7.5% THD

[Besoeker]

Not a matter of non-sinusoidal voltage generation by POCO. It is a matter of supplying from relatively weak power source.:slaphead:

Ah, not the POCO. Glad we agree on that now...............

Mods, this not bickering. It a serious and increasingly prevalent issue and it deserves to be better understood by many. I have been to a number of sites where there have been significant and costly failures.

@ Sahib. Voltage distortion of 7.5% is most certainly is something to be seriously concerned about. No, it isn't the POCO generating it. It is some customer causing it with probably large non-linear loads without a proper study of how they will interact with the supply that may be common with other users. The PCC or point of common coupling. Take heed. It may be to your advantage.

Another real life example. This was from a large paper mill in Kent, UK. We were installing some new DC variable speed drives. The power side was six-pulse phase controlled SCR bridges. Commissioning was a nightmare. Control of the firing angle for the SCRs used the supply to the drives. That supply had significant harmonic voltage distortion - of about the same order as than mentioned by the OP. The problem was that the new drives could not consistently determine the timing of zero crossing point.

My fix was to install a simple filter in the line that fed the timing circuit and make a small adjustment in the drive to compensate. Cheap to implement, very costly lost production time.

This is a long post by my usual standards. But I hope it serves to show, even if only by example, the nature of the issues and costs of harmonics

 

[Sahib]

Ah, not the POCO. Glad we agree on that now...............

Mods, this not bickering. It a serious and increasingly prevalent issue and it deserves to be better understood by many. I have been to a number of sites where there have been significant and costly failures.

@ Sahib. Voltage distortion of 7.5% is most certainly is something to be seriously concerned about. No, it isn't the POCO generating it. It is some customer causing it with probably large non-linear loads without a proper study of how they will interact with the supply that may be common with other users. The PCC or point of common coupling. Take heed. It may be to your advantage.

Another real life example. This was from a large paper mill in Kent, UK. We were installing some new DC variable speed drives. The power side was six-pulse phase controlled SCR bridges. Commissioning was a nightmare. Control of the firing angle for the SCRs used the supply to the drives. That supply had significant harmonic voltage distortion - of about the same order as than mentioned by the OP. The problem was that the new drives could not consistently determine the timing of zero crossing point.

My fix was to install a simple filter in the line that fed the timing circuit and make a small adjustment in the drive to compensate. Cheap to implement, very costly lost production time.

This is a long post by my usual standards. But I hope it serves to show, even if only by example, the nature of the issues and costs of harmonics

I think you misunderstood me: we do not agree.

I again stress if there is voltage THD at the PCC, POCO is to be blamed for it (as it is not you causing it, for example) and in many cases (e.g post # 9) POCO accepts it and may take remedial action to bring down the voltage THD by replacing the source transformer with a higher capacity one (weak to stiff source).

 

[Besoeker]

I think you misunderstood me: we do not agree.

I again stress if there is voltage THD at the PCC, POCO is to be blamed for it (as it is not you causing it, for example) and in many cases (e.g post # 9) POCO accepts it and may take remedial action to bring down the voltage THD by replacing the source transformer with a higher capacity one (weak to stiff source).

Why blame the POCO for a problem someone else is creating?
I'm done.

 

[Sahib]

Why blame the POCO for a problem someone else is creating?

Because the POCO lacked foresight to cover such contingencies in advance and its failure to ensure good quality power supply to every customer paying it on time, it is to take the blame and to take remedial action accordingly.

 

[Besoeker]

Because the POCO lacked foresight to cover such contingencies in advance and its failure to ensure good quality power supply to every customer paying it on time, it is to take the blame and to take remedial action accordingly.

The remedial action ought to be against the polluting customer(s).

 

[Jraef]

The remedial action ought to be against the polluting customer(s).

Rest assured, over here it is. IEEE 519 sets responsibility for the PoCo to ensure that THD-V is less than 5% at the PCC prior to connection. Yes, that does indirectly mean they cannot lower their transformer impedance to save costs and thus allow higher distortion, but in practice, what they really do is to trace down the “polluters” and force them to mitigate. I have yet to see a PoCo engineer admit to having installed the wrong transformer, it’s always someone else’s problem...

 

[chris kennedy]

This is very interesting.

Thanks to all.

 

[Besoeker]

Rest assured, over here it is. IEEE 519 sets responsibility for the PoCo to ensure that THD-V is less than 5% at the PCC prior to connection. Yes, that does indirectly mean they cannot lower their transformer impedance to save costs and thus allow higher distortion, but in practice, what they really do is to trace down the “polluters” and force them to mitigate. I have yet to see a PoCo engineer admit to having installed the wrong transformer, it’s always someone else’s problem...

The usual sequence of events here, and probably elsewhere, is that the invitation to tender will specify which spec has to be complied with. Often something like G5/4 or maybe IEC Standard 61000-3-6. In other words, the supplier (us) has to include the hardware and costs thereof for ensuring compliance and for testing to demonstrate that compliance. From memory, the limit is 4% THD.

Mostly we were in the industrial sector and 12 or 24 pulse systems were not uncommon in order to mitigate harmonic issues. It's up to us, not the power company to ensure compliance by whatever means we see fit. Ward Leonard systems would do but maybe not terribly competitive in today's markets.............

 

[GoldDigger]

In post #26 it should read "decrease transformer capacity" or "increase transformer impedance" to reduce cost, not the opposite.

Sent from my XT1585 using Tapatalk

 

[Sahib]

The usual sequence of events here, and probably elsewhere, is that the invitation to tender will specify which spec has to be complied with. Often something like G5/4 or maybe IEC Standard 61000-3-6. In other words, the supplier (us) has to include the hardware and costs thereof for ensuring compliance and for testing to demonstrate that compliance. From memory, the limit is 4% THD.

Mostly we were in the industrial sector and 12 or 24 pulse systems were not uncommon in order to mitigate harmonic issues. It's up to us, not the power company to ensure compliance by whatever means we see fit.

It is good you comply with relevant standards to limit the harmonics distortion at the PCC by your equipment supplied to your customer. But you can do nothing to reduce the background voltage distortion present at the PCC. Only the POCO can do something to reduce it and thus only the POCO is responsible for it.
.

 

[Besoeker]

It is good you comply with relevant standards to limit the harmonics distortion at the PCC by your equipment supplied to your customer.

It's mandatory.

 

[Sahib]

It's mandatory.

For MV customers only.

 

[Besoeker]

For MV customers only.

Not correct. Most of our installed base is 400V, 3-ph, 50Hz. There is some 690V, some 3,300V and some 11kV and ranging from a few tens of kW up to several MW.
It all has to comply.

 

[Sahib]

Not correct. Most of our installed base is 400V, 3-ph, 50Hz.

When that was implemented? Here in India no. For 11kV and above customers only applicable here.

 

[Besoeker]

When that was implemented? Here in India no. For 11kV and above customers only applicable here.

Then we are not comparing apples with apples.
Have a nice day.

 

[Sahib]

A large number of small capacity consumers such as home owners and few big consumers may be connected to same network. While POCO may force big consumers to make harmonics mitigation, the POCO can not force the small consumers to do so, despite their contribution to the harmonics distortion is significant.

 

[Russs57]

Shouldn’t the burden be on those that make equipment that causes these problems? In the USA computers have to be the worst offenders. Still a lot of stuff isn’t better than 10%. They seem to have tighter specs across the pond.

 

[Besoeker]

Shouldn’t the burden be on those that make equipment that causes these problems?

Totally agree.

 

[Sahib]

Shouldn’t the burden be on those that make equipment that causes these problems? In the USA computers have to be the worst offenders. Still a lot of stuff isn’t better than 10%. They seem to have tighter specs across the pond.

The omnipresent TV is worse offender, in large number, make the supply voltage flat topped.

 

[retirede]

The omnipresent TV is worse offender, in large number, make the supply voltage flat topped.