Application of Electrical Engineering in Mining Industry - 2019 Edition

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Application of Electrical Engineering in Mining Industry

2019 Edition

Application of Electrical Engineering in Mining Industry

2019 Edition

Preface This book is intended to provide a systematic approach to electrical engineering based on Australian Standards and NSW Work Health and Safety Legislations. Australia is one of the largest producers and exporters of coal in the world, and coal mining plays an important role in Australian economy. Thanks to the application of electrical engineering, modern coal mines and coal processing plants in Australia enjoy high level of automation, efficiency and reliability to be competitive in production.

Application of Electrical Engineering in Mining Industry 2019 Edition

Meanwhile, electrical equipment and installations in mining industry are strictly regulated by legislations and it is critical that electrical risks can be managed by implementing effective controls, such as maintaining fit for purpose equipment, appointing competent personnel, and following safe work procedures. Australian Standards and NSW Work Health and Safety Legislations are the key documentations for compliance, and electrical engineers are expected to develop sound practical skills and management skills to apply these documentations into practice. There is no such thing as good luck in mining industry, as good luck only comes from managing with persistent efforts. In this book, balance is kept between breadth and depth of engineering theories. Case studies and electrical diagrams are provided to facilitate understanding. Much contents such as industry examples, safety requirements and decision makings may not be covered in university curriculum. Overall, this book aims to assist graduate engineers to bridge the gap between tertiary study and industrial practice, as well as assist developing career path to engineering managers.

Electrical Engineering in Practice November 8, 2019 Newcastle, Australia

Application of Electrical Engineering in Mining Industry

2019 Edition

Contents Part I

 1

Australian/New Zealand Standards Electrical Installations (Wiring Rules)

 2

AS/NZS 3007: 2013

Electrical Equipment in Mines and Quarries – Surface Installations

 15

Chapter 3

AS 2067: 2016

Substations and High Voltage Installations Exceeding 1 kV a.c.

 30

Chapter 4

AS/NZS 2081: 2011

Electrical Protection Devices for Mines and Quarries

 53

Chapter 5

AS/NZS 3010: 2017

Electrical Installations – Generating Sets

 67

Chapter 6

AS/NZS 4871 Series

Electrical Equipment for Mines and Quarries

 79

Chapter 7

AS 61508 Series

Functional Safety of E/E/PE Safety Related Systems

 84

Chapter 8

AS 1674.2: 2007

Safety in Welding and Allied Processes (Part 2 – Electrical)

 97

Chapter 9

AS/NZS 60079 Series

Explosive Atmospheres

 108

Chapter 10

AS/NZS 2290.1: 2014

Electrical Equipment for Coal Mines (Part 1 – For Hazardous Areas)

 120

Chapter 11

AS/NZS 3800: 2012

Electrical Equipment for Explosive Atmospheres – Repair and Overhaul

 123

Chapter 1

“AS/NZS 3000: 2018

Chapter 2

Part II

Work Health and Safety Legislations

 128

Chapter 12

Legislation Compliance Requirements

 129

Appendix

Index

 156

Application of Electrical Engineering in Mining Industry

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Part I: Australian / New Zealand Standards

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Chapter 1 AS 3000: 2018 Electrical Installations (Wiring Rules)

There are two ways that allow an installation to be certified as compliant: AS 3000 Part 1 Compliance, or AS 3000 Part 2 Compliance.

Contents

As is described in AS 3000: 2018 Preface, Part 1 provides uniform essential elements that constitute the minimum regulatory requirements for a safe electrical installation; Part 2 provides installation practices that are deemed to comply with the essential safety requirements of Part 1.

Topic 1.1

Methods of Electrical Protection

2

Topic 1.2

Protection by Automatic Disconnection of Supply

3

Topic 1.3

Overcurrent Protection Devices

5

Topic 1.4

Risk Associated with Arc Flash

10

Topic 1.5

Electrical Commissioning and Approval to Energise Form

12

Topic 1.1 Methods of Electrical Protection Clause 1.5.1 Protection against dangers and damage The requirements of this Standard are intended to ensure the safety of persons, livestock, and property against dangers and damage that may arise in the reasonable use of electrical installations. In electrical installations, the three major types of risk are listed below: (1) Shock current: Shock current arising from direct / indirect contact. (2) Excessive temperatures: Excessive temperatures likely to cause burns, fires and other injurious effects. (3) Explosive atmospheres: Equipment installed in areas where explosive gases or dusts may be present shall provide protection against the ignition of such gases or dusts. Clause 1.4.38 Direct contact Contact with a conductor or conductive part that is live in normal service. Clause 1.4.39 Indirect contact Contact with a conductive part that is not normally live but has become live under fault conditions (because of insulation failure or some other cause). Clause 1.5.4 Basic protection (protection against direct contact) Methods of protection: (1) Insulation material, (2) Barriers or enclosures, (3) Obstacles (4) Placing out of reach

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Clause 1.5.5 Fault protection (Protection against indirect contact) Methods of protection: (1) Automatically disconnect the supply on the occurrence of a fault likely to cause a current flow through a body in contact with exposed conductive parts, where the value of that current is equal to or greater than the shock current, in accordance with Clause 1.5.5.3 (2) Prevent a fault current from passing through a body by the use of Class II equipment or equivalent insulation, in accordance with Clause 1.5.5.4 (3) Prevent a fault current from passing through a body by electrical separation of the system, in accordance with Clause 1.5.5.5. (Isolated supply) NOTE: Clause 7.4 provides further guidance on electrical separation. (4) Limit the fault current that can pass through a body to a value lower than the shock current.

2019 Edition

Clause B4.3 Disconnection times AS/NZS 60479 defines two components that permit the establishment of a relationship between the prospective touch voltage and its duration, that does not usually result in harmful physiological effects on any person subjected to that touch voltage. These two components are: (a) The effect on the human body of electrical currents of various magnitudes and durations flowing through the body; and (b) the electrical impedance of the human body as a function of touch voltage. Using the available information (as described in IEC/TR 61200-413), the required relationship between prospective touch voltage and disconnection time was derived shown in Figure 1.1.

NOTE: The most commonly used method of protection is automatic disconnection of supply.

Topic 1.2 Protection by Automatic Disconnection of Supply AS 3000: 2018 Appendix B4 defines the principle of protection by automatic disconnection of supply. Clause B4.2 Principle The principle of protection by automatic disconnection of supply is intended to prevent a person being subjected to a dangerous touch voltage for a time sufficient to cause organic damage, in the event of an insulation fault. In order to meet this requirement, in the event of such a fault the circuit protective device must interrupt the resulting fault current sufficiently quickly to prevent the touch voltage persisting long enough to be dangerous. This method of protection relies on the combination of two conditions: (a) The provision of a conducting path, designated the ‘earth fault-loop’, to provide for circulation of the fault current; and (b) The interruption of the fault current within a max time by an appropriate protective device. This maximum time depends on parameters, such as the highest touch voltage, the probability of a fault, and the probability of a person touching equipment during a fault.

Figure 1.1 Maximum Duration of Prospective 50Hz Touch Voltage (Copied from AS 3000: 2018 Appendix B)

These curves demonstrate that for normal conditions, A touch voltage of 50V may be sustained by a person indefinitely, and A touch voltage of 100V may not be sustained and must be disconnect. 3|P age

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As 230/400V is the most popular supply voltage, there is a requirement for maximum disconnection time for 230/400V supply voltage. Clause 1.5.5.3 Protection by automatic disconnection of supply (d) Disconnection times The maximum disconnection time for 230/400V supply voltage shall not exceed the following: (i) 0.4 second for final sub-circuits that supply (A) socket-outlets having rated currents not exceeding 63 A; or (B) hand-held Class I equipment; or (C) portable equipment intended for manual movement during use. (ii) 5 seconds for other circuits including submains and final sub-circuits supplying fixed or stationary equipment.

2019 Edition

Depending on the circuit considered, the factor đ?‘? may vary from 0.6 (e.g. a circuit very far from the source) and 1.0 (e.g a circuit supplied directly from the source). In the event of fault, in average approximately 20% of voltage drop is in upstream, and 80% voltage drop in final sub-circuit. It is assumed that phase conductor and the protective earth conductor are of the same size, i.e. half of voltage drop in phase conductor, and half in earth conductor. As a result, using a mean value of 0.8 for the factor đ?‘? and a ratio đ?‘š of 1, the prospective touch voltage đ?‘ˆđ?‘‡ for a circuit is given by: đ?‘ˆđ?‘‡ =

đ?‘?đ?‘ˆđ?‘‚ đ?‘š 0.8Ă—230Ă—1 = = 92 đ?‘‰ 1+đ?‘š 1+1

It can be checked in Figure 1.2 that, when 92V is applied to human body, the maximum duration is above 0.4 second and under 0.5 second for human touch. Thus, 0.4 sec is selected to be the automatic disconnection time.

NOTE: Maximum disconnection times will vary for other voltages and installation conditions. Appendix B provides further guidance regarding disconnection times.

Reasons for 0.4-second disconnection time are explained in Clause B4.3. Clause B4.3 Disconnection times A study was made of the influence of the variations in the different parameters on the value of the prospective touch voltage and the corresponding disconnection time. The prospective touch voltage đ?‘ˆđ?‘‡ for a circuit is defined by: đ?‘ˆđ?‘‡ =

đ?‘?đ?‘ˆđ?‘‚ đ?‘š 1+đ?‘š

Where đ?‘ˆđ?‘‚ is the nominal r.m.s. voltage to earth; đ?‘? is the proportion of the supply voltage available at the reference point during operation of protective device; đ?‘š is the ratio of the cross-sectional area of the phase conductor compared to the cross-sectional area of the protective earthing conductor in the circuit.

Figure 1.2 Maximum Duration of Prospective 50Hz Touch Voltage of 92 volts (Copied from AS 3000: 2018 Appendix B) 4|P age

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Reasons for 5-second disconnection time are also explained in Clause B4.3. Clause B4.3 Disconnection times (1) Faults in such circuits are less likely; (2) There is less likehood of persons being in contact with equipment supplied by such circuits during a fault; (3) Equipment supplied by these circuits is usually not gripped and therefore be released easily if a fault occurs; (4) Touch voltages are not expected to exceed the values in accordance with Figure 1.1 for the time/touch-voltage relationship.

Topic 1.3 Overcurrent Protection Devices 1.3.1 Time-current curves The tripping characteristics of a circuit breaker can be represented by time-current curve. The curve shows the amount of time required for a circuit breaker to trip at a given overcurrent level. The upper-left portion of the curve displays the thermal response of the circuit breaker. On low-fault current levels, thermal tripping occurs when a bimetal conductor in the breaker responds to heat associated with the overcurrent. The bimetal conductor deflects, de-latching the mechanism and mechanically causing the circuit breaker to trip and open the circuit. The larger the overload, the faster the breaker will operate to clear the circuit. The lower right portion of the curve displays the magnetic tripping response of the circuit breaker. This takes place when overcurrents of sufficient magnitude operate an integral magnetic armature which de-latches the mechanism. Magnetic tripping occurs with no intentional time delay. Electronic trip circuit breakers are characterized by their adjustability. By adjusting the settings of the available trip unit functions, different tripping characteristics can be achieved. Figure 1.3 shows various discrete segments of the trip curve that can be adjusted on a circuit breaker.

Figure 1.3 Typical time-current curve of circuit breaker and fuse

Long-time delay typically protects equipment in the event of overload; Short-time pickup and short-time delay are typically for motor starting, or transformer inrush conditions; Instantaneous pickup is to protect equipment during phase-to-earth fault or phaseto-phase fault. Useful Resources: Schneider Electric Data Bulletin No. 0600DB0105 - Characteristic Trip Curves and Coordination https://www.se.com/us/en/download/document/0600DB0105/ 5|P age

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2019 Edition

1.3.2 Definition of overcurrent

1.3.3 Protection against overload current

AS 3000 Clause B3.1 defines protection against overcurrent:

According to AS 3000 Clause 2.5.3.1, the operating characteristics of a device protecting a conductor against overload shall satisfy the following two conditions:

The term ‘overcurrent’ includes both overload current and short-circuit current. For circuit breakers: đ??źđ??ľ ≤ đ??źđ?‘ ≤ đ??źđ?‘?

The dangner to the system from overload currents is that the temperature of conductors and their insulation will rise to levels at which the effectiveness of the insulation and its expected service life will be reduced. Short-circuit currents may be up to several thousand times normal current and will cause overheating and mechanical stresses of conductors and associated connections.

đ??ź2 ≤ 1.45Ă—đ??źđ?‘? For fuses: đ??źđ??ľ ≤ đ??źđ?‘ ≤ 0.9đ??źđ?‘? đ??ź2 ≤ 1.6Ă—đ??źđ?‘?

Clause 2.5.1 requires active conductors to be protected by one or more protective devices in the event of overload or short-circuit. The protection of cable by circuit breakers and fuse is shown in Figure 1.4. The conductor is deemed to be protected if its damage curve is to the right of the time/current curve of the protective device.

Where đ??źđ??ľ The current for which the circuit is designed (e.g. maximum demand) đ??źđ?‘ The nominal current of the protective device đ??źđ?‘? The continuous current-carrying capacity of the conductor đ??ź2 The current ensuring effective operation of the protective device and may be taken as equal to either: (a) the operating current in conventional time for circuit breakers (1.45Ă—đ??źđ?‘ ); or (b) the fusing current in conventional time for fuses ( 1.6Ă—đ??źđ?‘ for fuses in accordance with the AS 60269 series). Note: To prevent cable damage, circuit breaker must trip within 1 hour when subject to 145% overload setting, while High Rupturing Capacity (HRC) fuses must trip within 1 hour when subject to 160% of overload settings. Thus, 1.6 Ă— HRC fuse size = 1.45 Ă— cable rating, and HRC fuse size = 0.9 Ă— cable rating.

Figure 1.4 Protection of cable by circuit breakers and fuse

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1.3.4 Protection against short-circuit current

1.3.5 Miniature circuit breaker types

According to AS 3000 lause 2.5.3.1, protection devices shall be provided to limit, as far as practicable, the harmful effects of a switchboard internal arcing fault (short-circuit current) by automatic disconnection.

Miniature circuit breakers (MCBs) are electromechanical devices which protect an electric circuit from an overcurrent. Mean tripping currents for Type B, C and D miniature circuit breakers are defined in Clause B4.5, and current curves are shown in Figure 1.5. Note that the curve type is “C curve�.

The arcing fault current between phases or between phase and earth, is deemed to be in the range of 30% to 60% of the prospective short-circuit current. Protection shall be initiated, when less than 30% of the three-phase prospective fault level is picked up. The general damage limit is given by:

đ?‘Ą= Where đ?‘Ą đ??źđ?‘“ đ??źđ?‘&#x; đ?‘˜đ?‘’

đ?‘˜đ?‘’ Ă—đ??źđ?‘&#x; đ??źđ?‘“1.5

Clearing time in seconds 30% of the prospective fault current Current rating of the switchboard 250 constant, based on acceptable volume damage. Figure 1.5 Mean tripping currents of Type B, C and D circuit breakers

For example, for an 800A-rated main switchboard with a prospective fault current of 16.67kA, đ??źđ?‘“ = 16.67Ă—30% = 5 đ?‘˜đ??´ đ?‘Ą=

đ?‘˜đ?‘’ Ă—đ??źđ?‘&#x; 250Ă—800 = = 0.566 đ?‘ đ?‘’đ?‘? (5000)1.5 đ??źđ?‘“1.5

The protective device settings must be set to clear an arcing fault of 5kA in less than 0.566 seconds.

Type B: 4 Ă— rated current; Type C: 7.5 Ă— rated current; Type D: 12.5 Ă— rated current.

Type B MCB trips between 3 and 5 times full load current. They are mainly used in residential or light commercial applications where connected loads are primarily lighting fixtures, domestic appliances with mainly resistive elements. The surge current levels in such cases are relatively low. Type C MCB trips between 5 and 10 times full load current. This is used in commercial or industrial type of applications where there could be chances of higher values of short circuit currents in the circuit. The connected loads are mainly inductive in nature (e.g. induction motors) or fluorescent lighting. Type D MCB trips between 10 and 20 times full load current. These MCBs are use in specialty industrial/commercial uses where current inrush can be very high. Examples include transformers or large winding motors etc. 7|P age

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1.3.6 Discrimination requirements AS 3000 Clause 2.5.7.2 Coordination of Protective Device describes circuit breaker curves and fuse curves with discrimination requirements.

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(iii) For ratings of đ??ś2 < 250A, Discrimination should be provided between overload curves, and is recommended up to the instantaneous setting đ??źđ?‘– or short-time pickup đ??źđ?‘†đ??ˇ of đ??ś1, but need not apply above the arcing fault current đ??źđ?‘Žđ?‘&#x;đ?‘? . Discrimination is deemed to be achieved if đ??ś1 ≼ 1.5 Ă— đ??ś2, e.g. đ??ś1 MCB marked C63 with đ??ś2 MCB marked C40 (time-current curves are both C curves).

Figure 1.6 Location of protective devices

As is shown in Figure 1.6, discrimination is achieved when Protection Device 1 remains intact while Protection Device 2 clears a fault on the load side. Thus supply is maintained to Protection Device 3 and the remainder of the electrical installation. Figure 1.7 Circuit breaker curves with discrimination requirements (Figure derived from AS 3000: 2018 Section 2)

As shown in Figure 1.7, two circuit breakers, connected such that đ??ś2 is the downstream device and đ??ś1 the upstream device, shall be selected as follows: (i) For ratings of đ??ś2 ≼ 800A, Discrimination shall be provided between overload curves and instantaneous settings, but need not apply above the arcing fault current đ??źđ?‘Žđ?‘&#x;đ?‘? . (ii) For ratings of đ??ś2 ≼ 250A up to < 800A, Discrimination shall be provided between overload curves, and is recommended up to the instantaneous setting đ??źđ?‘– or short-time pickup đ??źđ?‘†đ??ˇ of đ??ś1, but need not apply above the arcing fault current đ??źđ?‘Žđ?‘&#x;đ?‘? .

Note that the following terms are used: đ??źđ?‘ƒđ?‘†đ??ś đ??źđ?‘Žđ?‘&#x;đ?‘? đ??źđ?‘–

Prospective short-circuit current; Deemed maximum acing fault current (30% ~ 60% đ??źđ?‘ƒđ?‘†đ??ś ); Instantaneous setting;

đ??źđ?‘†đ??ˇ 0.01s

Short delay setting; The limit of the fuse time-current.

Discrimination is deemed to be achieved if the overload setting of đ??ś1 ≼ 1.5 Ă— đ??ś2, e.g. đ??ś1 1000A with đ??ś2 630A. 8|P age

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As is shown in Figure 1.8, two fuses connected such that đ??š2 is the downstream device and đ??š1 is the upstream device shall be selected such that the characteristics of the device provide discrimination (selectivity) on overload. Discrimination between HRC fuses is deemed to be achieved –

2019 Edition

As is shown in Figure 1.9, a fuse and a circuit breaker connected such that đ??ś2 is the downstream device and đ??š1 is the upstream device shall be selected such that the characteristics of the devices provide discrimination between the overload curve and the instantaneous setting or short delay setting (đ??źđ?‘†đ??ˇ ) of đ??ś2 and the timecurrent curve of đ??š1 .

(i) For overload when đ??š1 ≼ 1.6 Ă—đ??š2 , e.g. 16A with 10A (ii) For short-circuit when đ??š1 ≼ 2 Ă— đ??š2 , e.g. 20A with 10A Note: Overload curves are those for times > 0.01s. Short circuit data is based on the total đ??ź 2 đ?‘Ą of đ??š2 ≤ pre-arcing đ??ź 2 đ?‘Ą of đ??š1 .

Figure 1.9 Fuse and circuit breaker curves with discrimination requirements (Figure derived from AS 3000: 2018 Section 2)

Figure 1.8 Fuse curves with discrimination requirements (Figure derived from AS 3000: 2018 Section 2)

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Topic 1.4 Risk Associated with Arc Flash

2019 Edition

Hierarchy of controls Engineering controls

1.4.1 Causes and controls for arc flash In 2019 Energy Safe Victoria provided a guideline on arc flash hazard management. It explains the causes of arc flash as below: Arc flash incidents occur when low impedance electrical connections are inadvertently made across phases, phase to neutral or from phase to earth. These connections can occur by accidental contact across terminals from tools or equipment, a breakdown in insulation or from a build-up of contaminates such as carbon or dust. Most arc flash incidents occur when high risk activities, such as operating or racking of circuit breakers are being carried out, however arc flash incidents can occur at any time.

Contents Fixed circuit breakers over rackable breakers for new installation/upgrades Insulated bus bars Installation design consideration for isolation/maintenance tasks Replacement of fuses which provide faster clearance times Label all switch rooms, plant and relevant locations to identify incident energy levels and the appropriate actions / precautions that need to be taken Demarcation of arc boundaries Make arc flash registers and diagrams available for workers

This guideline provides controls for arc flash hazards shown in Table 1.1.

Administration Establish effective policy and procedure that reduces exposure, including training and inductions

Table 1.1 Hierarchy of controls for arc flash hazards (derived from guideline) Hierarchy of controls

Implement of an incident energy and PPE category system as detailed in IEEE 1584 and ENA NENS 09 – 2014 or equivalent published standards.

Contents

Eliminate

Eliminate the exposure of personnel to arc flash hazards by only interacting with de-energised and isolated equipment.

Substitute

Substitute manual operating systems for automated operating systems.

PPE is the least effective control and should not be relied upon unless combined with other controls. PPE does not prevent injury but may reduce severity.

Isolate personnel from the hazard by installing physical separation from energised equipment or conductors. Isolation

Switchboards can be constructed to contain the energy associated with an arc event. Limit incident energy with reduced fault current and/or reduced fault clearance times by adjusting circuit breaker settings.

Engineering controls

System modifications: Arc flash detection and suppression system Remote racking devices Upgrade switchboard form type Upgrade/modify boards to allow for racking with the door closed

PPE

To select the appropriate PPE for an electrical arc flash hazard environment, the following steps need to be undertaken. (1) Understand the hazard. (2) Identify assets or asset groups with arc flash/fault hazard potential. (3) Quantify the hazard – calculate the incident energy in each relevant location. (4) Assess the risk – using your organisation risk management framework. (5) Reduce the risk, so far as is reasonably practicable, using the hierarchy of controls. (6) Select the appropriate PPE if a residual risk of injury is present

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Arc fault category, incident energy and PPE requirements are shown in Table 1.2. PPE manufacturer can be consulted for the correct arc flash category. Table 1.2 Arc flash category and PPE requirement chart Arc flash Category 0

1

2

3

4

Incident Energy

0-4 cal/cm2

4-8 cal/cm2

8-25 cal/cm2

25-40 cal/cm2

>40 cal/cm2

PPE requirements Long-sleeve shirt Long pants Hard hat Safety glasses Arc-rated long-sleeve shirt Arc-rated pants or coverall Arc-rated face shield with hard hat Safety glasses Leather & voltage rated gloves Leather work boots Arc-rated long-sleeve shirt Arc-rated pants or coverall Arc flash suit hood with hard hat Safety glasses Leather & voltage rated gloves Leather work boots Arc-rated long-sleeve jacket Arc-rated pants Arc-rated face hood with hard hat Leather & voltage rated gloves Leather work boots Arc-rated long-sleeve jacket Arc-rated pants Arc-rated face hood with hard hat Leather & voltage rated gloves Leather work boots

Guideline on arc flash hazard management from Energy Safe Victoria: https://esv.vic.gov.au/wpcontent/uploads/2019/10/Arc_flash_hazard_guideline_Oct19.pdf

2019 Edition

1.4.2 Arc flash control action plan Your Electrical Engineering Control Plan shall take the following into account to manage the risks to health and safety from electricity at your coal mine. WHS (Mines) Regulation 2014 Schedule 2, Clause (3) (b) Identifies: The rating and design of plant for the prospective electrical fault level, electrical load, operating frequency, operating voltages and arc fault control. As a newly appointed electrical engineering manager you become aware that the aging electrical infrastructure within your mine has not been assessed or appropriate controls implemented to deal with arc flash control. a) Formulate an action plan to manage this risk at the operation in relation to arc flash control. Action plan to manage arc flash risk is listed in Table 1.3. Table 1.3 Arc fault control action plan Issue Switching procedures expose electricians to risk Electricians not aware of correct switching procedure Load flow study and arc flash study out of date Aging switchgears and equipment Remote switching not available in some areas Poor maintenance of switchgears PPE not suitable

Action

By who

Due date

Procedures to be updated for remote switching

Electrical Engineer

2 weeks

Training for correct switching procedure

Trainer Assessor

2 weeks

Electrical Engineer

4 weeks

Electrical Engineer

4 weeks

Electrical Engineer

6 weeks

Complete load flow study and arc flash study, assign arc flash category, review fault level and protection settings. Complete an audit for switchgears and review their conditions Implement remote switching such as remote control panel, pendant and/or SCADA Update inspection sheets Keep regular maintenance and testing of switching gears Ensure PPE with suitable arc flash ratings

Electrical Engineer Electrical Supervisor Electrical Supervisor

2 weeks 2 weeks 4 weeks

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b) You need to draft a memo to your Mine Manager in relation to these risks and the requirement for capital expenditure for arc flash control at your mine. What would be your key elements in the memo? Problems: Aging equipment arc fault control not meeting legislation requirement or Australian Standards. Risk assessment needs to be conducted for existing arc flash ratings. Risks to be controlled associated with arc-fault: electric shock, electric burn, ignition of gas/dust, fire. Short term solutions: (1) Complete a fault level and arc flash study for all electrical equipment on site, evaluate fault level, arc flash level, and the required protection settings. Label arc flash category, provide PPE with suitable arc flash ratings. (2) Develop procedures for remote switching (pendant, remote panel, SCADA) (3) Training for electricians for correct switching procedure. Long term solutions: (1) Complete an audit for switchgears and review their conditions. Investigate reducing arc fault levels by faster switchgear, arc-resistant switchgears or HRC fuses. (2) Implement remote switching devices for switchgears. (3) Routine maintenance of switch gears, check for dust build-up, overheating of insulation etc. Outcome: the likelihood and consequence of arc flash are reduced, and significantly improved safety for personnel. Note: Arc flash incident energy is proportional to fault clearance time. As a result, proper selection of short-circuit protective devices that quickly clear arcing faults is a powerful mitigation strategy.

2019 Edition

1.4.3 Arc flash risk associates with MCCs You are the electrical engineering manager at a mine and you have received a Safety Alert describing an incident where an electrician received an electric shock and an electrical burn to his hand whilst carrying out routine maintenance in a withdrawable 415V 37kW pump cell in a motor control centre (MCC). The MCC has a design fault rating of 65kA and the modelled maximum fault level of the installation is 25kA. a) List three design features you may find on the 37kW pump MCC cell to prevent contact with live conductors. Door interlock, enclosure, IP2X form rating, insulation b) List the design features you may find on the 37kW pump cell to eliminate or mitigate arcing faults. Arc resistant enclosure, segregated compartment, arc blast duct, protection device, remote switching c) List three administrative controls you would expect to see in place to manage the risks associated with this type of incident. Competency of workers, correct work procedure, remote switching, arc flash category signage, and provision of suitable PPE d) The following warning is provided in the manufacturer’s Installation manual: ATTENTION: De-energize, lock out, and tag out all sources of power to the MCC when you install or remove MCC units. If MCC units are installed or removed with power applied to the main power bus, follow established electrical safety work practices. List two key conditions you would include in a procedure for the withdrawal of an MCC unit with the main power bus energised. (1) Ensure offload; (2) Confirm arc fault category, and use suitable PPE that suitable for that category; However, if arc fault category is labelled “Dangerous” (above Category 4), then the bus shall be de-energised. 12 | P a g e

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Note: It is common that the 415V incomer circuit breaker (e.g. Terasaki Tempower 2 AR440S) has “Dangerous” arc flash level. If remote racking is unavailable and have to manually racking 415V incomer circuit breaker, the upstream transformer shall be de-energised by opening upstream high voltage circuit breaker.

2019 Edition

Note that for testing, multimeter of Category III and Category IV shall be used on a mine site. Handbook HB 187 – 2006 Guide to Selecting a Safe Multimeter defines the categories for multimeters, shown in Table 1.4. Table 1.4 Multimeter categories (copied from HB 187 – 2006)

Topic 1.5 Electrical Commissioning and Approval to Energise Form Category 1.5.1 Components of site electrical commissioning plan The requirements of commissioning are listed in AS 3000 Section 8 Verification. Typical site electrical commissioning plan should include: (1) Require a Certificate of Compliance (2) Verify circuits as per drawings (3) Test all safety functions (4) Test as per original equipment manufacturer (OEM)'s recommendations (5) Guarding as necessary during commissioning (6) Site notification about energization

CAT I – very low energy circuits CAT II – low energy circuits CAT III – medium energy circuits CAT IV– high energy circuits

Applications and fault current level e.g. Vehicles, battery-powered circuit (not connected to 240V) e.g. Domestic use (up to 5 kA fault currents) e.g. Industrial + commercial use (up to 25 kA fault currents) e.g. Industrial + commercial use (above 25 kA fault currents)

1.5.2 Inspection activities Visual inspection and testing (includes functional tests and measuring) are two major activities that you must undertake to ensure a compliant installation. Details of visual inspection are listed in clause 8.2; Details of testing are listed in clause 8.3. Mandatory tests are listed in Clause 8.3.3: The following tests shall be carried out on low voltage installations: (a) Continuity of the earthing system (main earthing conductor, protective earthing conductors and bonding conductors), in accordance with Clause 8.3.5. (b) Insulation resistance, in accordance with Clause 8.3.6. (c) Polarity, in accordance with Clause 8.3.7. (d) Correct circuit connections, in accordance with Clause 8.3.8. (e) Verification of impedance required for automatic disconnection of supply (earth fault-loop impedance), in accordance with Clause 8.3.9. (f) Operation of RCDs, in accordance with Clause 8.3.10. Note: High voltage installations may require additional test in AS 2067. 13 | P a g e

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1.5.3 Earth continuity test technique

1.5.4 Approval to Energise Form

To test the continuity of earthing system for a single-phase pump installation supplied 100 metres from the motor control centre (MCC), the below steps can be followed:

Approval to Energise Form shall be completed and approved by electrical engineering manager before energizing above extra-low voltage for electrical equipment and electrical installations.

(1) Complete isolation at MCC.

This form should include:

(2) At the motor, install a bridge between phase conductor and earth conductor. Measure resistance: đ?‘…đ?‘ƒâ„Žđ?‘Žđ?‘ đ?‘’ + đ?‘…đ??¸đ?‘Žđ?‘&#x;đ?‘Ąâ„Ž = đ??´

(1) Verification of basic information Person responsible for work Contract company name Equipment number and name As-built drawings Equipment description

(3) At the motor, remove the bridge between phase conductor and earth conductor. Install a bridge between phase conductor and neutral conductor. Measure resistance: đ?‘…đ?‘ƒâ„Žđ?‘Žđ?‘ đ?‘’ + đ?‘…đ?‘ đ?‘’đ?‘˘đ?‘Ąđ?‘&#x;đ?‘Žđ?‘™ = đ??ľ (4) Calculate earth conductor resistance: đ?‘…đ?‘ƒâ„Žđ?‘Žđ?‘ đ?‘’ = đ?‘…đ?‘ đ?‘’đ?‘˘đ?‘Ąđ?‘&#x;đ?‘Žđ?‘™ = đ?‘…đ??¸đ?‘Žđ?‘&#x;đ?‘Ąâ„Ž = đ??´ −

đ??ľ 2

đ??ľ 2

(2) Energisation checklist Confirm construction/energisation commissioning have been completed Completed commissioning test and inspections sheets are provided Confirm outstanding or defect Items detailed in construction punch list Confirm controls in place for punch list items to allow energisation to continue Drawings marked-up to ‘As built’ status Confirm Protection Settings correct and recorded Introduction to site paperwork attached Any defects and remedial actions shall be noted in comments.

One the form completed, it shall be signed off by electrical tradesperson, electrical supervisor and electrical engineering manager. Figure 1.10 Earth continuity test technique for motors

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