ABB RELION REX640 Technical Manual page 558

Protection functions
• Alarms (but no tripping) about high-ohmic earth faults in order to monitor the
insulation status of the network and provide early indication of evolving faults
before they cause tripping (by stages 1 or 2), stage 3.
Besides the internal start condition based on residual zero-sequence overvoltage,
MFADPSDE can also be externally released by using the RELEASE input. In this case,
the external release signal overrides the
internal limit to the minimum value.
Multi-frequency admittance calculation
The Multi-frequency admittance calculation module calculates neutral admittances
using fundamental frequency and the 2nd, 3rd, 5th, 7th and 9th harmonic
components of residual current and zero-sequence voltage. The fundamental
frequency admittance (conductance and susceptance) is calculated if the
magnitude of a harmonic in residual current and zero-sequence voltage is
measurable by the relay.
1
Y
=
0
1
Y
0
1
I
0
1
U
0
1
G
o
1
B
o
Im
where n = 2, 3, 5, 7 and 9
n
Y
0
n
I
0
Table continues on the next page
558
1
3 I
⋅
1 1
0
G j B
= + ⋅
o o
1
U
−
0
Fundamental frequency neutral admittance phasor
Fundamental frequency zero-sequence current phasor
Fundamental frequency zero-sequence voltage phasor
Fundamental frequency conductance,
Fundamental frequency susceptance,
 
⋅
n
3 I
 
= = ⋅
n
 
0
Im
Y j B
 
0
−
 n 
 U 
0
nth harmonic frequency neutral admittance phasor
nth harmonic frequency zero-sequence current phasor
Voltage start value setting and sets the
Re Y
Im Y
n
o
1MRS759142 F
(Equation 88)
1 1
( + +
I I
A B
( =
3
1
( +
U U
A B
( =
3
( )
1
0
( )
1
0
(Equation 89)
Technical Manual
1
)
I
C
)
1 1
+ )
U
C
)
REX640