What is a Balanced Voltage System?

[jim dungar]

That said, I believe that these systems are band-aids to fix devices with poorly designed power supplies and poorly designed ground referenced signal cables.

Actually I do see an advantage for "sensitive electronic equipment" to operates at 60/120V. With all loads connected L-L, lower voltages to ground may lead to less interference.

I just have a problem using the generic term "Balanced Power" when a specifically defined term is more appropriate.

I do not know how many times I have seen people simply specify an "isolation transformer" for an electronic load and then be disappointed that the supplied unit was not a K-rated constant voltage device with triple shielding. Short-cut and slang phrases often lead to problems when "outsiders" happen into the conversation.

 

[Anwar Pasha]

Balance Voltage System

Balance Voltage System

Is it not true that an electrical system will have balance load if and only if the voltages are balanced. In other words a balance voltage system is a synonym for balance power system. Just Guessing...

 

[dereckbc]

As I mentioned in the other related thread, I think that you are spot on that most standard power systems as installed in the US _are_ balanced power systems.

That is not accurate with respect to 3 phase circuits because of 120 degree rotation you do not get Zero Sequence Cross-over like single phase 240/120.

 

[dereckbc]

That said, I believe that these systems are band-aids to fix devices with poorly designed power supplies and poorly designed ground referenced signal cables.

I understand what you are trying to say, but I think you have overlooked some things. A/V equipment or any electronic equipment is required to have some sort of filtering installed on the line side for FCC purposes. If you look at schematics you will see components? installed L-G, and N-G like capacitors and MOV's. In addition you also have capacitive coupling between the circuit conductors this induces small currents onto the EGC and that develops voltage or noise which is picked up and amplified in audio, video, and other I/O devices.

Now when you change the architecture of the power system from say an unbalanced single phase 120 VAC, to a symmetrical 120/60 system you obtain a Zero Sequence balance between L-L. Since each phase conductor is 180% out, you eliminate the induced currents on the EGC.

Others are correct you achieve about the same thing with 240 single phase. The main difference of the 120/60 is they use precision wound, high Q&K rated, shielded transformers.

 

[richxtlc]

I found this explanation on the internet.
What is balanced power?
When 120-volt AC power is balanced, one side of the circuit has +60 Volts to ground while the other has -60 Volts to ground. (Across the circuit, the usual 120 Volts is still present. Fig. 1) A European 230 Volt balanced power system has +115 Volts and -115 Volts to ground on the conductors.

Standard unbalanced AC power systems have a "hot" conductor and a "neutral" conductor. In the US, the "hot" conductor nominally has 120 Volts to ground and the "neutral" conductor has 0 Volts to ground. (Fig. 2) Europe has a similar system but with 230 volts on the "hot" and 0 Volts on the "neutral."

In a balanced power system, the voltages on the system's two output terminals are 180 degrees out of phase to each other with respect to ground. The system reference (ground) originates at the output center tap of an AC isolation transformer. In other words, the system's grounding reference (zero position) is located at the system's mean voltage differential or zero crossing point of the AC sinewave. This is a far more effective way to establish a reference potential for an AC system. The center tap is then grounded to Earth for electrical safety and for referencing shields.

There is never any voltage or current present on the ground reference in a balanced power system. Transient voltages and reactive currents which normally would appear on the neutral and ground wires are also out of phase and likewise, sum to zero at the ground reference thereby canceling out AC hum and noise.

A balanced AC Power system works the same way as a balanced audio circuit but with a higher amplitude. Both balanced audio and balanced AC incorporate phase cancellation or common mode rejection to eliminate noise.

 

[roger]

In a balanced power system, the voltages on the system's two output terminals are 180 degrees out of phase to each other with respect to ground. The system reference (ground) originates at the output center tap of an AC isolation transformer. In other words, the system's grounding reference (zero position) is located at the system's mean voltage differential or zero crossing point of the AC sinewave. This is a far more effective way to establish a reference potential for an AC system. The center tap is then grounded to Earth for electrical safety and for referencing shields.

And the paragraph above basically describes an everyday 120/240 volt 3 wire residential system.

Roger

 

[jim dungar]

That is not accurate with respect to 3 phase circuits because of 120 degree rotation you do not get Zero Sequence Cross-over like single phase 240/120.

If you have all of the possible system conductors included in your circuit it will be balanced. If you are missing any one or more conductors you may not have zero sequence.

About the only reason that 60/120V 1PH 3W exists is because of the desire to use standard equipment (including plugs and receptacles) with a 120V input. If the equipment was designed appropriately, a normal 120/240V 1PH 3W system would offer most of the same advantages as does 60/120V, except for noise contribution from other L-N(G) loads.

As I said, I understand the need for 60/120V. I just think it is ambiguous to call it "Balanced Power" without any other clarifier. Does an authoritative definition for it exist?

 

[dereckbc]

And the paragraph above basically describes an everyday 120/240 volt 3 wire residential system.

Roger

Roger you are correct. The problem is a lot of electronic systems for consumers and most commercial operate at 120 and are not equipped or optioned to operate 240.

How many homes, churches, retail outlets are equipped with 240 recepts other than the laundry room. OK my church has them in the kitchen.

 

[dereckbc]

About the only reason that 60/120V 1PH 3W exists is because of the desire to use standard equipment (including plugs and receptacles) with a 120V input. If the equipment was designed appropriately, a normal 120/240V 1PH 3W system would offer most of the same advantages as does 60/120V, except for noise contribution from other L-N(G) loads.
As I said, I understand the need for 60/120V.

That is the point Jim. It would be a huge step forward in my opinion if the USA system were to convert from 120 to 240. To do so has some real advantages from installation cost to effeciency of use.

Think about it for a minute. Imagine wiring all the general purpose outlets and lighting in a home with a single 15 or 20 amp circuit, daisy chained or ring with either 14 or 12 AWG wire respectively. No more blinking lights or noise to chase down. Well maybe that is a bad thing to your pocket book and bank account.