NSW Resources Regulator 26th annual Mechanical Engineering Safety Seminar

1. Cadia Valley Operations
Foreseeing the unforeseeable
Mick Dewar

2. Cadia Valley Operations (CVO)

3. Cadia History
• 1997/98 Cadia Hill Open Cut mining operation and concentrator
commissioned
• 2000/01 Ridgeway Sub Level Cave and concentrator commissioned
• 2008/09 Ridgeway Deeps Block Cave and secondary crushing circuit
commissioned
• 2011 Cadia East Stage 1 (16MW Ball Mill) Commissioned
• 2011 Cadia East Stage 2 (Screening and Secondary Crushing Circuit)
Commissioned
• 2012 Cadia East Stages 3 and 4 (Flotation and HPGR Circuit)
• 2012 Cadia East UG commenced commercial production

4. Cadia East Project – Underground Overview
• +30 year mine life
• 7.7km of 1500mm belts
@5.5m/s
• 1:5.3 conveyor incline
• 3 x Krupps 63/75 Jaw
Gyratory Crushers
• Materials handling
design by SKM

5. Decline Belt Specifications
• ST5500 steel cord, 1500mm wide.
• Longest belt 1765m, shortest 1008m.
• Variable Speed Drives (VSD) to 5.5m/s.
• Head and secondary drive
arrangements with hydraulic TUW
controlling belt tension.
• Maximum installed power on any given
belt is 6MW.
• SIL isolation system for idler changes
and basic maintenance tasks.

6. Holdback Functionality
• At normal rate, longest belt has +350 tonnes of ore on the belt.
• Holdback torques were too large for sprag clutches.
• Design similar to a winder.
• Conveyor run back protection completely reliant on brake application.
• Newcrest owners team and conveyor designers identified this as a
significant future operational risk.

7. Brakes and Holdbacks
• 2,180mm diameter low speed disc brakes to each head and secondary drive
pulley.
• Primary drive disc:
• Duty brake caliper;
• Stand-by brake caliper;
• Duty hold-back caliper;
• Stand-by hold-back caliper.
• Secondary drive disc:
• Duty brake caliper;
• Stand-by brake caliper;
• Duty hold-back caliper;
• Stand-by hold-back caliper.
• Minimum required functionality combination … compliant to AS1755 but
above that is top secret.

8. Brakes and Holdbacks

9. Braking Ramps
• Normal stop:
• VSD drives down belt to standstill in 20 seconds.
• Brakes apply 0.5sec before standstill.
• Triggered by belt, chute and equipment protection trips.
• Used for routine controlled stops.
• Fast Stop:
• VSD drives down belt to standstill in 10 seconds.
• Brakes apply 0.5sec before standstill.
• Triggered by pull wire activation and decline mounted e-stops.

10. Normal & Fast Stop – Schematic

11. Braking Ramps
• Immediate Stop:
• No VSD influence.
• Brakes apply all braking effort via two solenoids.
• Triggered by loss of power, i.e. drive e-stop, transformer loss, power loss.
• Each belt brakes at it’s own rate dependent on burden and length.
• Some chute blockage and tail spillage can occur under this scenario.

12. Immediate Stop – Schematic

13. 31 March 2015 – Just Another Day …
• Process control commissioning work being undertaken in an underground
switch room.
• Technician inserts a network cable into the desired socket …

14. 31 March 2015 – Just Another Day …
• Wrong socket …

15. Sequence of Events
• The loop created a ‘network packet storm.’
• Incline conveyor network PLC reached 100% capacity and timed out.
• The VSD detected the loss of network communication.
• The VSD initiated a fast stop braking condition:
• The VSD drove the incline belts down a 10sec ramp profile.
• With 0.5sec to belt standstill, the VSD issued a command to the PLC to
apply the brakes.
• The PLC was unable to process the brake application request; the brakes
remained open …

16. Action and Reaction

17. Action and Reaction

18. What Stopped the Belt?
• A lanyard pull?
• An e-stop?
• ICBECS.

19. Braking Ramp - ICBECS
• ICBECS Stop:
• No VSD influence.
• Brakes apply all braking effort via all solenoids.
• Triggered by detection of reverse belt movement.
• Independently hard wired to the network, PLC and VSD.

20. ICBECS Stop – Schematic

21. ICBECS – Reverse Belt Motion Detection

22. Improvement Actions
• The network switches were upgraded to contain similar events.
• Network sockets were plugged with red plastic plugs to prevent inadvertent
socket engagement and strict controls put into place governing network
maintenance work.
• The PLC OEM was informed so that they could design corrective firmware;
it so happened they Cadia was the only user of the PLC model affected.
• An FMEA was undertaken on the ICBECS system to ensure no unforeseen
vulnerabilities existed.
• An ICBECS test rig was constructed to ‘stress test’ identified and unforeseen
failure modes and conditions.

23. ICBECS FMEA Outcome
• The FMEA identified that:
• ICBECS by-pass switches were readily accessible.
• ICBECS bypass switches were relocated into a locked cabinet.
• FPM Supervisors are the minimum security level able to access
the cabinet.
• ICBECS did not recognize standstill or forward rotation conditions.
• Standstill status was introduced.
• Forward motion status was introduced.
• A 6 month functional test of each ICBECS system was
implemented.

24. Conclusion