GE D90 Plus - Page 650

640 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
DISTANCE ELEMENTS CHAPTER 15: THEORY OF OPERATION
When memory expires, the D90
Plus
uses the actual voltage for polarization. The following
values are calculated for the mho phase A to ground distance element:
Eq. 74
The ground distance element checks for the following conditions for overcurrent
supervision and the difference angles.
Table 18: Mho phase A to ground element conditions
The results are shown in the following table.
Table 19: Mho phase A to ground element analysis
All the comparators and the overcurrent supervision are satisfied. The zone 1 mho phase A
ground distance element operates for this fault.
The zero-sequence directional difference angle for zones 2 through 4 (phase A) is | 19.8° –
8.4° | = 11.4° < 90°. Therefore, the phase A ground distance elements pick up, time out, and
operate.
Mho phase AB element analysis
The following values are calculated for the mho phase AB distance element:
Eq. 75
The phase distance element checks for the following conditions for overcurrent
supervision and the difference angles.
Parameter Condition
Overcurrent supervision 3 × I_0 >
Supervision
Mho difference angle | ∠(I
A
× Z + I_0 × K
0
× Z
R
+ I
G
× K
0M
× Z – V
A
) – ∠(V
A
_1M) | <
Comparator Limit
Reactance difference angle | ∠(I
A
× Z + I_0 × K
0
× Z
R
+ I
G
× K
0M
× Z – V
A
) – ∠(I_0 × Z) | <
Comparator Limit
Zero-sequence directional
difference angle
| ∠( I_0 × Z
D
) – ∠(V
A
_1M) | < Directional Comparator Limit
Negative-sequence
directional difference angle
| ∠( I
A
_2 × Z
D
) – ∠(V
A
_1M) | < Directional Comparator Limit
Fault type comparator
difference angle
| ∠( I
A
_2 × Z
D
) – ∠(I_0 × Z
D
) | < 50°
Parameter Calculation Requirement Condition met
Overcurrent supervision 3 × 13.7 A = 4.09 A > 3 A Yes
Mho difference angle | –3.9° – (–2.1°) | = 1.8° < 75° Yes
Reactance difference angle | –3.9° – 19.8° | = 23.7° < 75° Yes
Zero-sequence directional
difference angle
| 19.8° – (–2.1°) | = 21.9° < 75° Yes
Negative-sequence
directional difference angle
| 19.8° – (–2.1°) | = 21.9° < 75° Yes
Fault type comparator
difference angle
| 19.8° – 19.8° | = 0.0° < 50° Yes
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