BECKWITH ELECTRIC M-3425, Instruction Book

Page: 40 / 225

Application – 2
2–3
required. Several functions require proper setting of
these values for correct operation. The Nominal
Voltage and Nominal Current settings are needed
for proper normalization of per unit quantities. CT
and VT ratios are used only in monitoring and
displaying system primary quantities.
Relay System Setup
The system setup consists of defining all pertinent
information regarding the system quantities. Setup
screens shown here may be accessed through the
SYSTEM SETUP menu. Regardless of the functions
enabled or disabled, all information shown is
The secondary VT voltage when primary voltage is equal to the
rated
generator voltage. (V gen rated ! VT ratio)
The secondary CT current of the phase CT’s with rated generator
current. (I gen rated ! CT ratio)
Indicates VT connection. (See Figure 2-3, Three-Line Connection
Diagram.) When line-ground voltages are used, functions 24, 27,
and 59 may operate for line-ground faults. If this is not desired, the
line-gnd-to-line-line selection should be used to prevent operation
of these functions for line-ground faults.
When line-gnd-to-line-line is selected, the relay internally calculates
line-line voltages from line-ground voltages for all voltage-sensitive
functions. This line-gnd-to-line-line selection should be used only
for a VT nominal secondary voltage of 69V (not for 120 V). For this
selection, the nominal voltage setting entered should be line-line
nominal voltage, which is
S 3 times line-ground nominal voltage.
By enabling the Delta-Y Transform, the relay will internally consider the
30° phase shift through the delta-wye unit transformer for 51V and 21
functions.
This screen allows the user to select the phase rotation of the M-3425
to match the generator.
This screen allows selection of RMS or DFT for the 59 and 27
functions. The magnitude can be selected as the RMS of the total
waveform (including harmonics) or the RMS of the 60/50 Hz
fundamental component of the waveform using the Discrete Fourier
Transform (DFT). When the RMS option is selected, the magnitude
calculation is accurate over a wide frequency range (10 to 80 Hz)
and the accuracy of the time delay is +20 cycles. When the DFT
option is selected, the magnitude calculation is accurate near 50 or
60 Hz and the timer accuracy is
"
1 cycle. When a wider frequency
response is needed, select RMS. For generator protection applications,
it is recommended to use the RMS selection. RMS is the default
when shipped from the factory.
NOMINAL VOLTAGE
________ Volts
NOMINAL CURRENT
________ Amps
VT CONFIGURATION
line-line line-ground
!
"
line-gnd_to_line-line
DELTA-Y TRANSFORM
disable enable
PHASE ROTATION
a-c-b a-b-c
59/27 MAGNITUDE SELECT
rms dft