GE C70 Instruction Manual page 290

GROUPED ELEMENTS
The phase directional elements (one for each of phases A, B, and C) determine the phase current flow direction for steady
state and fault conditions and can be used to control the operation of the phase overcurrent elements via the
of these elements.
5
This element is intended to apply a block signal to an overcurrent element to prevent an operation when current is flowing
in a particular direction. The direction of current flow is determined by measuring the phase angle between the current
from the phase CTs and the line-line voltage from the VTs, based on the 90° or quadrature connection. If there is a
requirement to supervise overcurrent elements for flows in opposite directions, such as can happen through a bus-tie
breaker, two phase directional elements should be programmed with opposite element characteristic angle (ECA) settings.
To increase security for three phase faults very close to the VTs used to measure the polarizing voltage, a voltage memory
feature is incorporated. This feature stores the polarizing voltage the moment before the voltage collapses, and uses it to
determine direction. The voltage memory remains valid for one second after the voltage has collapsed.
The main component of the phase directional element is the phase angle comparator with two inputs: the operating signal
(phase current) and the polarizing signal (the line voltage, shifted in the leading direction by the characteristic angle, ECA).
The table shows the operating and polarizing signals used for phase directional control.
5-166
PHASE DIR 1

ECA: 30
PHASE DIR POL V1

THRESHOLD: 0.700 pu
PHASE DIR 1 BLOCK

WHEN V MEM EXP: No
PHASE DIR 1

TARGET: Self-reset
PHASE DIR 1

EVENTS: Disabled
Figure 5-78: Phase A directional polarization
VCG
Phasors for Phase A Polarization:
×
VPol = VBC (1/_ECA) = polarizing voltage
IA = operating current
ECA = Element Characteristic Angle at 30°
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL
Range: 0 to 359° in steps of 1
Range: 0.000 to 3.000 pu in steps of 0.001
Range: No, Yes
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
–90°
VAG (Unfaulted)
Fault angle
set at 60° Lag
VPol
VAG(Faulted)
IA
ECA
set at 30°
VBC
VBC
VBG
827800A2.CDR
CHAPTER 5: SETTINGS
inputs
BLOCK
+90°