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A diode rectifier is the lowest
cost and most simplistic type of
exciter. This type of exciter is
a combination isolation transformer
with numerous taps and a non-regulated
diode rectifier. The voltage output
of the rectifier is a direct ratio
of AC input to DC output. The exciter
output voltage can only be adjusted
by changing transformer taps. The
current passed to the field is a
function of the exciter voltage
and field resistance (Ohm's law
E=IR). The transformer taps can
only be changed with the motor and
exciter off line. Standard taps
provided are five 5% full current
capacity taps below the nominal
voltage. Total of six taps provided.
Kinetics manufactures all our own
transformers, with copper conductor
as our standard. Providing additional
taps to the primary or secondary
of the transformer is an available
customer option.
A full current rheostat can be
added to the output of a diode rectifier
for manual voltage adjustment to
the motor field. In many cases the
cost of adding a rheostat exceeds
the cost of a SCR regulated rectifier.
Depending on the field application
control scheme, a CP exciter may
or may not be applicable. Care needs
be taken to assure compatibility
between the exciter and field application
controls.
"CP" exciters tend to be used on
motors below 500 Hp. Units are available
for single phase or three phase
input at a customer's request.
The Kinetics model MVR is a heavy
duty, AC line regulated "CP" diode
rectifiers designed and rated for
highly inductive loads. A robust
design enables units to withstand
the spikes and surges commonly associated
with synchronous motor field applications.
Model MVR 1 to 20 KW incapacity
at 125 or 250 VDC nominal. Units
are with standard features of AC
line protection, EPT exciter power
isolation transformer, AC surge
suppression, semi-conductor fusing,
diode rectifier, DC surge suppression,
DC bleed resistance, annunciation
and enclosure or chassis assembly
for mounting in a switchgear cell.
Kinetics exciter units are designed
specifically for the high transient
power spikes and surges associated
with highly inductive loads. The
rectifier is protected with robustly
rated MOV surge suppressors, a DC
bleed resistance and diodes with
a minimum peak inverse voltage (PIV)
rating of 8 times the AC RMS voltage
into the diode primary.
"CP" exciter, model MVR, can be
supplied with a Kinetics' KinetSync-NB
digital logic annunciation and control
module.
Cautionary
note: The various manufacturers
of brushless synchronous motors,
have different configurations of
rotating excitation system circuitry.
When applying an off shaft exciter,
it is imperative that the off shaft
exciter be compatible with the on
shaft exciter field application
circuitry. Kinetics engineers are
available to assist in selecting
the correct off shaft exciter configuration.
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