May - Library

T h i rd l y, Pareto analysis of equipment downtime may miss
identifying: (i) individual events having high associated downtime or
(ii) frequently occurring failures that consume relatively little downtime
yet cause frequent operational disturbances. An example of the form e r
is the failure of the transmission in a mechanical mining truck. An
example of the latter are repairs to the truck’s driving lights. Failures
that frequently re-occur often have significant hidden costs. For
example, if the truck has to re t u rn to the truck shop to have a light
replaced, the time lost travelling to and from the shop may dramatically
increase the opportunity costs associated with lost production.
Fourthly, when there is a lot of data to analyse we commonly use
data stratification or hierarchical decomposition techniques. A Pare t o
histogram is pre p a red for downtime data grouped by major equipment
14.0%
12.0%
10.0%
8.0%
6.0%
4.0%
2.0%
0.0%
Downtime Priorities, Jack-knife Diagrams, Business Cycle
or functional failure type. More detailed Pareto graphs are prepared
for the downtime associated with those components or functional
f a i l u res judged to be the most significant contributors of downtime.
T h e re are two potential problems with the use of stratified Pare t o
analyses: (i) because hierarchical Pareto graphs are only pre p a re d
for the significant contributors of system downtime, failure s
associated with less significant components or functional failures will
not be explored. It is possible that we may miss identifying a
component, or failure mode that offers significant potential for
reliability improvement. (ii) The same failure mode may appear in
several of the lower level Pareto histograms. We may fail to identify
or underestimate the relative importance of these common cause
failure modes.
1 2 11 3 10 7 12 8 5 15 6 9 4 17 14 16 13
Failure Code
Figure 1: Pareto hisogram of unplanned shovel electrical downtime
Code Description Quantity Duration % Time % Cum.
(min)
1 Electrical inspections 30 1015 13.0 13.0
2 Damaged feeder cable 15 785 10.1 23.1
11 Motor over temperature 36 745 9.6 32.6
3 Change of substation or shovel move 27 690 8.8 41.5
10 Overload relay 23 685 8.8 50.3
7 Auxiliary motors 13 600 7.7 58.0
12 Earth faults 7 575 7.4 65.3
8 Main motors 12 555 7.1 72.5
5 Power cuts to substations 21 395 5.1 77.5
15 Air compressor 8 355 4.6 82.1
6 Rope limit protection 10 277 3.6 85.6
9 Lighting system 26 240 3.1 88.7
4 Coupling repairs or checks 15 225 2.9 91.6
17 Over current faults 6 220 2.8 94.4
14 Control system 7 165 2.1 96.5
16 Operator controls 5 155 2.0 98.5
13 Miscellaneous 9 115 1.5 100
TOTAL 270 7797 100
Table 1: Unplanned shovel electrical downtime.
100.0%
90.0%
80.0%
70.0%
60.0%
50.0%
40.0%
30.0%
20.0%
10.0%
0.0%
16