Functions
2.9 Thermal Overload Protection 49
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
156
Blocking
The thermal memory may be reset via a binary input („>RES 49 Image“) and the current-related overtem-
perature value is thus reset to zero. The same is accomplished via the binary input („>BLOCK 49 O/L“); in
this case, the entire overload protection is blocked completely, including the current warning element.
When motors must be started for emergency reasons, temperatures above the maximum permissible overtem-
peratures can be allowed by blocking the trip signal via a binary input („>EmergencyStart“). Since the
thermal replica may have exceeded the tripping temperature after initiation and dropout of the binary input, the
protection function features a programmable run-on time interval (T EMERGENCY) which is started when the
binary input drops out and continues suppressing a trip signal. Tripping via the overload protection is sup-
pressed until this time interval has elapsed. The binary input affects only the trip command. There is no effect
on the trip log nor does the thermal replica reset.
Behavior in Case of Power Supply Failure
Depending on the setting in address 235 ATEX100 of Power System Data 1 (see Section 2.1.3.2) the value of
the thermal replica is either reset to zero (ATEX100 = NO) if the power supply voltage fails, or cyclically buffered
in a non-volatile memory (ATEX100 = YES) so that it is maintained in the event of auxiliary supply voltage fail-
ure. In the latter case, when power supply is restored, the thermal replica uses the stored value for calculation
and matches it to the operating conditions. The first option is the default setting. For further details, see /5/.
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