Use of series relays for HV DC safety isolation
Use of series relays for HV DC safety isolation
(OP)
I am working on a project where I need to isolate a 1500W, 1kV power supply with an electromechanical relay/contactor as part of a safety system to meet the requirements of IEC category 3. I need to switch the output (1kV) but not under load. The primary switching element(s) need to be monitored by aux contacts. I am using a Banner GM-FA-10J gate monitor safety module and appropriate switch to control the Banner module.
I am having a hard time finding a single relay with aux contacts that is rated for 1kV DC to do this. I am considering using 2 contactors in series (each rated 690VDC)to perform the isolation function. Is a series connection of monitored contacts an acceptable solution? If not, any suggestions on a source for DC relays/contactors rated 1kV or more that are not enormous. I only need 1.5A rated contacts and most parts I have found are 50A or more.
Thanks in advance for any feedback
I am having a hard time finding a single relay with aux contacts that is rated for 1kV DC to do this. I am considering using 2 contactors in series (each rated 690VDC)to perform the isolation function. Is a series connection of monitored contacts an acceptable solution? If not, any suggestions on a source for DC relays/contactors rated 1kV or more that are not enormous. I only need 1.5A rated contacts and most parts I have found are 50A or more.
Thanks in advance for any feedback





RE: Use of series relays for HV DC safety isolation
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If we learn from our mistakes I'm getting a great education!
RE: Use of series relays for HV DC safety isolation
I would really like to know peoples opinion of using 2 contactors in series. This would effectively double the clearance distance between the open contacts and double the effective standoff voltage. The contacts will be monitored such that the failure of a single relay would be detected and prevent a subsequent power cycle. If anything I think there may be a net safety gain due to the redundancy of 2 series contactors.
RE: Use of series relays for HV DC safety isolation
In the two separate relay case there is always the chance of only one dropping out because its coil fails or one drops more slowly than the other. Both cases leaving a live, high temperature arc running. With daisy chained contacts in one relay they all drop out at the same time.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Use of series relays for HV DC safety isolation
http://relays.tycoelectronics.com/kilovac/
Ed
RE: Use of series relays for HV DC safety isolation
Ed: Thanks for your feedback. I looked at Kilovac but was unable to find an appropriate relay that has auxiliary contacts as required to tie in the safety controller.
I found this relay: www.schaltbau-gmbh.com/downloads/B_193e.pdf
The data sheet lists the nominal voltage as 750V but also lists Rated insulation voltage Ui to IEC 60947-1 as 1000V. Additionally they list the breaking capacity at 1kV. The manufacturer seems to market this as being usable to 1kV but why the lower nominal voltage? I am going to give them a call but wanted a second opinion to make sure they don't just tell me what I want to hear to get me to buy their contactors... not that a company or their sales guys would ever think of doing that...
RE: Use of series relays for HV DC safety isolation
Keith Cress
kcress - http://www.flaminsystems.com
RE: Use of series relays for HV DC safety isolation
Roy
RE: Use of series relays for HV DC safety isolation
Roy: Good reminder but fortunately I am very aware of this especially at 1kV, 1.5kW. The Shaltbau relay I am considering using is P/N: C193 A/ 24EV-U1. It is specifically designed for HV DC applications and has magnetic blowouts and baffles for arc quenching.
The folks at Shaltbau quoted 6-8 weeks for delivery of 2 sample contactors. Anyone know of a faster source? Anyone know if their delivery times run fast or slow? I am sure the coming holidays won't help...
Thanks again to everyone who responded to my post. I appreciate it!
Karl Edminster
www.electromechanica.com
Does that smell like burning FR-4? Nah...just the FETs breaking in...
RE: Use of series relays for HV DC safety isolation
How about dumping the supply power and simultaneously crow-barring the output thru a load resistor.
How about using a DP. Just use one of the poles as the aux.
htt
Keith Cress
kcress - http://www.flaminsystems.com
RE: Use of series relays for HV DC safety isolation
Just to further complicate matters, I just took a look at the Schaltbau relay you referenced, and I very much doubt (but could be wrong) that the Aux contacts are not of the "Force Guided" type. If they are not, they probably aren't suitable as MPCE monitor contacts.
However, you might investigate the Allen-Bradley 700S-PK. They claim 2 X NEMA P600, which would give you a standoff of 1200V. And sufficient current capacity.
And they're safety rated, with a force guided Aux contact, for positive feedback to your gate monitor.
Here's the data on it
http://tinyurl.com/yh5wqgh
Ed
RE: Use of series relays for HV DC safety isolation
Ed: Thanks for the AB suggestion. I agree with your suspicion that the aux contacts may not be force guided and are therefore unsuitable as a MCPE.
I am looking at the AB P/N: 700S-DCP310DZ24. If I read the spec correctly I can use 3 series contacts to create a switch with an equiv capacity of 1500VDC @ 1.5A (3 x 500V per contact @ 1.5A).
I think the 700S-PK series parts just use a double parallel contact to double the current capacity. Is that what is meant by 2x NEMA P600? I think that only affects the current capacity, not the voltage per contact but I may be wrong.
If this solution works it has the bonus of being cheaper and faster to get than the Shaltbau relay. I owe you a beer if this works out!
Karl Edminster
www.electromechanica.com
Does that smell like burning FR-4? Nah...just the FETs breaking in...
RE: Use of series relays for HV DC safety isolation
That 2 X might very well be for 2 parallel contacts. It was early and I was between the 1st & 2nd cup.
Another area you might look at would be the A-B Bulletin 100S-D IEC Safety Contactors. they actually spec a standoff of 1 kV. Series a couple contact sets, and you'll have a lot of headroom. plus current capacity that's waaaaaay overkill.
http://tinyurl.com/ybeaa5v
Ed
RE: Use of series relays for HV DC safety isolation
Karl Edminster
www.electromechanica.com
Does that smell like burning FR-4? Nah...just the FETs breaking in...
RE: Use of series relays for HV DC safety isolation
Don't be too quick to dismiss AC contactors: some have dual rating and are capable of DC service if the poles are wired in series to give multiple simultaneous breaks. I'm not sure they are good for 1kV.
The old clapper-type contactors from ABB, Hubbell, Siemens, and Telemecanique might be worth looking at if you're moving in to the realms of arc chutes and mag blowouts. Last time I looked ABB's R-Line was quite competitively priced. Telemecanique's DC contactors are capable of putting up with outrageous abuse without any problems - see folks, I occasionally do find something to praise about a Schneider product!
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If we learn from our mistakes I'm getting a great education!