transformer inrush [RE-wrenches]

[Mark Edmunds]

Hi Kirk,

I think the autotransformer should actually help keep the surge current
down, due to its added impedance. Do you have any way of measuring the peak
surge current demand from the load? I suspect one of the pumps starting up
while there is a high load may be going over the limit.

Fluke has a new line of clamp meters (The 330 Series) and most of them have
a "motor inrush" feature, which is quite handy for checking on this sort of
thing. I don't know how accurate this is but it will give a good indication
of surge current.
http://www.fluke.com/products/home.asp?SID=5&AGID=3&PID=30405 

Cheers,

Mark Edmunds
Xantrex Technology Inc.

-----Original Message-----
From: Kirk Herander, VSE [mailto:kirk at vtsolar.com]
Sent: Monday, January 05, 2004 9:26 AM
To: RE-wrenches at topica.com
Subject: transformer inrush [RE-wrenches]


Hello,

I have a SW4048 inverter used in a UPS mode to backup some household
critical loads - a septic and well pump and 2 fridges amongst others. The
system is always feeding the critical loads with grid ac through the
inverters transfer switch, supposedly rated at 60 amps. The surge potential
of the inverter is rated at 78 amps. The 120 vac output is fed into a
120/240 autotransformer, so 120/240 vac is supplied to the critical load
panel. My preference was to have only the 240 vac loads fed from the
transformer, but the electrician didn't set things up that way.

Twice in the last week the customer has called telling me that the inverter
has shut down due to an overcurrent error. It might be possible that
continuos plus/or surge currents from the critical loads could exceed 78
amps, but I'm wondering if the transformer could be adding to the problem.
If the primary of the transformer is constantly energized(core magnetized),
there should not be a high transformer-related inrush current, when a
motorized load turns on, adding to the surge requirement and creating the
overcurrent error, correct? Would it be helpful to just step up the voltage
for the sake of the 240 vac loads(water and septic pumps)?

Kirk

Vermont Solar Engineering
North American Board of Certified Energy Practitioners Certified Solar PV
InstallerT
Xantrex Certified Dealer Charter Member
Kirk Herander
PO Box 697
Burlington, VT. 05402
www.vermontsolar.com
www.backeastsolar.com
800.286.1252 - 802.863.1202
fax 802.863.7908

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