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GEH-6385 Reference and Troubleshooting, 2300 V Drives Chapter 2 Faults and Troubleshooting
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2-33
No. Name Type Description
136 AC line watchdog Trip
The AC line watchdog trip fault will occur when the AC line transient alarm
persists for about one second. Both the trip fault and the alarm are a result of
significant phase lock loop error or significant phase imbalance.
A phase imbalance signal is calculated by subtracting a control calculated
threshold from a filtered signal which is formed by filtering the sum of two
signals. One of these signals is the phase lock loop error and the other is the
error between the demodulated real component of line voltage and the
measured magnitude of the line.
The calculated threshold phase imbalance level which is computed by the
control is based on the magnitude of the input line voltage. This calculated
phase imbalance threshold represents a phase imbalance of about 18% or a
phase lock loop error of about 6.7 degrees. The phase imbalance signal
which is a result of the previously mentioned subtraction is equal to about
18% imbalance when it becomes positive.
The phase imbalance signal feeds an integrator designed to cause the AC line
transient alarm when the threshold has been exceeded for a very short time.
That amount of time is dependent upon the amount of the phase imbalance,
but the alarm will occur eventually if the imbalance signal remains positive. If
the alarm persists continuously for about one second, the AC line watchdog
trip fault will occur.
Primary causes:
AC line disturbances.
Transient phase imbalances.
Weak control of frequency on diesel generator sets or gas turbine generator
sets.
Very fast voltage magnitude changes.
Damaged reactor or transformer
Possible board failures:
VATF-SRC
FOSA
BICM
DSPX
137 AC line rev phs seq Trip
The AC line rev phs seq trip fault occurs when the control senses that the
rotation of the AC line is opposite of what is expected. This condition is
checked only one time after the control is powered up. When the phase lock
loop locks for the first time, just after the charging sequence has begun, the
sign of PLL frequency is checked against the expected sign. The expected
sign is determined by the setting of Phase rotation req. If Forward sequence
is selected, the sign of PLL frequency is expected to be positive, otherwise, it
must be negative. If the expected sign is not found, the trip fault is given. AC
line rev phs seq requires a hard reset to clear.
Before changing Phase rotation req, review the rotation of any AC cooling
pumps or blowers in the drive. Incorrect phase sequence can lead to
ineffective air or water flow in the cooling system.
Primary causes:
Control senses wrong phase sequence.
Possible board failures:
VATF-SRC
FOSA
BICM
DSPX
Possible wiring faults:
Main AC input lines to source are not in correct phase sequence.
Sensing wires to FOSA are in wrong sequence.