Level detector
The magnitude of the operating quantity is compared to the set
Start value
and
the magnitude of the polarizing quantity is compared to the set
Voltage start
value
. If both the limits are exceeded, the level detector sends an enabling signal to
the timer module. When the
Enable voltage limit
setting is set to "False",
Voltage
start value
has no effect and the level detection is purely based on the operating
quantity. If the ENA_MULT input is active, the
Start value
setting is multiplied by the
Start value Mult
setting.
The operating quantity (residual current) can be selected with the setting
Io signal
Sel
. The options are "Measured Io" and "Calculated Io". If "Measured Io" is selected,
the current ratio for Io-channel is given in Configuration > Analog inputs > Current
(Io,CT). If "Calculated Io" is selected, the current ratio is obtained from the phase-
current channels given in Configuration > Analog inputs > Current (3I,CT).
The operating quantity (residual voltage) can be selected with the setting
Uo
signal Sel.
The options are "Measured Uo" and "Calculated Uo". If "Measured Uo"
is selected, the voltage ratio for Uo-channel is given in Configuration > Analog
inputs > Voltage (Uo,VT). If "Calculated Uo" is selected, the voltage ratio is
obtained from the phase-voltage channels given in Configuration > Analog inputs >
Voltage (3U,VT).
Example 1: Io is measured with cable core CT (100/1 A) and Uo is measured from
open-delta connected VTs (20/sqrt(3) kV : 100/sqrt(3) V : 100/3 V). In this case,
"Measured Io" and "Measured Uo" are selected. The nominal values for residual
current and residual voltage are obtained from CT and VT ratios entered in Residual
current Io: Configuration > Analog inputs > Current (Io,CT): 100 A : 1 A. The Residual
voltage Uo: Configuration > Analog inputs > Voltage (Uo,VT): 11.547 kV : 100 V. The
Start value
of 1.0 × In corresponds to 1.0 * 100 A = 100 A in the primary. The
Voltage
start value
of 1.0 × Un corresponds to 1.0 * 11.547 kV = 11.547 kV in the primary.
Example 2: Both Io and Uo are calculated from the phase quantities. Phase CT-
ratio is 100 : 1 A and phase VT-ratio is 20/sqrt(3) kV : 100/sqrt(3) V. In this case,
"Calculated Io" and "Calculated Uo" are selected. The nominal values for residual
current and residual voltage are obtained from CT and VT ratios entered in Residual
current Io: Configuration > Analog inputs > Current (3I,CT): 100 A : 1 A. The residual
voltage Uo: Configuration > Analog inputs > Voltage (3U,VT): 20.000 kV : 100 V. The
Start value
of 1.0 × In corresponds to 1.0 * 100 A = 100 A in the primary. The
Voltage
start value
of 1.0 × Un corresponds to 1.0 * 20.000 kV = 20.000 kV in the primary.
If "Calculated Uo" is selected, the residual voltage nominal value is always
phase-to-phase voltage. Thus, the valid maximum setting for residual
Voltage start value is 0.577 x Un. The calculated Uo requires that all the
three phase-to-earth voltages are connected to the protection relay. Uo
cannot be calculated from the phase-to-phase voltages.
If the
Enable voltage limit
setting is set to "True", the magnitude of the
polarizing quantity is checked even if the
Directional mode
was set to
"Non-directional" or
Allow Non Dir
to "True". The protection relay does
not accept the
Start value
or
Start value Mult
setting if the product of
these settings exceeds the
Start value
setting range.
Typically, the ENA_MULT input is connected to the inrush detection function
INRHPAR. In case of inrush, INRPHAR activates the ENA_MULT input, which multiplies
Start value
by the
Start value Mult
setting.
1MRS757644 H
Protection functions
620 series
Technical Manual
389
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