ABB DCS 400 - Soft Network in Regenerative Mode

II K 6-23
Operating Instructions
n Soft network in regenerative mode
Soft network in regenerative mode is a specific prob-
lem of DC technology. If EMF of the motor is greater
than (Mains Voltage * 1,35 * 0,866) then fuses and
thyristors can be destroyed.
To protect the drive against damage as far as possible
see following recommendations:
• Fuses at DC site
Semiconductor fuses in the armature circuit must
be dimensioned for DC voltages, so as to assure
an adequate spark-quenching gap in the event of
a fault. A compromise is provided by two series-
connected fuses, as used in the power supply.
• DC circuit breaker
Semiconductor fuses constitute an optimum pro-
tection for the semiconductors only in “hard” net-
works; in “soft networks, and in the motor circuit,
the protection is questionable. In “soft” networks,
during regenerative operation, an increased risk of
conduction-through must be anticipated. In the
motor circuit, high-speed DC circuit-breaker
constitutes optimum protection.
• Parameter adjustment for Net Undervoltage
Set parameter Net Underv Trip (1.10) in a range
of 0…5%. That makes the drive sensitive for net
undervoltage and switches off the drive as early as
possible. Could avoid blown fuses and damaged
thyristors but may be the drive will switch off due to
fault F9-Mains Undervoltage very often. Then set
parameter Net Fail Time (1.11) different to 0.0 s to
activate the auto reclosing function.
• Parameter adjustment for armature voltage
Decrease value of parameter Arm Volt Nom (1.02)
to have more safety distance to the mains supply.
Then DCS 400 is using automatic field weakening
to achieve full speed but will lose torque in field
weakening range. Is a suggestion only may be
also a solution depend on application.
• Order a DC motor with lower armature voltage
If „soft network“ is already known during project
scheduling then calculate a DC motor with lower
armature voltage nominal. That could be a preven-
tive measure to have more safety distance be-
tween EMF and „soft network“ in advance.
Safety-oriented parameters:
Arm Volt Nom (1.02)
Net Underv Trip (1.10)
Net Fail Time (1.11)
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semiconductor
fuses
high-speed
DC circuit-
breaker
converter
protection
optimum
protection of
motor and
thyristor
M
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compromise
protection of
motor and
thyristor
semiconductor
fuses
semiconductor
fuses
converter
protection