power Factor Correction and Harmonic Resonance

[colosparker]

Installed Switched Power Factor Correction Capacitors in numerous facilities which have Adjustable Speed Drives throughout the building. Experiencing swelling capacitors, fuse tripping, burning wiring within the Switched PFC units. ASD's are the 6-pulse rectifier type. Suspect Harmonic Resonance to be the key problem with the Switched PFC units. Anyone else have similar problems working with this type equipment in a building. Switched PFC's and ASD's installed as part of a large energy management contract designed to payback with energy savings.

 

[ron]

Here's a good reference
http://www.lmphotonics.com/pwrfact.htm

 

[robbietan]

probably harmonics. any voltage readings/harmonic readings before and after the PFC installations?

 

[charlie tuna]

parker,
if your doing this type of work --- "energy management contract" --- one of the first tools you need is a data logger. and you need a good one if you suspect harmonics in you customer's systems. you can't see harmonics, nor if you saving your customer money without the ability to know whats happening in his system. these systems aren't cheap --- invest some of the profits back into your business and hand him a print out so he can determine his payback period --- you'll get more business!!!!

 

[ramsy]

Installed Switched Power Factor Correction Capacitors in numerous facilities which have Adjustable Speed Drives throughout the building. Experiencing swelling capacitors, fuse tripping, burning wiring within the Switched PFC units.

As I understand it, if triplen harmonics are present, VA likely increases and thereby decreases power factor. Total PF includes current THD, associated with adjustable frequency motor drives. If any displacement PF is corrected before THD, the existing harmonics could damage capacitor banks.

dPF = WATT/VA*Sqrt(phases)
PF(THD) = Sqrt[1/(1+THD^2)], where THD = current harmonics.
PF(TOT) = dPF * PF(THD)

Before installing displacement corrections, a qualified power-quality engineer should exhaust cost benefits of controlling harmonic-induced overheating, dielectric breakdown in capacitor banks/cables/transformers, or nuisance tripping OCD's, surge suppresser failure, relay malfunctions, and signal interferance in control circuits via common electrode systems/main bondings/transmission lines, or over voltage/excessive currents due to system resonance.

My limited look into system resonance shows it cancels the inductive reactance and capacitance only, not the resistance of the wire. Unlike integrated circuit boards, inside wiring code requires over-current protection sized to conductor circular mills (resistance).

Experiencing swelling capacitors, fuse tripping

If harmonic induced system resonance can damage unprotected capacitor banks or circuits boards, the inside wiring connected to breakers will remain properly protected.

..burning wiring within the Switched PFC units

Sever enough tripplen harmanics can still overheat, damage, or set fires with the grounded wires (unprotected by breakers).

My limited look into capacitors shows they correct a dPF lag from inductive reactance, but don't correct harmonics. Harmonic correction would require seperate 120/60v isolation transforers, or 6, 9, & 12 phase wave-canceling transformers, or filters, or perhaps Liebert's interesting all-in-one power conditioners, such as the Datawave magnetic synthesizer.

 

[jackofalltrades]

PF Correction and Harmonic Resonance

PF Correction and Harmonic Resonance

A 6 Pulse Drive is the most cost effective solution, but the worst choice in terms of being a harmonic generator.

Some Drive manufacturers offer optional Line Reactors to limit the Harmonic Interaction on the Feeder.

In my adventures, it has been proven that a particular current harmonic distortion will ring with the amount of Capacitance on line, causing an instantaneous overvoltage. I have seen many failed Caps and Fuses failed due to this.

Typically, Drives will have have high Current THD at the 5th and 7th Harmonic.

Typically, being wired in Delta, you should have negligable Triplens present, as they should cancel themselves out. On a Wye System, excessive 3rd will show a large Single Phase load out there somewhere, but the Positive, Negative and Zero Sequence Currents will tell the tale.

A 6 Pulse drive will have more Current THD than an 18 Pulse drive, due to the arrangement of the preferred Semiconductors.

An Active Front End drive is the cleanest of them all.

Some drives also offer PF Correction Capacitors as well.

A Power Systems Study will identify the culprit, thus leading you to a Solution.

Typically a Harmonic Filter tuned to a specific frequency will be needed to solve the problem.

Good Luck!

 

[jackofalltrades]

PF Correction and Harmonic Resonance

PF Correction and Harmonic Resonance

This is assuming a Delta to Wye Transformer from the Utility, then a Wye/Delta arrangement for your drives.

The Wye should have no Triplens present on the Distrubution Feeder that serves your facility, they should be trapped in the Transmission (Delta) Side, and the Delta wired from that typically wont show any either, unless there is an Issue.

I am currently Metering a facility in Alabama that has 15 to 18 percent 3rd Harmonic on their Power System due to Large Single Phase Spot Welders, as well as a significant amount of 5th also, from drives and such.

Hope this Helps a bit.

 

[RayS]

Typically a Harmonic Filter tuned to a specific frequency will be needed to solve the problem.

Good Luck!

You may also get lucky and find that you can "lock out" certain drive freq's that cause problems. I've seen this more for mechanical driven equip issues, but because it's already probably a feature of your drives, it may be a low cost help