GE NBVllA Series Instructions Manual page 9

N ote: If a suitable three-phase source of rated voltage is not available,
a good wave shape and rated frequency.
be tested at
4
and should be proportionally lower.
120
tested at
volts.
If the relay is found to be out of balance and the three-phase test voltage is
known to have a
120
unbalanced on a
adjusted until adequate balance is obtained.
achieved, then the test source probably contains harmonics.
N ote:
If the voltage across terminals
adjusting resistor R1, the problem may be harmonics in the voltage source.
This can be checked by connecting an
instead of a voltmeter.
should be a sine wave of fundamental frequency on the oscilloscope.
distortion due to harmonics may be hard to see at this point.
increasing the ohms in resistor R1; the magnitude of the sine wave should
decrease. Continue
occurs. As the magnitude of the wave decreases, it will be due to the
fundamental wave decreasing.
the same. When the point is reached where the fundamental goes to its
minimum value, if there is much harmonic content in the wave, the harmonic
wave will predominate.
the voltage left is all harmonic voltage.
oscilloscope will probably look like a sine wave but its frequency will be
higher than fundamental frequency.
second harmonic,
frequency twice the fundamental frequency.
If the voltage across terminals
120
for volt relays, or
by harmonics, then a harmonic filter is required.
A harmonic filter is available for use with the N BV relay when the line
supply to the motor has a harmonic content.
The harmonic filter consists of a parallel-tuned circuit.
when connected across terminals
has a high impedance to the fundamental frequency
lower impedance
harmonic filter therefore will bypass the harmonic content around the N BV
relay so as to minimize its effects.
GEI-50261
120 If this is done, the voltage observed across
volts .
volts, then observed voltage should be less than
120
v3 -4
x
=
20 8
good wave shape and is well balanced
volt source), then the setting of resistor R1 should be
With resistor R1 set for minimum ohms,
increasing
The harmonic content of the wave will remain
If practically no fundamental can be seen, then
then the wave on the scope will be a sine wave with a
1.5
volts for
to harmonics
9
For example, a
For example, if a
0 . 86 5
1. s
=
If adequate balance cannot be
3-4
cannot be made low enough by
oscilloscope across terminal
resistor R1 until
At this point, the wave on the
For example, if the harmonic is all
3-4
is above the m1. n 1.mum value (
208
volt relays) and is all caused
3-4
(balanced three-phase network output),
above the fundamental
208
volt relay may
208
volt relay is
0. 865
1/2
(not over
there
N ow start
the minimum voltage
1. 0
The filter,
(50 60
or hertz) but a
frequency.
3
volt
3-4
The
volt
The