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2 Functions
Coolant Tempera-
With 7UM61 the thermal model of the considers an external temperature value. De-
ture (Ambient Tem-
pending on the application, this temperature can be the coolant or ambient tempera-
perature)
ture or, in the case of gas turbines, the entry temperature of the cold gas.
The temperature to be considered can be input in one of the following ways:
• via Profibus DP interface/Modbus
• Via temperature detection unit (Thermobox, RTD 1)
The ambient or coolant temperature can also be detected by an external temperature
sensor, digitized and fed to the 7UM61 via the Profibus-DP Interface / Modbus .
If a temperature supervision feature is implemented using a thermobox (see Section
2.32) the RTD1 input can be used for temperature inclusion in the overload protection.
With coolant temperature detection in accordance with one of the three methods de-
scribed, the maximum permissible current I
ence of the coolant. If the ambient or coolant temperature is lower, the machine can
support a higher current than when the temperatures are high.
Current Limiting
In order that overload protection on occurrence of high fault currents (and with small
time constants) does not cause extremely short trip times thereby perhaps affecting
time grading of the fault protection, it is possible to implement current limiting for the
overload protection. Currents exceeding the value specified at parameter 1615 I MAX
THERM. are limited to this value. For this reason, they do not further reduce trip time
in the thermal memory.
Standstill Time
The above differential equation assumes a constant cooling that is reflected by the
time constant τ = R
Constant
tilated machine, however, the thermal time constant at standstill can differ consider-
ably from the time constant of a continually running machine, since then the ventilation
provides for cooling whereas at standstill only natural convection takes place.
Therefore, two time constants must be considered in such cases for setting.
In this context, machine standstill is detected when the current undershoots the
threshold value BkrClosed I MIN (see margin heading "Current Flow Monitoring"
in Section 2.3).
The thermal memory may be reset via a binary input (">RM th.rep. O/L"). The
Blocking
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 permissible overtemperatures can be allowed by blocking the
tripping signal via a binary input (">Emer.Start O/L"). Since the thermal profile
may have exceeded the tripping temperature after startup and dropout of the binary
input has taken place, the protection function features a programmable run-on time in-
terval (T EMERGENCY) which is started when the binary input drops out and continues
suppressing a trip signal. Tripping will be suppressed 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 in Case
For overload protection, together with all other thermal protection functions of the
7UM61 in the Power System Data 1 (parameter 274 ATEX100, see Section 2.3) it is
of Power Supply
Failure
possible to choose whether the calculated overtemperature will be stored throughout
a power supply failure, or reset to zero. This last option is the default setting.
60
max
· C
(thermal resistance and thermal capacitance). In a self-ven-
th
th
is influenced by the temperature differ-
C53000-G1176-C127-3
7UM61 Manual
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