Fast Distance Algorithm; Memory Polarization - GE D30 Instruction Manual

CHAPTER 9: THEORY OF OPERATION
Table 9-8: Non-directional quadrilateral ground distance functions
Characteristic Comparator inputs
Forward Reactance I × Z – V
Reverse Reactance I × Z
REV
Right Blinder I × Z – V
R
Left Blinder I × Z – V
L
Fault-type I_0

9.1.4 Fast distance algorithm

In order to improve operating speed of the phase and ground distance zone 1 and zone 2 elements under CVT transient
conditions for high SIRs up to 60, a fast distance algorithm is implemented in the relay. This algorithm uses a weighted
average digital filtering technique and runs in parallel with a regular distance algorithm, which uses a fixed digital CVT
filtering technique. The fast distance algorithm applies the same comparators as a regular distance algorithm.
The fast distance algorithm is activated upon detection of the system disturbance and is active for three cycles only. The
pickup and operate operands of the fast distance elements are internally OR-ed with regular distance elements, to achieve
integrated distance element optimal operating speed.
Note that fast distance is not active for the following applications:
• Use of the dynamic reach control for series-compensated line applications by selecting a non-zero value for the
voltage level setting in the Distance elements
• Non-directional option for the zone 1 and 2 Direction setting
• Phase Distance applications through power transformers, when the XFMR VOL CONNECTION or XFMR CUR
CONNECTION setting is other than "None"

9.1.5 Memory polarization

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 two-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 nominal, 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 shown in the figure. The self-polarized mho
characteristic is shifted in the reverse direction for a forward fault by an amount proportional to the source impedance,
and in the forward direction for a reverse fault.
D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
jΘ
j × I_0 × e or j × I_2
jΘ
× e
jΘ
– V –j × I_0 × e or –j ×
jΘ
I_2 × e
I × Z
R
I × Z
L
I_2
Limit angle
COMP LIMIT
COMP LIMIT
90°
90°
50°
DISTANCE ELEMENTS
9
9-7