Micom P634 - Tripping Characteristics

the summation of the current values from two user-selected transformer ends.
(In the latter case, MAIN: Current summation decides about which
transformer ends are included in the summation, see Section 3.12.5, (p. 3-72).)
Then the setting THRM1: Select current PSx specifies whether the maximum
RMS phase current (of the selected transformer end) shall be used, or the
residual current calculated from the three phase currents (of the selected
transformer end), or the residual current directly measured at the respective
current transformer.
3.25.4 Tripping Characteristics
The selected current (THRM1: I, see Section 3.25.3, (p. 3-176)) of the selected
transformer end is used to track a first-order thermal replica according to
IEC 255-8. The following parameters will govern the tripping parameters:
●
The set thermal time constant (τ) of the protected object
THRM1: Tim.const.1,>Ibl PSx
●
The tripping threshold Δϑ
trip
set at THRM1: Rel. O/T trip PSx
●
The accumulated thermal load Δϑ
0
●
The updated measured coolant temperature Θ
c
for the protected object
●
The maximum permissible coolant temperature Θ
c,max
set at
THRM1: Max.perm.cool.tmpPSx
●
The maximum permissible object temperature Θ
max
set at
THRM1: Max.perm.obj.tmp.PSx
●
If the value of the selected current (THRM1: I) is greater than 10·I
ref
then
only the fixed maximum value 10·I
ref
is used for calculating the tripping
time.
The object temperature is calculated from the selected current (THRM1: I) and
can be displayed at THRM1: Object temperat.,TH1. The coolant temperature
is either measured via the PT 100 input or via a 20 mA input, or a default
temperature value is used instead. This choice is governed by the setting at
THRM1: Select CTA PSx. The coolant temperature is displayed at
THRM1: Coolant temp. TH1. The difference between the settings for the
maximum permissible temperatures of the protected object and the coolant can
be displayed at THRM1: O/T f.Iref persist 1.
The tripping characteristics are then defined by the equation:
t = τ ⋅ ln
(
I
I
ref
)
2
− Δϑ
0
(
I
I
ref
)
2
− Δϑ
trip
⋅
(
1 −
Θ
c
− Θ
c,max
Θ
max
− Θ
c,max
)
The setting for the operating mode selects an “absolute” or “relative” replica. If
the setting is for “Absolute replica”, the P634 will operate with a fixed trip
threshold Δ
trip
of 100 %.
3 Operation
P634
P634/EN M/R-42-A // P634‑311‑653 3-177