Use of series relays for HV DC safety isolation 2

[kedminster]

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

 

[ScottyUK]

I think ABB have a variant of their contactors which are good for 1100V AC, which would probably meet your requirement as an off-load isolator but wouldn't be any use as a load switch. I'm at home at the moment so no part number, but 1100V is a voltage associated with mining equipment as far as I recall. I'll have a look when I get back to work - on Wednesday - if you haven't found anything by then.


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If we learn from our mistakes I'm getting a great education!

 

[kedminster]

Thank you for your feedback about the ABB part. I should have clarified that although the intent is to never make or break under power it is possible that the relay would need to break under power should the safety system detect an unsafe condition (operator opening the enclosure unexpectedly or other fault). The final contactor selected must be able to reliably open at 1kV DC between contacts and 1500W power. There will be a contact on both the positive and negative HV DC line

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.

 

[itsmoked]

Usually you daisy chain the multiple contacts of a single relay NOT run two relays in series.

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

 

[fangas]

Kilovac specializes in HV relays

http://relays.tycoelectronics.com/kilovac/

Ed

 

[kedminster]

Keith: Excellent feedback-thank you!. I agree with your concern about separate contactors not operating simultaneously.

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:

http://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...

 

[itsmoked]

Any chance you can just interrupt the power to the supply instead?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[roydm]

Make sure you use a DC relay, the AC type will not break the circuit if there is any significant current flowing.
Roy

 

[kedminster]

Keith: I considered interrupting the mains but there are large filter caps on the output. Under low/zero load conditions the outputs would remain hazardous for too long after cutting the incomming AC mains hence the need for isolation on the DC side

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

http://www.electromechanica.com

Does that smell like burning FR-4? Nah...just the FETs breaking in...

 

[itsmoked]

Just trying to do an end run on your issue.

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.

http://www.gigavac.com/products/relays/datasheets/g12/index.htm

Keith Cress
kcress -

http://www.flaminsystems.com

 

[fangas]

Karl,

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

 

[kedminster]

Keith: The resistor crowbar idea is interesting but I would have a hard time verifying it as a category 3 safety system. I would need some sort of fault detection to sense a failed resistor, etc. Using a DP relay is a good idea and I haven't discounted that quite yet...

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

http://www.electromechanica.com

Does that smell like burning FR-4? Nah...just the FETs breaking in...

 

[fangas]

karl,

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

 

[kedminster]

Ed: I looked at the 100S-D contactors you sent but they appear to only be rated for AC operation. The coils are available in AC & DC (perhaps this was the confusion) but the contacts needed to rated for switching DC. This means they need to have magnetic blowouts and/or baffles to quench the arc when opening under load. An AC only rated contactor will not be suitable but I still appreciate your help in looking into this.

Karl Edminster

http://www.electromechanica.com

Does that smell like burning FR-4? Nah...just the FETs breaking in...

 

[ScottyUK]

Karl,

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! - and the Siemens ones are typical Siemens: expensive, unpretty, and very well built.


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If we learn from our mistakes I'm getting a great education!