# Converted power range of three phase motor

Discussion in 'Electronic Design' started by nescafe, Oct 5, 2012.

1. ### nescafeGuest

Hi.

I have 11kw 3 phase motor controlled by variable frequency drive.
The drive can be powered with one phase and it can give 3 phase output.
So i was thinking to try this solution. I will connect one phase to the
drive to see how much power can i get on motor side.

My question would be, how to calculate maximum horsepower or KW used by
3 phase motor, if he is be connected to 220 / 50 HZ - 8KW source ?

Regards !

sqrt(3).

Jamie

3. ### Tim WilliamsGuest

Nope. Power factor goes from about 0.9 to 0.5. It's less than half, amp
for amp.

Tim

4. ### JamieGuest

Ok, so where's the problem? 0.9/sqrt(3) = 0.52

If there is going to be a useless debate, I won't be joining in.

Jamie

5. ### Tim WilliamsGuest

No, I mean in addition to the sqrt(3). You get the sqrt(3) from having
two wires instead of three. 10A at 240V 3ph is 4.16kVA, 10A at 240V 1ph
is 2.4kVA. The power factor is additionally less, or more like 1.2kW for
10A 240V.

I should actually say it's more like a quarter, amp for amp.

Tim

6. ### P E SchoenGuest

"nescafe" wrote in message
I have a 1.5 kW VFD that will work on single phase, but larger drives
typically need three phase for full power operation. If you can add enough
capacitance on the DC link to maintain minimum peak voltage during zero
crossing, you might get full rated power. Drive efficiency is typically 95%,
so you could get about 7.5 kW from an 8 kW source. However, you need to
consider power factor of the rectifier/capacitor circuit as well as that of
the motor. So if your source is actually 8 kVA, and power factor is 60%, you
might get only about 5 kW for the motor. If you use a PFC DC-DC converter to
get the DC link voltage, you might get the full 7.5 kW for the motor, but it
also depends on the PF of the motor and the power rating and losses of the
VFD.

If you add capacitors to the DC link, you may need to use larger rectifiers
than the 3 phase bridge in the drive. For 50 Hz you need a TC of at least 10
might be sufficient.

Paul

7. ### P E SchoenGuest

"P E Schoen" wrote in message
==========================================================
(nescafe replied by email, 3 times):

Thank you very much for this answer.
I got some additional answers on one other newsgroup but the idea is
almost the same. 2/3 of the power should be reached.

I use siemens micromaster that is connected to 11kw motor so if i have
8kw input and if i calculate the 2/3 of the original power then 7,5
should be reachable. The 8kw is real 8kw input.( 220 - 40A )

I dont understand the dc-dc part. My micromaster has dc-dc input link.
Sorry for this dump question but i didn't work with this kind of
configuration till now.

=========================================================
<> may be bogus?

Actually what I meant was an AC-DC power supply with PFC. If you just use AC
through rectifiers and a capacitor, you will get a very low power factor and
will draw about twice the current compared to a supply with PFC. And it
might be difficult to find a DC supply with the proper specifications. (360V
36A). In fact, if you can get close to unity PF, you only need 22.5 amps for
8 kW at 360V. So you might be able to use seven 48VDC 25A 1200W power
supplies to get the DC power you need.

You might be able to find a 10 kW single phase 240V UPS with PFC. It will
probably have an internal 300VDC bus you could use for the DC link.

Paul