calculated feed transformer for DECS200

[mottt]

i got a generator with the next excitation: 35 V dc and 8 A dc, and i´m looking for the transformer that feed power to the dec200, i was thinking on use a 660/120 V transformer but i wonder about the VA needed?
how do you see my calculations?
Excitation volts at full load: 35 V
Excitation amps at full load: 8 A
Excitation amps on short circuit: 24 A
Excitation volts on short circuit: 105 V
The formula i got is:
volts on short circuit*amps on short circuit* ratio input voltage/output voltage* ratio input amps/output amps*1,05*(voltaje short circuit/voltage full load)

this means 1162 VA, on monophasic way... maybe i use a triphasic maybe i could divide by square 3

 

[waross]

Hi motorxplosion;
Does your voltage regulator have any input specs?
My thoughts would be about 70 volts at 12 or 15 amps. A good AVR will use the extra voltage for boosting or field forcing to get fast response to block loading. I would consider about 500 KVA capacity. The supply transformer will be about 50% overloaded when forcing the field but this should be a short time event. A good AVR will supply full output for about 10 seconds and then shut down to protect itself.
If you wish to maintain short circuit output, consider a series boost circuit. Use one or more CTs in the generator output to develop about 90% of the excitation. By the use of diodes, the output from the CTs can be rectified and fed to the field so that this circuit will supply excitation in the event of a short circuit. If the short circuit time will be limited by the protective relaying, then consider overloading the CTs during short circuits.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mottt]

yes, i know i could use a boost system but i´ll like to use the net to feed the transformer and it´ll feed the short circuit time.... 10 seconds..... do you think 500 VA is enough.
three phases???

 

[Ceast]

motorx, don't undersize the PT. The difference in cost isn't worth the gamble. You'll need the power for fault current. I've installed 1000va PT's on units with an output of 1-3 amps @ 30volts. Looks like you're original #'s were close.

East

 

[waross]

?Try this site:

http://www.byramlabs.com/pdf/basler/szm8bull.pdf

Here are some comments to e aware of;
1- Inrush Current Reduction Module required when operating power of the DECS-200 is fed via a station service source.
2- Rated Continuous Field Voltage 32 Vdc 45 Vdc*
NOTE: Above parameters with nominal RMS power input.
*These areas indicate D.C. output levels that may be up to 50% greater than listed if:
1) 3 phase input power is used, or
2) Field current is significantly lower than that listed.
3- AC Operating Power
1 or 3 Phase Power Input
DECS-200 Output 32Vdc
AC Voltage Nominal 60Vac 56-70Vac ±10% Range (50-500Hz) Burden 780VA


Bill
--------------------
"Why not the best?"
Jimmy Carter