Timeline for What is the process to disconnect ground electric power before pushback?
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22 events
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| Aug 26, 2022 at 15:20 | history | edited | mins | CC BY-SA 4.0 |
Improved content, more pictures
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| Jul 11, 2022 at 22:22 | comment | added | mins | @Dannie: 60Hz, 180Hz, 240Hz, 360Hz, 400Hz and 800Hz were initially considered [...] the frequency selection must take into account also the generator operating speed [...] suitable frequency values were 400Hz and 800Hz. The Army Air Corps in 1943 chose 400Hz as the standard frequency, since it appeared to be more feasible for the generator speed (e.g. 12000rpm for 4-pole machines). This ‘standard’ [...] has been made mandatory for use by the US Air Force in 1959 (MIL-STD-704). Source. | |
| Nov 19, 2021 at 11:25 | comment | added | Dannie | @StephenS the higher frequency does make sense for the size of the magnetics, but going upto 400Hz from 50/60Hz is such a minor win (compared to the 100kHz kind of region you have in switching regulators) that the motor thing does seem more plausible historically. It's the Volts/Amps balance that seems crazy. If you're already changing frequency, changing voltage to, say, a much saner 1kV 100A for the same power is relatively little work and would save so much in terms of thermal/copper. I think it has to be all about history. I mean no one is charging EVs like this! | |
| Nov 18, 2021 at 18:49 | comment | added | mins | @StephenS: Ah this transformers legend found in many answers including on this site... 400 Hz was chosen for electric motors torque and speed and was practical for the constant speed generator, not to save 10 kg on a transformer. | |
| Nov 18, 2021 at 18:22 | comment | added | StephenS | @Dannie Aircraft use 400Hz AC because the transformers are lighter than 50-60Hz ones, and 110V because the standard was developed in the US. | |
| May 22, 2019 at 17:23 | comment | added | mins | @Dannie, sometimes they shoot themselves in the ear. 100kVA, not 10. Those cables are designed to sustain 4 kA per phase during 5s (300 A in normal use), while the temperature climbs to 200°C | |
| May 21, 2019 at 22:33 | comment | added | Dannie | Delivering 10kVA as 1kA at 100V (and at 400Hz) is insane! What on earth went on that such a mad standard was dreamt up? And I thought the railways excelled at shooting themselves in the foot, electrically! | |
| Nov 15, 2018 at 12:58 | comment | added | mins | @PeterGreen: Correct, this figure is wrong. The relevant value should be the P-N intensity in the last phase assuming other phases have already been disconnected. With this completely unbalanced system, assuming other protections didn't work and ignoring effects created by the sudden raise in current, that would be around 1 kA. P-P is 200 V ($\small \sqrt{3} \times 115$). | |
| Nov 15, 2018 at 10:58 | history | edited | mins | CC BY-SA 4.0 |
Correction, thanks to @Peter Green
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| Nov 15, 2018 at 7:16 | comment | added | Peter Green | "Currents required for 90 kVA under 115 V are about 100 A" your numbers seem to be off, 100A * 115V is 11.5KVA, even if we assume that it's a 115V P-N (~400V P-P) and the 100A is per-phase that still only adds up to 34.5KVA. | |
| Nov 14, 2018 at 23:06 | history | edited | mins | CC BY-SA 4.0 |
Reworked cable section, added lettered-pin connector.
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| Nov 14, 2018 at 18:47 | comment | added | mins | Yes, the two extra pins are to remote control the GPU from the aircraft interface. | |
| Nov 14, 2018 at 18:44 | comment | added | FreeMan | Ah! That makes sense. The green connector, then, actually has 2 extra pins (A, B, C, G, x & y) that, presumably, connect the various and sundry small wires shown in the somewhat generic cable cross-section. | |
| Nov 14, 2018 at 18:41 | comment | added | mins | @FreeMan: The two A conductors are connected to the same point at each end of the cable, same for B and C. This is just a way to move electrons for each phase such that no (inductive) reactance is created by having an homogeneous magnetic field which cancels itself. The two small pins are for ON/OFF remote control. | |
| Nov 14, 2018 at 18:20 | comment | added | FreeMan | Interesting that the image showing the cable layout is circular with 7 primary conductors, yet the connector you show is rectangular with only 6 connectors. Can you explain the difference or is that scope creep? | |
| Nov 14, 2018 at 6:04 | history | edited | mins | CC BY-SA 4.0 |
Added information on cable
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| Jan 23, 2017 at 13:54 | vote | accept | Stefan | ||
| Jan 20, 2017 at 11:47 | history | edited | mins | CC BY-SA 3.0 |
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| Jan 20, 2017 at 10:32 | history | edited | mins | CC BY-SA 3.0 |
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| Jan 20, 2017 at 10:25 | history | answered | mins | CC BY-SA 3.0 |