[Eric Weaver]

On 11/16/2015 06:47 AM, Scott Dorsey wrote:
Phil Allison wrote:
** In the USA, domestic power involves splitting single phase 240VAC into a pair of 120V AC lines that operate in anti-phase with a common neutral. This is not considered to be a two phase system.

This is because the two legs are fed off the same leg of the high voltage
distribution system... so even though you may be getting two legs into your
house, there is only one leg of 12kv at the pole.

One advantage is with electronic loads that draw current only during voltage peaks - the current pulses in each line are simultaneous and have opposite polarity, so cancel in the neutral.

With three phase systems, such peaks occur at different times, do not cancel and so can overload the neutral.

A large office building in LA burned down as a result of this back in the
seventies. Nobody had done the math.

A data center here in the SF Bay Area had a neutral-line meltdown due to
the "harmonic load" presented by switching power supplies. Not enough
power-factor correction in enough of them, or something like that.

[JackA]

On Monday, November 16, 2015 at 11:15:07 PM UTC-5, Eric Weaver wrote:
On 11/16/2015 06:47 AM, Scott Dorsey wrote:
Phil Allison wrote:
** In the USA, domestic power involves splitting single phase 240VAC into a pair of 120V AC lines that operate in anti-phase with a common neutral. This is not considered to be a two phase system.

This is because the two legs are fed off the same leg of the high voltage
distribution system... so even though you may be getting two legs into your
house, there is only one leg of 12kv at the pole.

One advantage is with electronic loads that draw current only during voltage peaks - the current pulses in each line are simultaneous and have opposite polarity, so cancel in the neutral.

With three phase systems, such peaks occur at different times, do not cancel and so can overload the neutral.

A large office building in LA burned down as a result of this back in the
seventies. Nobody had done the math.

A data center here in the SF Bay Area had a neutral-line meltdown due to
the "harmonic load" presented by switching power supplies. Not enough
power-factor correction in enough of them, or something like that.

Though two different monster, power factor and harmonics. Lots of harmonics around today due to (electronic) drive systems, requiring Harmonic Filters.
You can just Power Factor correction.

Jack

[[email protected]]

A data center here in the SF Bay Area had a neutral-line meltdown due to
the "harmonic load" presented by switching power supplies. Not enough
power-factor correction in enough of them, or something like that.

Though two different monster, power factor and harmonics. Lots of harmonics around today due to (electronic) drive systems, requiring Harmonic Filters.
You can just Power Factor correction.

Jack

power factor and harmonics are closly related

https://www.google.com/?gws_rd=ssl#q...+and+harmonics

Mark

[JackA]

On Tuesday, November 17, 2015 at 1:09:45 PM UTC-5, wrote:

A data center here in the SF Bay Area had a neutral-line meltdown due to
the "harmonic load" presented by switching power supplies. Not enough
power-factor correction in enough of them, or something like that.

Though two different monster, power factor and harmonics. Lots of harmonics around today due to (electronic) drive systems, requiring Harmonic Filters.
You can just Power Factor correction.

Jack

power factor and harmonics are closly related

https://www.google.com/?gws_rd=ssl#q...+and+harmonics

Mark

I guess one could claim they are, but you don't purchase Harmonic Filers to unify Power Factor, just like you don't don't purchase Power Factor Correction to sink Harmonics. Where they are both related are penalties from the Power Company.

Jack

[[email protected]]

On Tuesday, November 17, 2015 at 2:50:22 PM UTC-5, JackA wrote:
On Tuesday, November 17, 2015 at 1:09:45 PM UTC-5, wrote:

A data center here in the SF Bay Area had a neutral-line meltdown due to
the "harmonic load" presented by switching power supplies. Not enough
power-factor correction in enough of them, or something like that.

Though two different monster, power factor and harmonics. Lots of harmonics around today due to (electronic) drive systems, requiring Harmonic Filters.
You can just Power Factor correction.

Jack

power factor and harmonics are closly related

https://www.google.com/?gws_rd=ssl#q...+and+harmonics

Mark

I guess one could claim they are, but you don't purchase Harmonic Filers to unify Power Factor, just like you don't don't purchase Power Factor Correction to sink Harmonics. Where they are both related are penalties from the Power Company.

Jack

but they DO include what are called "power factor correction" circuits into electronic switching power supplies that reduce the current harmonics and therefore improve the power factor.

https://www.google.com/?gws_rd=ssl#q...ection+in+smps


Mark

[JackA]

On Tuesday, November 17, 2015 at 3:57:02 PM UTC-5, wrote:
On Tuesday, November 17, 2015 at 2:50:22 PM UTC-5, JackA wrote:
On Tuesday, November 17, 2015 at 1:09:45 PM UTC-5, wrote:

A data center here in the SF Bay Area had a neutral-line meltdown due to
the "harmonic load" presented by switching power supplies. Not enough
power-factor correction in enough of them, or something like that.

Though two different monster, power factor and harmonics. Lots of harmonics around today due to (electronic) drive systems, requiring Harmonic Filters.
You can just Power Factor correction.

Jack

power factor and harmonics are closly related

https://www.google.com/?gws_rd=ssl#q...+and+harmonics

Mark

I guess one could claim they are, but you don't purchase Harmonic Filers to unify Power Factor, just like you don't don't purchase Power Factor Correction to sink Harmonics. Where they are both related are penalties from the Power Company.

Jack

but they DO include what are called "power factor correction" circuits into electronic switching power supplies that reduce the current harmonics and therefore improve the power factor.

https://www.google.com/?gws_rd=ssl#q...ection+in+smps


Mark

Mark, I'm not disagreeing, but that is toy stuff size. I'm talking LARGE SCALE, like paper mills, mega-ton cranes, where HUGE drive motors exist, controlled electronically.

What I'd like to know, does anyone else see a modification to the US power grid? Here in NJ, they are replacing utility poles with taller ones. I'm guessing 2400V was common to feed pole transformers, but I can see 13,800V being distributed.

Jack