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

[inventor]

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.

[metalsculptor]

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]

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]

Originally Posted by PoweRex

...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).

[AndrewT]

Originally Posted by PoweRex

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.

[PoweRex]

Originally Posted by AndrewT

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,
What exactly do you want me to explain ?

[Andrew Eckhardt]

>my last three homes all have/had 3phase electricity supply.

In order to have that happen in USA you'd have to live in an industrial park.

[AndrewT]

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.

[AndrewT]

Originally Posted by PoweRex

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).

Originally Posted by PoweRex

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.

[zigzagflux]

Originally Posted by inventor

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.