Voltage Dependent Overcurrent Element; Current Setting Threshold Selection; Vco Implementation; Figure 97: Selecting The Current Threshold Setting - GE P642 Technical Manual

Chapter 9 - Current Protection Functions
4

VOLTAGE DEPENDENT OVERCURRENT ELEMENT

Where long feeders are protected by overcurrent devices, the detection of remote phase-to-phase faults may
prove difficult due to the fact that the current pick-up of phase overcurrent elements must be set above the
maximum load current, thereby limiting the element's minimum sensitivity.
If the current seen by a local device for a remote fault condition is below its overcurrent setting, a voltage
dependent element may be used to increase the sensitivity to such faults. As a reduction in system voltage will
occur during overcurrent conditions, this may be used to enhance the sensitivity of the overcurrent protection by
reducing the pick up level.
4.1

CURRENT SETTING THRESHOLD SELECTION

The threshold setting used in the level detector depends on whether there is a Voltage Dependent condition. The
Overcurrent function selects the threshold setting according to the following diagram:
V00673

Figure 97: Selecting the current threshold setting

4.2

VCO IMPLEMENTATION

Voltage Controlled Overcurrent Protection is implemented in the OVERCURRENT column of the relevant settings
group, under the sub-heading VCONTROLLED O/C.
The function is available for stages 1, 2 of the main overcurrent element. When VCO is enabled, the under voltage
detector is used to produce a step change in the current setting, when the voltage falls below the voltage setting
VCO>1 V<Setting for stage 1 and VCO>2 V<Setting for stage 2. To achieve this, the current setting is multiplied by
a constant, which is less than 1, set by VCO>1 k Setting for stage 1 and VCO>2 k Setting for stage 2.
Each of the stages can be set to HV Winding, LV Winding, TV Winding, T1, T2, T3, T4, or T5. If the current signal
chosen for a VCO stage does not belong to the winding where the VT is located, then the VCO element is blocked
and a configuration error alarm is asserted.
The operating characteristic of the current setting when voltage controlled mode is selected is as follows:
210
Start
Yes
Does a Voltage Dependent
condition exist?
No
Use the current threshold setting
defined in the OVERCURRENT
column
End
Use the threshold setting
calculated by the Voltage
Dependent function
P64x-TM-EN-1.3
P64x