600 VDC switches [RE-wrenches]

[John Berdner]

Bill:

600 Vdc is the abnormal (fault) condition.
This can occur if you wire the array to the inverter with polarity
reversed.
The free wheeling diodes conduct and pull the array to close to Isc
(really about 2.5 Vdc).
When you open the switch it sees full Voc and because PV is so fast it
also sees essentially full Isc.  SO the switch was tested at a Isc of 18
Amps.  IMHO, continuous don't apply because the arc occurs only as the
switch opens.

The switch is preconditioned for 50 cycles at the abnormal condition
then 6k cycles (corrects my earlier post)of the normal condition.  The
normal condition is the difference between Voc and Vmp.  By my
calculations the delta V is worst case 125 Vdc even for a 600 Vdc open
circuit array. As you know array voltage is based on temperature so Voc
- Vmp is essentially a fixed ratio.  Yes, I know you have to consider
the current coefficient in Vmp but it is so minor I choose to ignore it.


Square D ran it at 250 Vdc. Why ? because UL didn't buy the fixed
relationship between Voc and Vmp and from our data we thought the switch
could do it.  Hey, better to have too much than not enough.

If you have any questions or if I may be of any further assistance,
please do not hesitate to contact me.

Best Regards,

John Berdner


-----Original Message-----
From: Bill Brooks [mailto:billb at endecon.com] 
Sent: Thursday, February 13, 2003 03:41 PM
To: RE-wrenches at topica.com
Subject: RE: 600 VDC switches [RE-wrenches]

Brad,

Tim Townsend, a colleague of mine talked directly with Square D and
gives
this information:

"I spoke with Bob Miller and Tom Keene of Square D about this -- they
said
the 13 A [PER POLE] test was done at 250 Vdc and 6000 operations
(successfully), and also at 18 A [PER POLE] at 600 Vdc and 50 operations
(also successfully)." Tim

The 250 Vdc number is for the differential between Vmp and Voc under
load
(600V-350V=250V). The 600Vdc test is for worst case positive pole to
ground
short circuit. John B. can correct me if I have the information messed
up.

Hope this helps.

Bill.


-----Original Message-----
From: Brad Bassett [mailto:bsbassett at earthlink.net]
Sent: Wednesday, February 12, 2003 9:18 AM
To: RE-wrenches at topica.com
Subject: SPAM: RE: 600 VDC switches [RE-wrenches]


John,

I have not seen an answer to this question. If you feed an SB with two
strings of modules, the 13A limit is likely to be exceeded if it is not
rated for continuous. With the 165's it's exceeded even at PV 125%.

Thanks,
Brad


William Miller wrote:
> The rating is for 13 amps per pole.  Is this de rated for continuous,
or
> for PV?
>
> Thanks again,
>
> William
>
>




Brad Bassett
Schott Applied Power
Tumwater, WA office
bsbassett at earthlink.net

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