Edison never worked in very high voltage dc.
Most of his systems were three wire 120v / 0 / 120v systems.
However there were people who did...René Thury
René Thury (August 7, 1860 – April 23, 1938) was a Swiss pioneer in electrical engineering. He was known for his work with high voltage direct current electricity transmission and was known in the professional world as the "King of DC."
Gorzente River - Genoa DC 6kv
La Chaux-de-Fonds DC 14kv
St. Maurice - Lausanne DC 22kv
Lyon-Moutiers DC 75kv
Wilesden-Ironbridge DC 100kv
Chambéry DC 150kv
NOTE: This effect was not seen when connecting a single dynamo to an uncharged line.
Before a dynamo was connected to a trunk line it was first brought up to speed in an unloaded condition - ( when a dynamo is unloaded the voltage can be much higher than normal ). When the dynamo is up to speed it is connected through a knife switch or contractor to the main trunk line. There are a number of dynamos connected to one main trunk line at any given time based on consumer load.
So this gives us a high voltage dc charged line to begin with.. then when the knife switch is closed we are connecting a much higher voltage from the unloaded dynamo.. This is the only condition that manifested the supercharging effect. Pulsing a high voltage dc over a bias dc.
The abrupt sparks, which he termed "disruptive discharges", were found capable of exploding wires into vapor. They propelled very sharp shockwaves, which struck him with great force across the whole front of his body. Of this surprising physical effect, Tesla was exceedingly intrigued. Rather like gunshots of extraordinary power than electrical sparks, Tesla was completely absorbed in this new study. Electrical impulses produced effects commonly associated only with lightning. The explosive effects reminded him of similar occurrences observed with high voltage DC generators. A familiar experience among workers and engineers, the simple closing of a switch on a high voltage dynamo often brought a stinging shock, the assumed result of residual static charging.
This hazardous condition only occurred with the sudden application of high voltage DC. This crown of deadly static charge stood straight out of highly electrified conductors, often seeking ground paths which included workmen and switchboard operators. In long cables, this instantaneous charge effect produced a hedge of bluish needles, pointing straight away from the line into the surrounding space. The hazardous condition appeared briefly, at the very instant of switch closure. The bluish sparking crown vanished a few milliseconds later, along with the life of any unfortunate who happened to have been so "struck". After the brief effect passed, systems behaved as designed. Such phenomena vanished as charges slowly saturated the lines and systems. After this brief surge, currents flowed smoothly and evenly as designed.
The effect was a nuisance in small systems. But in large regional power systems where voltages were excessive, it proved deadly. Men were killed by the effect, which spread its deadly electrostatic crown of sparks throughout component systems. Though generators were rated at a few thousand volts, such mysterious surges represented hundreds of thousands, even millions of volts. The problem was eliminated through the use of highly insulated, heavily grounded relay switches. Former engineering studies considered only those features of power systems which accommodated the steady state supply and consumption of power. It seemed as though large systems required both surge and normal operative design considerations. Accommodating the dangerous initial "supercharge" was a new feature. This engineering study became the prime focus of power companies for years afterward, safety devices and surge protectors being the subject of a great many patents and texts.
Tesla knew that the strange supercharging effect was only observed at the very instant in which dynamos were applied to wire lines, just as in his explosive capacitor discharges. Though the two instances were completely different, they both produced the very same effects. The instantaneous surge supplied by dynamos briefly appeared super-concentrated in long lines. Tesla calculated that this electrostatic concentration was several orders in magnitude greater than any voltage which the dynamo could supply. The actual supply was somehow being amplified or transformed. But how?...
The high voltage of the dynamo exerted such an intense unidirectional pressure on the densified charges that alternations were impossible. The only possible backrushes were oscillations. In this case, charges surged and stopped in a long series until the supercharge was wasted away. All parameters which forced such oscillations actually limited the supercharge from manifesting its total energetic supply, a condition Tesla strove to eliminate. Indeed he spent an excessive time developing various means to block every "backrush" and other complex current echo which might forced the supercharge to prematurely waste its dense energy. Here was an effect demanding a single unidirectional super pulse. With both the oscillations and alternations eliminated, new and strange effects began making their appearance. These powerful and penetrating phenomena were never observed when working with high frequency alternations...
The sudden quick closure of the switch now brought a penetrating shockwave throughout the laboratory, one which could be felt both as a sharp pressure and a penetrating electrical irritation. A "sting". Face and hands were especially sensitive to the explosive shockwaves, which also produced a curious "stinging" effect at close range. Tesla believed that material particles approaching the vapor state were literally thrust out of the wires in all directions. In order to better study these effects, he poised himself behind a glass shield and resumed the study. Despite the shield, both shockwaves and stinging effects were felt by the now mystified Tesla. This anomaly provoked a curiosity of the very deepest kind, for such a thing was never before observed. More powerful and penetrating than the mere electrostatic charging of metals, this phenomenon literally propelled high voltage charge out into the surrounding space where it was felt as a stinging sensation. The stings lasting for a small fraction of a second, the instant of switch closure. But Tesla believed that these strange effects were a simple effect of ionized shockwaves in the air, rather like a strongly ionized thunderclap.