Innovation awards 2nd place – Peabody Moura Mining Pty Limited – Moura Mine

AIR BREAK SWITCH (ABS) ISOLATION SYSTEM

THE PROBLEM

Moura uses a 66,000 volt Ring-Main power distribution system to distribute power across the site. This system is used to minimize system down time that occurs as a result of faults or other errors. At Moura the process for switching the ring-main focuses on all Air Break Switches (ABS) in their normal operating state being closed throughout the circuit.

It was identified that although switching procedures required inspection of Air Break Switches before changing the system conditions, there was still the possibility of opening an ABS under high load in some circumstances and creating arcing across the switching mechanism. Such a high load condition might occur due to a second ABS at another point in the Ring-Main being in an open condition at the same time. Although the ABS’s are rated at 800A, the potential for injury and significant damage are still present. Inspection of all switches around an 80km Ring-Main is time-consuming and not always practical.

An occurrence of this nature also presents a significant risk to the safety of personnel performing the switching operation:

  • The arc can cause a high level electric current and/or high voltage to pass through the switching mechanism to the switch operator.
  • The arc can generate molten metal, which may shower the operator below.
  • Sparks and molten metal may cause a fire in ground cover surrounding the switch.

THE PROCESS

The electrical team (see appendix 1) at Moura Mine identified this issue, concluding that the High Voltage Switching book on its own was insufficient to control the occurrence of such an incident. They saw the need for a system whereby the status of all ABS’s could be represented in a central location giving the ability to Switch-Operators to quickly and reliably establish the status of all ABS’s along the ring-main prior to opening – without the need to physically inspect 80kms of power lines.

Having identified the problem, a series of discussions were held between individuals and each work crew. From these discussions a system was devised by which this need could be addresses, in addition to a side issue of positive and effective isolation of Air Break Switches.

A mimic board and other electronic indication systems were considered, however, it was decided to adopt a lock system, due to lock systems being an isolation method with which all personnel at Moura Mine are thoroughly familiar. The team implemented the system and created a cost effective method of increasing the availability of information thereby affording individuals greater control over associated risks.

THE SOLUTION

The ABS Isolation System consists of two uniquely keyed locks for each Air Break Switch, a “Ring-Main Condition Indicator Board” and a “Ring-Main Switching Instructions Book” secured under lock and key in a location that is central and readily accessible to authorised personnel only.

The “Ring-Main Switching Instructions Books” (Figure 3) is contained within the “Ring-Main Condition Indicator Board” cabinet and acts as a dedicated High Voltage Switching permit solely for use on the Ring-Main. It provides detailed information on those Air Break Switches that are being worked on, supporting the information shown on the condition indicator board.

The “Ring-Main Condition Indicator Board” (Figure 2) primarily acts as a supplement to the High Voltage Switching Book. It displays a schematic of the Ring-Main Power Distribution System along with the location of each Air Break Switch. Through the use of locks displayed in an easily recognizable arrangement, the status of all ABS’s can be determined at a glance.

The board is a typical whiteboard and has the added benefit of being able to write notes and other relevant information on it.

Each ABS has a large brass padlock for locking the ABS closed, and a smaller nylon lock for locking the ABS open (Figure 3). These are stored according to the appropriate ABS label on the Condition Indicator Board. The presence of a green key above a nylon lock and key indicates a “closed” status of the appropriate ABS.

The ABS Isolation System is designed as a supplement to the High Voltage Switching process strictly followed during switching operations. It also provides an added measure of security in positively and effectively isolating ABS’s by using individually keyed locks.

HOW THE SYSTEM WORKS

Prior to a switch operator commencing work on a specific section of the Ring-Main, he/she would consult the “Ring-Main Condition Indicator Board” to establish the status of the Air Break Switches to be opened. Under normal operating conditions, the ABS would be locked closed using the large brass padlock and the key to this lock placed on the corresponding ABS hook on the indicator board. The nylon lock would remain in position directly below the “closed” key. (See figure 4). This provides an instantaneous indication that the ABS is closed.

Having established the status of each ABS, the switch operator would then remove the nylon lock and key, and the green “closed” key for the ABS to be opened. A High Voltage switching permit would be completed and the switch operator would proceed to the ABS that is to be opened.

The “closed” padlock would be unlocked and removed using the green key (Figure 5). This enables the switch to be opened and the nylon “open” lock placed in the appropriate isolating point.

The brass lock and green key are returned to the Condition Indicator board and placed on the appropriate hook along with the key to the nylon “open” lock (Figure 6). This provides a timely indication that an ABS is opened. (Figure 7).

Isolation of the ABS is further ensured by two simple modifications that have been made to the switching mechanism. The diameter of the isolation point for locking the ABS closed is larger than the point for locking it open and vice versa. Further to this, the hole for the closed position is placed deeper within the switch so that only the larger, wider hasp of the large brass lock can be placed in the closed position. The large lock is physically unable to be placed in the open position due to the diameter of the hasp. This all serves to remove the possibility that the condition indicator board might indicate an ABS as open when it is in fact closed and vice versa.

The larger diameter hasp on the large brass lock is physically unable to be placed in the small diameter “Open” isolation hole in the base plate of the switching mechanism. (Figure 8).

The narrow hasp width and diameter of the nylon lock does not allow it to be inserted into the “Closed” isolation position in the base plate of the switching mechanism. (Figure 9).

THE BENEFITS

  • The risk to personal safety as a result of inadvertently opening an ABS under high load is reduced due to the ease with which information regarding ABS status can be acquired. This assists electrical personnel in their decision-making processes when performing switching operations so that an informed assessment of the risks involved can be made.
  • ABS Isolation is positive and effective due to the use of individually keyed locks for each ABS and because access to the locks that control the system is only available to personnel expressly authorised by the Mine Manager and Mine Electrician.
  • Minimal implementation cost. The cost of this system is minimal for the implementation of a practical system that effectively isolates and indicates the condition of Air Break Switches across site.

THE COST

Materials and labour to construct and implement the Air Break Switch Isolation System cost approximately $3 500.00 with the largest part of this expenditure being the cost of individual nylon locks for each of the Air Break Switches at Moura Mine.

APPENDIX 1

Special recognition and credit go to the following personnel within the Moura Mine electrical team who developed and implemented this system:

Ben ChadwickSteve Taylor

Tom CoughlinKim Tynan

Terry CraneScott Walsh

Ken HolmesLindsay Williams

Brad HansenKen Winter

Gary Hutchinson

Leigh Johnson

Cliff Kehl

Clive Long

Neil Moore

Shane Neumann

Rick Ostwald

Daniel Russell

Geoff Scott

Peter Stevenson