2 Functions
216
7SA522 Manual
C53000-G1176-C155-3
Short-circuit power at the beginning of the line:
S
k
' = 2.5 GVA
Current Transformer 600 A / 5 A
From that the line impedance Z
L
and the source impedance Z
S
are calculated:
Z
1
/s = √0.19
2
+ 0.42
2
Ω/km = 0.46 Ω/km
Z
L
= 0.46 Ω/km · 60 km = 27.66 Ω
The three-phase fault current at the line end is I
F end
:
With a safety factor of 10 %, the following primary setting value is calculated:
setting value I>> = 1.1 · 2150 A = 2365 A
or the secondary setting value:
i.e. in case of fault currents exceeding 2365 A (primary) or 19.7A (secondary) you can
be sure that a short-circuit has occurred on the protected line. This fault can immedi-
ately be cleared by the time overcurrent protection.
Note
: the calculation was carried out with absolute values, which is sufficiently precise
for overhead lines. If the angles of the source impedance and the line impedance vary
considerably, a complex calculation will have to be carried out.
A similar calculation can be carried out for earth faults, with the maximum earth current
occurring at the line end during a short-circuit being decisive.
The set time delays are pure additional delays, which do not include the operating time
(measuring time).
The parameter ,!!7HOHS%, (address ) defines whether the time delays
´!2&,QVW75,3µ (address 7110) and 7,SK!! (address ) can be bypassed
by the binary input 7,!! (FNo ) or by the operational automatic reclosure
function. The binary input (if allocated) is applied to all stages of the time-overcurrent
protection. With ,!!7HOHS%, = <(6 you can set the I>> stages to trip immediately
after the pickup, only if the binary input is activated. Set time delays for ,!!
7HOHS%, = 12 are always activated.
If the I>> stage is to trip when switching the line on to a fault with or without a short
delay, 627)7LPH'(/$< (address , see above and refer to Subsection “Gen-
eral”), the parameter ,!!627) (address ) is set to <(6. Any other stage can be
selected as well for this instantaneous tripping.
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