I have a few ABB UA95-30 contactores and they have printed a power
table in kvar, not in kw. Are they specialy made for condensers
aplications? Can i use the to build a delta wye motor starter?
Finaly, is there a phisical diference betwen the contacts in a kvar
contactor and a kw or hp contactor?
Fon any help, thenks in advance.
When you read the literature for these contactors, it states:
"The UA..RA contactors are fitted with a special front mounted block,
which ensures the serial insertion of 3
damping resistors into the circuit to limit the current peak on
energization of the capacitor bank. Their connection
also ensures capacitor precharging in order to limit the second
current peak occurring upon making of the main
Would I use these on a motor? As described in the acrobat file, no
The acrobat file does not show the mechanics of this contactor and how
the damping resistors fit in.
I'm guessing that the damping resistors are put in series with the
capacitor bank for a few seconds on initial closure, then once the
capacitor bank is charged up the resistors are taken out of the
circuit when the main poles on the contactor pull in.
But then when I read about the "precharging" part, that sounds like
the resistors are in the circuit when the main poles on the contactor
are open. If that's the case, then when the contactor is turned off
then there would still be voltage applied to the motor via the damping
Using these contactors, as built, as a motor starter would either blow
the resistors in the contactor or play havoc on the motor windings
during start ups.
I don't know if the "special front mounted block" can be removed from
the assembly to create a normal contactor. If so and if the contactor
acts like a normal across the line contactor, and if I was really,
really desperate, then I don't see why they couldn't be used to
control a motor in an act of desperation.
Even if I did put one in, I would definitely get the right type of
contactor ordered and installed ASAP. These contactors were probably
UL tested for capacitor banks, not UL tested for motor control.
To figure out KVAR to KW if used as motor starters, you need to
contact the motor manufacturer and find out the power factor for the
motor. US motors hardly list this on the nameplate, but I've run into
European motors that have either "pf" or "cos theta" on the nameplate.
The power factor is the cosine of the phase angle difference between
the current peak and voltage peak in an AC power system. For example;
in a typical factory the majority of loads are motors, which are
inductive loads. Voltage leads current in an inductive circuit [ELI
the ICE Man]. If the voltage waveform peak is used as the reference
or zero degrees, the current wave form will peak around 30 to 40
degrees after the voltage peak. The difference between these peaks,
in degrees, is the phase angle. Take the cosine of the phase angle
and that's the power factor.
The formula for KW, three phase system, is
The formula for KVAR, three phase system, is
[voltage]*[current]*[1.73]*[sine of the phase angle]
Once you get the power factor or cosine of the phase angle from the
motor manufacturer, take the arccos [inverse cosine] and get the
angle. Get the sine for that angle and plug the numbers in the KVAR
formula to see what the current rating is for that contactor, if it
was used to control a motor.
So, if you don't have any capacitor banks to power then maybe you
should put these on e-Bay and throw a kegger. Get some use out of
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