Question on harmonics

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T.M.Haja Sahib said:
Incomprehensible. :)
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I sorry you don't understand. Maybe someone else can explain it for you.


T.M.Haja Sahib said:
During energy audits with a power analyser.
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I've used Dranetz equipment but my usual method is using a digital storage oscilloscope with either a serial link or removable storage media and dump the results into a spreadsheet for mathematical analysis.
It has the merit that the kit is cheaper and I routinely carry it all with me.
 
ArchieMedes said:
So if transformers can transfer harmonics, it means that it would be difficult to isolate if the harmonics is generated by the transformer secondary/load side or from upstream of the transformer which is caused by other loads on the circuit connected on the same bus/circuit?
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difficult but not impossible. our Dranetz equipment can tell whether the harmonics are coming from upstream or downstream of the instrument.

utilities here are law bound to limit the harmonics in the voltage supply. as harmonics mostly come from loads, customers are notified if they exceed emission limits. these emissions tend to travel to the grid and end up in the supply of other customers.

the best example is the voltage supply of customers near a steel plant that uses an electric arc furnace
 
T.M.Haja Sahib said:
Power transformers do not just transfer harmonics; they themselves can be sources of harmonics. For example, in a star/delta or star/star transformer, if the neutral of the primary is not connected to the source neutral, the secondary voltage is distorted with triplen harmonics, even though there is no distortion of voltage on the primary side of the transformer.
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A correction. The star/delta transformer transformer has sine wave voltage for all practical purposes, even if neutral connexion with source is broken, due to presence of delta winding.
 
robbietan said:
difficult but not impossible. our Dranetz equipment can tell whether the harmonics are coming from upstream or downstream of the instrument.

utilities here are law bound to limit the harmonics in the voltage supply. as harmonics mostly come from loads, customers are notified if they exceed emission limits. these emissions tend to travel to the grid and end up in the supply of other customers.

the best example is the voltage supply of customers near a steel plant that uses an electric arc furnace
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Thanks for the equipment info.
 
robbietan said:
utilities here are law bound to limit the harmonics in the voltage supply. as harmonics mostly come from loads, customers are notified if they exceed emission limits. these emissions tend to travel to the grid and end up in the supply of other customers.
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One of the issues I've come across is harmonics from residential loads. Not any one in particular, just that there are huge numbers of them.
My own domestic supply has the typical flattened top signature of third harmonic distortion. My supply transformer is about a 1.5MVA 11kV/400V and all it feeds are residences.
 
Besoeker said:
One of the issues I've come across is harmonics from residential loads. Not any one in particular, just that there are huge numbers of them.
My own domestic supply has the typical flattened top signature of third harmonic distortion. My supply transformer is about a 1.5MVA 11kV/400V and all it feeds are residences.
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utilities tend to look down on emissions from residential customers as being "too small when compared against the total load of the utility transformer", just like in the case of low power factor of residential units.

however, there are some laws that limit the amount of current thd of an appliance. such as a 15% current thd limit for light fixtures
 
robbietan said:
utilities tend to look down on emissions from residential customers as being "too small when compared against the total load of the utility transformer", just like in the case of low power factor of residential units.
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In UK, the split in terms of power consumption is roughly one third each for the residential, commercial, and industrial sectors.
In the case of redential, it isn't big thing, just big numbers of things.


This is my domestic supply:

200210-01V.jpg


The harmonic distortion is significant. From my experiences in this field, I'm inclined that some of it at least is on the HV side of the local distribution transformer.
 
Besoeker said:
In UK, the split in terms of power consumption is roughly one third each for the residential, commercial, and industrial sectors.
In the case of redential, it isn't big thing, just big numbers of things.


This is my domestic supply:

200210-01V.jpg


The harmonic distortion is significant. From my experiences in this field, I'm inclined that some of it at least is on the HV side of the local distribution transformer.
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one other explanation is that you and your neighbors have a lot of harmonic loads and that is why the secondary voltage of the utility transformer is "a little bit" distorted
 
robbietan said:
one other explanation is that you and your neighbors have a lot of harmonic loads and that is why the secondary voltage of the utility transformer is "a little bit" distorted
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I have come across situations like that before where the secondary was similarly distorted with no load on it so it has to have been on the primary side.
 
Besoeker said:
Might I suggest that you read the document for which you kindly posted a link:

http://www.epc-website.com/PDF/Myth1.pdf
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Yes. The triplen harmonics can flow through the star/delta transformer, when it has the same phase relationship in a three phase supply as does a pure sinusoidal three phase supply. It is very uncommon to find such a situation. Can you quote one from your ''long'' experience? Thanks.
 
T.M.Haja Sahib said:
Yes. The triplen harmonics can flow through the star/delta transformer, when it has the same phase relationship in a three phase supply as does a pure sinusoidal three phase supply. It is very uncommon to find such a situation. Can you quote one from your ''long'' experience? Thanks.
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Pumping station, Holywell Hill, St Albans.
Nothing connected to the transformer secondary. All the odd harmonics including triple n measured from the primary VTs and CTs.
 
Besoeker said:
Pumping station, Holywell Hill, St Albans.
Nothing connected to the transformer secondary. All the odd harmonics including triple n measured from the primary VTs and CTs.
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With 120 degree phase shift?
 
I just inquired whether the 3rd harmonics in each phase of the three phase supply you measured had any 120 degree phase shift among them in the three phase supply as shown in the paper you stated.
 
T.M.Haja Sahib said:
I just inquired whether the 3rd harmonics in each phase of the three phase supply you measured had any 120 degree phase shift among them in the three phase supply as shown in the paper you stated.
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Of course its 120 degrees.
Delta primary, star secondary with a neutral.
 
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