CHAPTER 15: THEORY OF OPERATION DISTANCE ELEMENTS
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 639
Mho phase A to ground element analysis, before memory expires
Before the memory expires, the following values are calculated for the mho phase A to
ground distance element:
Eq. 72
The ground distance element checks for the following conditions for overcurrent
supervision and the difference angles.
Table 16: Mho phase A to ground element conditions
The results are shown in the following table.
Table 17: Mho phase A to ground element analysis
All the comparators and the overcurrent supervision are satisfied.
Mho phase A to ground element analysis, after memory expires
After memory expires, the D90
Plus
checks the actual positive sequence voltage and
compares it to 10% of the nominal voltage.
Eq. 73
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 × 1.377 A = 4.09 A > 3 A Yes
Mho difference angle | –3.9° – 0° | = 3.9° < 75° Yes
Reactance difference angle | –3.9° – 19.8° | = 23.7° < 75° Yes
Zero-sequence directional
difference angle
| 19.8° – 0.0° | = 19.8° < 75° Yes
Negative-sequence directional
difference angle
| 19.8° – 0.0° | = 19.8° < 75° Yes
Fault type comparator
difference angle
| 19.8° – 19.8° | = 0.0° < 50° Yes
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