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Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 12:41 AM

In our plant, we have 10 to 15 CNC machines for critical operations, all hooked up in auto mode. Due to sudden dips in the incoming power supply, the CNC machines switch off and the auto mode stops. Then each and every machine has to be reset to its reference mode for starting the auto cycle once again.

We have checked the voltage levels near the machine and it is +/- 3% of the rated value, earthing good, neutral to earth voltage = less than 2 Volts, voltage harmonics less than 2 % and every parameter within limits.

What would be best options to over come this phenomenon. It would be better to avoid the conventional solution of online UPS system.

Request the opinions of the domain experts.

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#1

Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/12/2015 1:35 AM

First you need to monitor the voltage supply and record frequency and length of power anomalies, creating a profile used to determine what size of system is needed...a voltage dip proof inverter system might be the way to go...

http://www.electricenergyonline.com/show_article.php?mag=11&article=81

http://www.measurlogic.com/PowerQuality/VoltageSagSupport/dpi-voltagedippr.html

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#2

Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/12/2015 1:52 AM

+/- 3% of the rated value ?

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#3

Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/12/2015 2:55 AM

Find and fix the loose wire? (It may not be that simple, but nothing mentioned so far really says otherwise.)

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#4
In reply to #3

Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/12/2015 3:25 AM

All the options have been tried out. The voltage variation at the equipment end is within +/- 2 % by means of On Load Tap Changer installed. No loose connections - each and every connections have been tightened.

Even harmonics level also has been checked and found to be within limits. Pursued with Power Supply authorities for necessary correction - which is impossible for them.

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#14
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Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/12/2015 4:00 PM

<...Al the options have been tried out...>

Either that statement is false, or the basis of listing the query on CR4 here is folly. Which is it, please?

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#20
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Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/13/2015 6:34 AM

LOL & True!!

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#5

Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/12/2015 3:56 AM

You say it's due to sudden dips in the incoming power...

Do you know this as a fact?

Could it be due to incoming spikes or noise rather than actual dips.

You need to get some sort of monitor/recorder on the line to find out what is actually causing the problem.

Del

Disclaimer:- Not my field of expertise

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#6
In reply to #5

Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/12/2015 4:06 AM

We have studied this phenomenon and found out that it is only the dips in the voltage. The nominal value of incoming voltage at the machine is 420 Volts 50 Hz AC.

It is not spikes. For the spikes, we have already provided surge suppressors in each of the machine.

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#22
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Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/13/2015 6:47 AM

I wonder if its due to the CNC machines themselves, possibly due to poor power supply design, overstressed power supplies, assuming that the mains wiring is not the problem for the moment.

You also neglected to mention just how the mains is laid, the size of the wiring, the positions of the CNC machines, the average, the min and max power needed for each machine....and and and.....

You also ought to log just how many machines were running when each interruption happens as well......

If say 50 % or less running = no problems, then there is a probable design problem with power or power supplies....

But it could still be the mains provider. So a second voltage monitor needs also to be at the first junction box as well, not just the final one = two mains voltage monitors working in parallel.

The reason being that a further big motor or similar may be starting and stopping somewhere near to you, causing dips in the supplied mains voltage....

You have a lot of work to do!!

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#21
In reply to #5

Re: Sudden Voltage dips in the power supply system affecting CNC machines

05/13/2015 6:36 AM

EXACTLY RIGHT!!!

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#7

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 8:19 AM

"sudden dips in the incoming power supply" ?

What are you using to monitor your incoming power? Accuracy, sample rate, transients, waveform capture, etc? Does it retail for less than USD$500?

Will it identify a degree of confidence for a determination of source direction of power quality problems?

Is your power monitor permanently installed and can give you useful information history when symptoms occur (under load)?

What else is going on when it trips?

What are the details on the transformer, the feeders, the connections, and the total voltage drop (under load)?

Is "critical operations" about making a profit, but your facility has not invested in the proper infrastructure?

I know, too many questions.... but the right information is often the best option.

Did you try a UPS on the control power for one machine and see if that helps?

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#8

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 8:23 AM

You reference a variation of +/- 3%. Then say dips in in the voltage supply. How great are these dips?

My take on what little information you have supplied is the utility company is poorly pressed to maintain a stable supply voltage do to reasons unknown. That the safety features of the motor controllers on these CNC shut down on low voltage. Which is a hiderance to production.

I would first make some determination on what the value of this lost production time is worth. Would weigh the loss to setting up to provide my own power. Which you then control. Which the excess power can be sold back to the utility company.

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#9

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 8:47 AM

Hello Kandi:

This thing simulates a "super-whole-lot-a-KVA" power source, if three phases are needed, buy tandem or stackable variacs, be careful to order the correctly rated variacs.

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#10
In reply to #9

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 8:49 AM

Of course, it compensates HUGE voltage variations.

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#19
In reply to #9

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/13/2015 6:03 AM

Old faithful autovolt transformer.

Available in 3 phase ready to go straight out of the box here, no need to stack.

Problem with these is the speed at which the servo motors react in either direction. If you have a dip and the servo winds the o/p voltage up it could be too slow and when the dip recovers you can have an overvoltge o/p until it winds back till normality is reached. They hunt a bit too. OK for motors only really.

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#11

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 9:58 AM

I suggest you first identify the root-cause of the unstable voltage.

If the issue is in the incoming power and you cannot get the supplier to correct the issue, consider installing a constant voltage transformer on each piece of equipment.

There are several high quality constant voltage transformer available in the market.

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#12

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 2:46 PM

Quote GP Kadni "Due to sudden dips in the incoming power supply, the CNC machines switch off and the auto mode stops."

How long does the voltage dip last? Do the motor contactors drop out due to low voltage? Does this happen more that once per day?

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#13

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 3:00 PM

Assuming that there really are voltage dips, ferro resonant transformer technology is old but it works.

It also eats up harmonics.

http://www.solahevidutysales.com/power_conditioning.htm

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#17
In reply to #13

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 9:04 PM

We still use Sola Hevi-duty FR transformers on instrumentation panels for surge, droop and harmonic protection.

They do generate heat (harmonics are burned off as heat) so we mount on the outside of the panel for air cooling.

And they need to be oversized if there are power loads because a ferro resonant clips peak currents so need extra capacity to make up for the clipping.

But they do clean up 3rd world electrical power.

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#26
In reply to #13

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/14/2015 11:39 AM

This will be one of the more easily implemented options, and has >95% chance of solving the entire problem. I suspect that (1) the building was laid out with X amount of usable current draw/power/power factor from the MCC to the machinery.

(2) Owner could expand, and did so by adding machinery, and not adding/upgrading the MCC.

(3)Owing to this marginally over-loaded MCC (just below the trip points), with all machines running, just one more motor start somewhere in the same facility or even next plant over results in this dipping in voltage (large shift in power factor of local supply).

this is probably the 5% reason the above might actually not work, but do indeed try it.

Disclaimer: I am not an electrical engineer, but if you hire one, you will find out, I am pretty near the right answer.

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#15

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 4:26 PM

More than likely it's your LTC. I sense that you have not correlated the trips to its operation, but I suspect that one of the contacts is burnt and/or arcing when it operates, especially if it does so when it switches all that inductive load. That's a lot of electrical noise and your control systems don't like it.

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#16
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Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 8:35 PM
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#18

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/12/2015 11:24 PM

13.5

This is a burning problem on the Indian sub continent to which many in the developed world may not relate. At least one reader has referred to it as " 3rd world " power, albeit disdainfully. Many industries for whom quality power is a critical input, are forced to run captive power plants or generators.

A huge market is waiting to be tapped with cost effective and reliable solutions.

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#30
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Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/16/2015 8:28 AM

This is a major problem in South Africa at the moment. The government expanded the supply to any body near enough to have a wire connected to the supply lines without considering the load capacity of the Lines, Transformers, Sub stations and generating power stations. Suddenly found them self running even emergency capacity to the brim, cables and transformers blowing up and Generators shutting down. No service and upgrade and repair time. All SA Factories, refineries, mines, every industry to have at least 3 to 6 hour Load shedding per week at any unexpected time. In the middle of production, the private households are switched of supposedly according to a supposed schedule for 2x 3 hours a day, in the middle of making supper, no time is inconvenient to the powers to be. you can plan nothing because the schedule is just a passifying piece of paper, fridges defrost, Alarm systems run out of battery life. Labour unrest has already added 5 years to the completion of the Madupi power station, with only 1 of planed 16 Generators on line after 10 years of construction. Put this in your pipe and smoke it.

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#31
In reply to #30

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/17/2015 1:07 AM

Yo don't state your locale but sounds like you may be in SA and living through this situation.

People get used to inconvenience that's out of their control. They adapt.

Sounds like a great place to be in the backup (primary?) genset, UPS and ATS business.

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#23

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/13/2015 9:37 AM

How about a flywheel?

http://www.power-thru.com/index.html

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#25
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Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/14/2015 12:34 AM

Every genset has a flywheel.

I was going to suggest that the OP use a local DG if the utility supply is so dodgy. Diesel is cheap now.

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#24

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/13/2015 4:34 PM

G P, you work in the factory, do you have 10 or do you have 15 machines. How many run in the auto mode. What is the incoming Voltage from the supplier, at the load you suggest it must be HV supply of 6,8kV and you must have an Transformer instalation with tappings to correct the secondary side Voltage. You need to get contractor with the correct qualifications to investigate your HV supply, the Transformer connections and the LV side before you can fault find your problem. What is the rated and supply voltages to the CNC's. Did you investigate the posibility that one of the machines do not cause a shutdown of the Auto sycle because of a fault. You need to answer all these questions to get advice and I think you are out of your save depth. Get professional help. Even 5% in a sound instalation will not cause a shutdown. Find out if there are other clients with heavy machinery on the supply line to your factory from the utility company.

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#27

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/14/2015 2:17 PM

Bud and Carl I was going to suggest the same thing. But until the poster gets off his butt and answers some questions I can't.

G P Kadni answer the questions or don't post here.

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#28

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/15/2015 3:16 PM

Are you in an industrial development? Other factories may have a large demand starting at different times that will momentarily cause your supply to degrade enough to cause your problem.

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#29

Re: Sudden Voltage Dips In The Power Supply System Affecting CNC Machines

05/15/2015 8:07 PM

You are describing a growing problem. Countries where power supply and distribution systems are aging at the same time as demand on them is skyrocketing at getting the worst of it. Then at the same time, equipment is getting more and more electronic and sensitive to voltage sags.

There is / was a company called Soft Switch Technologies (SST) that makes a product called a DySC system, which is a sag ride-through device. It's not a ferroresonant transformer or anything like that, it is a technology that's hard to describe, but works very very well. I had a lot of clients in the tech industry a few years ago who are VERY sensitive to voltage sags, and they are very happy with the performance of these devices. You can buy large units for the entire plant, or smaller units distributed for individual machines or groups of machines that are critical. They ride through sags of about a 5 second duration at best, so you had better identify the problem is greater detail with recording devices before spending any money.

A quick look for it on Google turns up that the company was bought by Rockwell Automation (Allen Bradley) a few years ago. That's hilarious to me because I work for them, didn't even know...

http://ab.rockwellautomation.com/Power-Supplies/Voltage-Sag-Protector

Side note because I used to work for Sola years ago. I'm frankly quite surprised that people are still using ferroresonant transformers for electronics. Yes, they ride through sags and "take care of" harmonics by burning them off as heat, but the down side is that they flat-top the sine wave themselves, and current limit. So anything that needs to draw current in high peaks can be adversely affected by a ferro. Things that draw current like that: VFDs, servo amplifiers and anything with a Switch Mode Power Supply, which comprise just about everything electronic now. Ferros were fine when we all used linear power supplies, but those days are gone. You can compensate by grossly over sizing them, in which case it gets to be about 60% efficient. That's why people have moved away from them.

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