GE L90 Instruction Manual page 475

CHAPTER 5: SETTINGS
2. If the voltage bank connection value is selected as "Delta", then the phase-to-phase nominal voltage is used to define
the per-unit value. If the voltage bank connection value is selected as "Wye", then the
setting further defines the operating quantity and per-unit value for this element. If the voltage mode is set as "Phase-
phase", then the operating quantity for this element is the phase-to-phase nominal voltage. Likewise, if the voltage
mode is set to "Phase-ground", then the operating quantity for this element is the phase-to-ground nominal voltage. It
is beneficial to use the phase-to-phase voltage mode for this element when the L90 device is applied on an isolated or
resistance-grounded system.
3. When the auxiliary voltage Vx is used (regarding the condition for "None" phase voltage setting mentioned above),
then the 1 pu value is the
divided by the
SYSTEM SETUP  POWER SYSTEM  NOMINAL FREQUENCY
4. If V/Hz source is configured with both phase and auxiliary voltages, the maximum phase among the three voltage
channels at any given point in time is the input voltage signal for element operation, and therefore the per-unit value
is calculated as described in Step 1. If the measured voltage of all three phase voltages is 0, than the per-unit value
becomes automatically 0 regardless of the presence of auxiliary voltage.
The element has a linear reset characteristic. The reset time can be programmed to match the cooling characteristics of
the protected equipment. The element fully resets from the trip threshold in
can be used as an instantaneous element with no intentional time delay or as a Definite or Inverse timed element.
The characteristics of the inverse curves are as follows.
Definite time
For the definite time curve, T(sec.) = TD multiplier. For example, setting the TD multiplier to 20 results a time delay of 20
seconds to operate when above the Volts/Hz pickup setting. Instantaneous operation can be obtained the same way by
setting the TD multiplier to "0".
Inverse curve A
The curve for the volts/hertz inverse curve A shape is derived from the formula:
where
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
SYSTEM SETUP  AC INPUTS  VOLTAGE BANK N  AUXILIARY VT N SECONDARY
Figure 5-161: Volts per hertz logic
GROUPED ELEMENTS
VOLTS/HZ 1 VOLTAGE MODE
setting.
seconds. The V/Hz element
VOLTS/HZ T-RESET
setting
5
Eq. 5-37
5-289