Siemens SIPROTEC 7UT613 series Manual page 222

2 Functions
Motor Startup
Emergency Start-
ing of Machines
Figure 2-98 Logic diagram of the thermal overload protection (simplified)
222
On startup of electrical machines the overtemperature calculated by the thermal
replica may exceed the alarm overtemperature or even the trip overtemperature. In
order to avoid an alarm or trip, the starting current is acquired and the resulting in-
crease of temperature rise is suppressed. This means that the calculated temperature
rise is kept constant as long as the starting current is detected.
When machines must be started for emergency reasons, operating temperature
above the maximum permissible operating temperature can be allowed by blocking
the tripping signal via a binary input („>Emer.Start O/L"). After startup and
dropout of the binary input, the thermal replica may still be greater than the trip tem-
perature rise. Therefore the thermal replica features a settable run-on time (T
EMERGENCY) which is started when the binary input drops out. It also suppresses the
trip command. Tripping by the overload protection will be defeated until the time inter-
val has lapsed. This binary input only affects the trip command. There is no effect on
fault recording, nor does the thermal replica reset.
7UT613/63x Manual
C53000-G1176-C160-2