Application Guide

63-706249
POST POWER UP CHECKS
1.
Power the VFD (with output disconnected).
2.
Ensure that all input phases are present and the display is correct. Refer to the device technical manuals for details.
3.
If all is well, power down and wait until the DC bus voltage has decreased to a safe level.
4.
Reconnect the output cables.
5.
Power the VFD again, ensuring that the
stop
command is present in the VFD terminal.
NOTE: If the
start
command is present on the VFD terminal, the VFD will likely start the load using default parameters.
6.
Program the following parameters before giving the
start
command:
a. Motor name plate voltage.
b. Motor name plate full load current.
c. Acceleration ramp.
d. Deceleration ramp.
e. Any minimum or maximum speed limits.
NOTE: Typical values for acceleration and deceleration times for first start:
Up to 10 Hp: 30 seconds acceleration and deceleration.
15 Hp to 50 Hp: 45 seconds acceleration and deceleration.
60 Hp to 100 Hp: 74 seconds acceleration and deceleration.
125 Hp to 160 Hp: 120 seconds acceleration and deceleration.
7.
Use either the terminal
start
command or keypad command
forward jog
, and observe the direction of rotation. If the load
rotates in the wrong direction, reverse the connection of the two cables on the VFD output. Reversing the cabling on the
input of the VFD has no effect on direction of rotation at the output.
8.
Start the machine with minimum speed reference and monitor the current drawn.
9.
If the system will safely allow this, while monitoring current drawn, gradually increase the speed until maximum speed is
achieved. Note any areas where overload or overcurrent occurs.
10.
Reduce the speed reference to minimum and monitor the DC bus voltage as the VFD decelerates the load.
a. If the deceleration rate is much too fast, an over voltage trip may occur immediately.
b. If the deceleration ramp is only marginally too fast the over voltage trip may occur at some speed approaching
zero.
NOTE: In either case, the deceleration ramp should be extended. If there is a specific need to decelerate the load at a
defined rate, this can require the addition of a braking circuit in order to dissipate regenerated energy.
11.
Make several starts and stops to simulate what happens during normal operation. Include power down and power up
during motoring. If the VFD trips, there is a problem with programming, cabling, or interfacing. A modern VFD should not
trip.
12.
Tune the primary control loop ensuring that the operation is stable and producing the desired results.
13.
Check the operation of any bypass circuits or downstream switching to ensure that these functions work correctly without
causing the the VFD to stress or trip.
TROUBLESHOOTING ON SITE
NOTE: Refer to the Safety section for guidance on safety.
With correct wiring, set-up and application, a modern VFD should rarely trip. Usually, if a VFD trips, the problem lies with the
application or programming. However, situations can exist that cause operational problems, but do not cause the VFD to trip.
These conditions can be difficult to diagnose.
Unstable Speed Control
If the speed reference value is available for display, this should be monitored when the VFD is not driving the motor and then
when the motor is running. The displayed speed reference value will normally be available to a high degree of accuracy and
therefore any deviation in this value will be immediately evident on the display. The VFD will attempt to follow this value. It is
also be possible to monitor the input terminals for this speed reference, with an appropriate instrument - again any instability
will be evident.
The reference value is normally Vdc or mA, so it is worthwhile to check reference terminals for any voltage level. Problems can
occur with control instruments and with poor wiring, because Vac can be superimposed on the DC reference signal. Any level
of Vac, particularly if it is at low frequencies, typically 60Hz power supply frequency produces modulation of the real reference
signal causing instability.
In some cases, the level of induced Vac can be so high that physical damage can occur to the components on the control
board of the VFD.