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Topic Title: A question for AlanCapon ....and others....
Topic Summary: G59 protection
Created On: 19 June 2010 09:30 PM
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 19 June 2010 09:30 PM
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My employer manufactures educational equipment. I am responsible for a range of equipment which teaches Power Systems (line losses, protection, load flows, real & reactive power etc).

Three of these products contain small alternators (2kVA) driven using an induction motor & an inverter drive. The units teach the principles of alternators.... speed v freq relationship, excitation current v generated voltage etc but also go as far as syncing onto the mains to teach the torque = real power, excitation = reactive power relationships etc.

These units also contain AREVA MiCOM protection relays to teach protection (including ROCOF & voltage vector shift)

My question is.... since these units actually operate in parallel with the mains (although they can't actually export real power since their prime mover is an induction motor fed from the same supply that is being paralled with) should I be seeking the permission of the DNO before connection of these or are they so tiny they cant affect the supply anyway. Obviously, there is zero chance of these units being able to create an island in the evt of a power failure.

Your thoughts......

 19 June 2010 10:24 PM
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I dont have the latest copy of G59 to hand, but from memory it only applies to generators over 3KVA. This means that most micro generation schemes are exempt. i.e small wind generators and photo-cells from B&Q.
I dont think you will have any problem with your demonstrations.
 19 June 2010 10:40 PM
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Generators less than 16A per phase at LV in the UK do not have to comply with G.59. They do however need to comply with G.83, which is what all the solar and wind based systems designed to run parallelled with the grid comply with. To some extent, G.83 is an easier standard, as it has generic settings rather than the site specific ones you may find with G.59. With G.83 you also have a generic certificate covering the product, rather than each unit needing individual testing on site.

In terms of notifying DNOs about a connection, that probably depends on the DNO. In the case of my employer, we would want to be notified, and we would require a copy of the G.83 certificate. If we had not seen the device before, we might want to witness test the first one.



Edit: As your demonstration machines use an induction motor for their power, I am not sure that they actually meet the requirements to be called a generator, as it would only be their inertia that would allow them to provide an export.
 19 June 2010 11:42 PM
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I take Alan's view, but suggest that the unit isn't a generator at all, based on the assumption that it's configured with a direct mechanical linkage between the drive motor and the generator, and that power to drive the motor isn't derived from another power supply. It then becomes a "black-box" representing a load on the network (until such time as perpetual motion, or better, can be achieved).

In the event of a power cut, if the motor input and generator outputs are different connections, then there might be a very short period of export due to inertia, however this is no different from any other motor on the system (where no G59 or G83 requirement exists).


 20 June 2010 09:33 PM
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Gentlemen, thank-you for your thoughts.

Jonathan - your assumptions are valid, the shaft of the induction motor is directly connected to the shaft of the alternator & the power to drive the induction motor does indeed come from the same source as the alternator is paralled to - the apparatus has only the one power supply. If I'd managed to invent perpetual motion then I'd be the employer not the employee :-) (although, due to mathematical error, I did get an efficiency of greater than 100% at one point!)

I'm also of the opinion that this apparatus can be treated as a load as far as the network is concerned. It can't export any real power, it could be a net exporter of reactive power but that would be limited to 2kVAr less transformer losses so I can't see that it could have any real influence on the network.

Alan - thanks for the info from the DNO viewpoint. I'll investigate G83 a little more, but hopefully I can persue the case that the unit doesn't actually meet the requirements of a generator.


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