All it takes to make high voltage AC is low voltage AC and a transformer.
To make high voltage DC, you have to chop it into (what else) AC, run it through a transformer, and then rectify it back to DC. Quite a bit more hardware is necessary.
So, with mass produced products, there's a strong economic bias to use AC high voltage, so that's what you'll see, unless there's a compelling reason that the high voltage needs to be DC.
Energy reflected by a mismatched line termination can be entirely separated from the forward-travelling wave, and then be dissipated in a temperature calibrated resistor, and accurately measured as I^2R heat.
This is more or less correct, with a couple of caveats.
First, it is possible to mostly, but not entirely separate the reflected wave. This is done a directional coupler. Practical directional couplers have isolation error, which causes a small portion of the input signal to appear at the measurement port, in addition to the reflected signal that is intended to be measured.
Second, the measurement is not typically done by heating a resistive element. This can be done and it is called a bolometric power sensor. However it's more common in my experience to use an rf detector based on a diode. The nonlinear response of the diode converts some of the rf energy to a dc voltage, which is read with a voltmeter.
Bolometric sensors might be used for very high power conditions, or when calibration to a non-electrical standard is required (e.g. a thermometer).
Edit Replying to your comment, "the generator supplies only the actual power that is transmitted to the load."
This depends a lot on the details of the generator. You refer to a white paper that suggests the following scenario:
Suppose a lossless line is terminated by a pure open circuit, and suppose the the line is exactly one wavelength long at the operating frequency. In this case the current at the generator will be zero, and so the current in its internal impedance will be zero, so there is no power dissipated in it.
This is correct if the generator is actually a perfect voltage source with a 50-ohm series resistance. But an actual benchtop generator might contain other circuits like a levelling circuit or power monitor between the actual generator and the front panel port. Also you rarely know the actual line length to the load --- maybe there is some internal transmission line between the actual source and its front-panel port. If you don't know you have perfectly tuned the transmission line length, then the reflected power is the power you should be prepared to absorb at the generator, even if you don't have to absorb that much in every case.
Also, the case of an open circuit termination and half-wavelength line means that the generator sees an effective open-circuit load (that's why the current is 0). But not every type of generator is designed to work correctly with an open circuit load. A practical circuit could end up demanding more power from other elements within it, or generating more harmonic content when incorrectly terminated. This could still damage the generator even if the ideal components view of the circuit says there's no power transferred in the standing wave.
Finally, if you did insert a directional coupler into this scenario, you would transfer power through the coupled port and into whatever terminates that port (assuming it's not a perfect open or short). This means you would have "separated the forward and reverse waves" as suggested by the author you quoted, even though you did it in a system that was not transferring power before you inserted the directional coupler.
Best Answer
HVDC is more efficient over such distance. Here are the reasons:
There is no inductive/capacitive reactance in the case of DC whereas in case of AC both capacitive/inductive reatances exist. Due to the absence of Inductance, the voltage drop in HVDC is very small as compared to AC (Provided that all other conditions are constant). Due to this reasons, the HVDC provides an edge over the voltage regulation of power system.
HVDC is free from dielectric losses. Also, there is no skin effect of conductor and whole conductors is utilised for power transmission.
In terms of cost of power system DC is more efficient and is least expensive. Firstly we only require two conductors instead of three. But the only problem we suffer is a generation of power at high voltages because we need HV for transmission. DC can neither be stepped up directly and neither can it be generated at very high voltages. So at present, the only solution is to use Solid state electronics and convert HVAC to HVDC for transmission purposes, then again convert it back to AC and step down for transmission purposes.