Bosch rexroth MBT, Manual

Page: 291 / 422

still operation in the following. The standstill operation is marked by the fol‐
lowing aspects:
●
The duration of the standstill operation is longer than 10 % of the re‐
spective thermal time constant T
th
● Motor does not move
● Motor performs only very small strokes (≤ 2 * Τ
p
)
● Motor moves only at very low frequency (f ≤ 0.1 Hz)
Due to the 3-phase system, during standstill operation in one of the three
phases there is always an instantaneous value of the current, the amount of
which is higher than the permissible continuous current. Does the current
flow continuously, the motor is overheated and thermally damaged. Also refer
to chapter 9 "Application notes" on page 259 ). The peak value of the instan‐
taneous current is equal with the amplitude of the sinusoidal assumed phase
current. Its value is higher by root 2 than the effective value of the continuous
current (I
N
). The power loss P
V
, created in the coil, is calculated using
Δθ Temperature difference between operation temperature and
20 °C
α
Cu
Temperature coefficient of the specific resistance of copper =
0.0039 Ohm * m / mm²
Fig. 9-18: Power loss coil
For the nominal current, a double power loss occurs in the affected coil.
Differentiate between the following cases:
1. Use tripple sensor SNM.150.DK
If the tripple sensor SNM.150.DK used to monitor the winding temperature,
all three phases are monitored. The motor winding is protected.
2. Use a single-phase sensor KTY84-130
The KTY84-130 is mounted in one phase only. Due to the utilization of the
KTY84-130, the other phases cannot be protected from thermal overload at
standstill operation.
If the KTY84-130 is used for thermal motor protection, the stand‐
still current I
0
specified in the motor data sheet must be reduced
to 71% of the specified value.
MBT High Synchronous Torque Motors 279/409
Application notes
R911298798_Edition 08 Bosch Rexroth AG