This presentation looks at the timeline and key events that occurred through the Moranbah North Mine longwall operation project to upgrade its AFC to variable speed drive to control both the torque and speed of drive motors to reduce chain and flyte damage. It covers key elements of the safety case presented by Ampcontrol to Moranbah North Mine and the Queensland inspectorate.

1. CASE STUDY:
MORANBAH 3.3kV AFC VSD
Electrical Engineering
Safety Seminar 2019
TIM WYLIE
AMPCONTROL

2. 1. Motivating factorsand projectoverview.
2. Primarydifficulty in applying a voltage sourceVSD underground.
3. Bulletins and safetyalerts:key learnings aroundVSDs.
4. Summaryof protectionsystemconstraints& cable properties.
5. NSW Legislative barrierand use of Class Exemption now released.
6. Questions.
PRESENTATION OVERVIEW

3. 3
PROJECT MOTIVATION
MNM Longwall AFC VSD Upgrade
Safety:
LW AFC Chain Failures contribute to injuries
• Back Strains
• Finger / hand lacerations
• Contusions / bruising
• MTIs & LTIs
Operational Performance:
The AFC is a large contributor
to unplanned downtime:
• Broken Chain / Flights
• Bogged Conveyor
Improved Safety &
Productivity
Reduced
Exposure
Consistent
Performance

4. 4
TORQUE COMPARISON
VSD vs Fluid Coupling
VSD
– Full torque through entire speed
range
– 2.2xFLT available for start up
– Minimal voltage drop on start up
– Accurate load sharing
– Numerous concurrent starts
possible
TTT
– Full torque for limited time <10
sec
– Large voltage drop to achieve
max torque
– Poor load sharing between
other couplings
– Large quantity of water required
<8 Sec>
15500NM

5. 5
FLUID COUPLING VS VSD
Starting comparison
Fluid Coupling Start
– Aggressive Speed Ramp
– Imbalance between all three
drive loads and torques
– Significant chain slack with
reduced tension control
– Low average torque applied
during start up
Legend:
AFC Speed
TG Motor Current
MG 1 Motor Current
MG 2 Motor Current

6. 6
DESIGN CHALLENGES
Three significant areas of difficulty identified …
• The implementation was to be an upgrade with majority re-use of the
existing electrical system and infrastructure.
– The existing system included legacy equipment and technology known to be
susceptible to the expected noise profile of the VSDs.
• The implementation had to comply with QCMSHR:2017.
– QLD Regs are prescriptive and set limits known to be difficult to achieve in
VSD applications.
– NSW Regs less prescriptive but the safety case must still be equivalent or
better in terms of residual risk to several Australian Standards written without
appropriate consideration of VSD applications.
• Directly address industry bulletins and safety alerts around
underground VSD applications
– Pike River, SB11-04, Joy GSN047 and many others …

7. 7
IMPLEMENTATION
Compliant in QLD, but NOT compliant in NSW
• First Australian longwall with high power
VSD drives operating in a hazardous zone
(4.5MW continuous installed power).
• Significant AFC chain benefits
–0.6% elongation after 5Mt
–Less damage & bogged hours
• First Australian underground hazardous
area electrical system with non-traditional,
hybrid earthing arrangement and non-
compliant cabling.
– part of the electrical system is conventionally
earthed, and
– part of the electrical system is earth isolated.
Shane to add
photo of Parkhurst
setup

8. 8
IMPLEMENTATION
Compliant to QLD Regulations
• The development of the new hybrid earthing
system included:
– Development of a new protection element not
presently described by AS2081 or AS4871.
– Physical tests and experimentation with actual
faults applied at full voltage and power to the
operating drive in Germany.
– Addressing a formal directive issued by the
Chief Inspector of QLD under Section 172 of the
QLD Coal Mining Safety and Health Act 1999.
– Witnessed electrical tests with faults applied at
full voltage on the longwall electrical system.
• Worse case measured touch potential on
VSD circuits under fault conditions is less
than 1V.

9. 9
IMPLEMENTATION CAVEATS
Earth isolate every VSD?
• The term “earth isolation” is misleading – there is always a reference to
earth either deliberately through a neutral/earth connection or
impedance or inadvertently through system or filter capacitance to earth.
• The hybrid earthing arrangement as implemented at Moranbah is
not universally extensible to all VSD applications.
• Careful control of return earth paths and return earth impedances is key
to a reliable and safe VSD application.
• There are a number of considerations that are extensible to any
VSD application study … there are many solutions to each
consideration – invariably a system design (not components in isolation)
is what counts.

10. KEY DIFFICULTY IN
APPLYING VSDs
UNDEGROUND

11. Product marketed inAustraliaas the Optidrive
BREUER 3.3kV 1200kW VSD
• In a two-level inverter,the DC voltage on the link capacitance ‘floats’
symmetrically either side of theAC main earth,i.e.: V+ and V- relativeto earth.
• Common mode voltage sourcesdo not exist in conventionalDOLmotor
applications.
• Common mode voltage sourcesexist in all VSDs with this topology.
V+
V-
3Ø
~

12. Standing earth leakage currentunder non-faultconditions
COMMON MODE VOLTAGE
• VSD commonmode voltage can be practically measuredbetweena high
impedancestar on the drive outputs and the cabled earth.

13. Can exceed several amps in normal, non-faultconditions
STANDING EARTH LEAKAGE
Vcm
Icm
Leg 1
Leg 2
Leg 3
Vcm

14. KEY LEARNINGS FROM
BULLETINS, ALERTS
AND SAFETY
INCIDENTS

15. BULLETINS & ALERTS
• 2010 Pike River incident
• 2011NSW mining regulatorbulletin SB11-04
• Joy Safety notice on failed NER, undetectedDC fault
• Electromagneticcompatibilityand maintaining all currentpaths within Ex
controls
Illustrative examples of key difficulties that must be addressed

16. PIKE RIVER
• Midday,19/11/2010the water supply to the Pike River mine was stoppedfor a
maintenanceshutdown.
• Late afternoon,maintenancework completedand the controlroomoperator
reactivateda main pump at pit bottomto restorewater to the mine.
• The coincidenceof the switching on of the pump and the explosion seconds
later suggested that an electrical cause (in particularthe VSD poweringthe
pump) may have been the ignition source.
• How could a VSD located a few hundredmeters away fromthe seat of the
explosionbe an ignition source?
VSD listed as the potential ignition source

17. PHYSICAL EARTH vs CABLED EARTH
• Any cable includes series inductance,so at high frequencythe cabled earth
impedanceincreases.
• The physical earth containsan infinite numberof parallel returnpaths so by
comparisonhas very low inductance.
• As frequencyincreases,the physical earth becomesmore attractive to return
currentthan the cabledearth.
• The physical earth forms a parallel currentreturnpath, and is in the hazardous
zone.
• We must ensurethe cabled earth is the preferredreturnpath at all substantial
frequencycomponentsgeneratedby the drive system.
• … a picture helps
A cabled earth has inductance

18. PHYSICAL EARTH vs CABLED EARTH
A cabled earth has inductance

19. KEY LEARNING
• Wideband common mode conducted emissions are inevitable in
direct connected voltage source VSD applications.
• Earth return impedance must be a design consideration,
explicitly controlled in the electrical solution to ensure normal
and fault currents remain within Ex controls, not via the
physical earth.
Explicit control of earth return impedance

20. NSW SAFETY BULLETIN SB11-04
• Primary concern is the drive switching frequency circulating currents
which are not restricted by the NER, particularly where multiple
machines are present on a common power supply.
• Earth fault currents can bypass the NER and significantly exceed
nominal earth fault limit, via un-instrumented current paths.
• Highlights need for system level design and analysis, prior to
introduction of VSDs on fault limited networks typical underground.
• Standing and fault earth leakage current is wideband.

21. FAULT AND NON-FAULT CONDITIONS
• Presence of multiple VSDs on a
common power supply creates
several circulating current paths
(not just via the NER) with
significant standing earth leakage
currents.
• Standing and fault E/L currents
circulate via the system
interconnecting cabling.
... Multiple VSDs fed from a common winding

22. CABLE TYPES & LENGTH
• An earth fault limited network is fundamentally reliant on the cabled earth.
• Systems incorporating VSDs must also consider touch potential under
normal operating circumstances (non-fault conditions) because of large
circulating currents.
• Wideband earth impedance (not just DC resistance) is a key design
parameter - plot shows over 800Vp-p on just 100m of 245 cable…
V
Earth return impedance – not just DC resistance

23. KEY LEARNINGS
• Deliberate (capacitive) impedances to earth (to control EMC) bypass
protection elements located at the NER.
– Un-instrumented fault current paths are protection blind spots
that must be eliminated.
– Touch potentials are much higher as the fault current is no longer
determined exclusively by the NER.
• Lower risk solutions would
• Avoid multiple VSD’s fed from a common supply winding.
• Reduce cabled earth return earth impedance
EMC filters

24. GSN0047 JOY SAFETY NOTICE
• Undetected electrical fault, installed protection could not detect DC.
• NER under-rated for the application.
• Ratings of the NER under a DC fault need to be twice that of an
equivalent AC fault, even higher if resonance occurs under fault.
Potential 100% overload on conventional NER designs.
• Iron cored CT’s do not detect steady state DC faults and are
desensitised to AC faults in the presence of a DC signal.
NER ratings must account for DC faults

25. Withsafetycriticalsystems across the face …
EMC & INTERFERENCE RISK
• IS systems (gas monitoring,
communications, signal line equipment
etc) are earth referenced.
• Primary interference is conducted, not
radiated. Common mode voltage
sources can drive return currents via
the physical earth as well as cabled
earth return – for the longwall face,
this includes the goaf …
• If the drive systems are also earth
referenced, there is significant
interference and ignition risk. Pilot-Earth continuity signal
with and without operating VSD

26. KEY LEARNINGS
• The earthing system must be specifically designed to force
current returns to preferred paths as opposed to sensitive
equipment and instrumentation also connected to the earthing
system.
• Current flow in the physical earth (so in the hazardous zone)
must be minimised by careful control of the cable return earth
impedance.
Conducted interference

27. SUMMARY OF
PROTECTION SYSTEM
CONSTRAINTS

28. SUMMARY OF KEY CONSTRAINTS
• The proposed protection system must:
– Control touch potential in terms of magnitude and duration to
safe levels in both normal operating and fault conditions.
– Limit energy under fault conditions delivered into the hazardous
zone.
– Preserve insulation co-ordination and withstand insulation stress
under resonant and pecking faults.
– Prevent uncontrolled current return paths via the physical earth
(and so the hazardous zone) under normal and fault conditions.
– Control both conducted and radiated interference with other
systems, including IS face systems.
… the selected cable must assist in explicitly managing

29. SUMMARY OF KEY CONSTRAINTS
• The proposed protection system must:
– Accommodate DC and wideband fault currents without un-
instrumented current paths or loss of sensitivity that
compromises protection.
– Be adequately rated in terms of power dissipation under fault and
non-fault conditions.
– Utilise techniques previously deployed successfully in operating
electrical distribution networks in Australia where compatible with
earth fault limited networks.
– … and comply with NSW Regulations.
… the selected cable must assist in explicitly managing

30. IMPLICATIONS OF
CURRENT NSW
LEGISLATION

31. The two requirementsfor safe operationof high power voltage source
VSDs in undergroundmines are:
1) A system design that takes into account the dynamic
nature of typical mining electrical infrastructure, as well
as the parallel nature of connected loads; and,
2) Suitable cables designed specifically to manage high
frequency currents by explicitly controlling both system
and return earth impedance.
Theserequirementsare universalfor all undergroundmines,not just coal
applications…
… for VSDs in all underground mines
SAFE OPERATION REQUIREMENTS

32. • Only cables compliantwithAS/NZS1802 are able to be used in a
reeling or trailing cable applicationin a hazardouszone.
• Only cables complianttoAS/NZS1972 can be used in a
hazardousarea machineapplication.
• There are multiple applicationsof VSDs undergroundin NSW that
are forcedto useAS/NZS1802 orAS/NZS1972 compliantcables,
when a non-compliantscreenedcable can be shown to be
superiorin termsof application residual risk.
• Ampcontrol started the processof applicationfor an exemption
with the Regulatorin June2018.
Containexplicit requirementsaround cable materials& geometry
NSW REGULATIONS

33. • Exemption applies to all NSW undergroundcoal mines and allows use
of non-compliantcables in a hazardouszone,on the proviso that:
(1) The cable has been design for use as part of an engineered system,
and only as a component of that system;
(2) The engineered system must result in a standard of safety at least
equivalent to utilising a compliant cable; and,
(3) The safety equivalence must be demonstrated by risk assessment,
engineering calculations and other information relevant to an
engineered system in use at the mine.
… released in March 2019
CLASS EXEMPTION

34. QUESTIONS