SIEMENS
Introduction
Protection strategy
1/4
Siemens D 86.2 · 2007
1
Reverse power
Due to the permanent magnets in the rotor, magnetic flux is con-
tinuously present in the motor and for each revolution of the rotor,
a voltage is generated at the motor terminals, even when the
feeding converter is switched off and disconnected from the
supply system.
Power from feeding converter
Also, when the rotor is at a standstill, voltage can still be present
at the motor terminals if the feeding converter has not yet been
switched off or the DC link circuit of the converter is not yet dis-
charged.
Notes on safety, application and design
If work is to be performed on the drive system (converter and/or
motor), the following safety measures must be implemented:
•
The converter must be isolated from the supply system by a
switch (isolating switch or circuit-breaker).
•
Prevent any rotary motion of the motor.
•
A separate protective device must be used for plants, in which
the rotor can be accelerated by an active load, for example a
circuit breaker must be used.
•
The field weakening range is limited to 120%. In case of an ac-
tive load (rotor can be accelerated by the plant) the DC link
must be protected against overspeed/overvoltage.
Safety precautions when working on
Maintenance or repair on the motor and/or the converter
after commissioning of the drive system may only be car-
ried out under the following preconditions.
Motor terminal box
Important!
Only permissible when the rotor
is at a standstill!
Before opening the motor terminal box it must be ensured
that
• the rotor is at a standstill,
• the converter is disconnected from the supply and
• the DC link of the converter is discharged.
Converter
On rotor standstill.
Before opening the converter it must be ensured that
• the converter is disconnected from the supply,
• the DC link of the converter is discharged and
• the rotor is at a standstill.
With a rotating rotor that is cou-
pled depending on the plant.
Before opening the converter it must be ensured that
• the converter is disconnected from the supply,
• the DC link of the converter is discharged and
• that the (coupled) motor is electrically isolated from the con-
verter by means of a suitable switch (for SINAMICS S120
Cabinet Modules a corresponding circuit-breaker on the out-
put side can be ordered with the converter opion
L34
).