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Discuss Ze measurement with a PV system connected? in the The Welcome Forum area at ElectriciansForums.net

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Hi, I’m new to this site and wanted some advice on the following,
I have a db with a 4kw PV system feed into it via a 16A cb. Gn3 tells me that a generating set which can feed in in parallel to a dB will effect the ze measurement. How can I carry out the ze, pefc and pssc test with this system connected into the dB. I’ve done the ze, pefc and pssc with it isolated so far. It’s a tn-s system.
Thanks .
 
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SparkyChick

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It will only affect the Ze measurement if you have the main earthing conductor connected to the DB. With it disconnected, and the solar fully isolated, it cannot affect a reading taken from the incoming terminals and the disconnected main earthing terminal.

Depending on how things are connected on the earthing side, you may need to disconnect the main earthing conductor from somewhere other than the DB.
 
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  • #3
Hi, thanks for the reply, so in terms of the final measurements for the EIC I don’t make any adjustments for its supply into the dB and record the results as if it wasn’t there ?
 

SparkyChick

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I would say this... Ze is the external earth fault loop impedance, the solar is not external, it is part of your installation. So you should look to measure Ze with it completely disconnected. But, you should look to measure PEFC with all earthing connected since these may provide parallel paths.
 
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Thanks, Gen3 says any pfc from a generator must be be included if it can operate in parallel with the supply, that’s what I really need to know who to calculate, sorry I should have been more specific that it’s pefc and pssc I need advice on ? Thanks.
 

Strima

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So do your PEFC/PSSC tests with parallel paths in place as it should be done.

Ze is done with the main earthing conductor disconnected to show the earth path back to the transformer is within tolerance. PFC should be done with parallel paths in place as these could reduce your Ze therefore increasing your PFC.

Too many people just stick the probes on, wait for the beeps to finish and write down what's on the screen without actually knowing or understanding what they are testing for.
 
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  • #7
Hi, yes I understand all of that, my specific question is how do I measure the PFC from the PV system that feeds into the dB? as required by GN3 p68, 2.6.17, para 3.
Thanks .
 

SparkyChick

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My copy of GN3 is in the van but if it is to be tested in parallel, I would assume you bring it on-line, and carry out a test fo PEFC and PSCC just as you would normally, because at that point with the solar on-line it is operating in parallel with the DNO supply.
 
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That’s what I thought, and what makes sense to me, but I just wanted to see if there was something specific I needed to calculate or account for.
Thanks for all the replies.
 

SparkyChick

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I've never installed a solar system or had need to carry out those tests on an installation with it, but based on what you've said (without referring to GN3), that's how I'd go about it. Maybe someone with more experience will chime in.
 

Strima

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You don't need to measure the PFC from the PV array as this would be done when you do your PFC test at source.

You need to take into account that normally PFC would decrease the further away from the source you get along a circuit. But you should take into account any generation that could effect PFC that connects to the installation other than the source.

For example you could have a garage at the end of a long garden with a very low PFC. The devices in the garage DB would only need to have a low breaking capacity but you need to ensure that they would disconnect under fault conditions.

However if you installed a PV array on the garage potentially the PFC would increase at the furthest point of the installation.

You may well end up with substantially different results throughout the installation. However in the vast majority of domestic situations the PV is normally connected near the source of supply.

You need to take into account varying PFCs across the installation and ensure the devices are suitably rated for this and that under fault conditions OCPD would operate within required parameters.

The designer should also know the expected PFC at each point of the installation and this should be verified by the installer and subsequent inspectors.
 
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  • #13
Thanks for the detail and reply, the PV comes into the dB through a 16A cb connected on the buzz bar as normal, as the PV doesn’t work unless it has an initial feed from the dB through that same 16a cb, I would need to close the main switch, energize that single 16a cb which would then allow the PV to produce.
I can then carry out the tests with just that cb closed so that I have both supplies feeding into the dB.
 
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