KEB COMBIVERT F6 - 6.4 Motor connection

6.4 Motor connection
6.4.1 General instructions
• The motor cables must be designed to the maximum continuous current.
• They are valid for 0...100 Hz (up to 300 Hz the cable losses increase by approx. 25
% due to the skin effect).
• The IGBT modules cause high-frequency interferences, the longer the motor cable
length the higher the discharge to the earth potential.
• The consequence is an increase of conducted interferences on the mains side.
• Ifthemotorcablesaretoolong,dampingofthemainsltersisnolongersufcient
and the permissible interference limits are exceeded.
• At the output of the drive converter, pulses of approximately 1.35-fold of the mains
voltage and very short rise times are generated independently of the output frequency.
• This is the case for all drive converters with modern IGBT inverter technology.
• The voltage of the pulses can almost double at the motor connections depending on
the characteristics of the motor cable.
• This can lead to additional load of the motor and the motor cable insulation.
• Modern speed-controlled drives with their fast rising voltage pulses and high switch-
ing frequencies can cause current pulses through the motor bearings which can
gradually damage the bearing raceways.
ATTENTION
Protect motor against voltage peaks !
► The connecting-up instructions of the motor manufacturer are gen-
erally valid.
► Drive converter switch at the output with a high rate of voltage rise.
Voltage peaks that endanger the insulation system at the motor
can occur especially in case of long motor cables (> 15 m). A motor
choke,adv/dtlterorsine-waveltercanbeusedtoprotectthe
motor.
6.4.2 Selection of the motor cable
Correct selection and laying of the motor cable is very important for high motor ratings:
• Smaller load of the motor bearings by bearing currents.
• Improved EMC characteristics.
• Lower symmetrical operating capacities.
• Less losses by transient currents.
• Due to the high currents, shielded motor cables can be connected in parallel be-
tween drive converter and motor.
• All three phases must passing through each line.
• The required cross-section is described in section => Cable cross-sections.
• To keep asymmetry as small as possible, all motor cables should have the same
length.
• The shielding must be placed always with large surface on both sides (mounting
plate and motor housing).
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ELECTRICAL INSTALLATION