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Chinese finger torture - It's for torture, obviously.

1 (5.3%)

Stops electrical system noise from getting into your power amp

4 (21.1%)

Stops electrical noise inside your amp from getting out into the electrcial system

2 (10.5%)

Stops Triplen Harmonic Current Buildup in 3-phase electrical systems

2 (10.5%)

Prevents radio signals from getting into your sound system

10 (52.6%)

Total Members Voted: 19

Voting closed: September 30, 2013, 01:31:36 PM

[Guy Holt]

Sounds like we need a new type of circuit breaker that also measures current in the neutral, and when that current exceeds a safe value, disconnects the hot/live lines related to that neutral.

Such a breaker, the electronic ABB TMAX, is pretty much standard in film disconnects. With the PR221DS-LS/I controller, it can be set to trip when current on the neutral reaches 50 or 100% of the over current protection setting for the phase legs. Over current protection  for the phase legs is variable between 160 and 400 Amps.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com

[Guy Holt]

... I have one report of an office building full of desktop computers with switching power supplies that burned up the neutral bus via Triplen harmonics. It's not just 3rd order harmonics, but also 5th, 7th, 9th, 11th, 15th, 19th, 21st etc... I don't think there's a top end to it. ...

It is not just the neutral conductor that we have to be concerned about. The predominant transformer used in commercial/residential applications, a Delta/Wye has some undesirable characteristics when significant amounts of harmonic currents are present on the load side. For instance, since a Delta primary does not have a neutral, the induced currents do not flow through the primary system, and if they are not cancelled, they become trapped in the primary where they continuously circulate causing extra heating. Called “Eddy Currents”, these currents produce heat that increases substantially at the higher harmonic frequencies. The relationship is as follows:

(Where: PEC = Total eddy current losses, PEC-1 = Eddy current losses at full load based on linear loading only.

Ih = rms current (per unit) at harmonic h , and h = harmonic # )

What is significant about the relationship of Eddy Current heat loss as a result of harmonic currents expressed in this equation is that the harmonic current (Ih) and harmonic number (h) are squared which means that instead of increasing in a linear fashion they increase exponentially. Put another way, the heat generated by harmonic currents just doesn’t increase gradually at higher harmonic frequencies, but it jumps drastically.

As indicated in the equation above, higher order harmonics will generate as much heat as the 3rd, but at much lower amplitudes. For instance, according to the equation above 1 Amp of the 5th harmonic will generate as much heat as 1.7 Amps of the 3rd, and 1 Amp of the 9th harmonic will generate as much heat as 9 Amps of the 3rd. For this reason, the higher order triplen harmonics contribute as much to distribution equipment  overheating as the lower frequency. For instance, it doesn’t take much 21st harmonic current to generate heat when, according to the equation above, the harmonic frequency (h) is squared for a multiplier of 441x (21²) compared to the multiplier of 9x (3²) for the 3rd harmonic.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com

[Keith Broughton]

As indicated in the equation above, higher order harmonics will generate as much heat as the 3rd, but at much lower amplitudes. For instance, according to the equation above 1 Amp of the 5th harmonic will generate as much heat as 1.7 Amps of the 3rd, and 1 Amp of the 9th harmonic will generate as much heat as 9 Amps of the 3rd. For this reason, the higher order triplen harmonics contribute as much to distribution equipment  overheating as the lower frequency. For instance, it doesn’t take much 21st harmonic current to generate heat when, according to the equation above, the harmonic frequency (h) is squared for a multiplier of 441x (21²) compared to the multiplier of 9x (3²) for the 3rd harmonic.

Guy Holt, Gaffer
ScreenLight & Grip
www.screenlightandgrip.com

That is a very interesting effect. Well explained.
Learn something every day here

[Kevin Graf]

For more on 3 phase AC power and harmonics see pages 6 & 7 of this Jim Brown paper:

"Power and Grounding For Audio and Audio/Video Systems -- A White Paper for the Real World"
http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

50 more Jim Brown papers:
http://www.audiosystemsgroup.com/publish.htm

[Keith Broughton]

For more on 3 phase AC power and harmonics see pages 6 & 7 of this Jim Brown paper:

"Power and Grounding For Audio and Audio/Video Systems -- A White Paper for the Real World"
http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

50 more Jim Brown papers:
http://www.audiosystemsgroup.com/publish.htm

I just read through some of the EMI/RFI problems and trouble shooting.
Compared to that, ground loops are easy!
Thanks for the links.

[ProSoundWeb Community]