Here I wish to share the "power" of a vector diagram and see if an animated gif will work on Lighting Gallery.
At the start the lamp is shorted out by a screwdriver so it is just the choke and power factor correction capacitor in parallel with the mains supply of 240 volts, 50Hz.
The supply voltage is used as the reference vector...the pink one sticking out to the left 240 volts long.
The green vector poking upwards and marked "Ic" is the current flowing through the power factor correction capacitor, it is "leading" (i.e., poking 90* up) because this is the nature of a capacitor where the current through it leads the voltage across it by 90* in phase. The length of this green vector represents the number of amps flowing through the capacitor.
The two red vectors poking straight down are the lamp/choke current, (Il) and current drawn from the supply by the whole setup, (Is). As the lamp is shorted out, Il is flowing through the short/screwdriver jammed across the lamp's base and the choke in series with it. These vectors are lagging (by 90*), because with the lamp shorted out there is just the choke, (inductor) also directly across the supply. And the nature of an inductor is to have current flow through it that lags the voltage across it, (in thus case the supply) by 90*.
The choke has a lower reactance than the capacitor so it draws more current and thus the Il vector is longer than the green capacitor vector.
Is, the current drawn from the supply is simply Il, the choke current..subtracted (because they are 180* out of phase) from the capacitor current...so if the choke draws 4A and the capacitor 1A, then the supply current is 3A! So Is is shorter than Il by the length of Ic! That 1A simply circulates round and round through the choke and capacitor in parallel.
The animation starts the instant the screwdriver is removed and the arc is struck inside the arc tube of the lamp. This arc behaves as a resistor so the voltage drop it develops is in phase with the current through the lamp and choke as they are in series with each other.
The lamp arc drop voltage "Vlmp" is the blue vector that appears the instant the screwdriver is yanked away and the short is removed. This voltage starts low because it is determined primarily by the low pressure conditions in the cold arc tube. But as the arc tube heats up, the mercury vaporizes and the pressure rises...so does this arc drop voltage.
At the same instant a second blue vector, Vl, the voltage across the choke...and initially eclipsing the pink supply vector because with the lamp shorted the voltage across the choke IS the supply voltage. When the short is removed and the lamp's arc voltage starts to rise, this choke voltage has to fall. If the choke were a resistive incandescent lamp (and there were no capacitor) all the vectors would lie on top of the supply vector...and I have made a mistake in the diagram...Vlmp, the lamp voltage actually lies along the upper right hand side of the upper green right angled triangle. But I am still just learning all this.
So with an incandescent lamp in series with the mercury lamp Vlmp would lie on top of the pink mains vector with the incandescent lamps voltage tacked to the end of it and the sum of those two equal to the mains as they are in series. As the mercury lamp runs up in series with an incandescent the mercury lamps voltage vector simply gets longer (and it gets brighter) and the incandescent's voltage vector gets shorter (and it gets dimmer) but they both lie atop the pink supply voltage and always add up to equal the supply as they are in series across that supply!
Now, with a choke, an inductor in series its voltage HAS to be at quadrature and leading its current...which is the lamp's current too as they are in series. So this FORCES the choke voltage and lamp voltage to be 90* out of phase so they cannot simply add in a scalar and direct way as with the incandescent lamp example...they have to VECTOR ADD....by Pythogras' Theorem as the two sides of a right-angled triangle...and their Vecror sum, like the simple Scalar sum with the incandescent lamp...HAS to equal the supply voltage...so that HAS to be the hypotenuse side of the triangle at all times during run up!
So as Vlmp, the arc voltage of the lamp, (and one side of the right angled triangle gets longer, Vl, the choke voltage drop, is the other side of the triangle and it gets shorter as the lamp runs up.
Now the voltage drop across the choke is always proportional to the current flowing through it, so as its voltage drops, its current drops too....as does the lamp's current because they are in series...so Il, the choke and lamp current gets shorter.
There is a second vector "addition" (actually it is a subtraction) going on between the lamp's current and the power factor correction capacitor's current, Il and Ic...these add up to Is...the current it draws from the supply. These two right angled triangles for this vector subtraction are shown in yellow.
So if everything is "correct" and the gear has been designed to match the lamp exactly, Is, the drawn current from the supply will come neatly into phase with the supply voltage and stop there increasing the power factor to unity amd making the power company happy!
At full run-up you can see Il, lamp current, is larger, (the vector is longer) than the supply current and Vlmp, the lamp's arc drop is less than the supply voltage. All the supply current goes through the lamp PLUS extra current that is simply "pumped" round and round in a triangle of series connected choke, capacitor and lamp...so in this sense it is "sort" of a "transformer" matching the characteristic voltage and current of the lamp to the supply.
A lot of other things can be gleaned from this sort of diagram...like...It draws far more current at starting and the power factor is very low initially.
The power factor only settles at unity, (Supply voltage, Vs and supply current, Is fall parallel) with the "correct" lamp the gear has been designed for.
If you stop the animation early...that simulates a higher power lamp than the gear has been designed for and it never runs up fully, and the power factor never reaches unity either!
If you "over-run" the animation, this represents running a lower power rated lamp than the gear was designed for and running it up "really hard"...in the most extreme Vlmp swings right round to Vs and the choke drop goes to zero...i.e, the poor mercury lamp right across the supply and Il has become infinitely long...or attempted to before the lamp exploded!
So, this is HOW control gear is designed by those really CLEVER electrical engineers, they "can look down from Heaven" on this diagram and see all ...and this is why so many of us "scramble around" asking the same gear related questions again and again...particularly our North American "120v 60Hz land" friends who have to use more complex gear with a more complex vector diagram....and since most aren't aware this diagram even exists, they get frustrated as hell...
"Why does this ballast run too hot with this lamp that's not really designed for it?"
"Why does this lamp cycle on this ballast?'
"Why can't I run this European lamp fully up on my "H3X" CWA gear?"
And on and on they go...almost endlessly...
I am determined to get to the bottom of this and find out just how North American Gear works, just how it was designed and why and how to tweak and march it to lamps it was not really designed to run...and extracting such a vector diagram for "CWA" and "Reactor" gear is the first step down the road to answering these questions finally and succinctly...once and for everyone!