GE D90 Plus Instruction Manual page 617

CHAPTER 15: THEORY OF OPERATION
Mho phase A to ground element analysis, before memory expires
Mho phase A to ground element analysis, after memory expires
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Before the memory expires, the following values are calculated for the mho phase A to
ground distance element.
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
Parameter
Overcurrent supervision
Mho difference angle
Reactance difference angle
Zero-sequence directional
difference angle
Negative-sequence
directional difference angle
Fault type comparator
difference angle
The results are shown in the following table.
Table 17: Mho phase A to ground element analysis
Parameter
Overcurrent supervision
Mho difference angle
Reactance difference angle
Zero-sequence directional
difference angle
Negative-sequence directional
difference angle
Fault type comparator
difference angle
All the comparators and the overcurrent supervision are satisfied.
After memory expires, the D90
compares it to 10% of the nominal voltage.
Condition
Supervision
3 × I_0 >
| ∠(I
× Z + I_0 × K × Z + I × K
A 0 R G
Comparator Limit
| ∠(I
× Z + I_0 × K × Z + I × K
A 0 R G
Comparator Limit
| ∠( I_0 × Z ) – ∠(V
Directional Comparator Limit
_1M) | <
D A
| ∠( I ) – ∠(V
_2 × Z _1M) | <
A D A
| ∠( I ) – ∠(I_0 × Z
_2 × Z ) | < 50°
A D D
Calculation
3 × 1.377 A = 4.09 A
| –3.9° – 0° | = 3.9°
| –3.9° – 19.8° | = 23.7°
| 19.8° – 0.0° | = 19.8°
| 19.8° – 0.0° | = 19.8°
| 19.8° – 19.8° | = 0.0°
Plus
checks the actual positive sequence voltage and
Plus
THE D90 DISTANCE ELEMENTS
) – ∠(V
× Z – V _1M) | <
0M A A
) – ∠(I_0 × Z) | <
× Z – V
0M A
Directional Comparator Limit
Requirement Condition met
> 3 A Yes
< 75° Yes
< 75° Yes
< 75° Yes
< 75° Yes
< 50° Yes
Eq. 55
Eq. 56
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