Availability of 3-phase AC mains supply at High-power Audio Installations

inventor

Member
2008-08-17 4:59 am
Dear Colleagues,

I am trying to find out about the availability of 3-phase AC mains supply at the point of installation of High-power Audio equipment (i.e. amplifiers).

I am neither an audio- nor a power-engineer. So, before asking my questions, let me first give my understanding briefly.

Some possible locations for high-power audio amplifier installations are:
  • Live Concerts (open air)
  • Stadiums
  • Concert Halls
  • Discotheques/Night clubs
  • Cinemas
  • Shopping Centres
  • Churches (esp. in the USA)
  • Music studios
  • etc. etc.
The total output power of the installed equipment, and hence the total input power required from the AC supply, can be in the order of multiple tens of kilowatts, even over 100kW in large installations, just for audio amplifiers alone (excluding any other AV or lighting equipment).

Most of professional high-power audio amplifiers come in 19"-rack mountable enclosures. As far as I know, all such commercially-available amplifiers provide only a single-phase AC mains power-supply input (which may accept a universal voltage range: e.g. 85-265V AC 1-ph). I think, this is true even for the highest-power audio amplifiers recently introduced to the market, e.g. 20KW output (music/program) power and ~ 3-5KW input (1-ph AC mains) power.

A similar situation exists with 19"-rack mountable DC power supplies (AC-DC converters in the KW range) for Computer Data Centres (CDC), with such high-power DC supplies accepting only 1-phase AC mains input. However, a recent tendency in CDC installations is to distribute AC power in 3-phase form and make it available to 19"-rack equipment also in 3-phase AC form.

Clearly, at high power levels, power transmission and distribution is less costly and more efficient in 3-phase AC form than 1-phase AC form.

My questions are:

  1. For high-power audio installations, why are audio amplifiers not available with 3-phase AC (400V or 200V class line voltage) power supply input?

  2. Is it because 3-phase AC mains supply is not readily available at such installation points/locations (as listed above)?

  3. If 3-phase AC mains supply is available in such installation points/locations, are there any reasons as to why high-power audio amplifier manufacturers do not make amplifiers accepting 3-phase AC mains for their power supply input?
I will appreciate any contributions, suggestions, ideas or feedback you may be able to offer.
 
It is a fragmented market.
In Australia 3 phase power is readily available large events often use portable generators which are 3 phase in all but the smallest sizes. 3 phase extension leads then feed power around the event to power boards full of single phase outlets. Most commercial premises have 3 phase power and it is rare for appliances consuming more than 4Kw to be single phase.

Europe, Australia and many Asian countries use 230V nominal star (wye) LV distribution making 3 phase a natural compliment of single phase, The US, Canada and Japan use fragmented LV distribution systems meaning that the standard single phase supply is not derived from the standard 3 phase LV supply so 3 phase may not be available in many areas.

Just brief list of 3 phase supply voltages in the US and Japan 200V, 208V 480V 575V, 200V is the most common in Japan and 480V in the US AFAIK 480V is 277V wye and 200V and 208V are delta.

I would speculate that the US Canadian and Japanese markets are large enough to affect the availability of sane power systems.
 

PoweRex

Member
2010-11-25 11:22 pm
Paris
3-phase power supply is indeed a very efficient energy source not only for high-power equipments but also for high quality sound reproduction systems where supply currents must be available instantly : I thought about this near 13 years ago !
The reason why manufacturers don't provide such amplifiers is the 3-phase mains rarity for consumer use : they could offer both single and 3-phase compatibility but it'd be expensive, heavy and bulky !
You can have access to 3-phase mains if you live somewhere equiped with a lift for example : in France, you'll have to ask the electricity provider and motivate your enquiry by specifying the reasons of your need.
Concerning the universal input amplifiers, their power supply is designed around switched-mode topologies where the single-phase mains input is first rectified then filtered before further treatment : you can feed them easily with 3-phase energy sources just by removing the single-phase rectifier and replacing it by a 3-phase one. Then, you'll have to convert the available 3-phase mains to a single phase one by a special transformer or by 3 independent single-phase isolation transformers.
 

PoweRex

Member
2010-11-25 11:22 pm
Paris
...you'll have to convert the available 3-phase mains to a single phase one by a special transformer or by 3 independent single-phase isolation transformers.

you'll have to convert the available 3-phase mains to a single phase one by a special transformer (if you use the original single-phase rectifier) or by 3 independent single-phase isolation transformers (if you use a 3-phase rectifier). ;)
 
you'll have to convert the available 3-phase mains to a single phase one by a special transformer (if you use the original single-phase rectifier) or by 3 independent single-phase isolation transformers (if you use a 3-phase rectifier). ;)
Hi,
could you explain in more detail.

BTW,
my last three homes all have/had 3phase electricity supply.
But I will never have a power requirement that cannot be met by our 240Vac UK supply ring system.
 
Hi,
in the UK it's there for the asking.
Pay the charge for digging up and repairing the roadway and they give you a 3phase supply.
In my current home I asked before they installed the mains cable. It cost me nothing extra.
The distribution system is, as far as I know, all 3phase. Homes get a tapping off one phase. To balance the loadings the next home gets a different phase tapping than the last.
 
you'll have to convert the available 3-phase mains to a single phase one by a special transformer (if you use the original single-phase rectifier) or by 3 independent single-phase isolation transformers (if you use a 3-phase rectifier). ;)

Hi,
What exactly do you want me to explain ?
what is that special transformer? Why is it needed, but only when a single phase rectifier is used.
Why three single phase transformers and then only if we use a 3phase rectifier?
I think there is a lot contained in your message that I don't understand. I need more help.
 
My questions are:

  1. For high-power audio installations, why are audio amplifiers not available with 3-phase AC (400V or 200V class line voltage) power supply input?

  2. Is it because 3-phase AC mains supply is not readily available at such installation points/locations (as listed above)?

  3. If 3-phase AC mains supply is available in such installation points/locations, are there any reasons as to why high-power audio amplifier manufacturers do not make amplifiers accepting 3-phase AC mains for their power supply input?

1. For high power installations, where you might have the availability of a three phase power supply, a three phase amplifier is still not necessary. The typical application would be many single phase loads (amps) connected in a balanced manner across each line-neutral, such that you provide a balanced three phase load to the power system. This is called a 'network' among electricians. Each individual amplifier is not "high powered enough" to justify a three phase xfmr internal to the chassis. However, the entire installation of multiple amplifiers does justify a three phase load, thus the single phase loads connected as a three phase network. This is not to argue that a three phase rectifier is not a great thing; it would be nice to have to filter less ripple. But cost vs practicality vs benefit dictate a single phase power supply. If you talk a single amplifier capable of multiple kW (such as an RF transmitter), then these are indeed three phase power supplies.

2. Definitely, in the U.S. three phase power to a residence is very rare. Farms often have three phase available for their operations, but to the house the utility still wires single phase only. I would love to have 208Y/120 brought to my house, it just ain't gonna happen. Most utilities have a minimum kW demand requirement before they will bring in three phase to a commercial establishment, so even there you have limitations. It's mainly demand-based.

3. Cost and weight does not justify the benefit when electrolytic capacitors are so cheap. A little bit of ripple on a high NFB push pull AB design is not detrimental to a PA sound system.

Sorry if this is repetitious, but it is an attempt to succinctly answer your questions without straying.
 
what is that special transformer? Why is it needed, but only when a single phase rectifier is used.
Why three single phase transformers and then only if we use a 3phase rectifier?
I think there is a lot contained in your message that I don't understand. I need more help.

That so called special transformer converts an available 3-phase mains to a single-phase one in order to feed your universal input amplifier which is designed to work with single-phase mains thus originally using a single-phase rectifier : this solution will let you use your amplifier where you only have access to 3-phase supply without modifications, but you'll not notice much sonic improvements.

If you want to profit entirely of the 3-phase supply benefits, you'd better install a 3-phase rectifier instead of the original single-phase one in your amplifier. I suggested the use of isolation transformers in this case as they will provide galvanic isolation from the raw mains with reduced capacitive coupling : this allows bi-directional smooth filtering of high-frequency junks and improves the signal-to-noise ratio of your amplifier allowing you to remove the LC mains filter from your amplifier as such filters degrade dynamic performances. If you're lucky enough to find only one 3-phase isolation transformer (3-phase in/3-phase out), then it's perfect but the 3 phases must be perfectly balanced (120° phase lag between each output, when loaded).

With a 3-phase power supply, you'll triple the ripple frequency accross the filtering capacitor : this allows you to divide the capacitor's value by 3 for the same ripple amount. For example, if your mains frequency is 50 Hz in single-phase conditions, the ripple frequency accross the capacitor is equal to 100 Hz : with a 3-phase mains, it will be 300 Hz. By the way, efficiency is higher with a 3-phase configuration (99%) where a single-phase configuration gives only 80% : these values are valid when dual-alternance rectifiers are used.

The advantage of smaller supply filtering caps is faster current delivery to the amplifier's output stage, in dynamic conditions, to feed the loudspeakers' low impedance rapidly. For my personal system, I've designed a 400 Hz single-phase mains generator where the rectified voltage of the amplifier's power supply is even faster than a 3-phase 50 Hz (800 Hz vs 300 Hz ripple) thus dividing the filtering capacitors' value by 8 for great sonic improvements ! Can't go back to 50 Hz anymore...;)
 
In the age of cheap silicon making a dual input amplifier is not that difficult either use a 3 phase full wave rectifier feeding a PFC circuit which will operate between 300 and 750V or use 3 separate switch mode power supplies feeding the common DC rails so the power supplies can be used ganged on single phase power and balanced on 3 phase supplies, though I still think multiple single phase amplifiers keeps the speaker voltages on the sane side as well as reducing the chance of wiring errors. For HiFi series connecting speakers is a bad idea.
 
That so called special transformer converts an available 3-phase mains to a single-phase one

Perhaps I am misunderstanding you, but there is no need for a special transformer to supply a single phase load from a three phase supply. All you need is a single phase transformer. Two primary leads of the xfmr are taken either line-line or line-neutral from the three phase system. Secondary leads feed the amp (either directly to the rectifier or simply providing 120VAC to the amp's plug). As long as the xfmr voltage ratings are suitable for the voltages used and desired, you're good to go.
The advantage of smaller supply filtering caps is faster current delivery to the amplifier's output stage
Hmmmm. Current travels at the speed of light, regardless of capacitor size and ripple frequency, but I understand your point. However, if we consider a 20 kHz signal, it really makes no difference if we are dealing with 100Hz or 300Hz recharge on the power supply capacitors. I would argue the same for the rising edge attack of a kick drum; by the time the dynamic attack has started and is over, a 300Hz recharge is actually quite slooooow, and cannot provide recharge fast enough.

The real advantage of higher ripple frequency is a reduced requirement on the LC filter size; this results in a lower source impedance as seen by the output stage. Apples to apples, three phase rectification results in lower peak-to-peak ripple.

Side note
To really get deluxe in the European DIY community, where three phase is available, you could incorporate delta-wye and delta-delta transformers, which will result in a 12 pulse rectifier. Now we're talking increasing our rectifier ripple to 600 Hz. Heck, take it another step with zigzag windings, and you can get out to 1200 Hz. As nice as this seems, the cost and weight of the iron just isn't worth the cost of a capacitor.
 
Common practise is to bring three phase to the amp racks, and split it there to supply single phase to the individual amps, at typical per module power levels (less then 10 KVA) it just is not worthwhile messing with three phase PFC inputs.

For example one of the racks at work has 6 * Camco Vortex 6 amplifiers (36kW nominal), it is fed from a 32A 5 pin three phase connector at 400V phase - phase, 230V phase-neutral (Nominally good for about 18KW continuous), of course program audio is ~1/8th average to peak power so and the heating in the connectors, fuses and breakers is proportional to the square of RMS Current, so in practise that 32A feed is just not a problem driving amps with a theoretical rating twice that of the supply connector.

Yea a three phase input is quite possible but given the switch mode PFC input topology normally used in modern lightweight power amps the caps are not that major a factor anyway.

Besides single phase amps have a huge advantage when it comes to needing to use one to run a toy 'speaker on a stick' rig down the rat and carrot for my mates sons band..... Also, easier to fix, and easier to bodge an emergency power supply for.

In the PA game, standard is IMPORTANT, I don't want something I cannot cross rent to the guy down the road because his distro wont power it, and if I need to get out of trouble, being able to plug into a domestic socket is very, very, useful. The advantages of having individual amplifiers on single phase massively override the smaller caps in an operational environment.

Besides, the elephant in the room when it comes to gig power consumption is lighting (at typically 1kW PER LAMP) not audio which is always penny ante in comparison.

The considerations when buying an amp for PA go something like (exact order to taste, but note that audio quality is seldom top of the list):

Reliability,
Weight,
Size,
Ability to drive very low Z loads,
Built in DSP?
Remote monitoring?
Airflow direction,
Sound quality.

The DSP and remote monitoring may or may not matter (application dependent), but for a road guy almost all the others will matter more then minor sound quality issues.

After all this is combat audio we are talking about and nine times out of ten the guitars will be stupid loud even with the PA shutdown, every patch on the keys will be a different level, and the drummer will insist on 57 china cymbals.... The amp rack not being a 6 man lift matters more then a little ripple on the DC rail.

Regards, Dan.
 
Log time ago I worked on a printer that used 3 phase 50 amp y power. One of the motors used all 3 phases. The rest of the machine power supplies motors etc used 2 of the 3 phases (220volts) or one of the 3 phases ( 110volts). None of the 220 or 110 parts were special, a lot of them were off the shelf parts and were used in other equipment that did not have the special 3 phase motor. Those products ran of off a 220volt 50 amp line. You can use a 110volt or 220 volt system almost anywhere but you can only use a 3phase system in a place that has 3 phase handy.
 
Without getting ultra exotic with inverters or motor-generator sets, the phase converter is a popular, efficient, and cheap way to get three phase from single phase.

Ronk Electrical Phase Converters - Run 3 Phase Equipment On Single Phase Power

These are really designed for motor load, though, and don't provide the best phase balance. Certainly wouldn't be the best choice for audio.

That printer must have needed constant torque in order to require three phase power, or maybe the hp was so large they were only available in three phase.
 
Without getting ultra exotic with inverters or motor-generator sets, the phase converter is a popular, efficient, and cheap way to get three phase from single phase.
These are not that useful without a step up isolation transformer either on the single phase or the 3 phase supply, only delta connected small motors in Australia use 240V 3 phase everything is 415V Europe is probably similar with 400V power.
 
Aint it funny how all large music festivals these days are 'green' yet they need as much power as a small town! All that lighting and those speaker arrays....
How bout a festival using horns and candle light?

I had a dude show up on a tube fest with a 300B SE build that had a 3phase supply. I happen to have a couple of 3phase outlets in my house so it was a cool setup. The <10watt amp had seperate supplies with seriously oversized custom 3phase toroids and all tube rectification. It weighed a ton and sounded ok, but really, once an amp is up to a certain level I doubt the effort is worth it...