Cadia Valley Operations Foreseeing the unforeseeable

Mick Dewar

Cadia Valley Operations (CVO)

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

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

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.

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.

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.

Brakes and Holdbacks

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.

Normal & Fast Stop – Schematic

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.

Immediate Stop – Schematic

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 …

31 March 2015 – Just Another Day …

• Wrong socket …

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 …

Action and Reaction

Action and Reaction

What Stopped the Belt?

• A lanyard pull? • An e-stop? • ICBECS.

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.

ICBECS Stop – Schematic

ICBECS – Reverse Belt Motion Detection

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.

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.

Conclusion