GE 845 Instruction Manual page 455

CHAPTER 4: SETPOINTS
IMPORTANT:
IMPORTANT:
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
The Synchrocheck cannot be performed if the three-phase VTs are Delta connected,
and the Wye single voltage input is selected under "Aux VT connection". "Wye"
voltages cannot be calculated from Delta connected VTs.
Once the Synchrocheck function is programmed, it will perform a voltage input
selection check, to determine that these voltage magnitudes are not different by more
than 5% of each other. This check depends only on the settings entered for phase and
auxiliary VTs under Setpoints/System/Voltage Sensing menu. If the difference between
the both selected voltage inputs by calculation is bigger than 5%, the Synchrocheck
will not work.
For example, the phase VT can be set to Wye connection with secondary voltage of
66.4V. The Aux. VT can be connected between phase A to B with the secondary voltage
set to 115V. Then, one of the Synchrocheck inputs can be set as the V
from the Wye connected phase VTs, and the other output can be the Aux. VT with
voltage V . Since the difference between the computed V
ab
setting is 0%, the Synchrocheck will work. However, if this difference is bigger than 5%,
the Synchrocheck will not work.
Path: Setpoints > Control > Synchrocheck 1(X)
FUNCTION
Range: Disabled, Enabled
Default: Disabled
BUS VOLTS INPUT
Range: dependant upon the order code
Default: Ph VT Bnk1-J2
The setting provides selection of the Bus Volts input; either three-phase voltages from
the three-phase VTs connected to the relay, or a single voltage from the Auxiliary VT also
connected to the relay Aux VT input. The setup of these VTs is outlined under the
SYSTEM/VOLTAGE SENSING menu.
LINE VOLTS INPUT
Range: dependant upon the order code
Default: Ax VT Bnk1-J2
The setting provides selection of the Line Volts input; either three-phase voltages from
the three-phase VTs connected to the relay, or a single voltage from the Auxiliary VT also
connected to the relay Aux VT input. The setup of these VTs is outlined under SYSTEM/
VOLTAGE SENSING menu.
MAX FREQ DIFFERENCE
Range: 0.01 to 5.00 Hz in steps of 0.01 Hz
Default: 0.20 Hz
The setting selects the maximum frequency difference in 'Hz' between the two sources.
A frequency difference between the two input voltage systems below this value is within
the permissible limit for synchronism.
MAX ANGLE DIFFERENCE
Range: 1 to 100° in steps of 1°
Default: 20°
The setpoint selects the maximum angular difference in degrees between the two
sources. An angular difference between the two input voltage phasors below this value
is within the permissible limit for synchronism.
CONTROL
voltage derived
ab
input and the Aux. VT
ab
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