Harmonics in Green Buildings

[T.M.Haja Sahib]

the IEEE standard for Harmonic total demand distortion ITDD at 5% should be more than enough to satisfy any "green building" requirement.

this is the limit that utilities use in measuring harmonic emissions from customers.

I think the limit of 10% of harmonic loads in the total loads in a green building is meant for another purpose. See the following lines for a hint:

''If the amount of drives is small(<15%) compared to the system loading, it islikely that a filter will be not needed to help control harmonics.''

from the article in

http://www.epc-website.com/PDF/Myth1.pdf

 

[Besoeker]

I am trying to learn from these posts sir; can you post how you arrived at each value above please? thank you.

OK. I don't know how much you already know so,
The motor on its own is 55kW output and I have assumed 0.8 power factor (cosphi)and 93% efficiency.

Input Power =Output power/efficiency
Or 55/0.93 = 59.14kW
Now power = 3V_LI_L cos(φ)
This gives IL = 59140/(V_L*3* cos(φ))
(Bear in mind that you need Watts rather than kW for the calculation so multiply by 1,000)
Or 107A.
That?s the supply current.

You can then get kVA from
kVA = (3V_LI_L)/1000
=59.14

Or, more simply, supply power divided by power factor.
59.14/0.8 = 59.14kVA

You can proceed the same way with the active front end VSD.
In this case I made in input power factor 1.0 and the overall efficiency 89% to account for the additional losses in the VSD.

One final point. These are calculations based on assumed data. For real world calculations actual data needs to ascertained


The funny symbol, if it does not display correctly, is the square root symbol.

 

[mivey]

You can then get kVA from
kVA = (3V_LI_L)/1000
=59.14

Or, more simply, supply power divided by power factor.
59.14/0.8 = 59.14kVA

Typo:

You can then get kVA from
kVA = (3V_LI_L)/1000
= 73.9

Or, more simply, supply power divided by power factor.
59.14/0.8 = 73.9kVA

 

[Besoeker]

I think the limit of 10% of harmonic loads in the total loads in a green building is meant for another purpose. See the following lines for a hint:

''If the amount of drives is small(<15%) compared to the system loading, it islikely that a filter will be not needed to help control harmonics.''

Might it perhaps depend on what the other >85% loading is?
Good article though.

 

[Besoeker]

Typo:

You can then get kVA from
kVA = (3V_LI_L)/1000
= 73.9

Or, more simply, supply power divided by power factor.
59.14/0.8 = 73.9kVA

Bummer.
It happens.
Distracted by work.

 

[T.M.Haja Sahib]

Might it perhaps depend on what the other >85% loading is?

Yes. It is just a requirement and by adhering to it by limiting the heavy harmonic producing loads such as VFD's to be within 10% of total loads, it is likely to reduce to power consumption by not providing harmonic filters and without considerably increasing the harmonics at the same time in a building.

 

[Besoeker]

Yes. It is just a requirement and by adhering to it by limiting the heavy harmonic producing loads such as VFD's to be within 10% of total loads, it is likely to reduce to power consumption by not providing harmonic filters and without considerably increasing the harmonics at the same time in a building.

But if the other 85% comprises computers, televisions, printers, power supplies, battery chargers........

 

[T.M.Haja Sahib]

But if the other 85% comprises computers, televisions, printers, power supplies, battery chargers........

The intent of 10% limitation of harmonic loads in total load of a green building is to reduce power consumption without use of filters and not increasing the harmonics considerably at the same time. What loads make up that 10% harmonic loads are dictated by the minimum achievable overall energy consumption at the least achievable capital expenditure.

 

[robbietan]

I think the limit of 10% of harmonic loads in the total loads in a green building is meant for another purpose. See the following lines for a hint:

''If the amount of drives is small(<15%) compared to the system loading, it is likely that a filter will be not needed to help control harmonics.''

from the article in

which is exactly why current ITDD is limited at 5%. it will take into account the peak load and the amount of harmonics produced by the loads.

in effect, why be concerned with 10% of the loads being harmonic producing loads when harmonic distortion is limited to 5% ITDD ?

one way to reduce power consumption is to have your air conditioners/water pumps/fans run on inverters. and these are usually the biggest loads in a building. is more power saved by limiting the amount of harmonic producing loads or by putting the largest building motor loads on VFDs ?

that question has long been answered by buildings happily counting their savings brought about by the higher efficiency of motors run by harmonic producing VFDs.

 

[T.M.Haja Sahib]

in effect, why be concerned with 10% of the loads being harmonic producing loads when harmonic distortion is limited to 5% ITDD ?

I think the utility adheres to 5% ITDD, only when the short circuit ratio Isc/I(load)<20. When that ratio is higher, higher ITHD per IEEE-519 and so higher ITDD may be permitted by the utility.

one way to reduce power consumption is to have your air conditioners/water pumps/fans run on inverters. and these are usually the biggest loads in a building. is more power saved by limiting the amount of harmonic producing loads or by putting the largest building motor loads on VFDs ?

Yes. Put a harmonic filter also to the VFD's to limit the harmonics to within standard limit. The other raw harmonic producing loads shall be limited to 10% of all the total loads in the building so that providing additional filters to these 10% harmonic producing loads are dispensed with.