7SR157 Technical Manual
Chapter 1 - Page 22 of 38
© 2022 Siemens Protection Devices Limited
3.3
Undervoltage Detector
There are two Undervoltage detector elements, one for the Line voltage and one for the Bus voltage. If enabled
these elements can block a Check Synchronising, System Synchronising or Close On Zero operation.
The Line Undervoltage Detector and Bus Undervoltage Detector Enabled/Disabled selection is made by changing
the
25 Line U/V
and
25 Bus U/V
in the VOLTAGE SETTING MENU.
The threshold settings (
25 Line Undervolts
and
25 Bus Undervolts
) are set as a percentage of the nominal
voltage. The relay sets an Undervoltage output when the voltage is below the threshold setting. The line and bus
voltages have independent Undervoltage outputs (
25 Line U/V
and
25 Bus U/V
).
There is 3% fixed hysteresis on the element drop off, to minimise ‘chattering’ of the element with frequency
excursion.
3.4 Differential Voltage Detector
The Differential Voltage Detector Element monitors the difference between the secondary RMS Line Voltage and
secondary RMS Bus Voltage. If enabled the element can block a Check Synchronising, System Synchronising or
Close On Zero operation.
The Differential Voltage Detector Enabled/Disabled selection is made by changing the
25 Voltage Diff
in the
VOLTAGE SETTING MENU.
The threshold setting
25 Volt Differential
is set as a percentage difference between the Line and Bus voltages.
When the difference exceeds
25 Volt Diff
setting,
25 Diff Voltage
output is set.
There is 3% fixed hysteresis on the element drop off, to minimise ‘chattering’ of the element with frequency
excursion.
3.5 Voltage Trim (Magnitude and Phase)
The relay incorporates a
Voltage Trim Magnitude
feature and a
Voltage Trim Angle
feature for both the line
and bus voltages; these are found in the CT/VT CONFIG menu. They allow small adjustments to the input
voltages and phase angles of the relay. The relay in service may not see exactly the expected nominal voltages in
sevcie. This could be due to losses from cable lengths and joints and also due to small inaccuracies in the voltage
transformers (VTs). Sometimes, interposing VTs are used to trim the voltages seen by the relay back to their
nominal values. This feature does away with the need for interposing VTs because the relay can digitally adjust
the incoming samples by a scaling factor back to their expected nominal values.
Each voltage input, V
Line
and V
Bus
, has an independent
Voltage Trim Magnitude
in the range of 0V to + 20.0V
with a step size of 0.1V. Each also has an independent
Voltage Trim Angle
in the range of -45° to + 45° with a
step size of 0.1°.
Содержание 7SR157 Argus
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