Caused by the thermal overload protection function, there can be a lockout to reconnect
the tripped circuit after operating. The lockout output
BLK_CLOSE
is activated at the
same time when the
TRIP
output is activated and is not reset until the device temperature
has cooled down below the set value of the
Reclose temperature
setting.
BLK_CLOSE
works also as hysteresis for the
TRIP
signal preventing a new
TRIP
signal activation
until
BLK_CLOSE
has reset. The
Maximum temperature
value must be set at least two
degrees above the set value of
Reclose temperature
.
The time to lockout release is calculated, that is, the calculation of the cooling time to a set
value. The calculated temperature can be reset to its initial value (the
Initial temperature
setting) via a control parameter that is located under the clear menu. This is useful during
testing when secondary injected current has given a calculated false temperature level.
t
lockout
release
final
lockout
release
final
n
_
_
ln
= − ⋅
−
−
τ
Θ
Θ
Θ
Θ
A070783 V3 EN
(Equation 15)
Here the final temperature is equal to the set or measured ambient temperature.
In some applications, the measured current can involve a number of parallel lines. This is
often used for cable lines where one bay connects several parallel cables. By setting the
Current multiplier
parameter to the number of parallel lines (cables), the actual current on
one line is used in the protection algorithm. To activate this option, the
ENA_MULT
input
must be activated.
The
Env temperature set
setting is used to define the ambient temperature.
The temperature calculation is initiated from the value defined with the
Initial
temperature
setting parameter. This is done in case the protection relay is powered up, the
function is disabled and enabled back or reset through the Clear menu. The temperature is
also stored in the nonvolatile memory and restored in case the protection relay is restarted.
The thermal time constant of the protected circuit is given in seconds with the
Time
constant
setting. Please see cable manufacturers manuals for further details.
4.5.1.5
Application
The lines and cables in the power system are constructed for a certain maximum load
current level. If the current exceeds this level, the losses will be higher than expected. As
a consequence, the temperature of the conductors will increase. If the temperature of the
lines and cables reaches too high values, it can cause a risk of damages by, for example,
the following ways:
Section 4
1MRS240050-IB C
Protection functions
298
REF615R
Technical Manual
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