HELP 3 phase supply keeps interchanging

[SAks]

PLZ HELP!3 phase supply keeps interchanging

Hey friends,

The power supplying company at my place keeps changing the phases on daily basis and this has caused a nuisance..

In my country the colour coding is "Red-Yellow-Blue"

I have to change the Main supply wired to "Blue-Yellow-Red" then again to "R-Y-B" the other day, until then the pumps i run keep tripping..

Is there a solution for this?? cause all my complaints to the power supplying department go in vain..

Please advise.

 

[dlgoff]

Changing (reversing) two phases supplying a three phase motor will change the direction of rotation. Is this what you mean by "the pumps keep tripping"? If they are indeed tripping out, I would suspect some other problem.

Welcome to Physics Forums

 

[SAks]

Changing (reversing) two phases supplying a three phase motor will change the direction of rotation. Is this what you mean by "the pumps keep tripping"? If they are indeed tripping out, I would suspect some other problem.

Welcome to Physics Forums

Yes, phase reversal is being done by the electricity provider itself(somewhere at power station or substation). This is the only problem cause i got the pumps checked out by the manufacturer and they say there aint anything wrong with pump or the starter panel..

I did inquire at my neighbor's and even they are facing the same problem.. whenever there is a phase reversal, i manually re-reverse the supply wires at the circuit breaker..

Is there any device which can detect the phase and rectify the phase reversal??

thanks for replyin..:]

 

[dlgoff]

Not that I am aware of. Sorry.

 

[Marquis]

Well theoretically there should be a way to make such a device right?
I'm not an engineer or anything but I'd imagine you could build some system with a small 9 volt toy motor connected to the netflow with a regulator and a switch or something which once hit will change cables or something. If you place the 2 cables close and the make a sort of trainrail switch alike mechanism for the cables (perhaps even use that part of a toy train set) I'd say all in total i'd cost you about 20 euro in my country if you shop smart.

If the motor starts turning to one direction he flips the switch to that direction (and if he starts turning to the other direction he flips ther switch to the other direction), switch activates toy rails which make the cables be reversed. You'll only have a short electricity fade of like 1-2sec on the pumps. If we're speaking about large pumps just use larger rail alike thing to reverse cable connection.

So if I can describe a way to make this I'm sure some real engineer has made something like that, I've found the rails alike switch thing think http://www.patentstorm.us/patents/4396811/description.html

 

[MThornton]

I run a small electrical utility, and can offer some insight

It is common to build distribution systems with some degree of redundancy. In this business, this is commonly done by building a series of distribution loops. This topology allows maintenance to be performed (via switching) with minimum overall disruption to continuity of service. The loops usually never completely close... there is always an open point for each loop. This approach allows for the circuit protection to operate correctly.

It is likely that your electric utility does not have all elements their distribution system in your neighborhood identically phased. This is not uncommon in areas where the majority of customers are residential, and thus mostly 1-ph. However, in industrial, commercial or agricultural areas, the utility will take careful measures to ensure identical phasing throughout their system. If you are a lonely 3-ph customer in a mostly residential area, then you are S.O.L.

Quick-fix :
Any VFD drive does not care what the incoming electricity phase sequence is. And you select the phase sequence out (remains unchanging regardless of ph-seq input). VFD drives are pretty cheap and easy for any electrician to install. Side-benefit is you get good speed control & your power factor may improve. Good for shop tools, blowers, pumps. Not good for high-starting-torque loads though.
Examples: http://www.automationdirect.com/adc/Shopping/Catalog/Drives"

Read the small print in your utility tariff. There may be a section on minimum performance standards that includes constant phase-rotation. Based on that... you will have some leverage. If not... then they have all the power... that you want... once again S.O.L.

Imagine a city down-town where this happens... none of the elevators would work 1/2 of the time.

BTW, in an area with older switching equipment (no phase sequence ID aid)... the solution to this problem may NOT be a quick & easy fix. The solution will take time to identify analyze & fix. Some modern switchgear (S&C Vista) does include this, making the job easy.

And no, I don't work for either Automation Direct or S&C

M

 

[SAks]

@Marquis

Yes, quite a good idea.. even i did think of cobbling such a thing using a servo.. but I am speaking of solid 20 Amperes of load at 440 volts.. things can go wrong with such a non-professional, homemade stuff which can potentially blow up everything in vicinity..

@Mthoronton

there are only 4 overhead transmission lines running in my area.. no redundancy:(:( and yes there r only a few 3-ph customers in my area. They all are manually unscrew the wires and put it in correct order daily..

as far as VFD is concerned, looks worth installing 1..

Thank you all :):)

 

[MThornton]

transmission and distribution mean different things.

Transmission generally involves higher voltages >= 69kV, sub-station to sub-station & over long distances. Phase sequencing errors very unlikely.

Distribution brings the electricity from the nearest substation, down every street & back alley to the transformer that feeds your building. Typically much lower primary voltage (ie 24,940/14,400V) than transmission.

Any mistakes in phase-sequencing from routine switching will likely be at the local substation & affect the distribution level, or else within the local distribution network.

 

[russ_watters]

Adding a variable frequency drive would be helpful. I'm not sure if they recognize and automatically correct for phasing changes (frankly, I'm not even sure how what you suggest would be possible, but that's a different issue...), but at least you can reverse the motors with the press of a button.

 

[MThornton]

VFD drives consist of 3 parts in series
1) a charge rectifier (moderately simple)
2) a DC capacitor bank (very simple)
3) Converter section : a transistor bridge array that converts the capacitor bank DC charge, into 3-phase AC (complex)

The charge rectifier does not care what the phase sequence applied to it is. It is irrelevant to the output of the converter. Some small VFDs simply use a 3-ph full-wave bridge diode rectifier... others use a controlled SCR rectifier.

The Converter section works off of the DC energy stored in the capacitor bank. The output phase-sequence is simply what is entered in the set-up parameters. It is whatever you want it to be, and will not change unless you specify.

 

[SAks]

"http://www.automationdirect.com/adc/Shopping/Catalog/Drives" is this the only place where i can find VFDs?? do you any other companies selling them, such as Hager..

 

[dlgoff]

http://www.ab.com/drives/"

 

[MThornton]

Here are a few more makes.
http://www.ctdrives.com/products/ac_drives.aspx"
http://www.abb.com/product/us/9AAC100211.aspx"
http://www.us.telemecanique.com/products/motor_control/Adjustable_Frequency_Drives/Index.html"
http://www.eaton.com/EatonCom/Marke...rControl/AdjustableFrequencyDrives/index.htm"

There is a lot to chew on here, and a huge price range.
Obviously a plant where a drive-failure results in downtime costing many $thousands/hour, then you will go with an engineered solution from a high integrity mfr. like ABB.
But, if I were a guy running a machine-shop in my garage, I'd just buy cheap one from AD & get an electrician buddy to hook it up.