Functions
6-141
7SA522 Manual
C53000-G1176-C119-2
The parameter
(address
) determines whether the delay times
) and
(address
) may be bypassed via the bi-
nary input “
” (F.No.
) or via the automatic reclose ready state.
The binary input (if assigned) is common to all stages of the overcurrent protection.
With the parameter
<HV
it is determined that the I>>–stages trip
without delay following pick up if there is an operating signal present at the binary in-
put; if the setting is
1R
the set delay times always come into effect.
If the I>>-stage is to trip when switching the line on to a fault with or without a short
delay,
(address
, see above and refer to Sub-section “Gen-
(address
) must be set to Yes. For this fast
switch on to a fault protection any other stage may also be selected.
Definite Time
Overcurrent Stages
Iph>, 3I0>
For the setting of the current pick-up threshold
(address
), the maximum
operating current that can occur is decisive. Pick-up due to overload must be excluded
as the device operates as short-circuit protection with correspondingly short tripping
times and not as overload protection. The setting is therefore: on overhead lines ap-
proximately 10 %, on transformers and motors approximately 20 % above the maxi-
mum expected (over-)load current.
When using a personal computer and DIGSI
®
4 to apply the settings, these can be op-
tionally entered as primary or secondary values. When applying the setting parame-
ters as secondary values, the primary currents must be converted to the secondary
side of the current transformer.
Calculation example:
110 kV overhead line 150 mm
2
as in the example in Sub-section 6.2.3.2 or 6.2.4.2:
maximum transmittable power
P
max
= 120 MVA corresponds to
I
max
= 630 A
current transformer 600 A/5 A
security margin
1.1
When applying settings with primary values, the following setting results:
Set value I> = 1.1 · 630 A = 693 A
When applying settings with secondary values, the following setting results:
The earth current stage
(address
), must still be able to detect the smallest
earth fault current that may be present. For very small earth currents the earth fault
protection is most suited (refer to Section 6.5).
The time delay
(address
) which has to be set is derived from the grading
plan of the system. If implemented as emergency overcurrent protection, shorter trip-
ping time delays (one grading time stage longer than the fast tripping stage) are ad-
visable, as this function is only activated when the
local
measured voltage fails.
(address
) can usually be set with a smaller time delay accord-
ing to a separate earth fault grading plan.
The set times of the definite time stages are pure additional time delays which do not
include the operating (measuring) time of the protection. If only the phase currents of
a particular stage should be monitored, the times of the earth current stage must be
Setting value I>
1.1
=
630 A
600 A
----------------
5 A
⋅
⋅
5.8 A
=
Summary of Contents for siprotec 7SA522
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