AccuSine PCS+: Voltage Harmonic issue

[NguyenMon]

Hello all,

Have a good day.

We have installed 2 AccuSine PCS+ units for a factory to reduce Harmonic Current below Transformer 5. The Harmonic Current, which is 28% before installing, downs to 7.6% (We set THDi Target at 8%). But the Harmonic Voltage didn’t decrease and remained the value at 7.5% (THDv), which made customer question us why?

We are wondering if the other transformer may affect to the Harmonic Voltage at Transformer 5 where we installed the AHF system? If we install AHF system for the other transformers, will the Harmonic Voltage decrease?

We demonstrate the electric power distribution system of the factory and the position of the 2 AHF units in the picture below.

I appreciate any help here.

Thanks in advance.

Best regards,

.

[TruongDoan_ESEC]

Hi Everyone,

After installing AHF+ but THDv does not decrease -> Is that normal?
while THDi decreased from 30% to 8%.
Thank you everyone for your support.

Truong Doan.

[Anonymous user]

Hello Arun @Arunprasad  , Can you look in to this question about Accusine PCS+.

@NicolasLarue  FYI

[Arunprasad]

@TruongDoan_ESEC  

Hi

Are you very specific to the escalation made by  NguyenMon , or you are taking about different  site experience, because, there are different reason to have Voltage distortion in the Network, please refer the reply given to the above case.

[Arunprasad]

@TruongDoan_ESEC 

Hi Everyone

Based on the discussion, i had with my L4- Mike Fry , i am sharing this explanation, in behalf of him

If you assume the 22kV line is an infinite source of current this could not occur.  The voltage distortion would be a function of the transformer impedance and the harmonic current through the transformer. 

However if the 22kV has impedance, this value will be primarily based on the length of the 22kV line.  If the 22kV is heavily loaded and a long distance increases the voltage distortion on the 22kV of each transformer primary.  As the harmonic current is reduced at each branch the THDv at the 22kV will go down.  The voltage distortion at the primary of each transformer is a function of the X of L of the 22kV line and the harmonic current through that impedance. 

This is assuming the AccuSines are correcting the complete load connected to the 400V TR5 transformer.  If there are other harmonic loads connected to the secondary of the transformer that are not being corrected by the AccuSine would also impact the THDv on the secondary of TR5. 

[Anonymous user]

Hello expert
I am very appreciate your support to answer the question of NguyenMon
However, our problem is a little bit different with what you are thinking about. Let me make it more clearly:

All the Transformers are placed inside the factory ( as visualized in the attached image_1 ). We use an Accuside PCS+ to eliminate harmonic current for load in the TR5 secondary side (the other Transformer are not involved). Beside that, this Accuside PCS+ placed in the secondary outgoing side of TR5 that can cover all the nonlinear load (as visualized in the attached image_2).

The original average THD voltage and current before installing Accuside were 9% and 20%, respectively. After installation, THD current could be reduced to 5%, but THD voltage were still the same ( around 9%).

Hence. My question is that if this phenomenon is normal? If Not, how can we solve it?
Thank you very much and looking forward to hearing from you soon.

Best regard

Image_1Image_2

[Arunprasad]

@Anonymous user 

Hi 

Let me get back to you, in the mean time, did you check with your local CCC team, Did you done any PQ audit,what is the nature of load application connected , can you share more details,  i think , you can write email to me and keeping my L4 on the loop. 

Arun Prasad <Arun.Prasad@non.schneider-electric.com>

Michael Fry <Mike.Fry@se.com>

[Arunprasad]

@Anonymous user 

Hi

I have a question, have you confirmed  the voltage on the 22kV is a perfect sinewave. We need to understand  these information.  If there is voltage distortion on the 22kV improving the THDi on the secondary of TR5 will not correct all of that voltage distortion. 

The Active Filter corrects harmonic current.  The current is improving.  Typically an improvement to current will improve the voltage distortion.  However if the voltage is distorted due to a parallel connected load that is uncorrected that voltage distortion will remain.  The THDv will be passed through the transformer.  See the drawing in your previous email. The other transformers also have harmonics.  Those harmonics could be causing voltage distortion on the 22kV bus.  That distortion on the 22kV will be applied to the secondary of TR5, even if the load current on TR5 is a perfect sinewave, or if TR5 has no load connected. 

The easiest way to prove or disprove the 22kV has THDv is, to turn off the loads connected to any of the transformers, ideally TR5, and measure the THDv on the secondary of the unloaded transformer.  If they measure THDv the 22kV is distorted.  

[Anonymous user]

@Arunprasad 

Hi

Thank you for your support, I got your ideal. However, there is something that I can not confirm to you, that is about the perfect Sine Wave of 22 kV power grid. Beside that, to turn off the loads connected to transfomer TR5 in oder to measure THDv is quite impossible, because the factory is working continuously.

Therefore, if you have any case study like this, can you share it to me?

Bui Van Trinh

[Arunprasad]

@Anonymous user 

Hi

You are welcome, I don't have any case study with me, but  you can approach local country offer team , they may  help you ,else you can approach Global offer Manager  @NICOLAS LARUE(AccuSine), contact him by the direct message,  i hope he may help you.

BR

Arun

[Anonymous user]

Hello Nguyen.  I'd also suggest looking at the base load harmonics when loads are at their lowest.  You'll want to check what the site's THDv is rather than what's coming in from the "street" side.  This is why correcting the THDi is important on some sites so you're not trying to "fix" the utility's poor THDv.  I'm assuming you did a Power Quality Audit before the AHFs were sized and installed, if so, what was the THDv when the TDD was at it's lowest?