I am interested to know if there is a specification for dielectric withstand test for aircraft. I can't find anything concrete in DO-160. I know of Mil-std-202, and expect I can apply it to civilian aircraft.
I have a client that insists he does not have to hipot and I disagree. My gut tells me that any gear that is isolated from ground should be tested in some manner. I think good engineering practice would dictate a test.
The unit runs off of 120vac wild power. That is I think 360Hz - 800Hz. Don't quote me but on that but it is close. We have caps to ground so would go with the DC hypot.
Yes, it is quite common to use the MIL-STD-202 method 301 and especially method 302 (insulation resistance) also for civil aircrafts.
It may be a good idea to make some measurements during the engineering tests (just to spot design flaws), but if you don't have a customer requirement that dictates it, I would avoid to mention it in your specification. Each additional test requires additional time and money during the qualification phase.
I believe his question is about the general safety requirement implying a hipot test. Not everything about a design has to be explicitly stated as a requirement.
In many cases aircraft power systems run the return or what would be called neutral in house wiring via the fuselage. That has always scared me but it's often the way it is. Not in very large passenger aircraft though with three-phase APUs and stuff.
If it is ground return via fuselage in your case there most likely will only be the usual DO-160 surge and undervoltage requirements, frequency range, EMC, et cetera.
Reminds me of an EMC debug on an experimental pusher prop aircraft. We got it fixed and no more buzz and stuff on the radio. Didn't help though, the test pilot landed half a mile short of the runway. It was a weird design IMHO. The engine upfront, a looong shaft running underneath the pilot seat to the rear where the prop was. On the way back, some vibration under the seat, RPMs dropped, more vibration, RPMs dropped some more, throttle all the way in .... rrrrat-tat-tat ... some clanging ... PHUT ... silence.
I remember when an engineer told me how he'd caught a monster truck guy who tied the ground lug under a screw. "But the manual says so!" ... "Yeah, but the dash is foam and it screws into plastic inserts" ... "Oh".
afaiu an aircraft gets hit by lightning once a air on average and it is an issue they had to consider when they started making aircrafts out of composites
There are alternators ("AC Generators") on the motors. The frequency is determined by the RPM of the engines so it varies. The voltage is controlled.
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The ACW bus refers to 'AC Wild'. In the Bombardier Dash 8 it's called "Variable Freqency AC".
In order to get 28VDC or 400Hz AC conversion can be used, but the ACW bus can can be used for large loads that are not so fussy such as de-icing, hydraulic pumps etc.
Unfortunately I don't know the answer to the OP's question. A quick Google finds that Boeing has called out Hipot testing for DC9 heaters in SR09340158, so it's not unheard of.
Regarding dielectric, I always wondered why headphones included a few strands of nickel with all those strands of copper. (Maybe just as messenger wire or something)
Of course, if you are developing on your own a "catalog" product (to be sold to anyone who wants to buy it), it's up to you to decide which standards to comply. But if you are answering to a specific RFI/RFQ or in general you have to develop a product based on a requirement, it is uncommon to add further requirements. If in the develompent stage you discover a serious hazard, usually you first discuss it with your customer. If the customer hasn't specified a safety requirement, in most cases it is because he expects that the product will never be in the conditions to require it. For example, hipot testing is very common for user-operated equipments, where there is a electric shock hazard for the operator. If you are developing an equipment that will be installed behind a panel or inside a closed compartment and will never be touched by anyone (when powered), hipot testing may be useless.
You misunderstand. When engineers are given requirements for a project, or are asked to develop requirements, they start with the requirements derived from user "wants". These are top level requirements which are further refined. Many requirements are derived from the general requirement for the craft to be safe.
That is *exactly* the situation I am describing. If a requirement is that the unit not catch fire when plugged into 220 volts even though it is designed only for 120 volt, this will generate requirements on specific parts of the design for specific ways of meeting the higher level requirement.
Well, of course. By following this reasoning, each engineering choice (like selecting a capacitor with a specific voltage instead of another) may be considered a requirement derived from another requirement and so on. I was just referring to top-level requirements, which in the aerospace sector have two very distinct characteristics:
(1) The customer gives you *all* the top-level requirements (functional, environmental, EMC, electrical, mechanical etc etc, usually some hundreds page of documents). Along with them, usually the customer gives you also the general requirements for the equipments that have to be installed on that specific aircraft(s). Usually some other thousand pages of documents. You have plenty of informations and don't have to assume or add anything. (2) You have to demonstrate the compliance only for the top-level requirements, and report the verification method on the compliance matrix (analysis, test, similarity etc). How you do achieve this compliance, is up to you.
Hipot testing is by all means a top-level requirement. Like I said, it's the manufacturer that decides whether it is required or not, based on the equipment position on the aircraft, on the others equipments connected to it, and so on. You usually don't have this kind of informations, and therefore it's not up to you to decide.
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