DIY Induction Motor / Asynchronous Generator Power Smoothing aka "Flywheel UPS" ?

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kenkeniff

628 posts

Ultimate Geek

#269958 17-Apr-2020 09:41

Living in a rural property a fair distance from the main power distribution I often encounter usually intermittent voltage drop.

Nominal is usually around 235V or 225V under heavy load (from other houses) however intermittently it can drop to as low as 200V usually for a split second when water pumps kick in, heavy appliances are going and/or the neighbour fires up their bench saw.

The intermittent voltage drop is the main problem as for a few seconds it causes UPS' to start flicking on and off, server fans to spin up to mach 10 and sometimes unprotected devices to power cycle (as well as lights flickering).

Unrelated to this I was looking into Asynchronous Generators and short of putting the whole house on an double-conversion UPS system thought it could be a simple way of smoothing out the power to the house.

i.e. Simply by having a large enough synchronous single phase induction motor plugged into the wall running; if the line voltage was to drop momentarily then the momentum of the motor windings (let alone any added "flywheel" or gearbox mass) would backfeed it's energy to compensate (this is basically how distributed power generation in the grid works anyway).

Consulting a number of "Flywheel energy storage calculator"s it appears a medium size electric motor ~10Kg internal mass @ 1500RPM (typical synchronous speed at 50Hz) would be capable of storing around 1300 Joules of energy = 1.3 Kilowatt-seconds.

So taking a typical household load of 3kW a fairly small motor could theoretically support a voltage drop of 235v to 200v (15% of 3kW = 450W) for (1.3kW.s / 450W = 2.8 seconds) or taking into account losses as least the 0.5 to 1.0 seconds I would actually need.

Most Flywheel UPS systems I've encountered are required to spin a flywheel at crazy-dangerous-high speeds (often in a vacuum on magnetic bearings) to achieve multi kW / gW energy storage intended to power an entire building for 3+ sec until the UPS or generators kick in however I'm wondering if anyone has done or seen anything similar for minor power smoothing as above?

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Uber Geek

#2464478 17-Apr-2020 22:49

You might want to have it inbetween your grid power coming in and the devices you are protecting, having an in-wall design might have negative consequences for people working on the power to your property (they expect the power to be off but your dynamo is still spinning and putting out volts ... linesmen hate that :-) )

kenkeniff

628 posts

Ultimate Geek

#2464479 17-Apr-2020 23:00

Mark:

You might want to have it inbetween your grid power coming in and the devices you are protecting, having an in-wall design might have negative consequences for people working on the power to your property (they expect the power to be off but your dynamo is still spinning and putting out volts ... linesmen hate that :-) )

The idea would be for it to simply be plugged into the wall like any other appliance.

No difference to any other induction motor running when the power cuts out...

Either the motor would quickly spin to a stop within a few sec due to the back EMF and/or current would suddenly spike tripping the breaker anyway - all within a similar time-frame probably to any other grid-tie inverter setup.

The aim is only to smooth out ~400W voltage ripples, not to store up multi kW to power a whole building...

You could almost "test" this with the right sort of washing machine...

Scott3

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#2464501 17-Apr-2020 23:28

What about something like this? would seem easier than trying to hold up line voltage in your local area:

https://www.apc.com/shop/nz/en/products/Line-R-600VA-Automatic-Voltage-Regulator/P-LE600I

I don't think an induction motor with a flywheel will boost voltage unless grid frequency drops.

I did a touch of work on a grid scale Synchronous condenser. (Not in an electrical engineering capacity). These sound more like what you are trying to achieve, but they are not something you would want to have at home.

SomeoneSomewhere

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#2464507 18-Apr-2020 00:07

You would need a single-phase regenerative VFD for that - simply connecting a motor directly to the grid won't help as the frequency doesn't drop (and will waste an awful amount of energy). I can't find any; regenerative drives are really only found with large loads which are all three phase.

A line-interactive or double-conversion UPS feeding only the sensitive circuits could work, as most of the large loads (cooking, vacuuming, heat pump, hot water) won't care.

It's better to try and reduce the inrush current where you can. Your well pump could get a soft starter for example. This is harder dealing with neighbours.

If your voltage at the point of supply (hard to measure, because this is where it crosses your boundary) is outside 230 +- 6% for more than a 'momentary' period, you may be able to ask the lines company to fix it. If you are never above 235V, you *might* be able to ask them to raise the transformer by a tap.

kenkeniff

628 posts

Ultimate Geek

#2464511 18-Apr-2020 00:48

Scott3:

What about something like this? would seem easier than trying to hold up line voltage in your local area:

https://www.apc.com/shop/nz/en/products/Line-R-600VA-Automatic-Voltage-Regulator/P-LE600I

Funnily enough I actually have "quite a few" 500W 100V auto voltage regulators I could literally setup on every appliance I have which supports 100-240V input.

However a) as they're electro-mechanical (basically an internal motor turning a variac) I'm not sure if they'd react fast enough to be much help and b) if I was going to go that way I'd probably look at some decommissioned 8kW+ datacentre online UPS to power the whole house.

Scott3:

I don't think an induction motor with a flywheel will boost voltage unless grid frequency drops.

I did a touch of work on a grid scale Synchronous condenser. (Not in an electrical engineering capacity). These sound more like what you are trying to achieve, but they are not something you would want to have at home.

Yes I'm not sure either - but that's the theory...

The idea isn't so much to "boost" voltage but rather to resist voltage intermittent voltage drop (at a consistent frequency).

My thinking was that the motor will run at a constant speed relative to 230-odd volts / 50Hz ("synchronised" with the grid). When an appliance in the premises causes the voltage to dip momentarily then theoretically the motor will be "over driving" on momentum at that point causing energy to be briefly fed back into the mains to compensate / hold up the mains voltage until the motor RPM decreases to the new voltage equilibrium and/or mains voltage spikes back up.

This obviously doesn't help for longer brown-outs however that's not really been an issue.

kenkeniff

628 posts

Ultimate Geek

#2464513 18-Apr-2020 01:05

SomeoneSomewhere:

You would need a single-phase regenerative VFD for that - simply connecting a motor directly to the grid won't help as the frequency doesn't drop (and will waste an awful amount of energy). I can't find any; regenerative drives are really only found with large loads which are all three phase.

To be honest I'm not too familiar with electric motors so not sure about the pros/cons of VFD for this?

Yes I imagined the frequency would remain stable so is any reason the an asynchronous motor wouldn't overdrive itself with its own momentum and backfeed into the mains if the line voltage tried to drop?

Or are you saying the motor wouldn't start over-driving if the mains voltage dropped but frequency remained at 50Hz? But maybe just lose some torque?

Yeah I haven't calculated what sort of efficiency I'd be looking at just keeping the motor spinning; as I guest once up to speed shouldn't take too much to keep it going with virtually no load (besides its own mass). Noise / vibration would obviously be a factor too.

SomeoneSomewhere:

A line-interactive or double-conversion UPS feeding only the sensitive circuits could work, as most of the large loads (cooking, vacuuming, heat pump, hot water) won't care.

It's better to try and reduce the inrush current where you can. Your well pump could get a soft starter for example. This is harder dealing with neighbours.

If your voltage at the point of supply (hard to measure, because this is where it crosses your boundary) is outside 230 +- 6% for more than a 'momentary' period, you may be able to ask the lines company to fix it. If you are never above 235V, you *might* be able to ask them to raise the transformer by a tap.

Yes in the meantime will be addressing all of the above to improve things where I can.

SomeoneSomewhere

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#2464514 18-Apr-2020 01:21

Funnily enough I actually have "quite a few" 500W 100V auto voltage regulators I could literally setup on every appliance I have which supports 100-240V input.

However a) as they're electro-mechanical (basically an internal motor turning a variac) I'm not sure if they'd react fast enough to be much help and b) if I was going to go that way I'd probably look at some decommissioned 8kW+ datacentre online UPS to power the whole house.

Claimed response time on those is 2 AC cycles, or 40ms. I'm not sure how much it's expected to compensate in that time - whether that's when it starts to act, or if it can actually move 10% or more in that time.

If you have the option to do a bit of circuit splitting, you might be able to cut that to ~3-4kW. As long as no-one will plug a kitchen appliance, hair drier, or vacuum into it, your loading is likely to be quite low.

My thinking was that the motor will run at a constant speed relative to 230-odd volts / 50Hz ("synchronised" with the grid). When an appliance in the premises causes the voltage to dip momentarily then theoretically the motor will be "over driving" on momentum at that point causing energy to be briefly fed back into the mains to compensate / hold up the mains voltage until the motor RPM decreases to the new voltage equilibrium and/or mains voltage spikes back up.

[...]

To be honest I'm not too familiar with electric motors so not sure about the pros/cons of VFD for this?

Yes I imagined the frequency would remain stable so is any reason the an asynchronous motor wouldn't overdrive itself with its own momentum and backfeed into the mains if the line voltage tried to drop?

Or are you saying the motor wouldn't start over-driving if the mains voltage dropped but frequency remained at 50Hz? But maybe just lose some torque?

Yeah I haven't calculated what sort of efficiency I'd be looking at just keeping the motor spinning; as I guest once up to speed shouldn't take too much to keep it going with virtually no load (besides its own mass). Noise / vibration would obviously be a factor too.

Asynchronous motors don't generate unless supply frequency is below the rotor frequency. Reducing the motor voltage at low loads is a common way to reduce power consumption on three phase VFD fed motors. It reduces available torque but that's it.

A VFD allows the frequency supplied to the motor to vary, allowing it to extract energy back out of the motor. However, you would need one that can then feed that back into the grid - most store a very small amount into the internal capacitor bank, and have an option to connect a braking resistor to dump it into. Regenerative drives are not very common.

I think variable excitation on a synchronous motor might be able to do this? They can certainly generate reactive power. Single phase synchronous motors are going to be very rare though.

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kenkeniff

628 posts

Ultimate Geek

#2464515 18-Apr-2020 01:32

Sorry linked to the wrong AVRs. These are the ones I have: https://global.rakuten.com/en/store/sacom/item/avr500e/

gregmcc

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#2464527 18-Apr-2020 06:03

You need to be very careful here, anything that you intend to wire in must be set up in such a way that when the power goes off it does not back feed in to the network.

2nd issue is, this is way beyond the scope of the homeowner exemption for doing electrical work, you will need to get a registered electrician involved, not just your domestic electrician, one with a good working knowledge on these type of systems, your average domestic electrician will not have this knowledge.

If you are getting voltage sags when other loads come on-line maybe you should be addressing the issue why, common causes are service lines that are too small and too long for the load they supply, or the transformer supplying multiple installations is too small, again time to get your electrician involved.

pipe60

127 posts

Master Geek

#2464535 18-Apr-2020 07:39

Have a look at an online UPS vs the offline one that it sounds like your using that how we protect PLCs etc on industrial sites with big start up loads.

sparkz25

750 posts

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#2464549 18-Apr-2020 08:37

I think you need to get a Sparky involved!

As Greg has mentioned and this goes for PV as well!!!!!

gregmcc:

Anything that you intend to wire in must be set up in such a way that when the power goes off it does not back feed in to the network.

If there were any underlying issues such as voltage drop and so on the sparky would be able to point this out and get the necessary testing in place and logging to provide to the lines company to rectify the issue.

I have seen situations where data loggers are in place for 6 months or more.

This would be a better interim and long term solution for the server by protecting it with an on-line UPS.

If I were you I would go down this path to protect your devices and put the devices that aren't on UPS on this UPS.

pipe60:

Have a look at an online UPS vs the offline one that it sounds like your using that how we protect PLCs etc on industrial sites with big start up loads.

cyril7

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#2464582 18-Apr-2020 10:42

Hi, as others have said you should investigate why you are getting such big drops, whilst I understand you are remote and it sounds like it the local 11k/440 transformer is either on a longer/hiherloss than ideal line or even worse you are on a single line earth return circuit, the lines company do need to provide a certain level of performance, they may need to be made aware your issues, again a well versed sparkie is required to monitor, record and provide evidence that this is so.

I did not see exactly what UPS's you are using to feed your IT/media equipment, but based on what you are saying I would recommend you look at Online UPS's rather than offline or interactive ones to power your IT/media gear. They are way more expensive and I would recommend you get ones that are way over rated for the load you intend to use, these will be less (if at all) effected by a drooping input feed.

Cyril

Scott3

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#2464592 18-Apr-2020 10:50

SomeoneSomewhere:

Claimed response time on those is 2 AC cycles, or 40ms. I'm not sure how much it's expected to compensate in that time - whether that's when it starts to act, or if it can actually move 10% or more in that time.

If you have the option to do a bit of circuit splitting, you might be able to cut that to ~3-4kW. As long as no-one will plug a kitchen appliance, hair drier, or vacuum into it, your loading is likely to be quite low.

The ones that are common on the Philippines have three states, and switch between them to keep output voltage within acceptable range;

Slight step up transformer
Direct on line
Slight step down transformer.

The ones I have used before, you can hear a click as they change state (and the indicator light on the front changes), so I assume it is using a mechanical relay to do the switching. Given it is switching, I think it is safe to assume that the entire switching is compete within 2 AC cycles. Hopefully your equipment has enough capacitors to keep the device online for the tiny outage when swiching.

kenkeniff

628 posts

Ultimate Geek

#2464603 18-Apr-2020 11:13

TL;DR:

Yes online aka double-conversion UPS' have been discussed including the initial post.
Yes I've addressed resolving the supply issue as well as limiting / distributing loads.
Yes currently the most sensitive devices are protected by 2x offline UPS' (not ideal) and the most sensitive (my server) is fed by both to dual 100-240v PSU which can tolerate the dips but causes fans to spin up for a few sec.
Yes obviously electrical safety & compliance goes without saying;

Although what I'm positing is whether a particular type of light duty electric motor which you may normally have plugged directly into to wall running anyway to drive some gear/belt or as part of a specific model of appliance (e.g. bench drill / saw, lathe, pump etc) could/would serve to smooth local voltage dips by virtue of it's natural momentum driven overdrive. It may well be that this would not occur in any standard motor configuration...?

kenkeniff

628 posts

Ultimate Geek

#2464621 18-Apr-2020 11:44

On a side note this is similar to the AVR's I have available however mine have a wider 180-260V input with 100V regulated output (without the external adjust) which have been meaning to see if could be converted 240V - as would help in a prolonged brown-out situation.

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