Baumuller b maxx BM4400, Инструкция по эксплуатации

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Methods to avoid an unexpected starting
Instruction handbook b maXX BM4400, BM4600, BM4700
Document No.: 5.12008.07 Baumüller Nürnberg GmbH
328
of 358
C.1
In the Baumüller converters of b maXX 4000 this is accomplished by the safety relay, which
switches the power supply off for the IGBT control.
The device models are available with one safety relay (BM4000 size 1 - 7) or with two safety
relays (BM4000, size 3 - 7). The version with one safety relay is shutdown path 1. The version
with double safety relay are the shutdown paths 1 and 2.
For a safe two-channel shutdown with one safety relay, a second shutdown path at the
Baumüller BM4000 controller LC3 is achieved via the pulse enable circuit of the controller. Ad-
ditionally the pulses for the IGBT control are disabled at this circuit.
Refer to Z C.2 Safe Torque Off (STO) – from page 330 for additional information.
Physical relationship
The precondition for starting an AC motor is the generation of a rotating field, which drives the
armature of the motor. When having variable-speed AC current drives, in the microprocessors
usually a complex pulse pattern is generated. Then the pulses are amplified and are used for
switching the power semiconductors. If no defined pulse pattern is available or the amplifying
connection is interrupted, e. g. by switching off the power supply with a relay (safety relay), then
a rotary field cannot be generated. An error at the pulse pattern generation therefore cannot lead
to a starting of the motor, as long as the second precondition, namely the interruption of the am-
plifying power supply is available and vice versa. The protection against unexpected starting is
reached by an electromechanical method which is superior to the electronics. This is reached
by a safe isolation, which is not executed in the load circuit.
Energy supply of the motor windings at a stop is reached by inhibiting the power semiconduc-
tors. Semiconductors can fail or can be started accidentally, due to electromagnetic interferenc-
es. The behavior of the shut down drive must be considered, in case of this error. The fail and
the accidental switching on of a single or of several power semiconductors at the same DC-link
pole, does not cause does not lead to an uncontrollable starting, as there is no current flow. If
an additional power semiconductor is enabled at another pole, current is able to flow through
the motor. If, thereby the DC link is directly short-circuited, the fuses which are upstreamed to
the converter are tripped, the motor doesn’t start. If the DC link is „short-circuited“ over a winding
of the motor, a magnetic field can be set up in the motor. If it is an asynchronous motor, then the
generated d. c. magnetic field cannot cause a movement of the rotor. By the permanent-mag-
netic synchronous motor the rotor will rotate into a notch position. The angular movement which
is covered is dependable of the choke ‘s position and the number of pole pairs of the motor. It
amounts to maximum 180°/number of pole pairs. Subsequently the enabled DC link operates
like a brake, this means after the ending of the movement the drive is in a blocked state. A start-
ing of the drive is impossible. If a machine with a synchronous motor is planned, the possible
movement must be considered, because it can lead to a dangerous movement. Therefore the
machine constructor must carry out a safety evaluation for the residual movement.