Managing the risks of high fault currents — Transcript

Full transcript

1. 0:05Hi. I'm Mark from the Electrical Safety Office.
2. 0:08Let's talk about high fault current or prospective
3. 0:10short circuit current.
4. 0:12Simply put, a fault current is the current that flows
5. 0:15when a short circuit occurs.
6. 0:16There have been several recent incidents where
7. 0:19workers were injured from high current arc flash
8. 0:21while working around energised parts.
9. 0:24Every day electrical workers are placing
10. 0:26themselves at risk if they do not understand the
11. 0:28potential hazard of high fault currents while
12. 0:30working on or around energised electrical equipment.
13. 0:34To get an idea of how powerful and deadly high
14. 0:36fault currents can be, let's think about your
15. 0:38average welder.
16. 0:39Using only 140 amps, the temperature of an electric
17. 0:42arc it produces is about 3,500 degrees Celsius,
18. 0:46and it melts metal.
19. 0:48Imagine the heat generated by 20,000 or 30,000 amps of
20. 0:52potentially uncontrolled current, which you could
21. 0:54find at certain electrical installations.
22. 0:57These fault currents can produce an arc flash with
23. 1:00temperatures up to 20,000 degrees Celsius.
24. 1:03This is hotter than the surface of the sun.
25. 1:06In installations with large switchboards or where the
26. 1:08supply transformer is close, the potential for
27. 1:11high fault current is very real.
28. 1:13For example, a 500KVA transformer with a five percent
29. 1:17impedance would have a fault level of 14,000 amps.
30. 1:21This is why it is very important to consider the
31. 1:23environment and the nature of the work you're about to do.
32. 1:26A switchboard with a high fault current requires the
33. 1:28highest levels of control, because the risks are very high.
34. 1:33Working near energised parts in these
35. 1:35circumstances can be just as dangerous as performing
36. 1:37actual live work, and appropriate control
37. 1:39measures must be implemented.
38. 1:42This includes testing and visual inspections.
39. 1:45Before you start working, determine the potential
40. 1:47short circuit current at the point within the
41. 1:49installation where the work will be done, and put the
42. 1:52controls identified during the risk assessment into place.
43. 1:55A quick visual indicator of the potential fault current
44. 1:58can be as simple as identifying the physical
45. 2:00location of the supply transformer.
46. 2:03Remember the highest level of risk control is to
47. 2:06eliminate the hazard altogether by isolating and
48. 2:09de-energising the equipment.
49. 2:11High fault currents are not just limited to
50. 2:13large main switchboards.
51. 2:15They can also occur within other locations
52. 2:17of the installation, such as smaller switchboards,
53. 2:20electrical supply pillars or large electrical equipment.
54. 2:24The level of prospective short circuit current will
55. 2:26vary due to several factors, such as the
56. 2:28electricity supply transformer fault current,
57. 2:31the circuit length and the cable size.
58. 2:34But won't a circuit breaker or fuse stop fault current?
59. 2:38In a high current arc flash, the protection may
60. 2:41not be enough to interrupt the fault current,
61. 2:44which can continue to arc across the protected device
62. 2:46even after it is operated.
63. 2:48This arc can self-sustain long enough to cause an
64. 2:51incredible amount of damage to equipment and severe
65. 2:55burns to anyone in the vicinity.
66. 2:57An arc flash can be caused by unsafe work practices
67. 3:01and procedures, foreign materials or a breakdown of
68. 3:03busbar insulation, electrical equipment
69. 3:06failure such as a switch, circuit breaker or loose cables,
70. 3:11contacting energised equipment when you're
71. 3:13using uninsulated tools, using test equipment
72. 3:16not designed or rated for the job.
73. 3:18Electrical work must not be carried out on electrical
74. 3:21equipment while energised simply because it's merely
75. 3:24convenient for the electrical equipment to
76. 3:26stay energised while the work is being performed.
77. 3:29Remember it is illegal to perform electrical work on
78. 3:33energised electrical equipment unless it is
79. 3:36necessary in the interests of health and safety that
80. 3:38the electrical work is carried out while the
81. 3:40equipment is energised - for example, it may be
82. 3:43necessary for lifesaving equipment to remain
83. 3:46energised and operating while the electrical work
84. 3:48is carried out on the equipment - or it is
85. 3:51necessary that the electrical equipment to be
86. 3:53worked on is energised in order for the work to be
87. 3:55carried out properly, or it is necessary for the
88. 3:58purposes of testing by a competent person to
89. 4:00determine whether or not the electrical equipment
90. 4:03is energised, or there is no reasonable alternative
91. 4:06means of carrying out the work.
92. 4:09You can also examine the fault current limit of the
93. 4:11installed local and upstream protective devices.
94. 4:14If you have any doubts regarding your safety or
95. 4:17that of the installation, confirm with the
96. 4:19manufacturer that sufficient protection exists.
97. 4:22If your investigation reveals inadequate protection,
98. 4:24advise the owner both verbally and in
99. 4:27writing of the hazardous situation.
100. 4:30More information about electrical work on
101. 4:32energised equipment, including mandatory controls,
102. 4:34can be found at electricalsafety.qld.gov.au.
103. 4:39Always remember the safest way is to de-energise the
104. 4:43electrical equipment prior to commencing any work.