ABB REJ 527, Technical Reference Manual

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16
1MRS 750616-MUM Directional or Non-Directional Earth-Fault Relay
Technical Reference Manual
REJ 527
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ϕ
E
°
The start and the tripping of the directional earth-fault stages with the sin(
ϕ
) or the
cos(
ϕ
) characteristic are based on measuring the earth-fault current, I
0
,
the zero-
sequence voltage, U
0
,
and the phase angle,
ϕ,
between the voltage and the current.
The sinus or cosinus value of the phase angle is calculated and multiplied by the
earth-fault current to get the directional earth-fault current, I
ϕ
. An earth-fault stage
will start when the following three criteria are fulfilled at the same time:
• The directional earth-fault current, I
ϕ,
exceeds the set start value of the
low- or high-set earth-fault stage.
• The zero-sequence voltage, U
0 ,
exceeds the set start value of U
0b
>, which is the
same for both stages in the deblocking mode.
• The phase angle,
ϕ,
between the voltage and the current falls within the operation
sector, corrected with
ϕ
c
.
When an earth-fault stage starts, a start signal will be generated and a start indication
shown on the HMI. If the above mentioned criteria remain fulfilled until the set
operate time elapses, the stage will deliver a trip signal and a trip indication will be
shown on the HMI. The trip indication will remain active although the protection
stage is reset. The direction of the fault spot is determined by means of the angle
between the voltage and the current. Directional earth-fault characteristic sin(
ϕ
)
corresponds to the earth-fault protection with the basic angle -90° and cos(
ϕ
) to the
earth-fault protection with the basic angle 0°.
Figures 4.1.4.2.-4 and 4.1.4.2.-5 show examples of the sin(
ϕ
) and the cos(
ϕ
)
characteristics.
Uo
Io
ϕ
∆ϕ
OPERATION SECTOR
ϕ
b=-90°
∆ϕ
=80°
Io>
LEAD LAG
Ba_-90_degrees