20-4 9424200996
Thermal Curve (49TC) Protection BE1-11m
The Voltage Configuration screen is shown in Figure 20-3.
Figure 20-3. User Table Curve, Voltage Configuration Screen
K Setting
The K setting determines how much the negative-sequence current will bias the equivalent thermal
current calculated by the BE1-11m. The equivalent thermal current is calculated in Equation 20-4. If the
IEC Curve is being used, then I
eq
is fixed at zero and this equation is not necessary.
I
= I
1 + k
I
I
Equation 20-4. Equivalent Thermal Current
Where:
I
eq
= equivalent thermal current in pickup (unit of thermal pickup current)
I = maximum phase current in pickup
I
1
= positive-sequence fundamental component of current in pickup
I
2
= negative-sequence fundamental component of current in pickup
k = constant used to determine additional heating from negative-sequence current in pickup
Hot and Cold Safe Stall Time
The Hot and Cold Safe Stall Time settings determine the thermal capacity level that is reached for
currents less than the 49TC pickup. The Running and Stopped Cool Time Constant settings determine
the rate at which the thermal capacity increases or decreases for currents less than the 49TC pickup. The
thermal capacity calculations are shown in Equation 20-5 and Equation 20-6. If the IEC Curve is being
used, then I
eq
= 0.
TCU
=
I
S SF FLA
1
hot safe stall time
cold safe stall time
Equation 20-5. TCU
end
Where:
TCU
end
= Thermal Capacity that the motor will eventually reach if current is maintained at present
magnitude.
τ = Cooling time constant (either running or stopped)
I
eq
= Equivalent thermal current (zero if IEC Curve is being used)
S = Overload Pickup setting
SF = Service Factor setting
FLA = Full Load Amps setting
TCU =
(
TCU
TCU
)
e
+ TCU
Equation 20-6. TCU
Where:
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