I think this is better than the 20$ option ebay has to offer.
http://www.ebay.com/itm/DUOYI-Digital-Insulation-Resistance-Tester-Megger-MegOhmmeter-Meter-1000V-DY30-1-/221763815393Ebay has some 46$ meggers that are just as sketchy, but ^that one goes to 2500vdc, the others only 1000vac at 50hz. and other hand cranked versions for 50$ to 500..
I can't estimate in my head what resistance a rather large alternator will be just due to its own self capacitance.. so i think you need a dc version to tell you if there is dc corona showing up.. and i see no need to dunk the alternator in water to perform this test.. if the windings are damaged i should think it would be obvious to see them shifted out of their place due to the shock of hitting the ground.
There are a number of options for efficiently extracting power from a turbine if all you want is to dump it into a waterheater, i'll list a few of them, anyhow, it appears the case that you can buy 4500 watt 240vac water heater elements for ~$7 each plus shipping.. but it can cost a great deal if you want a custom stainless water heater with a large number of water heater elements installed.
If you want to limit the number of heater elements as much as possible then you have to go the more expensive route of varying the power electrically.
There was someone here on the forum who had a lot of failures building a mosfet pulse width modulated resistor to make an efficient dump load, but its not impossible for you to do.
One option you have is simply buy a 240volt 20 or 30 hp 3 phase VFD.. and hook up a brake resistor.. use two or three 240v 4500watt water heater elements in parallel.. the vfd will hold the DC bus down by pwm'ing the brake resistor (most of the old dumb ones will not know if the power comes from a high line or a motor back feeding the system). you will then have 3 phase regulated ac power too.. but if you try and draw power from the vfd (say its set for nominal 240v 60h) then the problem is drawing more power than the turbine can deliver will trip the VFD off due to low input line voltage, so this is a potential disaster waiting to happen. --unless you want to install a ~340 volt dc battery system.. or set up a load management system to tell you how much power is available.
Another option you have is configuring a large number of relays or ac solid state relays to switch out the water heater elements (turning them on in binary code) according to the windspeed.. this can get complicated-- for example:
If you use a bunch of voltage controlled relays or some less expensive mechanism, you can get probably get close to 90% capture of the available wind power with i'm guessing.. 10 voltage controlled relays(or an arduino) and a few hundred diodes (look up diode logic) (or use an arduino) , and 12 solid state relays(3 per phase) and 12 water heater elements sized to draw about 5,10,20,40 amps from each phase.--at max output all of the will be turned on, so that's 75 amps per phase. (reduce all the numbers accordingly)
^ that could end up really expensive if you want to run 480 volts because you'll either need to find 480 volt heater elements or you'll need twice as many 240v heater elements, each in series to limit their power consumption.
but you can see that if you have an enslaved fairy to turn on and off the 12 switches.. you can get any arbitrary power level from 5 amps to 75 per phase, in 5 amp increments.
Another option you have is running a bunch of motor run capacitors in series with a number of water heater elements, (three required minimum).. this has potential to be the simplest but it may end up being expensive due to the number of motor run capacitors you'll need to put in series with the water heater. The mechanism by which this works is when the voltage and frequency goes up, the current flowing through the capacitors rises with both frequency and current, so you get a natural cubic function and you have the potential to very effectively capture the available wind power.
You'll have to buy a lot of large capacitors.. some folks here have experimented with running electrolytic caps back to back.. but you don't want to buy those new either. --this is where bumping the voltage to 480 would really help because motor run caps are easily found in 600 volt ratings, and you need a fourth as many microfarads when you double the voltage.