DC to AC motor conversion

[nic00b]

Good Morning,

We are looking at a motor conversion on one of our chain transfers drives. The motor is directly coupled to the chain sprockets and is used to transfer 12T plates.

Current Setup:

1 * 60 HP DC series wound motor (220Vdc) @ 525RPM
Frame : MD106 (foot mounted)
Arm Current : 235

We have asked an external company to quote for conversion and they have specified the AC motor to be that of a 90kW (VSD controlled).

I have not had chance to look over their proposal at present but 90kW seems a bit excessive, has anyone carried out DC-AC conversions and can offer advice?

Kind Regards
Nick

 

[Skogsgurra]

It depends a lot on what speed the AC motor is rated at.

The nearest higher (than 525 PRM) speed is either 900 or 600 (synchronous) RPM. The 600 RPM motor would be a technically good choice, but may be a problem to find. Then, the 900 RPM is a sound speed to use.

So, the math seems to be OK. The 90 kW at 900 RPM corresponds roughly to 50+ kW (65 - 70 Hp) at your speed. A little "overstrong" but that is only wise regarding the series characteristic of the existing DC motor.

I think that a geared standard motor fits better. If there is room for it.

I would say that you have found someone that understands the business.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[nic00b]

Apologies for not replying sooner Gunnar and thank you for the reply.

The other two chain transfer drives use AC slip ring motors with associated gearboxes (5.5kw!!!), unfortunately there is very limited room and the gearbox approach was not a viable option. If this DC-AC conversion is successful there may be a plan to change three other DC applications (60HP) fed from our MAR 220Vdc supply. Although, i need to do some cost analysis on this to justify the approach.

Thanks again
Regards
Nick

 

[mikekilroy]

As already stated, the 90kw sounds correct...

you have 60hp@525rpm now.

You did not tell us what the 90kw motor's base speed it: I will assume it is a 6 pole motor so 1200rpm.... Since HP=T*N/5252, if you have double the base speed, then the torque will be 1/2. So a 60hp motor in this new AC 1200rpm model will have 1/2 the torque of the old motor.

So to get the same torque as your old 60hp motor you need 120hp model now since you cannot use gearing to bring it back.

120hp motor is 90kw so a perfect match - assuming there is no need for real slow speed with the same rated torque as the old Dc could provide.

(90kw/120hp@1200rpm motor will produce same 525#-ft torque down to around 300rpm - below that it may overheat unless load is reduced or external cooling is added...

http://www.KilroyWasHere<dot>com