I work in aviation. I was told today that one of the systems of the aircraft had drawn more power than the generator could provide and that had caused it to fail, to get too hot. I don't understand how this could happen. How can a load draw more power than a source can provide? That doesn't make sense to me.
Assuming circuits are good and the MCB protecting the generator works I could suggest a short between the generator and MCB or failure of the windings insulation causing an internal short, both subject to failure due to age, vibration, or manufacturing fault..
It should have said safely provide.
But also, there's often a confusion between drawing power and drawing current.
For example, you can get the maximum power out of any voltage source if your load has exactly the resistance of the internal resistance of that source.
You can of course also plug in a much, much lower (practically, a "short") resistance load. The power flowing into that load will then be lower than the maximum power of the source, but the current will be much higher than what's flowing at the max power point (at the expense of the voltage dropping very significantly).
As an example, take an AA battery. (THOUGHT experiment. Don't do this at home, kids.) Let's say that has an internal resistance of 0.2 Ω. Now, when you take a 0.2 Ω resistor (which would probably be something like a piece of thin steel wire), that resistor would get very hot – the maximum amount of power the battery can supply gets converted to heat.
Next, really short the battery with a thick piece of copper and very good contacts (that's where you usually get into trouble - 0.2Ω isn't all that much, and making a contact way better than that is hard) and short-circuit your battery. What will now get hot?
Right, the battery, and not so much the copper wire. The power converted to heat in the copper wire isn't very high, and most of the power is "wasted" across the internal resistance of the battery.
I'd recommend not shorting batteries, by the way. It's dangerous. They can get extremely hot, depending on the type catch fire, or even explode.
The aircraft generator should be protected by a series of fuses and/or circuit breakers to constrain both the maximum current in each sub-circuit and the maximum total current.
Think of the wiring in your home- there is a main breaker and a bunch of breakers in a panel to protect each circuit. For example, there might be a 300A fuse protecting a main 28V bus, and a series of 30-100A aircraft-rated magnetic/thermal breakers protecting various sub-circuits. As well as protecting the generator itself, it is necessary to protect the wiring in the aircraft so that a fire cannot easily occur as a result of a simple overload.
If the (very expensive) generator failed due to overload then there may be an engineering issue with the electrical system. Those in charge of maintenance will probably want a DAR (Designated Airworthiness Representative) or other qualified person to have a look at it.
The way it could happen is simple- imagine you have a 15A home circuit and you plug two 12A kettles into it. The 15A breaker should blow protecting the wiring, but if it is faulty (or deliberately bypassed) the wiring could overheat. In your case, both the wiring and the generator itself could overheat. This could be dangerous and will probably be expensive.
The reason you get confused, is that the statement is incomplete. "...the aircraft had drawn more power than the generator could provide (without overheating) and caused it to fail."
The statement in parenthesis is what is missing. The reason it is missing, is that it is commonly understood that the given power rating is for continuous use, without overheating the generator.
However, the generator is capable of delivering more power (at the cost of overheating) for a short period of time (the time it takes to burn the generator's winding).
You should now be able to see that a generator can provide more power (called max power), even if it is just for a short time, than the "normally quoted" power (called continuous power).