U
U
s
s
e
e
r
r
M
M
a
a
n
n
u
u
a
a
l
l
Revision 8.6
SECTION 6 : OPERATION OF CONTROL PANEL
89
Faulty motor stator windings (open circuit on all 3 phases).
Faulty Thyristor stack. None of the Thyristors is conducting this is more likely to be caused
by a faulty phase shifter card.
6.8.5.
Stack Temp
The Thyristor stack temperature exceeds 95
o
C.
Possible causes
Excessive continuous slow speed operating , which is causing the temperature to rise
excessively due to the motor currents being higher than the thyristor stack rating for long
periods of time
Ambient temperature higher than 60°C, which then reduces the allowed temperature rise of
35%, reducing the thermal capacity of the thyristor stack.
Temperature measuring switch mounted on the thyristors stack faulty (permanently open
circuit) or loose connection on the switch.
6.8.6
Overload Trip
– (
This feature is not yet implemented)
The motor full load current is exceeded for extensive periods of time above the limit determined by the
I
2
t Class 2 or Class 5 terminal curves.
Possible causes
Crane has been overloaded.
Excessive long periods of slow speed operation.
Unusual mechanical friction caused by failure of mechanical components such as the brakes
not releasing, faulty bearings, travel wheel flanges running against the rails and seized guide
rollers or rope sheaves etc.
The thermal capacity is displayed in a form that when the display shows 100% it means that the
thermal capacity has been reached or exceeded.
After an overload trip it is advisable to allow the thermal capacity to recover to normal to enable a fair
amount of motor cooling to occur.
This facility was designed to protect the motor against current overloads that can cause high thermal
stresses. It does not take the actual motor temperature into consideration at any time, or the failure of
the motor cooling fan. It is therefore recommended to install PTC probes whenever possible and the
associated relay for efficient temperature monitoring of the motor.
6.8.7
Overcurrent
The stator currents (one, two or all three) are in excess of 4 x motor current for a period longer than 1.5
seconds.
Possible causes
Motor windings in short circuit or down to earth.
Motor stator or rotor cables in short circuit or down to earth.
