currents at the same time using the Control Knob. The test current is the current shown on either
of the current channels amplitude displays.
3.3.3 Harmonic Restraint Test
One V/I Generator could be used to do differential or harmonic restraint tests when the voltage
channel is converted to a current source. This is useful when the unit only has one V/I Generator,
and if the required operating current doesn’t exceed 5 amperes and the restraint current doesn’t
exceed 15 amperes (Model MPRT 8415) or 30 amperes (Model MPRT 8430).
Two V/I Generator current channels may be used to obtain the desired current output to conduct
harmonic restraint tests on differential relays. One of the current channels provides the second or
higher harmonic output and the other current channel provides the fundamental current.
There are two methods available to do harmonic restraint tests: the first method uses a pure
harmonic (2nd, 3rd, 5th, etc) of the fundamental from one current channel summed with the
fundamental current from a second current channel at the relay; The second method uses the
unit "HWAVE" feature. The HWAVE simulates the "diode method" recommended in some relay
manufacturers instruction literature. When the HWAVE is selected, the output module provides a
"half-wave" sinewave (similar to what you would see if using a diode in series with a current
source).
NOTE: Some recommended test procedures prefer using 4 DC amperes of half-wave. Since
the unit displays the full RMS sine-wave quantity, it will be necessary to set 8.89 amperes RMS
on the selected HWAVE current channel to achieve the desired equivalent of 4 DC amperes half-
wave. Use the following formulas to calculate other values of DC half-wave:
414
.
1
*
Irms
Ipeak
and
)
(
=
=
π
Ipeak
halfwave
IDC
Therefore,
π
414
.
1
*
)
(
Irms
halfwave
Idc
=
Or
45
.
0
)
(
halfwave
Idc
Irms
=
Solving where:
4
=
Idc
89
.
8
45
.
0
4
=
=
Irms
or
Irms
33
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