Danfoss VLT AHF 005 Service Guide

A higher reading or an open circuit indicates a failed SCR
or a faulty connection.
SCR test part II
1. Check the connections of the gate cables to the
SCR/diode modules.
2. If the connections are good, replace the failed
SCR/diode module.
If the SCR checks are successful and there is still no DC bus
voltage, replace the inrush board.
8.5.9 Output Imbalance of Motor Voltage
and Current
Checking the balance of the drive output voltage and
current is a way to measure the electrical functioning
between the drive and the motor. In testing the phase-to-
phase output, both voltage and current are monitored.
Conduct static tests on the inverter section of the drive
before performing this procedure.
If the voltage is balanced but the current is not, the motor
can draw an uneven load. This condition can be the result
of:
•
A defective motor.
•
A poor connection in the wiring between the
drive and the motor.
•
A defective motor overload, if applicable.
If the output current and the voltage are unbalanced, the
drive is not gating the output properly. This condition can
be the result of:
•
A defective control card.
•
A defective power card.
•
A defective gate drive card.
•
Improper connections between the gate drive
card and IGBTs.
•
Improper connections in the output circuitry of
the drive.
NOTICE
COMPATIBLE VOLTMETERS
Use a PWM-compatible digital or analog voltmeter for
monitoring output voltage. Digital voltmeters are
sensitive to waveform and switching frequencies and
commonly return erroneous readings.
The initial test can be made with the motor connected and
running its load. If suspect readings are recorded,
disconnect the motor cables to isolate the problem further.
1. Monitor 3 output phases at motor terminals 96
(U), 97 (V), and 98 (W) with the clamp on the
ammeter. An analog device is preferred. To
achieve an accurate reading, run the drive above
40 Hz, which is normally the frequency limitation
of such meters.
A balanced output current from phase to phase is correct.
A variation of more than 2–3% is not correct. If the test is
successful, the drive is operating normally.
2. Using a voltmeter, measure AC output voltage at
motor terminals 96 (U), 97 (V), and 98 (W).
Measure phase to phase checking U to V, then U
to W, and then V to W.
A variation of more than 8 V AC among the 3 readings is
not correct. The actual value of the voltage depends on
the speed at which the drive is running. The volts/hertz
ratio is relatively linear (except in VT mode) so at 50 Hz/60
Hz the voltage is approximately equal to the mains voltage
applied. At 25 Hz/30 Hz, it is about half of that voltage.
The exact voltage reading is less important than balance
between phases.
If a greater imbalance exists, disconnect the motor cables
and repeat the voltage balance test.
Since the current follows the voltage, it is necessary to
dierentiate between a load problem and a drive problem.
If a voltage imbalance in the output occurs with the motor
disconnected, test the gate drive circuit for proper ring.
Proceed to chapter 8.5.10 IGBT Switching Test.
If the voltage was balanced but the current imbalanced
when the motor was connected, then the load is suspect.
There could be a faulty connection between the drive and
motor or a defect in the motor itself. Look for bad
connections at any junctions of the output wires including
connections made to contactors and overloads. Also, check
for burned or open contacts in such devices.
Test Procedures
VLT
®
FC Series, D1h–D8h, Da2/Db2/Da4/Db4, E1h–E4h, J8/J9
110 Danfoss A/S © 02/2019 All rights reserved. MG94A502
88

Danfoss VLT AHF 005 Specifications

General

Brand	Danfoss
Model	VLT AHF 005
Category	DC Drives
Language	English