Service manual

6.2 Introduction
WARNING
DISCHARGE TIME!
Frequency converters contain DC-link capacitors that can
remain charged even when the frequency converter is not
powered. To avoid electrical hazards, disconnect AC mains,
any permanent magnet type motors, and any remote DC-
link power supplies, including battery backups, UPS and
DC-link connections to other frequency converters. Wait for
the capacitors to fully discharge before performing any
service or repair work. The amount of wait time is listed in
the Table 1.1. Failure to wait the specified time after power
has been removed before doing service or repair could
result in death or serious injury.
This section contains detailed procedures for testing
frequency converters. Previous sections of this manual
provide symptoms, alarms, and other conditions which
require additional test procedures to diagnose the
frequency converter further. The results of these tests
indicate the appropriate repair actions. Again, because the
frequency converter monitors input and output signals,
motor conditions, AC, and DC power and other functions,
the source of fault conditions may exist outside of the
frequency converter. Testing described here isolates many
of these conditions as well. Disassembly and Assembly
Instructions (H or I-frame sizes frequency converters,
respectively), describes detailed procedures for removing
and replacing frequency converter components.
Frequency converter testing is divided into Static Tests, and
Dynamic Tests. Static tests are conducted without power
applied to the frequency converter. Most frequency
converter problems can be diagnosed simply with these
tests. Static tests are performed with little or no
disassembly. The purpose of static testing is to check for
shorted power components. Perform these tests on any
unit suspected of containing faulty power components
before applying power.
CAUTION
For dynamic test procedures, main input power is required.
All devices and power supplies connected to mains are
energized at rated voltage. Use extreme caution when
conducting tests on a powered frequency converter.
Contact with powered components could result in
electrical shock and personal injury.
Dynamic tests are performed with power applied to the
frequency converter. Dynamic testing traces signal circuitry
to isolate faulty components.
•
Digital voltmeter/ohmmeter capable of reading
real RMS
•
Analog voltmeter
•
Oscilloscope
•
Current meter
6.3 Static Test Procedures
All tests should be made with a meter capable of testing
diodes. Use a digital volt/ohmmeter (VOM) set on the
diode scale or an analog ohmmeter set on Rx100 scale.
Before making any checks, disconnect all input, motor, and
brake resistor connections.
Static tests are performed without applying power to the
frequency converter.
WARNING
Whenever power is applied to the frequency converter,
never disconnect the input cable. Disconnecting the input
cable could result in electrical shock, personal injury, and
death.
The purpose of performing static test is to check for any
possibility of short circuit of the power components.
6.3.1
Pre-requisite
•
Prepare the work area according to the ESD
regulations. Ground ESD mat and wrist strap.
Ensure that the ground connection between
body, the ESD mat and the frequency converter is
always present while servicing the drive. Handle
disassembled electronic parts carefully and always
ESD protected.
•
Perform the static test before powering up the
fault unit.
•
Perform static test after completing the repair
and assembly of the frequency converter.
•
Connect the frequency converter to the mains
only after completion of static tests.
•
All necessary precautions for system startup must
be completed before applying power to
frequency converter.
Test Procedures
VLT
®
HVAC Basic Drive Service Manual
48 MG90X202 - VLT
®
is a registered Danfoss trademark
6
6