Siemens SIMOTICS S-1FT7 - Page 141

Technical data and characteristic curves
6.1 Explanations
S-1FT7 synchronous motors
Configuration Manual, 09/2018, A5E45099423B AA
139
Calculating and determining points P1, P2, P3 and P4
P1
n
1
= 380 V • 1000 / 87 • 0.95
n
1
= 4597 rpm
P2
n
2
= 4597 rpm • 290 V / 380 V
n
2
= 3508 rpm
P3
M
limit
at n
N
= 3000 rpm and V
Mot
= 380 V read: M
limit
= approx. 8.8 Nm
P4
M
limit new
= ((290 V - 261 V) / (380 V -
261 V)) • 8.8 Nm
M
limit new
= 2.14 Nm
P4 is the point of intersection of M
Limit, new
and n
N
. The new voltage limiting characteristic is
obtained by connecting P2 and P4.
Enter and connect points P2 and P4.
This line is the new voltage limiting characteristic for V
Mot, new
= 290 V.
❒
Typical M/I characteristic
Because of saturation effects, the achievable torque cannot be calculated linearly from the
current (particularly at high currents).
1
Best case
2
Worst case
Figure 6-5 Torque-current characteristic curve for self-cooled motors
From M
0
(or I
0
), you can calculate the torque or the torque constant as a function of the
current using the following formulas:
k
T
(I) = M / I
Torque constant k
T
(I) / Nm/A
Torque M / Nm
Current I / A
k
T
(I) = ( M
0
/ I
0
) + (( I - I
0
) / ( I
max
- I
0
)) • (( M
max
/ I
max
) - ( M
0
/ I
0
))
Static torque M
0
/ Nm
Stall current I
0
/ A
Maximum torque M
max
/ Nm
Maximum current I
max
/ A