SAF OPAL Pro MS6 - Manual (Page 22)

MS6 REDUCED VOLTAGE STARTER
Page 21
7.5 SHORTED SCR DETECTION
• This option provides protection against the unlikely event of a shorted Silicon Controlled
Rectifier (SCR).
• The state of the SCR’s are checked every time a start or jog command is initiated. An SCR
that shorts while the Opal Pro is running will not be identified until the next time the Opal
Pro attempts to start or jog.
• This fault should be used in conjunction with a shunt trip circuit breaker or an in-line
contactor.
• In the event of a shorted SCR, it is not sufficient to merely trip the starter. The incoming 3
phase power must be removed. The danger associated with a shorted SCR is that even when
the starter is not running, current may pass freely through the motor.
• If a shorted SCR is detected, the Shorted SCR relay is energized. The form C relay
contacts on terminals 15, 16 and 17, are provided for means of opening the circuit breaker
or contactor used.
• When a shorted SCR fault occurs you will have to use an ohm meter to find out which SCR
is shorted. This can be done by turning all the power off and using an ohm meter to
measure the resistance between L1 and T1. The resistance should be greater than
10Kohms. If it is a short either SCR 1 or 2 is bad. Repeat this for L2 and T2, which will
check SCR’s 3 and 4. Then finally check L3 and T3, which will check SCR’s 5 and 6.
7.6 SOLID STATE FULL SPEED REVERSING
• This option provides a smooth, current controlled, motor rotation reversal without any
current surge or torque jerk. Motor stopping is not required. Additions to the Opal Pro
include a reversing card, CA531, plus four additional SCR's.
• With the reverse input (terminal 6) enabled the starter will fire the reverse bridge.
• Terminals 20 and 21 dry contact used to indicate the direction selected and by-pass
contactor sequencing for a reverse/by-pass combination.
• When the motor is running and the forward/reverse switch changes states, the Mirco Opal
turns all SCR's off. After a time delay, the Opal Pro is switched back on, triggering a
different set of SCR's. This effectively switches two output lines, decelerates the motor
down to zero speed, and continues to accelerate it to full speed in the opposite direction.
The motor reversal is performed under complete current control via the RAMP (parameter
1002) and STEP (parameter 1003) settings.
• If a CA531 card is not present on the Opal Pro the reverse command will be ignored for
normal running but will still be active for jog reversing.