132kV Connection

A First for N.S.W Coal Mining

Introduction

• Where is Boggabri – Situated between Gunnedah and Narrabri in north west N.S.W approx. 115km West from Tamworth.

• Boggabri Coal Operations commenced mining in 2006 • A significant expansion of site infrastructure was undertaken in 2014/2015 • The 132kV connection was a joint project by Transgrid and Boggabri Coal

Operations. • Included was 15kM of single structure, double circuit, 132kV transmission line,

132kV switching station and the 132kv/11kV substation.

Overview • Boggabri Coal Operations were an LV customer (HV was

managed by the utility) at inception. • Site demand was below 2MVA • An 11kV rural feeder from Boggabri Substation was the

only mine supply source. The service extended over 25kM (voltage regulation was required).

• Expansion of site infrastructure required power system demand exceeding the 11kV capability.

• Overall site demand increased to 8MVA (design capacity) • Local services could not meet the demand – Transmission

was the only option.

Why 132kV Connection

? A first for Mining and Transgrid

Network Layout

Network Connection

Boggabri Coal Substation

Network Connection

Protection Schemes

Inter tripping

• 132kV trip signals are duplicated through protection relays from Boggabri Coal to Transgrid

– Zone Protection (overcurrent, short circuit etc) – TX Differential – Emergency stops – Fire system – Back up Earth Leakage – Neutral Earth Resistor failure via NER monitor. – Transformer Protection (Oil temp, explosion, winding temp, over pressure) – Arc Fault Detection (11kv Bus)

• Protection devices, Circuit breakers, are in Transgrids Switching Station. • Faults are cleared by transgrid for all 132kV primary protection or

Intertrip faults

Logic Diagram Example

Load shed Arrangements

• Transmission systems demand stability • Transgrid Load shed scheme means exactly what is

sounds like • 4 Tiers are implemented which shed different load

blocks • Bus voltage is monitored at the switching station for

trip signal initiations

EARTHING

• Common earthing system between Transgrid and Boggabri Coal • Design requirements - Allowable touch and step voltages were

derived from different standards

• Transgrid – AS2067 ( Calculated) • Boggabri Coal – AS3007 (step/touch potentials v’s clearance times)

• Transfer voltage levels required separation between

“mine infrastructure area” and the 132kV facility. A 164M exclusion zone has been established for earthed services entering this zone.

EARTHING

Challenges • Design was completed by Transmission orientated Engineers with a different approach to mining

“Risk management base” • Design review was undertaken by a QLD based engineering company • Disconnect between project team and the end user of the facility • System operation – original design philosophy was to run 2 x 10MVA TX’s in parallel which allowed

for a 65kA fault level on the 415V system (terminals of the 3MVA TX supply) • Fundamental protection schemes, secondary systems, required further development prior to

energistaion. • HV and LV services crossing operational boundaries. Boggabri Coal and Transgrid share HV and LV

services originating on both sides of the installation. • Differences in isolation procedures, including hardware between both Transgrid and Boggabri Coal • Transgrid having a major facility “next door” to the mine substation. • Unrestricted earth fault levels on the 132kV connection (max 15kA) – transfer voltages • Reliance of primary protection clearing faults is by the utility – No 132kV protective devices are

owned or operated by Boggabri Coal Operations.

Advantages • Transgrid monitoring

• Transgrid system control monitor the status of Transgrid equipment, including the 132kV circuit breakers, 24/7

• Remote operation of 132kV circuit breakers from Transgrid system control

• Stability of Supply • The 132kV connection is part of the overall, north west area “Ring Main”. This means the system is very

stable and subject to minimal outages or faults.

• Reduced Arc Flash Categories • Increased equipment clearances (above 3M) and protection schemes allow for arc

flash categories to be reduced

Key Outcomes

• Transgrid and Boggabri Coal Operating agreement implemented This document identifies

– Equipment isolation instructions, each piece of equipment has an agreed isolation procedure – Communication protocol’s – Key contacts for events – Use and transaction of “High Voltage Equipment Outage” permits.

• Connection Agreement – Highlights the obligations of each party – Deals with access and safety scenarios . – Modifications to the agreed installation and protection settings are dealt with here

• Operational and Maintenance, hazard identification and risk analysis via consultation with designer, supplier, installer, operator and utility (Transgrid).

– This process expedited the risk mitigation process due to designer information being supplied by key engineers

• Designer based training for operational staff – Maintenance, Isolation and Operational documents were developed and used as training material

for electrical staff by the designer. Training was delivered onsite.

Recommendations

• Where plant and installations are being constructed, for the purpose of mining operations, statutory functions should be involved in the key decisions.

• Collaboration with mining and transmission industries requires further development. Mindsets are differing around system operations and protection functions.

Thank You!