ETL 1110-2-560
30 Jun 01
t′ = adjusted time variable (i.e., operation time)
t = calendar time variable
d = duty cycle factor
For example, electrical equipment such as transfer switches are normally energized 100 percent of the
calendar year resulting in a duty cycle of 1.0. However, the duty factor for lock gate and valve electrical
equipment is directly related to the number of lockages or hard operations that occur at a facility. The
number of lockages may vary over time, and hence the duty factor may vary. In this example, the
lockages or cycles increase with time. The duty factor is calculated for each year as follows: For year 5,
the lock performs 11,799 open/close cycles. Assuming the operating time of an open or close operation is
120 sec (or 240 sec for a combined open and close cycle) and using a total mission time of 8,760 hr per
year then
Operating time = [(120 * 2) sec/cycle * 11,799 cycles/year] / 3600 sec/hr
= 786.6 operational hr/year
= 786.6/8760 hr/year
d = 0.0898
(2) Each component time variable was adjusted as applicable to its duty cycle. Even though the lock
gates and valves are operated with a system duty cycle of 0.0898, the duty cycle for the gate and valve
electrical equipment must account for the two-speed operation. The slow speed portion of each system
operation is 3 sec/120 sec or 2.5 percent of the system duty cycle. The final duty cycle factor used to
adjust the time variable for the slow speed components of the gate and valve equipment was 0.0022, and
the associated high-speed factor was 0.0898 - 0.0022 = 0.0876. For forward and reverse starters the
applicable duty factor was further reduced by 50 percent to compensate for the alternating use of the
starters during a lockage cycle.
(3) The emergency generator duty cycle was calculated assuming a maximum standard operation of 2
hr in 24 hr (0.08). The dam gates were calculated at 0.007 as demonstrated in Appendix D. The dam
feeders were calculated at 0.5 using an assumption that each feeder is alternately energized uniformly.
d. Distribution. The modes of failure for electrical equipment are very complex (i.e., they involve a
wide variety of distresses such as temperature, vibration, mechanical stresses, etc.) resulting in an
inability to select β values for a Weibull distribution. Since the values were not known, a value of 1.0
was used, which reduces the Weibull distribution equation to the exponential distribution for the
computation of the reliability value. The exponential reliability equation is
R(t) = e-λ′t′
(E-9)
E-5
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