ELR Protection for Unbalance Load

1 elr + 1 cbct+ 1 shunt trip coil. that's all u need. take a look at this

http://www.global-download.schneider-electric.com/85257578007E5C8A/all/07DF7F0624989FC9882575780031A786/$File/48049%2D546%2D01.pdf

Another option would be to put an RCCB in each of the outgoing single phase supplies at the dis board.

Another option would be to put an RCCB in clusters of each outgoing supply from the dis board, say one per phase.

An imbalance is simply the expression of the single phase loads. If there is no earth leak, the vector sum of the currents in the three phases and the neutral will be zero at all times.

GA

Best post up to now.

The OP does not understand what an unbalanced load has to do with earth leakage.....NOTHING!!!!

Aw, shucks.

that may not be true! cos in some earthing schemes the neutral connection is closed trough the earth, and if there´s a change in the local soils there may cause a unbalance in the flow of currents!

Why should soil type play a role? Or are you talking about systems where there is no neutral per se, only a feed back via the ground itself? Like in some parts of Africa and Australia.....? Safety features are quite different on such systems. I am not sufficiently informed to make a comment on such systems, but plenty here are.

therefore I am assuming for the moment you are talking about 3 phase systems with a neutral and earth, where the earth and neutral are bonded together at the substation where the "house-mains" voltage is developed, as I believe is used in all of Europe and many other areas of the world for 110 and 230v systems.

Therefore what has your post to do with the question of safety with regards to earth leakage on a single phase? If installed correctly, unbalanced loads (which are seen everywhere where single phase loads are used), should not play a role, assuming that the correct type of safety equipment has been installed in the beginning.

I simply cannot follow your reasoning, so please be so kind as to explain in depth for us all, I may be completely misunderstanding your post!....thanks in advance for your insights.

Here in Germany, we have 3 phases brought into the house, but almost 100% of the power used is as unbalanced single phase loads. I have the modern equivalent of an ELCB on each phase in my house. If an earth happens on some equipment in the house, just that phase gets dropped, which can in itself be problem enough, if it happens at a time when its dark and you lose the associated lighting as well.....(it has not happened up to now!)

My memory is that a fault path to earth only needs to take/divert some 30 milliamps or so (0.03 Amps) to cause that phase to drop. (having caused one to drop at the office many years ago using my finger, I can vouch for the fact that it is still a painful business!! Not to be recommended)

But whether the loads are unbalanced or not does not/should not play a role in single phase working, nor should it......think about it, in a worse case situation where it mattered, you would have to switch on or off 3 lights of the same wattage, one on each phase at a time. Totally unpractical in any household....

But as someone else has already posted, if the earth safety equipment was originally designed only for 3 phase loads (which are usually "balanced" of course!!), then you will drop all phases, even when just unbalanced.....as an unbalanced load in such a case, could be for example an indicator of a motor with a damaged field winding, but not even necessarily to earth as well!

Quite a lot of questions. First I don't know what kind of installation the poster were referring to, so I just gave a general opinion. I don't recall if he was referring to a single fase , to a three fase , or a poli-phase sistem...

1)the soil is a resistance as to the earth circuit refers to;

2)the electrical properties of the soil are relevant when you want to consider the gear and sensitivity of the protection systems;

3) In a given installation you can close the neutral circuits trough the earth, and give the "mass" of the electrical apparatus a independent circuit for they protection;

4) the earth-trough-earth is but a regular manner to make the protection circuit;

and there were some more other things to say about this...! and in cases (not so few as we could wish for) there are many electrical problems that are generated in the soils... hope that I made myself more clear now !?

I still don't understand your comments fully, does anyone here?

It may be normal for Portugal (but I am really surprised) but using THE earth as an earth path is not usual in most westernized countries that I have heard of (but always willing to learn something new!). Though houses for example are "ground referenced" locally for safety reasons.....but any fault current uses a path via a cable, not the soil.....unless something has gone wrong.....

But generally speaking soil as a connection could have a very high resistance in say times of drought, therefore very unreliable....though I have heard (here on CR4) that India for example does use such methods....

In some parts of Africa & Australia, they do use the "Planet Earth" as a "power" return path (not "earth or safety ground").....I was simply assuming that Portugal was a) more modern and b) not so large that such practices would ever be required....

What many people forget, is that the earth and the neutral are bonded at the substation transformer. At that point they are identical.

Then as far as I am aware, these are then fed to all the local users.....the get power lines, neutral and earth.

In some rural areas, in Germany for example where the old 3 phase 110 volt system was once used, they changed to 220v 3 phase, but only brought the neutral throug as before, no earth, but then in each house a neutral to earth connection is made, just for that house. The same way that the substation bond is made between neutral & earth. It makes no difference as long as when all the cables are fed through, it does not happen twice......

Thus any fault current will find its way back to the DB in that house, by way of the earth wiring inside the house, this will be seen as a "leakage" and drops an ELCB or similar in the house....an ELCB monitors for any difference in current flowing over the phase and neutral lines. If an imbalance is seen above a certain level, then the breaker trips.

On houses without ELCBs, one hopes that the resultant current flow will drop the normal over current breaker/Fuse before any wiring gets hot! I don't like such old fashioned ideas of safety myself.

The point being is that at no point does any earth leakage pass between two points via a "soil" connection.....Ground referencing of piping in a house does not imply any current flow via ground as I am sure you are aware.

Please let us know more about the way the Portuguese electrical system works using soil earth connections......thanks in advance.

"It may be normal for Portugal (but I am really surprised) but using THE earth as an earth path is not usual in most westernized countries that I have heard of"

R: really?

"What many people forget, is that the earth and the neutral are bonded at the substation transformer. At that point they are identical."

R: really? the earth and the neutral are bonded? you have neutral distribution trought power transformers? I am choked!!!

"The point being is that at no point does any earth leakage pass between two points via a "soil" connection.....Ground referencing of piping in a house does not imply any current flow via ground as I am sure you are aware."

R: really? no I am not aware. but you are right... there should be not any current flow trough pipes...

Dear Electonick,

you should change your name to Old Nick....

They call me already many names... but, maybe someday, I could made a review! but shucks, Hitekredneck was taken ! Have a nice day :)

just to end this thread, and to answer your question correctly, remember:

The Neutral circuit is a return path for Currents in Circuits;

The Earth circuit is a return paht for Default Currents;

and it is all about it. the way you arrange the circuits are a few

You did not qualify the statements first which you should have done for the first comment, such as:-

For single phase loads only

The Neutral circuit is a return path for Currents in Circuits;

3 phase loads do not generally need or use neutral, you need to be as accurate as possible.

But they are still the first almost correct statements you have made!

You took your time getting there, but you did get there!!

Well done!!

yes, always going and coming, story of my life ! you are getting very good in geography as well, so keep on searching those points in the map ! and, in any case keep the neutral in all circuits...it can became handy in the future.

This aspect of leakage current passing through earth intrigued me. It doesn't seem only an Indian practice, as per this Schneider paper ect114.pdf

You can also, if possible, change the earth connection scheme, ones are better than others, for unbalanced charges. But I don't know what kind of usage, or installation, you have there

Why do you want an RCD on a MCC panel?

The out going from the MCC to the DB I can understand.

Just use a CBCT + trip or a standard 3Ph+N RCD unit to feed the DB.

@SHAMITHGAMBHIR1
Thanks, but your solution works only for a balanced load, for example: three phase motor, as the sum of all currents = 0. But my DB is supplying various kind of single phase load, while one phase is supplying lighting triggered by PE cell, that will only be turned on at night.

So what?

An RCCB is for personal protection against electric shock in the first instance.

• 1-phase ones are available.
• 3-phase ones are available.
• 3-phase + neutral ones are available.

Just fit whatever is needed. It isn't the proverbial rocket science.

@ SHAMITHGAMBHIR1, @ PWSlack
Sorry all, it's my mistake. I didn't see that the N goes into the Toroid, so the sum of all currents = 0 at all time.

See #2⇑.

Local_Eng:

An unbalanced load will NOT trip an RCCB or ELR. All four wires, RYB and N will pass through the CBCT. So the vectorial sum is always zero. When there is an earth leakage, this vectorial sum will not be zero and the RCCB/ELR will trip.

Please search the web, there is far too much stuff. Also on CR4 itself.

One last question:

Will it still work in a 3 phase system without neutral?

regardless of balance or otherwise (unbalance) . . . regardless of number of phases . . . regardless of presence of a neutral . . . any RCCB will work as long as all the electronics is working and the CBCT is working and aux supply is available and connections are correct and all conductors including the return path are passed through the CBCT in the correct direction . . . get it?

how to know if it works?

simple vector calculation . . . all current from source equals all current in return paths and net CBCT sensed current is zero (or below leakage threshold set point) -then RCCB will not trip . . . when a leakage path allows a current higher than the set value and the RCCB expectedly trips - HURRAH! jump out of that bath and run around happily coz the shock didn't kill you . . .

No neutral? No earth ? Is this a real situation ? Or are you just curious ?

It is not worthwhile learning this subject piecemeal. As i said before, there is a lot of stuff on the web, for example ECT114 from Schneider Electric.

This happens more than one might like....

I have seen some pretty hairy wiring pictures from around the world, as well as situations in which earth/neutral/phase(s) become disconnected. Sometimes a real PITA to track down!

Of course.

In such a system the neutral current is zero, as there is no neutral conductor. However well the load is made there will inevitably be a difference in the phase currents. So long as the vector sum of them is zero at all times, the unit will not operate.

In order for it to operate, some of the current passing between the source and the load has to be going otherwise than through the unit. If the only other conductor is the earth itself, then the vector sum of the phases will be equal and opposite to the earth current, therefore the unit will operate when this sum exceeds its trip setting on the assumption that it is a possible electric shock fault that is causing the earth current.

"Simples!ζ".

Dear Mr..,

You can use CVCT (Core Balance CT) passing all four (Four ie 3 ph and N) through it.

In Case of Unbalance / Unbalance loading condition, net current passing through CVCT will be zero and during earth fault there will net current as fault current will take some different path subjected to earthing of neutral point at upstream / source.

Secondary of CVCT will have relay

Thanks

Anurag Singh

Delhi /NCR

You seem to be under a misconception that ELR operates on load unbalance!

ELR relay will not and should not operate due to unabalance in loading of three phases, IF CORRECTLY IMPLEMENTED.

We come across ELR operation during no earth leakage conditions due to three reasons:

1. The neutral is earthed at some of the consumer points downstream of the ELR location. This causes disturbance in the current balance (sum of three phase currents vs neutral current) and causes maloperation of ELR. It is important to ensure that the neutral is not earthed at any other point downstream of the ELR location and once ensured the relay maloperations will stop.

2. ELR being sensitive current based relay, it can operate leakage currents through conductor insulation downstream of its location. This happens for two reasons: One - the total wiring downstream of the ELR is too large resulting in leakage current magnitudes reaching the relay operating current; Second - The wiring is too old.

3. The ELR operating current is low - Problem of wrong selection.

Raghun - well listed.

my thoughts -

your pt#1 - is that not a case of EARTH LEAKAGE through incorrect neutral connection?

your pt#2 - old wiring - old wiring and leakage in insulation can cause elr to trip only if there is a net leakage to earth. any leakage from line to line will still not register as net current in cbct to operate the ELR.

your pt#3 - selection of set point - here again the ELR will operate only in presence of leakage current.

therefore i do not understand why / how : "We come across ELR operation during no earth leakage conditions due to three reasons:"

Your excellent comment of :-

You seem to be under a misconception that ELR operates on load unbalance!

IS SO TRUE.

I bet at least 50% of the posters here do not understand this simple fact. Then they should not be posting at all as their knowledge is generally faulty if such a simple concept is not fully and correctly understood....

Many thanks.

We have all (including me) been talking of the 'Vector' sum of all the line+neutral currents, which should be zero when there is no earth leakage/fault. i have also urged various people to download and read ECT 114 from Schneider Electric. Here is a small extract of that document.

_{3.2 Detection of insulation faults}

_{An insulation fault may be the consequence of insulation deterioration:}

_{1 between two live conductors,}

_{2 between a conductor and the ECPs or the protective conductor,}

_{3 on a single live conductor, making the conductor accessible to touch.}

_{An insulation fault between live conductors becomes a short-circuit.
In all other cases, a fault (in common mode) causes current to flow to earth. This current, which does not flow back via the live conductors, is called the earth-fault current. It is the algebraic sum of the instantaneous values of the currents
flowing in the live conductors, hence the name "residual current".
Remark: If the currents are sinusoidal, Fresnel vector representation may be used and it is possible to speak of the "vector sum" of the currents. However this representation is not relevant in the presence of harmonic currents and the term "algebraic sum" is therefore more generally applicable.}