Manual MRI3-ITER GB
Woodward
DOK-TD-MRI3 ITERE Rev.A
17
The thermal equivalent ( T =
) is described by an exponential function.
for (
>
0
):
(
t‘)=
0+(
max
-
0
) (1-
)
after transposition:
(
t)=
max
+(
0
-
max
)
·
If (t’) k
2
·
100% the alarm or trip element is activated.
The temperature after dt can be calculated as follows:
1
=
max
+(
0
-
max
)
·
After 2 times dt:
2
=
max
+(
0
-
max
)
·
or
2
=
max
+(
1
-
max
)
·
general:
n
=
max
+(
n-1
-
max
)
·
Thus, a recursion formula was established from which in order to calculate the thermal equivalent
n
:
The last value
n-1,
the stationary final value
max
for the actual current,
the adjusted time constant
,
and the time since the last calculation dt must be known.
Analogous, for the temperature equivalent
with
max
the following formula is applied:
t
I
k · I
B
· 100%
I
k · l
B
· 100% · e
with I = highest measured phase current.
In each new calculation step n, the momentary temperature equivalent is determined as follows:
·
· 100%
I
k · I
B
· 100% ·
with I
n
:
Highest measured phase current in
calculation
step
n
dt:
Time interval between the individual
calculation
steps
n-1: Temperature equivalent of the
preceding
calculation
step
