1-22 Functional Description
7000-TD002A-EN-P – September 2007
SCR Rectifier Active Off-Line Diagnostics
In the active diagnostic test, each device is gated at maximum
blocking voltage. For a healthy SCR, the feedback will normally
change from high to low when gated. However the drive will
receive a high state (light) both before and after gating if the
device is open-circuited, there is an incomplete gating fiber-optic
path or a damaged gate driver. When this occurs the drive will
issue an Offline Open fault for the device. If the drive receives a
low signal (no light) in both states, there may be shorted device
or an incomplete feedback fiber optic. If this occurs drive will
issue an Offline Shrt fault for the device. Failed or open-circuited
snubber connections will shift the device blocking voltage (when
not running) which may case either fault to appear. It should be
noted that during the active diagnostics stage a dc link voltage
which is close to rated voltage will appear due to interaction with
the snubber circuit.
PWM Rectifier Active Off-Line Diagnostics
For the PWM rectifier, the active diagnostic test can differentiate
between a failed device and a broken fiber-optic path because the
gate driver toggles the feedback differently when gated as shown
in Figure 1.10. As in the SCR rectifier active offline diagnostics,
each device is gated at peak blocking voltage (if MV is available).
Devices which could cause a line to line short circuit are not
gated. If the drive detects a failed device, an Offline fault is
issued for the device. A weak gate power supply may also cause
a device fault. If the drive receives no light signal (5V on the
diagnostic test point) both before and after gating, then there
may be an incomplete feedback fiber-optic and a DiagFkbLoss
fault will be issued. A completely failed or unplugged power
supply will also cause this fault. If the drive always receives a
light signal (0V on the diagnostic test point) both before and
after gating, the device may not have received the gating signal
and a Gating Loss fault will be issued. The drive will not allow
the contactor to be closed if it detects enough failed devices to
cause a line to line short circuit.
Machine Converter off line diagnostics
The inverter diagnostics are performed when the drive control is
powered up and when the drive receives a start command. The
drive also performs off line diagnostics when a drive reset command
is issued. These diagnostics are capable of detecting a bad device,
loss of feedback fiber optic and loss of gating fiber optic.
The inverter off-line diagnostics are similar to the PWM rectifier
diagnostics except that: no passive diagnostic is done, no
consideration is given to line-to-line short-circuits and the input
contactor is not involved. The inverter off-line diagnostics will
generate Device Flt Fbk FO Loss and Gat FO Loss faults.
Power Semiconductor
Diagnostics (cont.)
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