Siemens SIPROTEC 7SK80 Manual page 148

Functions
2.9 Thermal Overload Protection 49
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 has
taken place, 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 pro-
tection is suppressed 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) 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, the thermal replica uses the stored value for calculation and matches it to the operating
conditions. The first option is the default setting (see /5/).
148
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010