Functions
2.11 Thermal Overload Protection (ANSI 49)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
83
Blocking
The thermal memory may be reset via a binary input („>RM th.rep. O/L“). The current-induced excessive
temperature value is reset to zero. The same is achieved by entering a blocking („>BLK ThOverload“); in
that case the overload protection is blocked completely, including the current alarm stage.
When machines must be started for emergency reasons, operating temperatures above the maximum permis-
sible operating temperatures are allowed (emergency start). Then exclusively the tripping signal can be blocked
via a binary input („>Emer.Start O/L“). Since the thermal profile may have exceeded the tripping temper-
ature after startup and dropout of the binary input has taken place, the protection function features a program-
mable run-on time interval (T EMERGENCY) which is started when the binary input drops out and continues sup-
pressing a trip signal. Tripping by the overload protection will be defeated until this time interval elapses. This
binary input affects only the tripping signal. It has no effect on the fault condition logging nor does it reset the
thermal profile.
Behaviour on Power Supply Failure
For overload protection, together with all other thermal protection functions of the 7UM62 in the Power System
Data 1 (parameter 274 ATEX100, see Section 2.5), it is possible to choose whether the calculated overtem-
perature will be stored throughout a power supply failure, or reset to zero. This latter option is the default set-
ting.
The following figure shows the logic diagram for overload protection.
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