Iskra FPC 200 - Page 51

Functionality
USER MANUAL FPC 200 - 3/2017 51
2









n
I
I
I
Equation 8: Temperature which would be reached at
specific current.

t
II
e

 )(
0
Equation 9: temperature which would be reached at
specific current I in specific time t, started from 
0
temperature.
I – Present machine current.
Θ
I
– final temperature that would be reached in infinite
amount of time, maintaining constant current.
Θ
0
– Initial temperature.
Θ – Current temperature.
τ – Heating or cooling time constant.
t - time
2.5.2.1.2 Hot state temperature detection of the
machine
It is considered that the machine is in hot state when
calculated temperature exceeds Hot state level.
 
HCRK
HH
 1
Equation 10 Hot state level equation.
K
H
– Hot state level
Θ
H
– Temperature level above which is considered hot state of
the machine.
HCR – Hot to cold ratio
2.5.2.1.3 Start of overheated machine Inhibition
In certain cases when start of the machine would cause
the temperature to exceed insulation class of the
machine the high temperature signal is stated. The
estimation is based on equation:
 
run
sta rt
t
starttripstarthigh
e



Equation 11 High temperature equation.
t
start
– correction factor.
I
start
– positive sequence.
Θ
start
– Thermal class of machine.
Θ
high
– Thermal class of machine.
Θ
trip
– Thermal class of machine.
2.5.2.1.4 Negative sequence component Influence
Additional negative sequence current can occur in
rotating machines with coiled rotors. Difference in
calculated heat can be taken into account by using the
Current unbalance factor.
2
1
2
1









I
I
Kk
N
Equation 12 Current unbalance current influence.
k
N
– correction factor.
I
1
– positive sequence current.
I
2
– Negative sequence current.
K - Current unbalance factor.
Recommended parameter settings of Current
unbalance factor:
2
175
LRC
IK 
Equation 13 Typical current unbalance factor.
2
230
LRC
IK 
Equation 14 Conservative current unbalance factor.
I
LRC
– Locked rotor current of rotating machine.
2.5.2.1.5 Accounting for ambient temperature
The function can take into account the ambient
temperature. Temperature can be obtained from
external sensor or most common maximum operating
temperature of machine 40 °C is used.
amb
amb
amb
k



max
max_max
Equation 15 Calculation of ambient temperature influence.





 

 

Equation 16 Equivalent current calculation.
k
amb
– Correction factor.
Θ
max
– Thermal class of machine.
Θ
amb_max
– Maximum ambient themperature.
Θ
amb_max
– Current ambient themperature.
I
eq
– Equivalent machine current.
2.5.2.1.6 Time to trip and time to drop out calculation
equation
Time to trip and time to drop out calculation equation
where there the longest time of separate phases is