Neutral/earth bond for inverters

[Isetech]

I dont have time at the moment to do a series of tests, I am going to connect the relays to be on the safe side. I am not happy with this high current on the neutral/earth bridge.

When the work flow slows down a little I will go to one of the sites and spend a few hours doing a whole bunch of tests.

[Dylboy]

Agrees me too.

I went and got a couple in line fuse holders to use on the sites I have the bridges in before we can get to go and install a relay. Issue with these sites is there is no space and a DB needs to be installed to house this.

All have been added with a wire as call outs for the earth leakage tripping when the grid fails and or returns.

Weird thing is most worked fine for months or a year and only started recently.

I feel grid deterioration due to switching and loose connections in the street and thus Earth being used as return path etc and hence current in bridge as well.

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[Isetech]

I also have a space problem on one of the sites so instead of the 6 amp control fuse, I plan to fit an inline fuse for the 40 amp relay with an inline fuse.

Had a good sleep last night and got a lot done today and even sold a couple inverters. The train has left the station and boy is it moving fast. This is when I wish I still had my 10 man plus a supervisor team. Maybe its time to grow again. There is certainly enough work to go around. Just one catch, you need to make sure you have the right contacts to get stock, otherwise you going to blow the profits on idle teams.

[MarkN]

Agrees me too.

I went and got a couple in line fuse holders to use on the sites I have the bridges in before we can get to go and install a relay. Issue with these sites is there is no space and a DB needs to be installed to house this.

All have been added with a wire as call outs for the earth leakage tripping when the grid fails and or returns.

Weird thing is most worked fine for months or a year and only started recently.

I feel grid deterioration due to switching and loose connections in the street and thus Earth being used as return path etc and hence current in bridge as well.

Sent from my CPH2197 using Tapatalk

DB space is always an issue. I install a sperate AC Inverter Panel along side the inverter for all the bits and bobs, like the contactor, the mcb for contactor coil, a bypass change over switch if the inverter needs to be put in maintenance mode, etc. Without this, it just becomes a painful installation to maintain, especially if additions are needed later.

[Justloadit]

From Load - There will always be slight leak to earth from stoves , geysers , any element will generally leak to earth - Light fitting ballasts even electronic have slight leaks

On source - Unless the phases are balanced 100% there will be current from the star point ( neutral) to earth - In my opinion when you have a better earth neutral bridge on your premises you could end up with some of the incoming imbalance from the street trying to earth itself on your star point

I disagree with respect to the unbalanced loads causing the current to flow from the star point to earth. The Neutral is there to ensure a return path of the 3 phases to the supply transformer. If any current is flowing through Earth to the transformer Neutral Star point, then it tells me that there is an issue some where at the loads, which either have a bad Neutral connection, and that specific site has a Neutral Earth connection at the DB board, where Earth has a better electrical connection than The Neutral, or there is a Neutral missing on one of the DBs and that Earth is being used as the return path to the transformer.

[Isetech]

Anyone figured out why we have a high current on the neutral/earth bridge ?

I have a couple of inverters on my workbench, hopefully I can run na series of tests using a True RMS fluke meter, power quality analyser capable of measuring KVA, KVAR, KW, PF and all that interesting stuff.

The batteries should arrive today or tomorrow. I dont have a R100k float in the supplier account yet, so I have to wait for my money to clear

[Dylboy]

My guess is is that the GRID has a poor N and E connection on supplier side.

However if in the installation there is a light circuit with a N and E touching then that to me woukd show current, HOWEVER if memory serves the current in the bridge wire goes away when the grid is off. So then I think it is supplier side.

Because if that current was there in load shedding with Grid off it would tell me the install has current flowing in the E and mostly likely from something not on Earth Leakage.

I too am yet to do some testing.

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[Isetech]

I have been putting a bit of thought into this high neutral current, thinking about other issues I encountered in the past with FSD/VSD' etc, Transients spikes and all the the other funnies that go on in electrical networks, measure that are put in place to prevent noise/junk, etc. watching the last video by Sunsynk KVA and KW got me thinking about what filter they use to prevent all those complicated AC issues caused when converting DC to AC versa versa.

What I would like to see is Sunsynk/Deye showing a video of one of their standard inverter units connected to a properly quality analyzer (Fluke/Kyoritsu or one of the other quality testers)

How much "junk" these units create and what filters they use to prevent the "junk" going back into the elctrical network. If you are installing a couple its would be find, but now we are taking a huge number.

It might also shed some light on the ELU tripping issues.

I am not going to into details, but the guys who know a little more about electricity than V=IXR will understand what I am talking about.

I am just waiting for the supplier to delivery my batteries, I have 2 units on the workbench (5 and 8 kva) connected to a fluke 435. Lets see what happens

The Fluke 435 can measure KW/KVA/KVAR/dips swells/ transients/ harmonics/ frequency/ you name it.

I might be way off the mark, but I have a feeling I am going to see what I am expecting to see.

[Justloadit]

There is a difference between a VSD and an inverter supplying your home.
The VSD has a highly inductive load, namely a motor, which is a very nasty fellow when you are attempting to control the RPM. When ever the RPM goes higher, the VSD has to slow down, this in turn cause the regenerative current from the motor being injected back into the VSD, in the same manner to speed up, the VSD drive has to increase the drive power. What is not in the VSD drive is any filtering from the switching bridge directly to the motor, and it relies on the motor inductance to absorb the high switching pulses used to create the so called sine wave. If you place an oscilloscope on the VSD output terminals, you will see a changing square ware, this is known as PWM (Pulse Width Modulation), however if you use a current clamp on one of the phases on your oscilloscope, you will see a sine wave. So now WTF?

You can not filter the voltage switching, but the current is filtered by the motor inductance. A little difficult to wrap your head around this. But the phase angle has something to contribute to this, simply because the current follows the voltage.

Now enter the inverter, it uses similar technology as the VSD, but it has one difference, there is a built in filter which is designed to match the inverter capacity. The filter is made up of an inductor and a capacitor, this is the reason that even with no load, the inverter uses power, because the filter is actually sucking up a small amount of power to clear up the switching and giving you a sine wave. This is the reason that one of the inverter specs is THD % or Total Harmonic Distortion, this gives you the quality of the filtering circuit.

If you overdrive the inverter, then the inductor saturates, and becomes a resistor, and then there is no filtering, if you under load the inverter, there is a certain amount of lost energy to the filter.

[Isetech]

My plan was to use a N/C (fail safe contact for the neutral/earth bond, however some of the inverters have a 230 power surce to control the relay, energised to make and denergised to break. This becomes a small challenge because you need to use the islanding mode in a sunsynk and because the inverter takes a couple of seconds (as long as 60 seconds) it is important to connect it to the correct terminals.

[Justloadit]

My plan was to use a N/C (fail safe contact for the neutral/earth bond, however some of the inverters have a 230 power surce to control the relay, energised to make and denergised to break. This becomes a small challenge because you need to use the islanding mode in a sunsynk and because the inverter takes a couple of seconds (as long as 60 seconds) it is important to connect it to the correct terminals.

If I am not mistaken, there is a 230V output that can be programmed on the SunSync that is active during Islanding mode, including the delay time before switching over to Mains.

[Isetech]

There is a default delay switching of 60 seconds which can be adjusted, however I am not aware of the output adjustment.

A 3.6 kva has a relay, however an 8 KVA has a 230 output.

I will need to keep one of the 5 kva units.

If I am not mistaken, there is a 230V output that can be programmed on the SunSync that is active during Islanding mode, including the delay time before switching over to Mains.

[Justloadit]

Creating an Earth Neutral bond on a #Sunsynk Hybrid Inverter

Adding an automatic add bond to the Sunsynk inverter

[Isetech]

I was hoping to connect N/C contact, so if the relays fails, it becomes a permantant bond until it is replaced.

I have been thinking about it today, it might not be a good idea to have the coil engergised for a long period of time. The amoutn of time in will be in islanding mode will be a lot less than normal.

I am just going to use a N/O contact with a light. When there relay is engerised the light will be on.

[Isetech]

I started removing all the permenant neutral earth bonds to day and changed over to the relay.

Got some interesting test results.

Whilke running in grid mode with a permanant bond, the current on the link wire ranges between 1.5 amps and 10 amps, Yes Iam talking about the neutral wire connected to he earth wire.

I then removed the permanant bond and connected the relay.

Current on the link wire while in grid mode, as expected zero (no link)

Then I switched off the power and the current on the link wire was 24 mA.

So the question I ask myself, do I feel safer having a more than 1 amp flowing on bridge wire (considering, less than 1 amp will kill you)

What I did notice with the Sunsynk unit I was working on, the lights flicker duration was longer than when it switches the power over after the 60 seconds.

If you can tell me why using a relay is more dangerous and support the information with test results, I am listening because one of these days someone os going to get hurt and that court case is going to be one that I wil lbe following.