Functions of Regulators and Capacitor Banks 12

[Stonemug]

I currently conduct investigations on Power Influence and Noise Metallic in telephone exchanges throughout our company. I know a good deal about Telephone outside plant engineering, but my commercial AC power theory is in need of some assistance. I use a Spectrum Analyzer and a wand to detect faults that could cause influence in the telephone cables. Most of the time these faults are ran down to either open cable shields, which is something we as a telephone company can repair by properly bonding and grounding our cable, but on some occasions the problem is found to be coming from a capacitor bank or defective transformer.
I have been trying to get a power engineer to explain what exactly a capacitor and regulator do for the power Companies facilities, but they seem a little relentless to share any information. Correct me if I’m wrong but a capacitor increases the voltage/ amperage on a line and a regulator regulates the voltage on a line? The down side to this is when the PSC (Public Service Commission) conducts an audit of an exchange and finds high Power Influence readings the Telephone company is the one responsible for finding the problem, even if it the power company causing the influence. I figure the more I can learn about the AC power designs the better I will be able to troubleshoot these problems.
We currently have a location that has been under investigation for several years. We have had the power company in the area remove all the capacitors from service and still have the same problem. The spectrum analyzer leads us to believe the influence is coming from the sub-station in the area. Can the Sub-Station produce this type of influence? Any help would be greatly appreciated.

 

[Skogsgurra]

I do not think that the capacitors contribute to the disturbance level at all.

They are used to compensate for the inductive part of motor loads etcetera. The controller supervises the power factor (phase angle) and switches more capacitors in when the phase angle gets larger. The switching is restricted so that it does not happen too often (wears the switches out) and the shortest time between switching is usually a few minutes. The capacitors do not disturb anything and the switching occurs so seldom that it cannot be a problem to a telephone line.

It is possible that you are talking about a switch mode power supply - it CAN disturb telephone lines. Or even more likely a PWM motor controller. They are among the worst polluters. SCR controllers and dimmers are also bad polluters. Look out for such things - not power factor capacitors and controllers.

 

[dpc]

I agree with skogsgurra that capacitors should not generally be a source of noise.

What frequency is causing you problems? If it is 180 Hz, you are dealing third harmonics.

If it is higher frequency noise, it could just be a bad insulator and/or a bad or corroded connection. Loose or corroded connections can act as diode causing rectification and broadband noise.

 

[busbar]

 
Some references in ANSI/IEEE Standard C62.92.4-1991 …Application of Neutral Grounding in Electrical Utility Systems, Part IV—Distribution Searchword “telephone” shows 20 hits pages 16-31.

Contents described at..

http://standards.ieee.org/reading/ieee/std_public/description/surge/C62.92.4-1991_desc.html

Procurement

http://shop.ieee.org/ieeestore/Product.aspx?product_no=SS15107

Apparently, utility-distribution Y-grounded capacitor banks can contribute to telecomm noise. Appreciable voltage-regulator noise may indicate defective tapchanging components.

 

[busbar]

 
IEEE Std 519-1992 contains some incidental references..

http://standards.ieee.org/reading/ieee/std_public/description/staticp/519-1992_desc.html

§6.9 Telephone Interference 6.9.1 TIF Weighting Factor 6.9.2 Methods of Reducing Interference

Longshot links

http://www.sncmfg.com/telecom/semnar2.html

http://www.sncmfg.com/telecom/tapes.html

 

[alehman]

While capacitors should not be a source of noise by themselves (unless something is wrong), they may contribute to inteference from a system with high harmonic voltage distortion. Capacitors have low impedance to high frequencies which can result in elevated harmonic current near the capacitor.

Inteference might also be produced if the capacitor creates a resonance on the system that coincides with a harmonic frequency where other significant sources of distortion exist (e.g. rectifiers, motor drives, etc).

 

[vtakev]

Check where are connected exactly the capacitor banks. If there are asynchr. motors with drives and/or DC motors with ddrives, some bad choise of capacitors, missing of reactors etc. can a reason for appearing of high level harmonics (5, 7 and 11 usually) and capacitors "reinforce" them.

 

[tinfoil]

I have to disagree with several of the posters here:

Distribution-class capacacitors CAN create noise in the frequency range of interest to the TELCOs.

I have had some experiences where the capacitors 'buzzed' enough to create an audible problem on telephone cables in the vicinity.

Capacitors can magnify the effects of harmonics (due to resonance), and the residual or 'zero-sequence' harmonics (3rd, 6th, 9th, etc) can create a 'dc voltage bias' on all nearby conductors, inclusing telephone and sometimes even CATV.

In addition, capacitors may begin to develop a breakdown in their insulation or dielectric, over time. This can create noise (audible or RF).

All transformers, including substation class, distribution class, or voltage regulators, create losses when energized. Some of these losses manifest as noise in the audible and even in the RF range.

The CEA (Canadian Electric Association) delivered a workshop series in 1992 in association with the CRTC (Canadian equivalent to the FCC) on electrical/communication system interactions. The documentation was prepared by M.S. Tibensky. This was 'pre-internet', so I am not sure if electric copies exist of them.

 

[tinfoil]

Stomemug: ignoring the product hype, you might check out:

http://www.cooperpower.com/images/icons/pdf2.gif

http://www.cooperpower.com/images/icons/pdf2.gif

 

[corrosivo]

Stonemug

From your post, I understand that you have detected power frequency hum in the communication cables, maybe your shield is part of a ground loop of the power system ground; verify this.

The site below, shows a good graphical description of some of the causes and solutions of your noise problems. I´m sure this site will give some graphical insight of what the fellow posters are explaining about this noise issue.

regards

http://www.pserc.wisc.edu/ecow/get/...csemin1/seminars20/jewell_seminar_sep2002.pdf

 

[Stonemug]

I would like to thank everyone for his or her information. From what I have had time to read so far, this information should help. To answer some of your questions:
The frequencies that usually give the most influence are 180, 300, 540, 720, and 900 Hz. Just so you know how we find a defective AC device I will try to give you the short and sweet version of it. The device we use to detect the source of these frequencies is called a Spectrum analyzer and wand or antenna. We set the frequency to one of the ones listed above and when we get near the problem (Capacitor bank, transformer, regulator, or other) the dB readings on the display will go high and then back down once the problem is passed.
I know when a capacitor bank is working correctly it shouldn't cause any influence on our cable, but we have had several capacitor banks since I have been conducting these investigations that were found to be the source of offending influence. I have never been able to find out from the power company what exactly was wrong with the banks, just that they were defective. Example, today we had the local power company pull a set of capacitor banks off line in an area we had previously investigated and the readings changed as follows:
<u>Power Influence</u>
Before: 111 dB
After: 75 dB
(Range allowed by PSC >80 dB)
<u>Noise Metallic</u>
Before: 35 dB
After: >5 dB
(Range allowed by PSC > 20 dB)
I’m just searching for the theory behind how they work in the AC environment and what influence they have when they malfunction. I know they will not always be the source of our problems, but understanding them will help me when they do influence our cable. My knowledge is primarily in DC power so understanding how the components of the commercial AC circuit work (Capacitors and regulators) should help me in figuring out how they will affect our plant if they are not operating properly. Once again thank you for your information.

 

[Stonemug]

On a further note: When we find a set of capacitor banks that are proven to be influencing our cable we place a device from SNC called a Harmonic Shunt on the pole that is wired into the capacitor bank. The device counteracts the effects of the offending harmonics the capacitor bank is influencing on our cable. So with this in mind, we do have a way to counteract the problems when they are found, it's just the location of a defective component that can be difficult at times. Thanks

 

[Skogsgurra]

Stonemug,

The problem is not in the capacitors. The problem is that you have harmonics in the mains voltage and that these frequencies are more or less shorted by the capacitors.

The frequencies you mention are 3rd (180), fifth (300), ninth (540), eleventh (I think that you meant to write 770 and not 720), and fifteenth (900 Hz). There is probably also 420 Hz, which is the seventh harmonic.

The reason that you see a drop in these frequencies when the utility disconnects the capacitors is not that the capacitors are at fault but simply that the "short circuit" that the capacitors constitute is eliminated. Remember that high frequencies like 300 and 540 Hz pass the capacitors a lot easier than the fundamental 60 Hz frequency.

If you do a voltage harmonics survey, you will probably find that there is a rather high level. You will also find that the harmonics level drops when the capacitors are connected. There are rules regarding harmonics (talking EU now, not sure about US) and if the grid contains too much harmonics, something should be done about it.

But - I repeat - the capacitors do not produce the harmonics. And they are not faulty.

 

[Skogsgurra]

Correction to above post: I "meant to write" 660 Hz, not 770, which does not exist at all in a 60 Hz system.

The 720 Hz - if it exists - is a bad sign and implies that there is some kind of rectification and partly DC load in the grid. 720 Hz is the 12th harmonic and cannot exist with symmetrical loads, how non-linear they ever are.

Also, it should be said that the capacitor bank shorts the harmonic currents to ground (or neutral), which increases the magnetic field (and coupling into the telephone system) at the harmonic frequencies.

 

[peebee]

What alehman, tinfoil, and skogsgurra said. I agree completely. Stars all around.

Stonemug -- regarding your repeated requests for a description of how capacitors work -- the above posts have tried to answer that a couple times in terms understandable to a layman: They are there to correct for the inductive loads of motors, and they look like short circuits to high frequency harmonics on the power system (120Hz, 180, 240, 360, etc).

If you want to know more about caps than that, you really need to take a class in basic electrical theory, or buy a book or Google it -- BUT -- unless you're willing to invest some serious time into learning about basic RLC circuits, you won't gain much more of an understanding about capacitance than what has already been posted above.

 

[busbar]

Agree with peebee

http://www.usda.gov/rus/electric/pubs/1724d112.pdf

 

[cuky2000]

Can the Sub-Station produce this type of influence?
You may want to assure that your power company checks for:
- Tree branches and foliage that comes in contact with high voltage lines
- Defective line insulators.
- Loose or unbounded hardware.
- Discharges from defective lightning arrestors
- Defective transformers
- Circuit breakers.
- Load switching devices.

Notice that pole capacitors may have some of the devices listed above.

After determine the cause of interference, a remedy or mitigation could include filtering at the noise source, shielding and bypassing as close as possible to its source.

See if the enclose book reference could help.

http://www.arrl.org/catalog/?item=9055

 

[Stonemug]

I now understand what everyone has posted. I have taken classes on circuit board components and I how a capacitor works on a circuit board. I just wanted to make sure they function the same way in an AC commercial network. You all have answered my questions. Thanks everyone for you information.

 

[mc5w]

Cleveland Electric Illuminating Company transposes their 34.5 KV subtransmission 120 degrees once every 2 miles or so to hepl keep down telephone influence.

Your harmonic spectrum sounds a lot to me like there is a nearby factory or commercial building with a lot of motor drives that are injecting harmonics into the powerline. A bad insulator could also generate this kind of noise spectrum.

It is also theoretically possible for copper oxide, aluminum oxide, or iron oxide in a metal joint somewhere that is acting a a frequency multiplier by means of nonlinear conduction. There are instances of this happening at radio frequncies in the Amateur Radio literature but I would rather place my bets on faulty insulators or a bunch of motor drives.

Also, one of the things that the capacitor banks do is reactive voltage support just like how telephone people used to put loading coils into telephone lines to increase impedance to get the insulation to do more of the work. In the case of capacitor banks the reative compensation is to lower the impedance of the line so that more power can be pushed through the fabric of space. Think of the capacitors as making the line behave as if the wires are closer together during peak periods when the capacitors are switched on.

Mike Cole, mc5w@earthlink.net