2051 forum posts
This came up in a recent EPE magazine, a brownout protector for induction motors..
So, it explains on the page briefly what it's all about..
"Brownouts occur when the mains voltage drops to a very low level, say below 100 VAC and this causes incandescent lamps to be very dim (hence the term) or "brown". But as well as making your lights go dim, brownouts can cause induction motors to burn out because they cannot start properly."
They go onto explain that these used to be quite common in rural areas when power lines had very long runs and a happenstance falling tree or animal might cause a drop in voltage, and end up putting too much amperage through your motor, however they have become more common in urban areas now where the electricity grid runs close to capacity.
Anyway, i'm wondering how useful a device could be to protecting an induction motor in a suburban workshop, or even an inverter-fed 3 phase motor?( I presume an electrical reactor here would be more useful for stabilizing mains AC single phase supply.)
I occasionally notice lights flickering in my house, but I presume this is due to an intermittent drop rather than a full-on brownout so to speak. Which I have no memory of ever occurring.
Edited By Michael-w on 10/06/2017 12:45:19
7709 forum posts
I think the need would depend very much on the quality of your supply. I stayed in a French hotel once where the ancient lift dimmed all the the lights in the building and the street lamps outside! They had a severe problem.
In the last 30 years in the UK I've only noticed a couple of brown-outs lasting more than 30 seconds or so, both due to faults ending in a power-cut. Flickering is more common, for example my vacuum cleaner causes it.
I don't think I need BOD on my power tools. Others might not be so lucky and of course there are many places in the world with erratic electrics, not just in the third world! The US has had bad experiences and the UK is within 5% of an overload. I have a theory that the push to install Smart Meters is to allow targeted load shedding to minimise brown-outs.
Computers, including the embedded types as might be found inside a VFD, almost always have BOD. The purpose is to stop the computer running amok due to an unstable power supply. I'd guess that any machine with an electronic control would have a degree of protection.
Certainly a useful device to know about: I wonder if they are available commercially?
|Brian Sweeting||10/06/2017 18:31:16|
|453 forum posts|
Low voltage safety breakers have been part of the commercial world fir many years.
One of the potential problems in the UK is the stability of the mains frequency due to the varying inputs from green energy.
It used to be that the generators, power stations, could set their power output at 50Hz and there it would stay. Now however they have to keep adjusting it to compensate for the inputs outside of their control.
This has most affect on VFD and can cause frequent tripping off.
[Edit]Live data here... http://www2.nationalgrid.com/uk/Industry-information/electricity-transmission-operational-data/
Edited By Brian Sweeting on 10/06/2017 18:35:52
Edited By Brian Sweeting on 10/06/2017 18:37:02
124 forum posts
From time to time some gimmicks appear on the market, i have confidence only in the proven products that served industry for many decades, I refer to a simple unit that plugs into a 11 pin base which is adjustable for the percentage of protection required, over volt and under volt. A sales person once tried to sell me a REVOLUTIONERY new product for electric water heaters that will bring your elect consumption down by 50%. after listening to this man for some time, i asked him if his trying to tell me that there's no relationship between ohms, volts and amps. He could not tell me the difference between inductive and resistive load. I however offered my company to be an outlet for his "wonder" product on condition that a unit be sent to us for testing and examination over a period in our lab, needless to say i never heard from him again. I'm unable to read the description on the pic above and agree that under volt will not let the motor start and burn out, but disagree with the statement that under volt will cause an increase in current, see Ohm's Law
Edited By Mikelkie on 10/06/2017 19:58:37
|john swift 1||10/06/2017 20:57:14|
318 forum posts
it looks very like the circuit from Silicom Chip Magazine in December 2008 !!
|Andrew Johnston||10/06/2017 21:13:27|
6323 forum posts
The supply frequency in the UK has always varied throughout the day, within set limts, as the load on the network varies. It's nothing to do with green energy. The outputs from green energy supplies, like solar panels, synchronise to the frequency (and phase) of the external supply before connecting.
When I had a tour of a power station in the early 70s it was explained that the frequency, and supply voltage, was varied as the load varied, but there were strict limits on the average frequency over a 24 hour period so that items like mains driven clocks didn't drift unduly.
The input stage of a VFD is essentially a rectifier, to provide a DC voltage for the output bridge, so I can't see why it would be affected by small frequency variations. I've just looked at the VFD I bought for my Pultra lathe and the input is specified as 50/60Hz so I doubt a small variation on 50Hz is going to be noticed.
2051 forum posts
|Low voltage does damage motors which is caused by an increased draw in amperage. See this
"The amount of power the motor draws has a rough correlation to the voltage 2current (amps). Thus, when voltage gets low, the current must increase to provide the same amount of power. An increase in current is a danger to the motor only if that current exceeds the motor's nameplate current rating. When amps go above the nameplate rating, heat begins to build up in the motor. Without a timely correction, this heat will damage the motor. The more heat and the longer the exposure to it, the more damage to the motor.|
Edited By Michael-w on 10/06/2017 22:12:08
2904 forum posts
I think the notion is that a directly connected induction motor (no VFD) could stall and overheat if a sustained brownout condition occurred. However, I've never seen such a condition nor heard of motors burning out like that. I'd suggest that if you start suffering from burnt out motors due to brownouts, you should be checking for dodgy wiring rather then reaching for the soldering iron and Veroboard. The supply in our country rarely suffers from brownouts, so you should be concerned about the risk of fire from the local wiring rather than overheating of the motor.
Interesting to note the AC socket shown in the diagram. This is consistent with the Australian reference (and similar to Chinese).
Edited By Muzzer on 10/06/2017 22:23:10
|Kiwi Bloke||13/06/2017 07:15:26|
|619 forum posts|
This project originated in the Australian magazine 'Silicon Chip' a few years ago, and was updated recently. The main worry is burning out the start winding of induction motors if the voltage is insufficient to allow the motor to speed up enough for the centrifugal switch to disconnect the start winding. This type of motor is usually rated for so many starts per ten minutes (or similar) for the same reason - to protect the start winding from overheating.
In NZ, and the primitive offshore island to the west, power lines, especially in the rural areas (rather a lot of them...) are above ground. Whenever we have strong winds here, trees come down, often across power lines. We had an impressive brown-out here, a few years ago. One phase failed. Unfortunately, that was the phase supplying the power to the house. Because of parasitic coupling, there was a variable voltage on the live line, between 90V and 130V, if i remember correctly. Freezers, 'fridge and water pump didn't like it at all, but I don't know whether any of them were truly at risk - I don't know what type of motors they have. The really impressive thing was the strange strangled squealing noises coming from the electricity meter(s). I pulled the main fuses.
After that, I thought I'd make up a couple of Brownout Protector kits. They are kitted by Altronics, in Oz. Perhaps unsurprisingly, they are not stocked by the NZ distributor of Altronics kits. Kiwis are risk-deniers... I'm not, so have a stand-by generator!
|Martin Kyte||13/06/2017 08:44:30|
2609 forum posts
So a new zero input voltage to a motor results in a near infinite current?
Sounds like a very strange version of ohms law?
|Mike Poole||13/06/2017 08:49:07|
3099 forum posts
I think there is more chance of a monitoring device failing than a motor failing due to a brownout in the UK.
|Mike Poole||13/06/2017 08:58:16|
3099 forum posts
There is a wide range of monitoring devices for motors in industrial applications, voltage level, phase failure and shaft Motion detection are a few. Phase failure on a monorail system is a real risk as the supply is via busbars and brushes so the the risk of a brush losing contact is high and a motor running on two phases will not be happy for long.
|Clive India||13/06/2017 09:12:33|
213 forum posts
Yes, I think it's a waste of time - a project without a need. But then, sitting with your bum on a little truck behind a tiny steam locomotive looks like that to some people?
2051 forum posts
I think you're missing the point, the voltage isn't near zero, it's just less than what the motor needs to run It doesn't happen to all motors, just that induction motors will draw to compensate under load. This is from the wiki on brownouts..
"Commutated electric motors, such as universal motors, will run at reduced speed or reduced torque. Depending on the motor design, no harm may occur. However, under load, the motor may draw more current due to the reduced back-EMF developed at the lower armature speed. Unless the motor has ample cooling capacity, it may eventually overheat and burn out.
An induction motor will draw more current to compensate for the decreased voltage, which may lead to overheating and burnout. If a substantial part of a grid's load is electric motors, reducing voltage may not actually reduce load and can result in damage to customers' equipment."
if you still don't believe neither me, nor that, then the E.P.E article or a quick google of brownout + motor, is the reason why i'm saying this, if that can't change your mind then you're beyond help. Simply put theres a lot of literature from experts and unfortunate motor owners in remote areas who support this view.
Edited By Michael-w on 13/06/2017 09:35:38
2051 forum posts
I would agree, the likelihood of it happening in my circumstances is pretty slim, unless there's a huge shift in energy demand.
I will probably make it as a project out of sheer interest and maybe put it to the test, but i'm not going to rig up my equipment to it. An electrical reactor would be more useful in the case of a V.F.D maybe, and result in slightly smoother control.
|3447 forum posts|
The Grid is taking steps to stabilise the effects of the variable green enrgy supplies, An IET lecture I attended spoke of the necessity to invest up to £100M to deal with problems arising.
SoD, the push for Smart Maters is to ensure that, with 1/2 hourly metering it is possible and practical to vary the energy charges at similar intervals to "ration" demand, especially as the failure to invest in replacement generating plant has taken us closer to the dark ages.. The Ontario state in Canada already is using this facility with peak demand tariffs.
|Martin Kyte||13/06/2017 10:01:52|
2609 forum posts
I was being a little tongue in cheek Michael. I know all about slip and I generally agree. The biggest issue is that the motor stalls then you are on dangerous ground. I cannot see that in a home workshop brown out protection is going to help you. You can take a suitable action when it happens yourself. Just turn your lathe off. Much of todays electronic equipment has switching supplies which are universal voltage input down to around 90 to 100 volts in a lot of cases and when the input goes wildly out of spec will shut down.
That said brownouts are a pain and can cause damage to somethings. I just dont think our machinary motors will come to much harm as they have us to supervise them.
2051 forum posts
Well, I'm glad to see that this has generated some discussion at least, which is what this is all about.
1253 forum posts
We had a strange episode with our electrical supply about 12 months ago, sitting watching the TV about 9 o'clock in the evening and suddenly all the lights went very dim for about 30 seconds then there was an almighty surge and we lost all power. This affected everyone in our area. It was off for about 10 minutes and was then restored, unfortunately our tumble dryer was running at the time of this event and when power was restored it refused to run. Subsequent repair by a service engineer found that the heater element and the control panel circuits were well and truly cooked, (expensive replacements, good job insured). Would this event qualify as a "Brownout"?
2904 forum posts
Sounds like it - and very poor design. what make was it? Sounds like one to avoid.
It shouldn't be possible to bugger the heater and controls during a brownout. Earlier we were talking about a dumb / passive induction motor. Now this is a controller we are talking about.
Are you sure the guy who mended it was an engineer? What was he doing mending clothes driers?
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