I'm going by actual experience with generators and alternators from 50kW to 4gW. This experience was had due to tests requiring the demonstration of a 'worst case scenario'. With the exception of electrostatic induction, as Grumpy describes, shorting the secondary does indeed apply some load to the primary after the initial surge during the short circuit. This load is very minimal because in all cases with conventional devices no potential always equals no current. The only reason there will be some minimal current is because the coil means there is some induction. Since induction is involved, some potential will be allowed to build up between winding turns. This will show as some load on the primary. The way transformers are designed they will fry if they reach this point because the shorted secondary will cause the primary impedance to drop. This drop causes the primary to cook. Try it. Short the secondary of a regular transformer. After the smoke clears look at which windings burned. (Not really. Please don't cook a transformer on my account  ). In the power, pump and compressor industries it is called 'freewheeling'. >>> Edit Too wordy, again. I should have just said: Spin up an MG set (Motor-generator). Short the generator leads and watch the RPM of the motor drop for an instant and then race beyond normal speed before synchronizing with the line frequency again. The motor current will also drop to a near unloaded value. <<< Sorry folks but until something beyond conventional is proven, in my mind this cannot be argued. I really hope this device is using something other than electromagnetic induction. If it is, I would love to see enough info to replicate it. I don't see enough yet.
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