Motor-Generator vs. VFD? 1

[doehl1]

I have an application where my existing power control room runs about 250kVA of load at 480V, 3P3W, 60Hz. This PCR will be shipped to a 400V, 50Hz country. My initial solution was to use a motor-generator set (50Hz motor turning a 60Hz Generator) due to its simplicity, few parts, and pure sinusoidal output. However, my customer is requesting an option for a VFD. My concern was that the output may be a square wave, reliability, more complex, etc. Moreover, the loads would all be powered by this single VFD. The loads consist of motors, lighting, HVAC, resistance heating, electrical outlets.

Thoughts on VFD vs. motor generator? Any experience using VFD for multiple varying loads?

David

http://www.mavenpower.com

 

[ScottyUK]

VFD is almost certainly an awful solution. A UPS configured as a frequency converter - i.e. without the battery - would be a more credible solution. Beware of the limited fault-clearing capability of most power electronic systems: under short-circuit conditions it is quite possible for the inverter to shut down before a breaker or fuse clears a fault. The old-school M-G sets do have certain advantages, and fault clearance is one of them.

But first think a few things through...

[ul]
[li]Resistance heaters don't care about frequency, so leave them on 50Hz.[/li]
[li]Most lighting isn't bothered either.[/li]
[li]Buy 50Hz HVAC. Your customer will have to support it in a 50Hz country where 60Hz parts aren't available: maintenance nightmare; your customer will hate you.[/li]
[li]What are you plugging in to the electrical outlets? If it is customer load then it will be happy with 50Hz because that is likely what it expects.[/li]
[li]That leaves motors. Individual VFD per motor, or maybe just change the gearing or pulley sheaves if you can?[/li]
[/ul]

 

[itsmoked]

Well put Scotty!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[doehl1]

Well formulated Scotty. Thanks. Had forgotten about the limited interrupting ability of these VFDs...

David

http://www.mavenpower.com