Siemens SINAMICS PERFECT HARMONY GH180 Function Manual page 61
Advanced motor protection for type: 6sr variable frequency drives
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Also See for SINAMICS PERFECT HARMONY GH180:
- Function manual (538 pages) ,
- Operating instructions manual (224 pages) ,
- Reference manual (48 pages)
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Enable State Out1
Fixed Parameter Thermal Overload Ena‐
ble State
Enable State Out2
Fixed Parameter Thermal Overload Ena‐
ble State
Fixed Thermal Overload is mutually exclusive with Variable Thermal Overload.
Discussion of Fixed Parameter Thermal Overload Protection Model
The thermal overload function uses a differential equation model to predict the amount of
thermal capacity used. The equation calculates H(t), an H(t) value of 1.0 indicates that 100%
of the thermal capacity of the machine has been used and basically that the machine is at the
maximum allowable temperature.
The differential equation is given by:
( )
H t
One of the inputs to the equation is ieq(t) is the equivalent heating current expressed in per unit.
One per unit current in this context is equal to the rated current of the machine being protected.
Both H(t) and ieq(t) are functions of time while the other variables in the equation are fixed
(although adjustable) parameters.
The equivalent heating current is a function of the RMS value of the stator current and the
negative sequence stator current. ieq(t) is given by:
i
=
eq
Where:
i
avg
The equivalent current is a function of the average RMS stator current plus a term related to the
negative sequence current i2. The q factor weights the negative sequence current in the
calculation of the equivalent heating current ieq. The q factor should be adjusted to account for
the additional heating effects of negative sequence current and in many cases of induction
machines should be chosen to be equal to the ratio of negative sequence rotor resistance to the
positive sequence rotor resistance.
Advanced Motor Protection for Variable Speed Operation
Manual, AA, A5E46373908A
6.14 Device 49T - Machine Thermal Model - Fixed Parameter Thermal Overload
ID
7350
7351
2
( )
i
t
∆
t
eq
=
+
F
a
τ
+ ∆
k
t
2
2
i
qi
+
avg
qi
i
i
i
+
+
arms
brms
crms
=
3
Advanced Motor Protection and RTD Protection Functions
Units
Default
Value
Disabled
Disabled
τ
(
)
− ∆
H t
t
τ
+ ∆
t
Values
● Disabled
● Alarm
● LatchedAlarm
● Trip
● Block Start
● Disabled
● Alarm
● LatchedAlarm
● Trip
● Block Start
59
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