Digitax DBE1100S, Руководство пользователя, Страница: 37 / 96

DigitAx User Guide
Issue code: dgxu4
5-9
these motors are started, a dip is produced
in excess of 20% of the actual supply
voltage
... excessive peak current may flow in the input
power circuit of the Drive. This may cause nuisance
tripping or, in extreme cases, failure of the Drive.
A line reactor should be connected in each phase of
the supply to each Drive. Line reactor(s) add the
required impedance to the
AC
supply in order to
reduce current transients to a level that can be
tolerated by the Drive.
Caution
RFI filters (for EMC
purposes) do not give
adequate protection against
these conditions.
Three individual reactors, or a single three-phase
reactor should be used. Each Drive must have its
own reactor(s).
Typical values
Model Value
(mH)
DBE140 4.1
DBE220 2.8
DBE420 2.5
DBE600 1.7
DBE750 1.4
DBE1100S 0.9
DBE1500 0.7
DBE2200 0.5
Current ratings
Continuous: Not less than the continuous current
rating of the Drive
Peak: Not less than twice the continuous current
rating of the Drive
5.8 Connecting an internal or
external braking resistor
Warning
Electric shock risk
The voltages present on the
braking resistor, its
associated components and
terminals on the Drive are
capable of inflicting a severe
electric shock and may be
lethal.
Introduction
When an AC motor is decelerated, energy is
returned to the Drive from the motor. When a high
inertia load is decelerated in a short time, the energy
returned can be too great for the Drive to absorb.
The effect is to increase the voltage of the DC bus,
with the possibility of the Drive tripping due to
overvoltage on the DC bus.
When the DC-bus voltage exceeds a predetermined
level (750V), a braking resistor can be connected to
the DC bus by an internal transistor in order to
absorb the excessive energy. All models except
DBE1500 and DBE2200 have an internal braking
resistor; this resistor or an external resistor can be
used.
The required value of the braking resistor is
determined by the maximum required braking
torque. The required power rating of the resistor is
determined by the amount of energy to be
dissipated, duty cycle, repetition time and cooling
available for resistor. When the resistor value and
power rating have been calculated, a decision can be
made to use an external or the internal braking
resistor (when fitted).
Precautions
When the internal or an external braking resistor is
used, it is strongly recommended that a
thermal
overload protection relay is fitted in the
braking-resistor circuit in order to protect the
resistor against overheating. Overheating can
damage the resistor and the Drive, as well as
increase the risk of fire.
Overheating can be caused by the power-rating of
the resistor being inadequate for the application or
the internal braking transistor becoming
short-circuit.
The maximum DC-bus voltage is 800V. Ensure the
(external) braking resistor, connecting cables and
insulation are suitable for this operating voltage.