60Hz vs 50Hz shock

[mbrooke]

In no way am I advocating working live, but at one plant in town there are multiple motor generator sets that spit out 50hz for import tools. The output at 120 volts seems to 'freeze' your muscles more than at 60 hz, at least it feels that way. Which has got me wondering, is any one frequency more dangerous than the other? And yes, even at 120 volts working live is a bad idea, so don't do it. Just trust me on that:rant::lol:

 

[charlie b]

Higher frequencies tend to ride along the outside of the conductor (in this case, skin). Lower frequencies (including DC) tend to run deeper. But that would only make a significant difference when the choices are 60 and 400, not so much between 50 and 60. I have heard it said that 60 HZ is a close match to the frequency at which nerve cells and heart beats operate, which would indicate that 60 HZ is the more dangerous. But here again, I doubt that the difference is that significant.

 

[meternerd]

I would guess the lower the freq, the closer to DC, and I can tell you from personal experience that 125 VDC hurts a LOT more than AC. Must be because your muscles stay contracted. Most substation control voltage is 125 DC and it's everywhere behind the switchboards. Accidents happen. You have to work it hot because shutting it down means an unprotected sub, and switching the sub offline is not practical. Gloves reduce your dexterity too much for delicate work. That all sounds like excuses, but that's the real world I used to live in. Retirement is GOOOOOD!

 

[mbrooke]

I would guess the lower the freq, the closer to DC, and I can tell you from personal experience that 125 VDC hurts a LOT more than AC. Must be because your muscles stay contracted. Most substation control voltage is 125 DC and it's everywhere behind the switchboards. Accidents happen. You have to work it hot because shutting it down means an unprotected sub, and switching the sub offline is not practical. Gloves reduce your dexterity too much for delicate work. That all sounds like excuses, but that's the real world I used to live in. Retirement is GOOOOOD!

:lol: Reality is like that. Sometimes you have to work hot

DC makes your muscles sharply contract, which get really sore after words, that's for sure. AC is more like pins and needles that goes away after the shock.

 

[iceworm]

I ...You have to work it hot because shutting it down means an unprotected sub, and switching the sub offline is not practical. ...That all sounds like excuses, but that's the real world I used to live in.

:lol: Reality is like that. Sometimes you have to work hot ...

I don't agree. I'll say sometimes you (that's "all y'all" in general, not pointed at "you" personally) choose to work it hot. Mostly cause you want the money. And yes, it is practical to shut it down - it is just money. But your grandfather did it, you do it, and so will your kids - cause that is the way it has always been done - and none of you are wimps.

And, human life does have a price. It's disgusting, I don't like it, but it does. Here is an example: Live Line Bare Handed transmission line work. The only thing that drives that is money.

I'm not immune. I don't do live line work - but that is only because it was never offered. If it had been - I'd go for the money. Plenty of times I've put on hot gloves and sunglasses and had at it.

I finally got old enough to realize that it is choice, and the reasoning for doing it hot are just excuses. I'm not saying I won't still do it, I'm just not kidding myself - it's for the money..

According to one contractor I worked for, "Contractors are no different than anyone else. If the customer has money - we generally have time." He actually phrased it a bit different that that. This is the bowdlerized version - and close enough.

And no, I'm not concerned about troubleshooting 120V, (AC, DC, 50 or 60, or 400Hz), or disconnecting battery banks. Tight fitting rubber insulating gloves, electric shoes, safety glasses, and insulated tools work well for those.

Just an opinion - no authority here

ice

 

[starbolin]

... Which has got me wondering, is any one frequency more dangerous than the other? ...

A hundred years ago they used to argue such things. Both will kill you just as fast.

I've been bit by an ungrounded 1200 volt transformer. Very lucky for me there was no return path. Not proud of that. Working on old radios we used to get bit by the 90-300V DC grids all the time. Always one hand in pocket remember! Were really just getting leakage current through our pants our our shoes. Really hurt if your palm brushed the chassis. I've has my hands across two grounded chassis radios once or twice. Don't wish to ever repeat that. Working with HF 20KV is when I first learned that concrete is actually a very nice conductor!

Problem is, take two people the same age and the same body size and put a voltage across them. Say 60V to 90V. One might not hardly feel anything at all while the other will be dead before he hits the ground. No way to know.

Should add that, after seeing the arc-flash videos, I've swore off working on live panels.

 

[fmtjfw]

I would guess the lower the freq, the closer to DC, and I can tell you from personal experience that 125 VDC hurts a LOT more than AC. Must be because your muscles stay contracted. Most substation control voltage is 125 DC and it's everywhere behind the switchboards. Accidents happen. You have to work it hot because shutting it down means an unprotected sub, and switching the sub offline is not practical. Gloves reduce your dexterity too much for delicate work. That all sounds like excuses, but that's the real world I used to live in. Retirement is GOOOOOD!

I've found that 500 or 1000V gloves and goatskin gloves not to be much of a problem in handling small objects. What were the problems you had?

 

[Jraef]

Do you know for sure they are M-G sets being used to change the frequency, or is someone just telling you that? Because it almost sounds like the output is PWM from an inverter. AC from a PWM source only looks like AC when feeding an inductive load or when heavily filtered, but is really DC pulses at extremely high carrier frequencies. So although the measured RMS voltage will look like AC at your 50Hz requirement, the effect it has on human contact is not the same, we are not inductive loads nor do we make very good filters.

Even if they are M-G sets, if the machine is critical enough yo have to worry about the frequency difference, they might be feeding the 50Hz through a UPS. It likely would have been easier to get a double conversion UPS that could change the frequency, they make those, but often times people don't ask the right questions or to the right people and end up with some kluge job like that.

 

[mbrooke]

Do you know for sure they are M-G sets being used to change the frequency, or is someone just telling you that? Because it almost sounds like the output is PWM from an inverter. AC from a PWM source only looks like AC when feeding an inductive load or when heavily filtered, but is really DC pulses at extremely high carrier frequencies. So although the measured RMS voltage will look like AC at your 50Hz requirement, the effect it has on human contact is not the same, we are not inductive loads nor do we make very good filters.

Even if they are M-G sets, if the machine is critical enough yo have to worry about the frequency difference, they might be feeding the 50Hz through a UPS. It likely would have been easier to get a double conversion UPS that could change the frequency, they make those, but often times people don't ask the right questions or to the right people and end up with some kluge job like that.

They look like MGs, motor-shaft-generator and produce 3 phase 50Hz output. Units have I believe a gear box because changing the poles alone wont get the right ratio.

 

[iceworm]

one plant in town there are multiple motor generator sets that spit out 50hz for import tools.

Alright - I like it. I've always wanted to build a 12 pole synchronus motor driving a 10 pole alternator. Good clean sine waves and none of this wimpy semi-conductor stuff to repair every time there is the least bit of a spike.

 

[GoldDigger]

Alright - I like it. I've always wanted to build a 12 pole synchronus motor driving a 10 pole alternator. Good clean sine waves and none of this wimpy semi-conductor stuff to repair every time there is the least bit of a spike.

Not to mention a really robust surge capacity from flywheel effect.
(There was a maker of wind turbines who famously rated their output for a particular wind speed as "peak" instantaneous output, admitting if you pressed him that if you kept that load on for any length of time the turbine would slow down.)

 

[iceworm]

Not to mention a really robust surge capacity from flywheel effect. ...

Nah. It's a synchronus motor, can't load it to more than a 90 degree power angle or it will pull out - can't slow it down. But since I've never seen one or ever even heard of one, this is only built in dreamland. We get to pick any specs we want.:roll:

I suspect the ones described by mb have a gear box to make up for the slip of an induction motor driver as well as to make up the 5/6 speed reduction - but I don't know that.

ice

 

[GoldDigger]

I suspect the ones described by mb have a gear box to make up for the slip of an induction motor driver as well as to make up the 5/6 speed reduction - but I don't know that.

Or else they deliver 50Hz +0/-3%

 

[iceworm]

Or else they deliver 50Hz +0/-3%

Yes, they could use a .83 underdrive and get 50Hz +0/-3%

Or, they could use a .86 underdrive and get 50Hz +1.5%/-1.5%

I''ll let you pick out the one that is better. :roll:

ice

 

[meternerd]

[I've found that 500 or 1000V gloves and goatskin gloves not to be much of a problem in handling small objects. What were the problems you had?]


[And yes, it is practical to shut it down - it is just money.]

I don't disagree that sometimes money is involved, but in my world, troubleshooting substation trips requires that inputs from CT's, relay inputs/outputs, breaker status, etc. be analyzed that are not available if the station is off line. Thus, you need an energized sub to determine what possible problems you have that may be related to wiring, settings, transformer inputs, etc. that may have contributed to the station trip. A utility tries to provide safe and reliable power. If a sub trips off for no apparent reason, you have to dig into every part of the protection system to determine the cause. As a relay tech, it's my job to try to determine if a problem exists that can be corrected to prevent further trips. The only way to do that is to analyze inputs from all of the sensing devices. That requires an energized, on-line sub. Kinda like trying to figure out why your car idles rough without starting the engine. Can't be done. Of course, all safety precautions that are practical are used, but sometimes you just can't do the job and follow all of the rules. When working hot 480V in our pump stations, a full Class 3 flash suit is often required. That includes 20,000 KV (primary) rubber gloves. Good luck trying to lift wires or install jumpers in a control circuit while wearing those...not to mention the hood, which fogs up the minute you put it on. Nobody wants to be a hero, but if I don't fix it, somebody else will have to. Just my opinion, though. Do what you want.

 

[mbrooke]

Nah. It's a synchronus motor, can't load it to more than a 90 degree power angle or it will pull out - can't slow it down. But since I've never seen one or ever even heard of one, this is only built in dreamland. We get to pick any specs we want.:roll:

I suspect the ones described by mb have a gear box to make up for the slip of an induction motor driver as well as to make up the 5/6 speed reduction - but I don't know that.

ice

They do See post #9. They are beautiful machines, noisy, but put out a real sine wave

 

[fmtjfw]

[I've found that 500 or 1000V gloves and goatskin gloves not to be much of a problem in handling small objects. What were the problems you had?]


[And yes, it is practical to shut it down - it is just money.]

I don't disagree that sometimes money is involved, but in my world, troubleshooting substation trips requires that inputs from CT's, relay inputs/outputs, breaker status, etc. be analyzed that are not available if the station is off line. Thus, you need an energized sub to determine what possible problems you have that may be related to wiring, settings, transformer inputs, etc. that may have contributed to the station trip. A utility tries to provide safe and reliable power. If a sub trips off for no apparent reason, you have to dig into every part of the protection system to determine the cause. As a relay tech, it's my job to try to determine if a problem exists that can be corrected to prevent further trips. The only way to do that is to analyze inputs from all of the sensing devices. That requires an energized, on-line sub. Kinda like trying to figure out why your car idles rough without starting the engine. Can't be done. Of course, all safety precautions that are practical are used, but sometimes you just can't do the job and follow all of the rules. When working hot 480V in our pump stations, a full Class 3 flash suit is often required. That includes 20,000 KV (primary) rubber gloves. Good luck trying to lift wires or install jumpers in a control circuit while wearing those...not to mention the hood, which fogs up the minute you put it on. Nobody wants to be a hero, but if I don't fix it, somebody else will have to. Just my opinion, though. Do what you want.

Aha. I thought you were working with 120V / 5A metering circuits and 125V DC station battery.

 

[iceworm]

... but in my world, troubleshooting substation trips requires that inputs from CT's, relay inputs/outputs, breaker status, etc. be analyzed that are not available if the station is off line. ....

As I noted in post 5, I don't have any objection to troubleshooting controls live. Like you said you have to - that's not news.. However, I'd be very surprised if the controls you are t-shooting are 480V and up, high arcflash energy circuits - that would be unusual. Cat 4 suits and t-shoot controls don't usually happen in the same breath.

And once you go to work - well, then you are in the "R" part of "ts&r" - I'm failing to see the need to do this part hot - except convenience, downtime. Like I said, I'm not against doing the work. I'm just not kidding myself - it's about the money.

.... Just my opinion, though. Do what you want.

Thanks - appreciate that.

ice

 

[meternerd]

Aha. I thought you were working with 120V / 5A metering circuits and 125V DC station battery.

Maybe I wasn't too clear. I read my post again and I was confused myself. Two different jobs. Substation controls (125VDC) require secondary (1000 V) rubber gloves and leather glove protectors, along with safety glasses. No problem most of the time, but when working trip circuits with a multimeter or other test leads, any slips can lead to instant trips and a whole lot of people crying their eyes out. DC is fused for most applications, limiting fault currents, but on trip circuits, fusing is not used because of the possibility of a blown fuse disabling trips. That could lead to disaster. But I'll admit that the few shocks I've gotten were due to my stupidity or inattention, so no excuses there.

480 is another story. Sometimes you have to have the covers off and the pump breakers on while troubleshooting to find the problem. This means Class 3 arc suits. No room and terrible visibility. Just can't be done with a hood and 20KV gloves.

Likely if an accident happens, I'd be the bad guy for not following the rules, but like I said...If I didn't fix it, somebody else would have to. Not an excuse, just a reason. Not good enough for OSHA, I'm sure! I did wear the suits when doing metering work. Bigger stuff and unprotected circuits ahead of main disconnects. Scary! Any new guys just starting out....forget everything you read. ALWAYS wear the required PPE!:happyyes:

 

[fmtjfw]

Maybe I wasn't too clear. I read my post again and I was confused myself. Two different jobs. Substation controls (125VDC) require secondary (1000 V) rubber gloves and leather glove protectors, along with safety glasses. No problem most of the time, but when working trip circuits with a multimeter or other test leads, any slips can lead to instant trips and a whole lot of people crying their eyes out. DC is fused for most applications, limiting fault currents, but on trip circuits, fusing is not used because of the possibility of a blown fuse disabling trips. That could lead to disaster. But I'll admit that the few shocks I've gotten were due to my stupidity or inattention, so no excuses there.

480 is another story. Sometimes you have to have the covers off and the pump breakers on while troubleshooting to find the problem. This means Class 3 arc suits. No room and terrible visibility. Just can't be done with a hood and 20KV gloves.

Likely if an accident happens, I'd be the bad guy for not following the rules, but like I said...If I didn't fix it, somebody else would have to. Not an excuse, just a reason. Not good enough for OSHA, I'm sure! I did wear the suits when doing metering work. Bigger stuff and unprotected circuits ahead of main disconnects. Scary! Any new guys just starting out....forget everything you read. ALWAYS wear the required PPE!:happyyes:

WORK SAFE!!

Look for test probes that expose just 1/8 inch or less of the metal tips. I just bought a Craftsman hook-type current DMV. It had two leads with removable covers for the probes that just exposed the pointy part. The covers came off to give you the ability to put the probe into a narrow hole and to screw on the accessory alligator clip(s). [20% off vets discount, it never hurts to ask!]