GE D30 Instruction Manual page 462

DISTANCE ELEMENTS
• Overcurrent supervision: | 3 × I_0 | = 4.09 A > 3 A
• Mho difference angle = | –3.9° – 0° | = 3.9° < 75°
• Reactance difference angle = | –3.9° – 19.8° | = 23.7° < 75°
• Zero-sequence directional difference angle = | 19.8° – 0.0° | = 19.8° < 75°
• Negative-sequence directional difference angle = | 19.8° – 0.0° | = 19.8° < 75°
• Fault-type comparator difference angle = | 19.8° – 19.8° | = 0.0° < 50°
All four comparators and the overcurrent supervision are satisfied, so the MHO phase A ground element operates for this
fault.
9.1.6.3 Mho phase A to ground element (after memory expires)
After the memory expires, the relay checks the actual positive-sequence voltage and compares it with 10% of the nominal
voltage:
| V _1 | = 58.83 V > 0.1 × 69.28 V
A
After the memory expires the relay uses the actual voltage for polarization.
I × Z + I_0 × K0 × Z + I
A
V _1 = 58.83 V ∠–2.1°
A
I _2 × Z = 1.37 V ∠19.8°
A D
I_0 × Z = 19.11 V ∠19.8°
I_0 × Z = 1.37 V ∠19.8°
D
• Overcurrent supervision = | 3 × I_0 | = 4.09 A > 3 A
• Mho difference angle = | –3.9° – (–2.1°) | = 1.8° < 75°
• Reactance difference angle = | –3.9° – 19.8° | = 23.7° < 75°
• Zero-sequence directional difference angle = | 19.8° – (–2.1°) | = 21.9° < 75°
• Negative-sequence directional difference angle = | 19.8° – (–2.1°) | = 21.9° < 75°
• Fault-type comparator difference angle = | 19.8° – 19.8° | = 0.0° < 50°
All four comparators and the overcurrent supervision are satisfied, so the Zone 1 MHO phase A ground element operates
for this fault.
• Zero-sequence directional difference angle for zones 2 and higher (phase A) = | 19.8° – 8.4° | = 11.4° < 90°
Zones 2 and higher phase A ground elements pick-up, time-out, and operate.
9.1.6.4 Mho AB phase element
(I – I ) × Z – (V – V
A B A
)_1M = 112.08 V ∠30.0°
(V – V
A B
) × Z = 103.50 V ∠–21.2°
(I – I
A B
) × Z = 7.39 V ∠–21.2°
(I – I
A B D
• Overcurrent supervision: | (I
• Mho difference angle = | –78.7° – 30.0° | = 108.7° > 75°
• Reactance difference angle = | –78.7° – (–21.2°) | = 57.5° < 75°
9
• Directional difference angle = | –21.2° – 30.0° | = 51.2° < 75°
The mho comparator is not satisfied, so the MHO AB phase element does not operate for this fault.
Repeating this analysis, one concludes that out of the six distance elements only the ground element in phase A operates
for this fault.
9.1.6.5 Quad phase A to ground element (before memory expires)
I × Z + I_0 × K0 × Z + I
A
9-10
× K0M × Z – V = 103.33 V ∠–3.9°
G A
) = 88.65 V ∠–78.7°
B
– I ) / | = 4.27 A > 3 A
3
A B
× K0M × Z – V = 103.33 V ∠–3.9°
G A
CHAPTER 9: THEORY OF OPERATION
D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL