Memory Polarization - GE D60 Instruction Manual

8.1 DISTANCE ELEMENTS
Table 8–6: NON-DIRECTIONAL MHO GROUND DISTANCE FUNCTIONS
CHARACTERISTIC
Offset mho
Fault-type
Table 8–7: NON-DIRECTIONAL QUADRILATERAL PHASE DISTANCE FUNCTIONS
CHARACTERISTIC
Forward Reactance
Reverse Reactance
Right Blinder
Left Blinder
Table 8–8: NON-DIRECTIONAL QUADRILATERAL GROUND DISTANCE FUNCTIONS
CHARACTERISTIC
Forward Reactance
Reverse Reactance
Right Blinder
Left Blinder
Fault-type
All distance functions use memory polarization. The positive-sequence voltage – either memorized or actual – is used as a
polarizing signal. The memory is established when the positive-sequence voltage remains above 80% of its nominal value
for five power system cycles. The memory voltage is a three-cycle old voltage.
Once established, the memory is applied for the user-specified time interval. The memory timer is started when the voltage
drops below 80% of nominal or when the user-programmable condition is asserted to force memory polarization. After the
memory expires, the relay checks the magnitude of the actual positive-sequence voltage. If it is higher than 10% of nomi-
nal, the actual voltage is used; if lower, the memory voltage continues to be used.
A provision is added to force self-polarization from any user-programmable condition.
The memory-polarized mho has an extra directional integrity built-in as illustrated below. The self-polarized mho character-
istic is shifted in the reverse direction for a forward fault by an amount proportional to the source impedance, and in the for-
ward direction for a reverse fault.
8
The same desirable effect of memory polarization applies to the directional comparator of the quadrilateral characteristic.
8-6
COMPARATOR INPUTS
I × Z – V I × Z
REV
I_0 I_2
COMPARATOR INPUTS
I × Z – V I × Z
I × Z – V I × Z
REV REV
I × Z – V I × Z
R R
I × Z I × Z
– V
L
COMPARATOR INPUTS
I × Z – V j × I_0 × e
I × Z – V –j × I_0 × e
REV
I × Z – V
R
I × Z
– V
L
I_0
X
Self-polarized mho
Figure 8–2: DYNAMIC SHIFT OF THE MHO CHARACTERISTIC
D60 Line Distance Relay
LIMIT ANGLE
– V COMP LIMIT
50° (removed during open pole conditions)
LIMIT ANGLE
COMP LIMIT
COMP LIMIT
90°
90°
L
jΘ jΘ
or j × I_2 × e
jΘ jΘ
or –j × I_2 × e
I × Z
R
I × Z
L
I_2 50° (removed during open pole conditions)
Memory-polarized mho
(Reverse fault)
Memory-polarized mho
(Forward fault)
R
8 THEORY OF OPERATION
LIMIT ANGLE
COMP LIMIT
COMP LIMIT
90°
90°

8.1.4 MEMORY POLARIZATION

837719A1.CDR
GE Multilin