ABB RELION REB500 Technical Manual page 178

Section 5
Bay protection functions
t [s]
0.5
1
1.5
2
2,5
The characteristics according to BS 142 are set as follows:
normal inverse:
very inverse:
extremely inverse:
long time earth fault:
Definite minimum time tmin
Where the inverse time earth fault overcurrent function is being applied as backup protection
for a directional ground fault protection, the definite minimum time t
follows:
• t
min
• t
basic
• t
comp
Interconnections between Inverse time earth fault overcurrent
protection and directional E/F functions
The inverse time earth fault overcurrent protection is non-directional.
Directional operation can, however, be achieved by linking the directional signal (MeasFwd,
that is, fault in forwards direction) from the ground fault protection to the blocking input of
the inverse time earth fault overcurrent protection. The input must be inverted so that
blocking of the function is cancelled by an active forwards signal.
When using this arrangement, it must be noted that, when MeasFwd does not pick up, the I0-
Invers function cannot trip when the reference voltage of the ground fault function is too low.
If tripping is required for this case, the directional ground fault signal MeasBwd must be
applied to the blocking input.
Applications with single-phase reclosure
In schemes involving single-phase reclosure, the I0-Invers function has to be blocked for the
time that one pole of a circuit-breakers is open if the minimum tripping time
than the single-phase dead time. This avoids false three-phase tripping due to the load
currents in the healthy phases.
Typical settings
• I : to be calculated
B
• IStart: 1.1 I
• c: depends on the protected unit
• k : to be calculated
1
• t
min
172
k [s]
1
2.5
5
7.5
10
12.5
k = 0.14 s
1
k = 13.5 s
1
k = 80 s
1
k = 120 s
1
= tbasic + tcomp
= basic time of the ground fault function
= comparison time of the ground fault function (1 s)
B
: 0.00
© Copyright 2019 ABB. All rights reserved
1MRK 505 406-UEN B
must be set as
min
tmin is set less
Bay protection functions REB500
Technical manual