ABB RELION REX640 - Page 558

• 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 Voltage start value setting and sets 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.
Y
I
U
G j B
o o0
1
0
1
0
1
1 1
3
=
⋅
−
= + ⋅
(Equation 88)
Y
0
1
Fundamental frequency neutral admittance phasor
I
0
1
Fundamental frequency zero-sequence current phasor
(
( )
)=
+ +
I I I
A B C
1 1 1
3
U
0
1
Fundamental frequency zero-sequence voltage phasor
(
( )
)=
+ +
U U U
A B C
1 1 1
3
G
o
1
Fundamental frequency conductance,
Re Y
0
1
( )
B
o
1
Fundamental frequency susceptance,
Im Y
0
1
( )
Im ImY
I
U
j B
n
n
n
o
n
0
0
0
3




=
⋅
−








= ⋅
(Equation 89)
where n = 2, 3, 5, 7 and 9
Y
n
0
nth harmonic frequency neutral admittance phasor
I
n
0
nth harmonic frequency zero-sequence current phasor
Table continues on the next page
Protection functions 1MRS759142 F
558 REX640
Technical Manual