An electrician received an electric shock of 1.83 Joules while performing a high voltage megger test on an 11kV motor at the Cadia Valley mine site. The shock occurred when the electrician came into contact with exposed rotor windings during the discharging process. An investigation found the megger tester was not used properly and risk assessments failed to identify megger testing as a significant electrocution risk. Recommendations included developing training on megger testing hazards, adding megger testing to the annual regime, and updating site documents to address megger testing risks.

1. High Voltage Megger Electric Shock
27th Electrical Engineering Safety Seminar
Omer Saeed
9th November, 2017

2. High Voltage Megger Electric Shock
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Cadia Valley Operations
Site Overview
• Location
- Orange, NSW.
• Operation
- Commercial production commenced in 1999.
- An underground mine (Cadia East) and Ore Processing Facility.
• Electrical Infrastructure
- 132kV Incoming Supply from Orange with160MVA Installed Capacity.
- 33kV Power Transmission and Distribution.
- 11kV Area Reticulation, Fixed Plant Motors above 2000kW.
- 80MW Grinding & Milling Capacity.
- 30MW Conveying Capacity.

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Incident Description
• Incident Date/Time: 15:15 on 8th January, 2015
• Task: Megger Testing of a spare 11kV Ball Mill Motor
• Equipment: TECO 11kV, 8MW Wound Rotor Induction Motor
• Test Unit: Kyoritsu Insulation Tester
No calibration sticker attached
Test Voltage Range of 5,000V and 10,000V
• Incident Details: Electrician came in contact with the exposed rotor windings, during the discharging
process, resulting in an electric shock.
Date Time Description
8/1/15 07:00 Electrician commenced dayshift work at the surface concentrator
8/1/15 15:15
Electrician received electric shock
Megger and earth lead removed from incident site
Patient self presents to ERO medical facility for assessment. EROs perform initial treatment then
transfer patient to Orange Health Services.
8/1/15 15:30 Scene frozen and secured
8/1/15 15:50
Electrical inspector notified and preliminary information provided.
Scene released by DTI inspector subject to patient being released from hospital and completion of
incident data collection
8/1/15 17:05 Patient released from hospital
8/1/15 17:15 Scene released to enable incident data collection
9/1/15 20:40 3312-ML-2004 energized and ball mill operational

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Overall View of Incident Scene

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Overall View of Incident Scene

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Incident Scene

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Incident Scene

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Electric Shock Energy Estimation
• Step 1: Determine Energy Source
- Capacitive energy source.
• Step 2: Residual Capacitive DC Voltage on the Rotor Circuit
- Vc = Vo e-t/RC
= 5,000 x e (-5/1.5GΩ * 153nF)
= 4,892 V

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Electric Shock Energy Estimation
• Step 3: Total Body Impedance
- AS/NZS 60479.1:2010
- ZT = RT = 1050 Ω @ 5000V

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Electric Shock Energy Estimation
• Step 4: Internal Partial Impedance of Human Body
- Figure 2 (AS/NZS 60479.1:2010)
- Zip = (5.1+8.0+1.3+5.2+9.9+3.3+10.9+1.8+26.4) x total body impedance ZT
- = 71.9 % x 1050 Ω
- = 755 Ω

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Electric Shock Energy Estimation
• Step 5: Capacitor Discharge Calculations
- AS/NZS 60479.2:2002
- Peak Discharge Current = Ic(p)= 6.48 A
- RMS Discharge Current = Ic(rms)= Ic(p) / 6 = 2.65 A
- Time Constant = T = RC = 116 µsec
- Discharge Duration = ti = 346 µsec
- Outcome: No Fibrillation

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Electric Shock Energy Estimation
• Step 6: Capacitor Discharge Calculations
- AS/NZS 60479.2:2002
- Discharge Energy = 𝑊𝑐
= Τ1
2. C.V2
= 0.5 * 0.000000153 * 4892 * 4892
= 1.83 Joules
- Outcome: Painful

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Associated Site Risks
- 0.0002 to 0.002 J : energy levels required to ignite flammable vapour
- 0.02 J : typical static electricity energy level
- 0.125 J : typical auto sparkplug energy
- 0.3 J : typical Taser energy level
- 1.83 J : this incident
- 10 to 50 J : energy level range to cause ventricular fibrillation (VF)
- 80 J : energy level in 5kV megger test of Cadia East 33kV cables to PC2
- 102 J : energy level in 5kV megger test of 240mmsq 11kV cables (6km) e.g. Ridgeway, CE
- 200 J : Defibrillator energy level – minimum setting
- 360 J : Defibrillator energy level – maximum setting
- 322 J : energy level in 10kV megger test of Cadia East 33kV cables to PC2
- 410 J : energy level in 10kV megger test of 240mmsq 11kV cables (6km) e.g. Ridgeway, CE

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Key Findings
- Electric shock was calculated as 4892 VDC with a peak current of 6.48 A.
- Electric shock energy was 1.83 Joules which is below the life threatening threshold of 10-50
Joules.
- Similar activities on other electrical circuits at CVO have potential energy levels that greatly
exceed the life threatening threshold.
- Electrician did not receive any injuries as a result of the incident.
- Risk Assessment failed to identify electrocution from performing a HV megger testing as a
significant risk.
- Lack of awareness that a megger test electric shock is a notifiable incident as defined within
the mining legislation.
- Lack of appropriate barriers around worksite to prevent unauthorized personnel from entering
with the safe approach distance of the circuit.
- Test instrument was not used in accordance with the OEM recommendations.

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Recommendations
Item Description
1
Develop presentation package for site electrical personnel on the following:
• Potential lethal energy associated with megger testing
• Requirement to enact the electric shock protocol
• Requirement to notify the electrical inspectorate
• Correct usage of the megger test leads to ensure correct discharge of circuit
• Requirement for adequate barricades and PPE
2 HV Megger to be added to annual testing regime.
3
Include megger presentation major points in next revision of the Electrical Engineering Control Plan
and Electrical Workers Induction.