Moderated Discussion Areas
ContinuousWave: Small Boat Electrical
Loss of Electrical Power
|Author||Topic: Loss of Electrical Power|
posted 12-27-2011 08:03 PM ET (US)
Many readers may have experienced a dead battery. How about a loss of electrical power on a major ship? Interesting reading:
Report on the investigation of the catastrophic failure of a capacitor
posted 12-27-2011 11:05 PM ET (US)
Interesting indeed Jim - thanks.
There had to be a lot of energy involved to cause that much damage. And then, those capacitors are BIG - and probably big enough to swamp the BWs that many of us have.
I also appreciated their conducting the investigation - not in the interest of blaming someone.
And then, I didn't fully realize how the frequency controlled motors were controlled.
Thanks again ----- Jerry/Idaho
posted 12-28-2011 07:04 AM ET (US)
The Harmonic Filter (HF) described in the report is designed to shunt higher-order harmonic energy in the 60-Hz 11,000-VAC power. The HF components are a series-resonant L/C circuit with values of
C = 108.8-uF
as shown in Figure 14, Rank 11.3 of harmonic filters
The resonant frequency of that combination is found from
F = 1 / (2 * pi * LC^0.5)
and for those values computes to be 677.6-Hz
The relationship to the primary frequency is
677.6 / 60 = 11.29 --> 11.3 (and hence the name of the filter component)
At series resonance the filter has a low impedance and should tend to shunt any current around that frequency present in the 60-AC. I don't know anything about high-power and high-voltage AC power conditioning, but it seems like a brute force method. Even though the elements are reactive, and assuming they are very high-Q, low power-loss devices, there must be some significant power flowing through them.
If we consider that the harmonic content of the power could be about 7-percent, it should be noted that the power levels are measured in Mega-Watts, so 7-percent of a couple of Mega-Watts is still nothing to sneeze at.
On a non-electrical note, I found it interesting that when the QM2 lost propulsion power and was not able to maneuver, the narrative notes that "the 'not under command' [navigation] lights were switched on." That would be an interesting sight to see--a major ship at sea showing those navigation lights. By the way, the NOT UNDER COMMAND indication is "two all-round red lights in a vertical line where they can best be seen." Cf.:
The mnemonic used to help remember the navigation lights for NOT UNDER COMMAND is "red over red; the captain is dead." The equivalent day shape is two black balls. There is also a memory aid for that, although a bit vulgar: "the captain's dead; his b*lls are in the rigging."
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