Calculating inrush current for magnetic ballasts

[davesparks]

I was actually repairing some Thorn 2KW MBILs last night! Cartridge fuses will naturally cope with the inrush of almost all circuits. Where I was working have groups of 8 2KW lamps switched on at a time, these are fed from standard Merlin MCBs, though unhelpfully I can't remember the type or rating...

Were they single or three phase circuits?

Is that 8 lamps on one MCB?


Each individual lamp on my site has an MCB, though they are all random sizes and types ranging from B16 to D20.

Each bank of 9 is on one circuit which is protected at 63A by an MCCB currently.

 

[freddo]

8 lamps (415V) on one 3 phase MCB, the lights are balanced as well as you can balance 8 lights across 3 phases. The MCBs for each light are 2 pole 16amp some are B type others C type.

 

[davesparks]

8 lamps (415V) on one 3 phase MCB, the lights are balanced as well as you can balance 8 lights across 3 phases. The MCBs for each light are 2 pole 16amp some are B type others C type.

I assume they are normal MCB's not the physically bigger C120 range?

If that installation doesn't have any issues with nuisance tripping then I can't see 9 being any different.

 

[freddo]

Just the usual C60 range.

If that installation doesn't have any issues with nuisance tripping then I can't see 9 being any different.

I agree. The install was put in ~20 years ago and hasn't had any nuisance tripping.

 

[davesparks]

Just the usual C60 range.

I agree. The install was put in ~20 years ago and hasn't had any nuisance tripping.

That makes me think we should be fine on C60 MCB's here then. The circuits feeding the columns should be good for a 63A D type once we've completed remedials for the poor earthing, I'll know more once I have the new Zs readings tomorrow.

These floodlights are around 25 years old.

 

[freddo]

These floodlights are around 25 years old.

I do like these lights, the 220,000 lumen output is certainly impressive.

 

[davesparks]

I do like these lights, the 220,000 lumen output is certainly impressive.

They're pretty damn bright, even in daylight you can see the effect on the pitch.

 

[marconi]

See first table in which makes recommendations on ratings and types of CB and contactors:

https://www.veelite.com/wp-content/uploads/Protection-of-Lamp-Circuits3.pdf

I will see if I can find anything else.
[automerge]1597809686[/automerge]
See page 4 of:

http://www.moeller.net/binary/ver_techpapers/ver955en.pdf

and see table in which has starting surge current and its typical duration:

Discharge lamps - Electrical Installation Guide - https://www.electrical-installation.org/enwiki/Discharge_lamps

 

[Lucien Nunes]

I too would test on site, but using a scope and a shunt or CT. There's nothing like seeing a picture of it to get a proper feel for what is going on.
There are three separate causes of inrush here:
PFC capacitor charging: less than half a cycle, instantaneous current could approach PSCC for a time constant of Zs x C. Worst when contacts close just before V=Vpk
Magnetic saturation: Worst when contacts close at V=0 since this causes the greatest magnetic excursion. Instantaneous current could approach V/(Zs+Rwindings). Duration usually a few cycles while the core gets into step with the mains.
Starting current: Lower, longer, depends on lamp and well documented by the lamp makers.

Watching the waveform would reveal each of these components and allow a good estimation of the I²t that the breaker has to put up with.

 

[Ian1981]

I too would test on site, but using a scope and a shunt or CT. There's nothing like seeing a picture of it to get a proper feel for what is going on.
There are three separate causes of inrush here:
PFC capacitor charging: less than half a cycle, instantaneous current could approach PSCC for a time constant of Zs x C. Worst when contacts close just before V=Vpk
Magnetic saturation: Worst when contacts close at V=0 since this causes the greatest magnetic excursion. Instantaneous current could approach V/(Zs+Rwindings). Duration usually a few cycles while the core gets into step with the mains.
Starting current: Lower, longer, depends on lamp and well documented by the lamp makers.

Watching the waveform would reveal each of these components and allow a good estimation of the I²t that the breaker has to put up with.

Took the words right out of my mouth ?