IMO

After reconsidering the different questions for this subject I could exclude my previous hypotheses that "lead" may refer to the physical entry of the MEL or to shifting the leading edge by phase-angle control contained in the MEL (i.e. by cutting parts of the sinus wave). Due to some hints given by my appreciated peer Tony in the discussions I retrieved one of my other terms (i.e. lagging phase angle).

We have now the contrary situation, a leading phase angle. This means that the generator "consumes" or compensates the reactive power supplied by the capacitive load.

There is also a difference between a lagging and leading power factor. The terms refer to whether the phase of the current is leading or lagging the phase of the voltage. A lagging power factor signifies that the load is inductive, as the load will “consume” reactive power, and therefore the reactive component Q is positive as reactive power travels through the circuit and is “consumed” by the inductive load. A leading power factor signifies that the load is capacitive, as the load “supplies” reactive power, and therefore the reactive component Q is negative as reactive power is being supplied to the circuit.
https://en.wikipedia.org/wiki/Power_factor#Lagging_and_leadi...

Area Mathematics - Functions / Sinusoidal quantities
IEV ref 103-07-07
en phase lead
lead positive phase difference
fr avance de phase, f
différence de phase positive
http://www.electropedia.org/iev/iev.nsf/display?openform&iev...

As the ST contains a lot of grammatical errors, obviously not being written by a native speaker and/or specialist in the field, the phrase it’s very difficult to rephrase it in the intended manner and we have to interpret it by using our technical understanding.

I understand "Adjust reactive power to lead side to MEL pickup point with voltage setter" as
"Adjust the reactive power of the leading phase angles at the MEL pickup point by excitation voltage regulation"
=>
Ajustez le facteur de puissance en opérant sur le côté de la phase en avance [par réglage de la tension d’excitation] au point de mesure MEL."

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Note added at 1 jour 22 heures (2018-11-11 06:09:59 GMT)
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lead = conducteur dans ce contexte précis, c'est la terminologie Schneider...

'est un groupe a essence classique: Moteur Bernard et Alternateurs ... allongé et avec un embout fileté du coté opposé aux cosses de branchement.