when the motor currents drop below a programmable minimum current setting BkrClosed I MIN (refer to
"Current Flow Monitoring" in Section 2.1.3 Power System Data 1). For externally-cooled motors, cables and
transformers, the Kτ-FACTOR = 1.
Blocking
The thermal memory may be reset via a binary input (
>RES 49 Image
) and the current-related overtempera-
ture 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 over-
temperatures 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
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 Power System
Data 1) 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 failure. 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/ Additional description for
the protection of explosion-protected motors of protection type increased safety “e”).
The following figure shows the logic diagram for the overload protection function.
Functions
2.10 Thermal Overload Protection 49
148 SIPROTEC 4, 7SJ80, Manual
E50417-G1140-C343-A8, Edition 12.2017
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