The requirement in this network is that the ground fault protection shall have
sensitivity so that ground faults with resistance up to 3 000 Ω shall be detected and
cleared.
The residual voltage at 3 000 Ω works out as:
0
138000 3
0 52 79674 41431
3 3 3000
1
1
9561
Phase
o
f
V
/
V . V
R
Z
= = = × =
× ×
+
+
GUID-788DE8BD-9D07-463D-90D8-BAE663628155 V1 EN (Equation 31)
This corresponds to 52 % of residual voltage at non-resistive (solid) phase-to-ground
fault.
The active current works out as:
0
0 52 25 13
j,active Rn
Phase
V
I I . A
V
= × = × =
GUID-1CA3ABED-3D49-477D-B0D2-9CCEEB24684F V1 EN (Equation 32)
This corresponds to 52 % of the neutral point resistor rated current. The setting
OpModeSel can be set to:
• 3I0Cosfi where the current component is related to the set characteristic angle
relative to the reference voltage.
• 3I03V0Cosfi where the power component is related to the set characteristic
angle relative to the reference voltage
• 3I0 and fi, measuring the total residual current if the angle fi is within the set
range.
In this case 3I0Cosfi is chosen.
2. Set DirMode to Forward
The setting DirMode can be set Forward or Reverse. Forward is chosen.
3. Set RCADir to 0°
The setting RCADir (Relay Characteristic Angle) determines the angle between the
residual current and voltage giving maximum sensitivity. If a neutral point resistor
is used the setting 0° is used. If capacitive residual current is measured (isolated
networks) the setting -90° is used.
4. Set RCAComp to 0°
The setting RCAComp (Relay Characteristic Angle Compensation) can be used for
compensation of instrument transformer angle error.
5. Set ROADir to 90°
The setting ROADir (Relay Open Angle) is the angle sector where the protection can
operate. Normally 90° is used. In special cases with very large capacitive current fed
from the line this sector can be limited to avoid unwanted trip at fault on another line.
6. Set INCosPhiPU to 1.3 % (corresponds to 13 A primary current)
The setting INCosPhiPU provides the sensitivity of the protection. Above, the
required current sensitivity (active ground fault current) is calculated to 13 A.
1MRK 506 334-UUS A Section 3
REL650 setting examples
87
Application manual
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