multiply it by (50/60)² or 1,000 x 0.6944 = 694.4 lbs F (Force) when operating at 50 Hz. Conversely, if your application requires 694.4 lbs F at 50 Hz, the inverse of the previous factor applies or (60/50)². So 694.4 x 1.44 = 1,000 lbs F would be required for a 60 Hz vibrator to end up with 694.4 lbs F when operating at 50 Hz.
Now that we’ve cleared that up, you may wonder if there is any way to recover the loss in force output due to 50 Hz so you don’t have to upsize the 60 Hz vibrator accordingly? The answer is yes. But, only if you are willing to use a VFD (variable frequency drive) to control your vibrator, which is the second option.
You will find that most VFD’s offer a range of input voltages, so I’ve found that typical 480 volt models will actually accept a range of 380 to 480 input voltage and it can be 50 or 60 Hz. You can therefore input 380/3/50 to the VFD and it will output 380/3/50 to the vibrator. We’re still good as we’ve established that the 460/3/60 vibrator will run off of 380/3/50 power.
So what about the force output? I’ve been told by VFD suppliers that they recommend upsizing the VFD (like 1 HP to 2 HP presumably due to the higher amp draw at 380 volts) which will allow you to set the VFD at 60 Hz. In doing so, it will now rotate the eccentric weights of the 460/3/60 vibrator at its full rated speed and therefore produce its maximum rated force output. Ultimately, an upsized VFD will allow you to run off of 380/3/50 power without losing 30% of the force output.
Lastly, you should also be aware that some of the motor vibrator manufacturers have begun offering vibrators that will accept either 380/3/50 or 460/3/60 power without affecting the maximum force output. This is done by having two scale plates for adjusting the eccentric weights, one for 50 Hz and one for 60 Hz. It follows the same logic above as the eccentric weight setting compensates for the loss in force due to the slower RPM when operating at 50 Hz. Essentially the eccentric weights that are set at 100% on the 50 Hz scale would equate to roughly 70% (69.44 to be precise) at 60 Hz, but it will actually be set as 100% on the 60 Hz scale. So the vibrator has the same maximum centrifugal force output regardless of whether you operate with 380/3/50 or 460/3/60 power.
You now have the answer with options that will allow you to utilize stock 460/3/60 vibrators internationally where 380/3/50 power is available including the technical explanation to back it up so you can enlighten others who may be skeptical. Use your power wisely my friends!
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