How much distortion is acceptable on residential utility power?

[Dennis Berkowitz]

Hi all,

If I monitor the incoming AC power with my scope it is a very distorted
sinewave, top and bottom are clipped.

The details: assuming the fundamental to be 0db, the 3rd harmonic
(180Hz) is -28.4db (6.674 Vrms) and the 5th harmonic (300Hz) is -24.5db
(7.33 Vrms).

(I wanted to rule out any equipment in my house as causing this, so I
turned off all my breakers and checked it again right at the breaker box
and got the same result, using a battery powered Fluke scopemeter).

Is this normal? I live in a residential neighborhood, with one pole-pig
feeding about 15 houses. Is the power company really supplying such
crappy waveforms, or are one of my neighbors running some really noisy
equipment?

Thanks everyone.
DB

 

[MooseFET]

Hi all,

If I monitor the incoming AC power with my scope it is a very distorted
sinewave, top and bottom are clipped.

The details: assuming the fundamental to be 0db, the 3rd harmonic
(180Hz) is -28.4db (6.674 Vrms) and the 5th harmonic (300Hz) is -24.5db
(7.33 Vrms).

(I wanted to rule out any equipment in my house as causing this, so I
turned off all my breakers and checked it again right at the breaker box
and got the same result, using a battery powered Fluke scopemeter).

Is this normal? I live in a residential neighborhood, with one pole-pig
feeding about 15 houses. Is the power company really supplying such
crappy waveforms, or are one of my neighbors running some really noisy
equipment?

The power company tries to supply a near perfect sine wave. The
generators tend to make very good sine waves. The impedance of the
local part of the power network and the nearby nonlinear loads are
going to be the main source of the distortion.

The fact that the waveform appears clipped suggests that there hasn't
been a lot of phase shift applied to the harmonics. The most common
sort of nonlinear load is the rectifier feeding a capacitor sort.
These tend to clip the peaks. Phase shifts will tend to slide the
wiggle down towards the zero crossing.

 

[me]

Hi all,

If I monitor the incoming AC power with my scope it is a very distorted
sinewave, top and bottom are clipped.

The details: assuming the fundamental to be 0db, the 3rd harmonic
(180Hz) is -28.4db (6.674 Vrms) and the 5th harmonic (300Hz) is -24.5db
(7.33 Vrms).

(I wanted to rule out any equipment in my house as causing this, so I
turned off all my breakers and checked it again right at the breaker box
and got the same result, using a battery powered Fluke scopemeter).

Is this normal? I live in a residential neighborhood, with one pole-pig
feeding about 15 houses. Is the power company really supplying such
crappy waveforms, or are one of my neighbors running some really noisy
equipment?

Thanks everyone.
DB

Operator error?...

 

[Dennis Berkowitz]

Operator error?...

I tried two different probes, and both channels on the scope. I also
monitored the waveform from a 9VAC wallwart and its the same shape. So
its not my scope thats clipping due to high voltage.

 

[Eeyore]

Hi all,

If I monitor the incoming AC power with my scope it is a very distorted
sinewave, top and bottom are clipped.

The details: assuming the fundamental to be 0db, the 3rd harmonic
(180Hz) is -28.4db (6.674 Vrms) and the 5th harmonic (300Hz) is -24.5db
(7.33 Vrms).

What's the total THD ? 2.5% is not uncommon IME. Never looked at the
individual harmonics much except when compliance testing.

Graham

 

[Sylvia Else]

The power company tries to supply a near perfect sine wave. The
generators tend to make very good sine waves. The impedance of the
local part of the power network and the nearby nonlinear loads are
going to be the main source of the distortion.

And expect to see it get worse as people replace incandescent lamps with
compact fluoros.

Sylvia.

 

[Eeyore]

I tried two different probes, and both channels on the scope. I also
monitored the waveform from a 9VAC wallwart and its the same shape. So
its not my scope thats clipping due to high voltage.

It's called 'flat topping' amongst EMC people and is indeeed usually due
to the use of 'conventional' rectifier - capacitor input power supplies
which draw current only around the peak voltage of the waveform.

As 'power factor correction' - more correctly harmonics compliance ( see
IEC 61000-3-2 ) becomes more and more common, the effect will reduce. It
is already mandatory for many classes of equipment in the EU for example.

Graham

 

[Phil Allison]

"John Larkin"
Sillier thanAnyone Else

I suspect that the population of cf's tends to clip one polarity peak
more than the other.

" That is one of the most crass statements I've seen in all my time on
Usenet"

ROTFL....



....... Phil

 

[MooseFET]

And expect to see it get worse as people replace incandescent lamps with
  compact fluoros.

I expect that the mains power will improve over the next many years.
A lot of equipment draws its current in thin spikes at the peaks.
Modern designs do this less so.

The CFLs will tend to draw current over a wide part of the cycle. The
capacitor after the rectifier is small enough that the the ripple is
very large. The transistor circuit makes no effort to regulate
anything. The inductor feeding the lamp controls the current. This
makes the load appear more resistive than would normally be expected

When LEDs become common, I expect that they will draw well behaved
waveforms. It is likely that someone will make a chip for the
purpose. Mains goes here, the capacitor here, the inductor here and
the LEDs over there. The first guys to get a low cost part on the
market, would likely end up owning the whole market

 

[Phil Allison]

"MooseFET"


The CFLs will tend to draw current over a wide part of the cycle.


** 100% WRONG !


The capacitor after the rectifier is small enough that the the ripple
is very large.

** Means the charging time is very short - fool.


The transistor circuit makes no effort to regulate
anything. The inductor feeding the lamp controls the current.

** All got nothing to do with the actual charging time of that first
electro.


This makes the load appear more resistive than would normally be
expected


** Total BOLLOCKS !!

Go measure the current draw waveform of a few CFLs - instead of sitting
on you FAT ARSE making up WRONG theories and misinforming people.

Have look at figure 11 for a typical current wave.

Figure 12 shows the same lamp operated from a common triac dimmer at full
setting.

http://sound.westhost.com/articles/incandescent.htm#pf



...... Phil

 

[Eeyore]

And expect to see it get worse as people replace incandescent lamps with
compact fluoros.

The load from CFLs is too small really to have a significant effect and PCs
are now getting active PFC, so it *ought* to go the other way but I
understand your point.

Graham

 

[Eeyore]

I suspect that the population of cf's tends to clip one polarity peak
more than the other.

Why ?

Graham

 

[Eeyore]

I expect that the mains power will improve over the next many years.
A lot of equipment draws its current in thin spikes at the peaks.
Modern designs do this less so.

The CFLs will tend to draw current over a wide part of the cycle. The
capacitor after the rectifier is small enough that the the ripple is
very large.

Poor man's way of improving harmonic currents !

Graham

 

[Eeyore]

"MooseFET"

The CFLs will tend to draw current over a wide part of the cycle.

** 100% WRONG !

The capacitor after the rectifier is small enough that the the ripple
is very large.

** Means the charging time is very short - fool.

Suggest you re-think that. Do you have a simulation program ? Large ripple >
larger conduction angle.

Graham

 

[MooseFET]

"MooseFET"

The CFLs will tend to draw current over a wide part of the cycle.

**  100%  WRONG  !

The capacitor after the rectifier is small enough that the the ripple
is very large.

**  Means the charging time is very short  -  fool.

No it doesn't. Where did you get that idea. The capacitor will start
charging when the mains voltage has passed the voltage that the
capacitor has discharged down to and continue until some time after
the peak. Try reducing the capacitor to zero and consider what
fraction of the cycle the diodes will conduct for.

The transistor circuit makes no effort to regulate
anything. The inductor feeding the lamp controls the current.

** All got nothing to do with the actual charging time of that first
electro.

Actually it does effect it in a very important way. Consider the
capacitor equal to zero and the transistors trying to regulate case
and you will see why.

You are both wrong and rude.

 

[MooseFET]

Poor man's way of improving harmonic currents !

Cutting production cost, allowing cheaper rectifiers and fitting into
smaller space also come from that one design choice. Th funny thing
is that brand to brand, there seems to be a large variation. I've
seen 2uF and 10uF.

 

[Phil Allison]

"Eeysore"

Suggest you re-think that.

** I suggest YOU got get fucked.

Do you have a simulation program ?


** Irrelevant crap when a simple test on REAL CFLs proves the point
beyond all doubt.

FUCKHEAD !!

Have look at figure 11 for a typical current wave.

Figure 12 shows the same lamp operated from a common triac dimmer at full
setting.

http://sound.westhost.com/articles/incandescent.htm#pf


GO DROP DEAD.



...... Phil

 

[Phil Allison]

"MooseFET"
"Phil Allison"

The CFLs will tend to draw current over a wide part of the cycle.

** 100% WRONG !

The capacitor after the rectifier is small enough that the the ripple
is very large.

** Means the charging time is very short - fool.

No it doesn't. Where did you get that idea.

JESUS CHRIST you are ONE ARROGANT **** !!!!!!!!

I posted ACTUAL data and YOU FUCKING SNIPPED IT !!

YOU ASSHOLE - YOU FUCKING ASSHOLE !!!!

----------------------------------------------------------------------


Go measure the current draw waveform of a few CFLs - instead of sitting
on you FAT ARSE making up WRONG theories and misinforming people.

Have look at figure 11 for a typical current wave.

Figure 12 shows the same lamp operated from a common triac dimmer at full
setting.

http://sound.westhost.com/articles/incandescent.htm#pf


The capacitor will start
charging when the mains voltage has passed the voltage that the
capacitor has discharged down to


** The charging time constant is very short for a CFL, typically about 50
uS.

Peak current is reached in 200-500uS and then drops off rapidly.

Go measure the current draw waveform of a few CFLs - instead of sitting
on you FAT ARSE making up WRONG theories and misinforming people.

Have look at figure 11 for a typical current wave - ASSHOLE !!

Figure 12 shows the same lamp operated from a common triac dimmer at full
setting.

http://sound.westhost.com/articles/incandescent.htm#pf




...... Phil

 

[Eeyore]

Because there may be a prefered direction to hook up the half-wave
rectifiers.

Half-wave rectifiers are not allowed any more AFAIK.

Graham

 

[Eeyore]

"John Larkin"
Eeyore

** " That is one of the most crass statements I've seen in all my time on
Usenet"

I can see this one's going to stick ! ;~)

Graham