ELCB1 @ DB1 and ELCB @ DB2 Tripped same time.

My Friend,

Your problem(s) have similarity to the problems that consulted me. I can not help you in words' rectification. Send me your one line/single line diagrams showing the protection and relaying system.

It is only a matter of simple network coordination among relay settings. I hope that this is for building system only.

Eren

Hi Eren, 1st of all, i would like to thk u for replying. Yup, this is in a buiding, the circuitry is simple like what u see in every building, i will try to get the circuitry, mean time, i can draftly let u imagine, the DBs are situated in the elevator motoroom, each DB contain 3 phase(415V), 1 Neutral, n 1 Earth busbar , a MCB, ELCB, mccb, red yellow blue light bulb indication, Voltmeter, Ammeter, incoming fuse, n outgoing fuse, tats all, i have pic taken, please take a look at the links below, http://i23.photobucket.com/albums/b387/ufo3k/image501.jpg http://i23.photobucket.com/albums/b387/ufo3k/image504.jpg http://i23.photobucket.com/albums/b387/ufo3k/image499-1.jpg http://i23.photobucket.com/albums/b387/ufo3k/image503.jpg http://i23.photobucket.com/albums/b387/ufo3k/image502.jpg THK

Dear all,

I would like to see one-line diagrams for better judgement.

From the photos, I can see an earth-leakage relay in each DB. I guess the Main MCCB is equipped with the earth leakage relay.

Earth-leakage relay setting seems 30mA. My first guess is that the nuisance trip of Earth-leakage relay in DB2 occurred by cable charging current of DB2 branch circuits.

Regards

Thanks for the photos. But it will not give you a help.

But, We need the one line/single line diagram, showing all protection relaying system.

Usually, you will find it in the bunch of "turnover" documents and drawings with stamped of "as-built". Try to find these and have xerox copy and convert these to pdf and send these to us. Include Akihito-san.... Okay?

Eren

hi guest

not so simple, this is a phenomenon? no its circuit theory !!!

the E/L on DB 2 will trip if there is a poor ground continuity, check your earth loop impedance for the distribution panels and verify that it is under 1 ohm. you might have forced some current through the E/L 2 in the reversed direction during the line to ground fault that occurred, and that operational circuits that were on a single phase supply through E/L 2 had the ability to allow some of the fault current to dissipate through the other 2 lines through the load impedance. this would have caused the imbalance in the E/L relay and hence the resulting trip. true it is not part of the circuitry that was associated to the line to ground fault of E/L 1 but the fact that they share common ground may have made the two circuits to be a ring. same applies to a three phase system at large, if you remove the neutral conductor or if the neutral terminal goes into an high resistance disconnection, then you will find that the single phase circuits have suddenly been applied with line voltage and the system is a two phase system now, between any two lines that have connected loads that once shared neutral, you will find sensitive loads damaged by this. I'm uncertain of your background but sketch two three phase circuits and both with neutrals and earth common grounded, remove the suppliers earth and follow the current flow from a line to ground fault and check what happens to the current via the load back to the lines of E/L 2, recall that you connecting one of the lines to the common or ground conductor that are connected to an impedance that is then fed from the load side of an E/L relay and with a small leakage current as little as 25mA -35mA, the E/L should trip.

still not sure let me know!!!!

regards z ally

Hi all again, many thks for replying, here is the circuit for DB1, the other DB2 is same.

[IMG]http://i162.photobucket.com/albums/t279/hyperkido/circuit.jpg[/IMG]

Tq:)

Dear all,

Assuming cable capacity is 0.3 microF, and total cable length at DB2 is 1km.

The capacitive reactance of the cable is 10.6 kOhms.

During an earth-fault at phase A, in DB1, the charging voltage to the cables connected to DB2 is 400V, thus charging current for phase B and C at DB2 is 33.7mA.

ELR at DB2 will see the total charging current of phase B and C which is 65.3mA.

If ELR at DB2 is set to 30mA, surely the ELR will operate to trip.

Refer to the sketch here.

http://www.akihito-shigeno.com/files/ELCB_Nuisance_Trip.pdf

Regards

Thks for ur reply Akihito

As u can see from the photo of elcb, iboth has the same setting of 0.25s @ 1Amp , wonder why the setting so high.

Thks

Dear all,

I was thinking the ELR setting was 30mA, 0.25sec. However, the photo shows the setting is 1A, 0.25 sec.

Since the ELR is not for human safety but for equipment protection, 1A setting is reasonable. For human safety, in Europe, 30mA should be used (and in the USA this must be 5mA) and installed for receptacle branch.

In the first place, ufo3k mentioned "colleague accidentally touched one of the live wire to body(earth)", however, human can not withstand 1A for 0.25sec. So, I guess there was an earth falut with a metal connection.

Since ELR set points is 1A, nuisance trip by charging capacitance need 5 micro F per phase. If some connected load has such capacitance, the nuisance trip can be occurred. If you can measure the capacitance between line and earth from DB, and the capacitance is more than 5 micro F, my guess is still right.

Many multi-meters can measure capacitance, so, I recommend ufo3k to measure it.

Best Regards

Hi akihito, my bad for misinterpreting, my colleague actually mishandling the live wire n thus the live wire touches the metal parts of its body

thx

Dear All,

Now the picture is getting clearer.

Assuming the nuisance trip was caused by capacitance, the solution is to measure the capacitance and change the ELR setting.

A procedure is here, the values included in the procedure are for example only.

http://www.akihito-shigeno.com/files/ELCB_Nuisance_Trip_Solution01.pdf

Best Regards

Hi akihito

thks for propmt reply n theory explaination. so ur concluding by setting both elcb to 3.1A would stop the other elcb from tripping? Is this safe frm saving a human in case shorted? Since someone did said its for equipment protection, how much exactly an equipment elcb suppose to set?

thks

Dear all,

The values shown were just for calculation example. They must be changed according to the field measurement. Nuisance trips will be avoided by higher setpoint, or removing the load which has high line to neutral capacitance.

If an ELCB is intended to protect people, ELCB must be at branch circuit for receptacles. Since the current set point of ELCB for human protection is 30 mA in Europe and 5 mA in USA, it will not fit to the mains.

The ELR to trip main MCCB is to protect connected equipment.

Earth fault must be cleared within 5 sec in Europe. So, if MCB or MCCB trips within 5 seconds after starting an earth-fault, there is no need to install ELR. ELR set point can be as small as possible because the smaller is the better. But it must not too small to cause a nuisance trip.

Regards

Thks Akihito, i will try to measure live to earth capacitance if the management allow me to do so.

Best regards

ufo