PLC Voltage Regulator

Good day!..

i would like to ask if adding a voltage regulator in plc can prevent current surges??


thank you

What do you mean by current surges?

Are you talking about putting something like a constant voltage transformer or pure-sine UPS system in front of the PLC power supply?

its like.. " everytime were having brown out.. the components of the machine will be damaged due to current surges".. so were planning to put a voltage regulator in the supply of the plc to prevent the IO card to damage..is it ok??..we dont have UPS in the machine..

We normally use UPS for our PLC's CPU and surge protection for the whole cabinet.

rj061991 said:

its like.. " everytime were having brown out.. the components of the machine will be damaged due to current surges".. so were planning to put a voltage regulator in the supply of the plc to prevent the IO card to damage..is it ok??..we dont have UPS in the machine..

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It's fine. Use a high quality UPS that doesn't switch from line to battery... It must always be running off of the inverter.

veristors are normally used in main supply to prevent surges

ive ask some automation engineers about this matter and they told me that i should used surge supressor... we used to replaced the damaged IO card frequently and its very expensive.. by the way im using siemens s7 300 plc..

I use line suppression as a standard on the power to the entire control system, Phoenix Contacts, Sola. and many other options for line suppression after the Control transformer, I really don't see another option unless you want to UPS the PLC power supply but that won't help the I/O from getting a surge on the Control Power. And truthfully (knock on wood) my customers don't have surge issues in the panels..

the machine have 3 induction motors controlled by VFD nd PLC, and 5 solenoids...we use siemens s7 300 input module, output module, output relay module, and analog module to give signal to the VFD..the voltage regulator we used is from 440 to 24vdc.... we dont have UPS in our system just a voltage regulator.we have not use fused terminal block.. Last month one of our input module has been damage.. so we replace it with a new one.. after 2 weeks of operation, the output relay module has been damage so we replace a new..And finally this week, one of the induction motor don't reverse...so what im thinking now is that the analog module has been damage...I think its all about surge problem..I hope my manager will listen this time to my recommendation...haha

rdrast said:

It's fine. Use a high quality UPS that doesn't switch from line to battery... It must always be running off of the inverter.

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+1 for this.

I had a GE 90/70 in a cement plant which was attached to a low-cost UPS.
Every time a crusher started, the UPS switched over, and, when it did, the PLC went into halt mode.
Changed out the UPS with an ON-LINE model, and all was well.

ect_09 said:

veristors are normally used in main supply to prevent surges

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Varistors and MOV's are passive devices that burn out. They are fine for occasional spikes, but will fail for any longer duration over voltage condition. They also can't adsorb a lot of energy, so if you get a 150% surge for a few seconds, consider those devices fried.

They also do nothing to "Prevent" surges, they simply try to clip them to a manageable level, which can still be over the rating of attached devices.

rj061991 said:

the machine have 3 induction motors controlled by VFD nd PLC, and 5 solenoids...we use siemens s7 300 input module, output module, output relay module, and analog module to give signal to the VFD..the voltage regulator we used is from 440 to 24vdc.... we dont have UPS in our system just a voltage regulator.we have not use fused terminal block.. Last month one of our input module has been damage.. so we replace it with a new one.. after 2 weeks of operation, the output relay module has been damage so we replace a new..And finally this week, one of the induction motor don't reverse...so what im thinking now is that the analog module has been damage...I think its all about surge problem..I hope my manager will listen this time to my recommendation...haha

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That all doesn't necessarily mean a surge on the supply side, especially as you have a SMPS in there. You might try getting an isolation transformer before the SMPS, or even putting in a 440 to 110VAC transformer, then feeding a 110 to 24VDC supply, but it sounds more like your problem is from switching transients on the output.

Just guessing on this isn't going to help much, can you get any instrumentation on the supplies to the input/output modules? Preferably a datalogger? Even decent multimeters have long term loggers or peak-hold features. Leave one hooked up for 24 hours.

rj061991 said:

its like.. " everytime were having brown out.. the components of the machine will be damaged due to current surges"..

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So many things are wrong with that answer.

First, a surge is a massive current increase. A brownout is a voltage reduction. The two are not related.

Second, voltage can drop so low that incandescent bulbs dim to 50% intensity. Even voltage that low is perfectly normal for any properly designed electronics. That is what a power supply is for - rock solid DC voltages are output over a widely varying AC voltage range. Some appliances so no DC voltage changes on any AC voltage from 85 to 265 volts.

Why would anyone worry about brownouts? Because brownouts are harmful to motorized appliances. So a utility cuts off power if it cannot maintain sufficient voltage - to protect motorized appliances.

Third, what does a surge protector do? Read numbers on its box. A let-through voltage of 330 volts means it does absolutely nothing until voltage on 120 VAC mains well exceeds 330 volts. What does that do for a brownout? Absolutely nothing.

Fourth, you are observing damage, then wildly speculating as to why. IOW all conclusions are not based in perspective (ie numbers) - that must exist to have a useful answer.

Fifth, if surges are doing damage, well, destructive surges occur maybe once every seven years. If you are having surges more often, then tiny surges (that don't cause damage) probably exist daily. IOW identify the defect long before curing its symptoms.

I do not see any damage that justifies your conclusions. To say more is why, for example, you should have installed power monitors (datalogger) long ago. Meanwhile a regulator on 440 volts must withstand thousands of volts without damage. More likely, failure is due to something completely different.

Sixth, surge protector: a typically destructive surge is hundreds of thousands of joules. How many joules does an adjacent protector absorb? Hundreds? Thousand? Did that automation engineer also provide numbers to justify his recommendation? No numbers is a first reason know someone is only reciting hearsay. A completely different solution - also called a protector - means you can say where hundreds of thousands of joules harmlessly dissipate. This solution is routine in any facility that cannot have damage - as was true even 100 years ago. And located to make the all so critical 'less than 10 foot' connection to single point earth ground.

But again, that does nothing for brownouts. That is only a solution for one unique anomaly. Nothing (no numbers) has been posted to even identify which anomaly is relevant.

rj061991,

You have two problems that I see, so lets separate them.

#1 brownouts have two parts: the voltage sag and the voltage recovery.

Voltage suppressors work in reducing the damage caused by the recovery part of the brownout. I learned this first hand from an industrial plant 2 hours from work. Two times in a week the plc lost its program in a brownout. Ab told me that this happens when the processor realizes the power requirements are to low and starts to do a shutdown. In the middle of the shutdown the power comes back and the processor tries to power back up during the shutdown and also deal with the power spike.

This is when we installed a corcom filter in and the plc has not lost a program since. It may shut down as if the power was lost, but it no longer looses the program. Voltage suppressors are now a standard on all equipment I design or buy.

You can install a constant voltage transformer which is what I recommend or install a true sine wave UPS. My sister plant uses siemens plc's and regular ups units didn't work.

#2 VFD drives.
Vfd's at 440 volts have certain requirements When the distance from the drive to the motor starts to reach 50 ft. (going from memory), line and load filters must be used to prevent the drive from creating a counter voltage. This counter voltage can be 4 or 5 times the input voltage of the drive. If you don't have these filters, the I/o cards and devices connected to the drives may be damaged or destroyed.

regards,
james

James Mcquade said:

rj061991,
#1 brownouts have two parts: the voltage sag and the voltage recovery.

Voltage suppressors work in reducing the damage caused by the recovery part of the brownout. I learned this first hand from an industrial plant 2 hours from work. Two times in a week the plc lost its program in a brownout.

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First, low voltage never damages electronics. All properly designed PLCs include voltage monitors. Voltage is perfectly fine even when so low that incandescent bulbs dim to 50% intensity. If voltage is lower, that monitor simply powers off a PLC - no damage. If that monitor does a power off, then it also delays a power on. Only assumed is an anomaly that also must not hamper any properly designed PLC. More likely, the anomaly is something completely different.

Sudden power recovery in properly designed PCs causes its power controller to initiate a safety lockout. That safety lockout must be cleared by disconnecting its power cord. PLCs use a more complex solution required for real time hardware. Then a PLC can recover on its own without manual intervention. Recover from a hardware safety lockout.

Second, recovery from a brownout does not create over 330 volts on 120 volt mains. A voltage suppressor (ie protector) does nothing until voltage well exceeds 330 volts. Meanwhile international design standards (before IBM PCs existed) required electronics to withstand up to 600 volt transients without damage. Today's properly designed computers and PLCs are even more robust. Why assume a brownout causes well over 330 volt spikes? Then declare that as a fact?

Third, a Corcom filter (or equivalent line filter) must be a standard feature in every computer and PLC. Why install what should already be inside every PLC? That filter does nothing for voltage variations. That filter is for a completely different anomaly called noise.

By making a conclusion only from observation, then speculation said a brownout can be cured by a protector. And that voltage variation is solved by an AC line filter. IOW conclusions only from observation; by not first learning how stuff works, what it does, and what the actual anomaly is.

Fourth, view an output from a pure sine wave 120 volt UPS in battery backup mode. 200 volt square waves with spikes of up to 270 volts. Why is that perfectly good power for computers and PLCs? Defined above are volt numbers that every computer and PLC must withstand without damage.

Meanwhile that is also a pure sine wave UPS. Since square waves and spikes are nothing more than a sum of pure sine waves. Because 'pure sine wave' is only a subjective term often used to manipulate naive consumers. A 'pure sine wave' UPS that is really clean will provide numbers that define it - such as %THD. Why were such numbers not posted? What is the %THD for each UPS? Above are numbers for a 'pure sine wave' UPS that is als some of the 'dirtiest' power in the building. And not problematic for properly designed electronics.

Yes something did correct a problem. Probably cured symptoms. In each case, the anomaly is only defined by speculation - not by facts and numbers. Many solutions do not even claim to solve that suspected anomaly. Too many conclusions only from observation - and not by first defining the problem and defining what each solution actually does.