GE M60 Instruction Manual page 326

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.
Table 5-22: Operating and polarizing signals
Phase Operating signal
A angle of IA
B angle of IB
C angle of IC
Mode of operation
When the function is "Disabled" or the operating current is below 5%  CT nominal, the element output is "0"
•
When the function is "Enabled," the operating current is above 5%  CT nominal, and the polarizing voltage is above
•
the
PRODUCT SETUP  DISPLAY PROPERTIES  VOLTAGE CUT-OFF LEVEL
phase angle between the operating and polarizing signals:
– The element output is logic "0" when the operating current is within polarizing voltage ±90°
5-198
Figure 5-108: 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°
Polarizing signal V
pol
ABC phase sequence
angle of VBC  (1ECA)
angle of VCA  (1ECA)
angle of VAB  (1ECA)
–90°
VAG (Unfaulted)
Fault angle
set at 60° Lag
VPol
VAG(Faulted)
IA
ECA
set at 30°
VBC
VBC
VBG
827800A2.CDR
ACB phase sequence
angle of VCB  (1ECA)
angle of VAC  (1ECA)
angle of VBA  (1ECA)
value, the element output is dependent on the
M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
inputs
BLOCK
+90°