Troubleshooting/Maintenance 5-1
5
Troubleshooting/Maintenance
5.1
Overview
This chapter provides information useful in troubleshooting and maintaining the drive
hardware. It presents the theory of operation, schematics, power electronics
troubleshooting procedures, and general maintenance issues. It also provides a list of
field-replaceable components.
5.2
Troubleshooting
This manual is not intended to provide in-depth service instructions. For service beyond
that described in this manual, please contact Unico or your representative.
!
Attention
High voltage may be present even when all electrical power supplies are
disconnected. After switching off electrical power, wait at least 15 minutes
for bus circuit capacitors to discharge before working on the drive or
associated equipment. Use an appropriate voltmeter to further verify that
capacitors are discharged before beginning work. Do not rely exclusively on
the bus voltage indicator. Dangerous voltage levels may remain even when
the indicator is off.
5.2.1
Theory of Operation
The general function of the drive is to convert a fixed voltage and frequency from an
electrical power source into a variable voltage and frequency for controlling an AC
motor. The block diagrams of the 1100, 1105, 1110, 1120, 1130, 1200, and 1230 drives
are shown in Figure 5-1 through Figure 5-13.
A
rectifier section
is used on the 1100, 1105, 1110, and 1200 drives to convert the fixed
AC line voltage into a DC bus voltage. The 1120 is a modular design intended for
operating a number of units from a common DC bus. Low-power drives use a diode
rectifier and resistors to charge the bus capacitors, which is then bypassed by a contact
once the bus is up to full voltage. Medium- and high-power drives use silicon-controlled
rectifiers (SCRs) to control the charging of the bus capacitors. High-power drives provide
for optional twelve-pulse (six-phase) connection of the input to reduce harmonic currents.
The 1110 drive is designed for single-phase operation using two, rather than three, AC
line voltage terminals. A
rectifier control
coordinates the charging of the bus.
A
link chok
e and
bus capacitors
in the 1100, 1105, and 1110 drives form a filter that
smoothes the output of the rectifier section into a steady DC voltage. An optional
dynamic brake
device on these units allows regenerative energy from the load to be
dissipated in an external resistor when the drive is braking. The dynamic braking device
turns on when the bus voltage exceeds a preset value, causing the braking current to flow
Summary of Contents for 11100
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