4 replies to this topic

[GGOSS]

Hey there,

I am wanting to build a "type 2' co-ordinated VFD based motor control system ie suitable for fault currents to 50kA without VFD failure.

Any guidance would be greatly appreciated?

Regards,
GGOSS

[BigMax]

Mr GGOSS,

I've heard of this requirement before, though I have to admit it makes no sense to me....

If I'm not mistaken, type 2 co-ordination generally allows for minor motor starter damage (light contact welding etc) in the event of high fault currents. Theretically you replace some HRC fuses and away you go....

How can the above apply to a variable speed drive? For example, if you short the output of a VSD in theory it simply protects itself and trips on overcurrent protection. If it doesn't and IGBT or other failure occurs the upstream protection device (fuse c/b) clears. In such a case, simpy resetting the c/b or replacing the fuse(s) will not result in a serviceable 'motor starter'.

Am I missing the point here?

Cheers all!!

BigMax

[GGOSS]

Thank you BigMax.

No, I don't think you are missing the point at all. The request for Type 2 co-ordinated VFD systems is one that I come accross with some regularity and like you, I'm not so sure that it is valid.

You may well be on the right track with your comment the drive will act to protect itself and trip on over-current! I could possibly accept that this would be the case if the drive was started with a bolted short on its output, however I am not so sure that the same would occur if the short was applied during run.

Any thoughts / comments?

Regards,
GGOSS

[theDOG]

GGOSS/BigMax;

I completely agree with both of your comments.

However, there is a global switchgear supplier that has a Type 2 co-ordination table listing components required for Type 2 co-ordination of Variable Speed Controllers. Perhaps you may want to contact them and ask how this is achieved.

If you want the name of the supplier, send me a "U2U" message.

[GGOSS]

Hello theDOG,

I am pretty certain that I know which global switchgear supplier you are referring to, however if you look closely at their published information you will note they show only a circuit breaker, a contactor and a variable frequency drive against nominal kW ratings.

This published information therefore suggests the drive is able to withstand fault currents of up to 50kA without failure!

How is this possible? Have the drives been tested to withstand 50kA or is this just another case of marketing people up to their old tricks?

I for one would greatly appreciate you thoughts/comments.

Regards,
GGOSS