Siemens SIMOTRAS 6SG7050, Operating Instructions Manual

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01.04 Description
SIEMENS AG 6SG7000-0BA76
3-5
SIMOTRAS HD Operating Instructions
3.3.4 Method of operation of electronic phase reversal with plug braking
The drive starts up with the positive speed and stabilizes at point a. A constant load profile is
assumed during this process. If a lower setpoint or a setpoint with the opposite polarity is connected
when in this state, the SIMOTRAS HD will be switched to counter-torque operation. The thyristors
that are currently conducting for the clockwise rotating field are first blocked. The thyristors for the
anti-clockwise rotating field are then fired. This changes the phase sequence on the output
terminals to produce a new direction of rotation, point b.
The motor then starts plug braking and reduces its speed.
A slip value s = 2 exists on the machine immediately following the switchover from motor operation
at point a with the speed n = n
N
to braking operation at point b. With a direct switchover at full
supply voltage, the motor current would now be greater than the start-up current (slip s=1,
maximum current). SIMOTRAS HD therefore automatically reduces the motor voltage at this point,
thereby limiting the maximum current.
n
N
-n
M
L
s = 2
Positive
torque
M
load
= const.
+n
+M -M
-n
N
-M
L
n = 0
Clockwise field
Anti-clockwise field
a
b
Plug
braking
n
0
Figure 3.3.4.1 Speed-torque characteristic curves at phase reversal