Previous in Forum: Residential Energy Meters in India   Next in Forum: Required Number of Lighting Fixtures?
Close
Close
Close
13 comments
Guru
Popular Science - Cosmology - New Member Technical Fields - Technical Writing - New Member Engineering Fields - Energy Engineering - New Member Engineering Fields - Electrical Engineering - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Electromechanical Engineering - Old Member, New Association

Join Date: Apr 2008
Location: Lexington, KY
Posts: 1639
Good Answers: 72

Power Surge, Noise and Harmonics

09/02/2009 1:32 PM

Good day to all,

Recently, our utility company allowed the line voltage to exceed 10% above nominal on a weekend for about an hour and a half. Among the damages were several servo drive units where the only problem seems to be disintegrated 100 watt shunt resistors and fuses that protected these devices. Since the equipment was in "standby" I am a little perplexed as to why the shunt resistors disintegrated (burned up in different ways but obviously involved arcing).

Secondly, I have been aware (for some time now) of switching noise on the power line that can cause transients that will pass through the power supply and into the control system. In one case, I captured a substantial wobble (about 780 Hz) on the 60 Hz line that persisted only about 6 mSec, but at a magnitude that was about 25% of the (zero to peak) line voltage.

Previously, representatives from the utility company have stated that "voltage is king" when talking about the desired waveform. This means that as long as the voltage is sinusoidal, every thing is OK. But comparing the measured waveform to an ideal sinusoidal, it becomes apparent that some 3rd harmonic distortion is really there. And about every 20 minutes (24/7) I see a spike that actually resets some of the monitoring equipment I have connected. Obviously, I need to attenuate the noise or find it's source and do something about it. But until then, I am looking for means of protection.

So, it looks like I need protection from spikes, wobbles, and over voltage issues. And I suspect a 3 phase reactor (or Ferrite beads) may help a little from transients, but I need a different V-RMS monitor to keep me within the specified ± 10% tolerance window that the utility company promises (but doesn't always deliver).

What would you address first and why?

__________________
A great troubleshooting tip...."When you eliminate the impossible, whatever remains, however improbable, must be the truth." Sir Arthur Conan Doyle
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 8378
Good Answers: 774
#1

Re: Power Surge, Noise and Harmonics

09/02/2009 2:42 PM

If it was me I would try and address the over voltage problems first. They can do the most damage the fastest. Possibly putting in simple line voltage monitoring devices that will tell the system or specific equipment to shut down and disconnect if a upper limit is reached may be all thats needed for that problem.

Second I would go after the odd line noise issues. If its coming from your own equipment its your responsibility to eliminate it. If its coming in from the utility companies side its their responsibility to find it and eliminate it or at least provide you with proper filtering. It may take a joint effort between both your business and them to correct that type of problem.

Lastly adding better surge and spike protection through out your power system is a very good idea. In this area there is no such thing as too good. The down side is its a potentially avoided cost type investment. Your spending money to prevent a 'someday it could happen and cost more than what was spent on it being installed 'situation from happening. Thats a tough sell unless there is strong proof that it has already cost money and time and shows that its likely to happen again with potentially far worse results. Do you spend $10000 and then never have a problem or do you not spend $10000 and then have a $50000 problem result from it some day later?

At least your trying to address the problem! Thats far more than most ever do!

Register to Reply Score 1 for Good Answer
2
Guru
United States - Member - New Member

Join Date: Jun 2008
Location: Alabama
Posts: 1605
Good Answers: 62
#2

Re: Power Surge, Noise and Harmonics

09/02/2009 7:33 PM

The utility is responsible for maintaining the voltage at a specified level. I my area it is 120 volts +/- 6%. Some areas may be +/- 10%. This is regulated by the state public service commission. If this is not done you need to make contact with them. You would need a recording meter to show that you are having problems. The problem in you post regarding the 1 1/2 hr over voltage could have been a stuck regulator and the utility would have not known it. However, they are still responsible.

As far as the power quality, the utility generally will deliver a sine wave without problems. Many time these spikes are the result of your equipment or others connected to the utility circuits. When you say that "I have been aware (for some time now) of switching noise on the power line that can cause transients that will pass through the power supply and into the control system." , the utility does not perform switching an a daily basis. As far as the 3rd harmonics, that will come either from your equipment or others that are close by. Suggest that you carefully eliminate all of you equipment as possible sources of these problems.

Register to Reply Good Answer (Score 2)
Member

Join Date: Jun 2009
Posts: 8
#3

Re: Power Surge, Noise and Harmonics

09/03/2009 12:02 AM

Get a UPS. The UPS will have batteries for back-up during times when the utility is down. It will also reproduce good clean voltage at all times.

Register to Reply
Guru
Popular Science - Cosmology - New Member Technical Fields - Technical Writing - New Member Engineering Fields - Energy Engineering - New Member Engineering Fields - Electrical Engineering - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Electromechanical Engineering - Old Member, New Association

Join Date: Apr 2008
Location: Lexington, KY
Posts: 1639
Good Answers: 72
#8
In reply to #3

Re: Power Surge, Noise and Harmonics

09/03/2009 4:40 PM

See comment #7 in response to comment #5

__________________
A great troubleshooting tip...."When you eliminate the impossible, whatever remains, however improbable, must be the truth." Sir Arthur Conan Doyle
Register to Reply
Commentator

Join Date: Jul 2008
Posts: 93
#4

Re: Power Surge, Noise and Harmonics

09/03/2009 8:12 AM

I have question regarding UPS:

When the utility is down and then resumed after long while and the UPS battery become flat, is it possible to connect the load to the UPS right away or we have to wait until the battery is fully charged ?

Register to Reply
Power-User

Join Date: Apr 2009
Location: USA MD
Posts: 372
Good Answers: 9
#5
In reply to #4

Re: Power Surge, Noise and Harmonics

09/03/2009 10:57 AM

This should be another forum, but quickly a good UPS will power the load and recharge the battery at the same time. Make sure you know what you are buying.

__________________
What is right is not always popular. - What is popular is not always right.
Register to Reply Off Topic (Score 4)
Guru
Popular Science - Cosmology - New Member Technical Fields - Technical Writing - New Member Engineering Fields - Energy Engineering - New Member Engineering Fields - Electrical Engineering - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Electromechanical Engineering - Old Member, New Association

Join Date: Apr 2008
Location: Lexington, KY
Posts: 1639
Good Answers: 72
#7
In reply to #5

Re: Power Surge, Noise and Harmonics

09/03/2009 4:39 PM

Why would people regard comment #4 as off topic? As to "This should be another forum", I think it is fine as a topic even though it covers a lot of ground. And U_NO_WHO is right if he (or she) means that noise and harmonics on the powerline deserves additional discussion. Next, I'm not sure that all UPS's will handle an over voltage of 10% for an hour and a half. I don't know if they all kick in when the power line is in over voltage.

In some cases, when the UPS battery goes flat, the UPS will not recover until the battery is replaced. Deep discharge is not always prevented but it should be.

And, "Make sure you know what you are buying" is exactly right. I've had more equipment salesmen lately trying to sell me stuff I didn't need or want.

So, if you accidentally voted to mark his comment as "off topic" please change you vote because I think he (or she) is dead on.

__________________
A great troubleshooting tip...."When you eliminate the impossible, whatever remains, however improbable, must be the truth." Sir Arthur Conan Doyle
Register to Reply Off Topic (Score 5)
Power-User

Join Date: Apr 2009
Location: USA MD
Posts: 372
Good Answers: 9
#12
In reply to #7

Re: Power Surge, Noise and Harmonics

09/04/2009 8:28 AM

NotUrOrdinaryJoe

Sorry, it was a bit presumptuous of me to consider zacky's question off topic because it did not answer your question and seemed (to me) to be starting a new subject. You will note I did not rate his post as off topic, because in my opinion only you or he can do that. I rated my post as off topic.

UPS back up systems, as with many products, have different designs, features and options. As a possible solution for your issue, you would need one that powers the load continuously through the inverter and the incoming power (when available) both charges (or upkeeps) the back up battery and is rectified to provide the DC input to the inverter (which is on all of the time). All of the other types (switched or line synchronized) which fire up the inverter when incoming power is lost, would not normally provide a "conditioned" AC output, unless it had overvoltage and filtering options included. What I mean to say is that just buying a cheap UPS is not going to help your problem.

You had already received adequate direction on your issue, so I did not have anything additional to offer. I hope this information helps your issue (and provides a little more insight into zacky"s question, as you are generous to allow). Again, I'm sorry if I offended, it was not intended.

__________________
What is right is not always popular. - What is popular is not always right.
Register to Reply
Member

Join Date: Jun 2009
Posts: 8
#11
In reply to #4

Re: Power Surge, Noise and Harmonics

09/03/2009 9:00 PM

If the charger is sized correctly, (to charge the batteries and power the load at the same time) then yes it can be connected right away.

But usually the UPS need to be manually started up after a low battery shutdown.

Register to Reply Off Topic (Score 5)
Power-User

Join Date: Dec 2008
Location: Anthem, AZ
Posts: 392
Good Answers: 8
#6

Re: Power Surge, Noise and Harmonics

09/03/2009 2:26 PM

You will need proof for the Utility company in order to get them to respond at all. I used to use a scope to trigger on the faults, and store the display to disk.

In order to trigger when the signal is distorted, I used a 60 Hz notch filter, which is pretty easy to make. The output of the notch went to channel 2 for triggering. If the signal was in spec, there was no trigger. As soon as any transient occurred, the notch would allow the signal through and cause a trigger. Ch1 was hooked to the MAIN, so the distortion would be captured. The scope was set up to store to hard drive on trigger, after which it would re-arm and trigger on the next fault. Time stamp on the file proved how often the faults accurred.

Register to Reply Score 1 for Good Answer
Guru

Join Date: Apr 2007
Location: Hyderabad, India
Posts: 596
Good Answers: 12
#13
In reply to #6

Re: Power Surge, Noise and Harmonics

09/05/2009 5:04 AM

I used Fluke 434 power analyzer to monitor & data logging power quality and could address the problem right way.

__________________
Subramanyam
Register to Reply
2
Guru

Join Date: Jul 2008
Location: Mallorca, Spain
Posts: 567
Good Answers: 15
#9

Re: Power Surge, Noise and Harmonics

09/03/2009 5:53 PM

Hi Joe,

Simple, cheap solution to the over-voltage problem might be to add a fast blow fuse in the line and a metal oxide varistor across the input line after the fuse to all sensitive bits of kit. Select the components as close as possible to your max acceptable voltage. All the chargers I deal with are protected this way and we regularly get units in for repair where the yacht crew have connected the boat to 400V-LL instead of 230V-LN. These two components almost invariably protect the rest of the system.

For overvoltage only just outside the window you will probably need a voltage sensing relay which you can use to trip out all of your sensitive equipment. Look at http://docs-europe.electrocomponents.com/webdocs/0242/0900766b802429c8.pdf

or any one from http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&binCount=18&Ne=4294957561&Ntt=voltage+monitor+unit&Ntk=I18NAll&Nr=AND%28avl%3auk%2csearchDiscon_uk%3aN%29&Ntx=mode%2bmatchallpartial&N=4294964102+4294954277&Nty=1

I'm sure you can find more of the same.

regards

Chas

__________________
En la casa del herrero, cuchillos de palo!
Register to Reply Good Answer (Score 2)
Guru
Hobbies - Model Rocketry - New Member

Join Date: Jun 2007
Location: East of Seattle, Washington state Republic of the 50 states of America
Posts: 2045
Good Answers: 36
#10

Re: Power Surge, Noise and Harmonics

09/03/2009 6:49 PM

If you have data that shows the power company is at fault (no pun intended) site the data in an affidavit and have put into the public record. Now send the Power Co. CFO an Affidavit listing: fault; damages; costs incurred, in positive averments, then negative averments, requesting they show proof in 30 days or less that this is not true, and a non reply is binding tacit agreement. Affidavits need a notary witness. Now send it to the CFO by registered mail.

After 30 days bill them for the costs incurred. If you filled a proper Affidavit and it goes to court use the said affidavits to request a summery judgement. This is pre judicial and lawyers are not needed so they will not tell you about it.

If the power co. is smart they will just pay the incurred costs. But you also have the option of basing a lien on the affidavits.

__________________
(Larrabee's Law) Half of everything you hear in a classroom is crap. Education is figuring out which half is which.
Register to Reply
Register to Reply 13 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

capblanc (1); kiansen (2); kvsubramanyam (1); NotUrOrdinaryJoe (2); tcmtech (1); U NO WHO (2); U V (1); wareagle (1); WoodwardDL (1); zacky (1)

Previous in Forum: Residential Energy Meters in India   Next in Forum: Required Number of Lighting Fixtures?
You might be interested in: Electrical Utility Services, Noise Standards

Advertisement