Star Delta

You can try it.....but I make no guarantee of success....

why no gaurantee ? what is the technical issue . regards

No specific technical issue, but the integrity of the existing wiring system is unknown...You can only make so many compromises before the system becomes unreliable....

If your system is in reasonably close balance, this should work.

The system is only the three phase motor of 60A rating .i suppose it is balanced

I see no reason at all why you can't do that provided of course that the neutral you use is associated with the phase conductors. If it is from a different circuit then safety factors prohibit the practice. The coil will draw a minimum of current so I don't see balance being an issue.

One of my senior told me that there will be an issue of " reverse supply" . i asked him how and from where ? but he failed to explain . is there such an issue ?

I have no idea what he is talking about.

Get him to write his explanation down and post it for us.

Perhaps your control system is all 400V and there is a possibility of the 400V contactor control signal being back fed onto the 230V coil.

Even if the 230V contactor coil does work and is safe to use make sure to clearly update the effected drawings, equipment and wiring on site, etc so someone doesn't accidently think it is still 400V sometime later on and accidently damages some equipment.

Ideally get the right 400V contactor or replacement 400V contactor coil. Some contactors allow for coil removal and replacement, if your 230VAC and 400VAC coil contactors are identical check to see if you can just swap the coil over!!!

While possible, it is not a desirable solution, just on general principles. Unless you convert all contactors to 230v for example. Uniformity of control circuit is best. No technical reason. This falls under the famous 'jugaad' technology. The reversed phase happens sometimes due to the electricity board staff applying the same 'jugaad' thinking. For example, if one fuse blows, they wireup one of the healthy phases to that phase. And when power is restored, there is no guarantee that the phase relationship is maintained.

kvsridhar said "For example, if one fuse blows, they wire up one of the healthy phases to that phase. And when power is restored, there is no guarantee that the phase relationship is maintained."
??? I would have thought that solution would produce 2 of one phase and one of another.In that scenario, assuming the starter even actuated, the motor would single phase and pop the overloads.I can't imagine any supply authority being so remiss as to do such a thing.

Brich said "oh, and make sure you have enough NO/NC contacts to control the new coil or you will end up feed 400 volts into the 230 volt coil".

Perhaps I need educating here, but I don't see a need for any further contacts etc. Simply fit the new contactor coil into the existing control circuit with the phase supply coming from the controls, the other phase removed and the neutral connected to the other side of the coil. There is no danger of 400v being supplied to the coil if the neutral is connected to it.

Perhaps a review of a star delta starter control circuit would help.

The first circuit is as original with all 415v control wiring, second circuit is with the delta coil on 240v, note the only difference to the circuit is the removal of the 2nd phase and connection of the neutral in its stead.

Happy to be shown where feedback danger exists.

Yes, the motor does see single-phasing, and a good relay trips. Not always, we still have non-spp relays in India. They don't always trip. However, AFTER this trip, the phase connections are restored, and the phase relationship may be reversed. i have seen this happen several times, especially in rural areas. You are welcome to come and see for yourself.

Hi Spades,

One situation in your circuit in which feedback would be bad, starter is in delta, motor running, delta and main contactor are both in (energised). If the stop button is pushed, current would flow through coil KM3, through contact #2, Contact #4 and #6 and through coil KM2. The timer may turn off or maybe not, this would depend on the minimum voltage to maintain it, and KM2 & KM3 may remain in as contactors require less voltage to hold them in.

It may or may not cause an issue, but I wouldn't recommend doing this at all.

Cheers,

Trevor.

That circuit will certainly exist, but is it a concern?

Here's the math:-

Figures are approximate for 15kW contactors as are likely to be installed in this starter, I will use pure resistance only, there will be XL in the circuit, but it's close enough for this exercise.

1. 415v coil KM3 will have a typical resistance of 1800Ω, coil current at 415v will be 230mA.

2. 240v coil KM2 will have a typical resistance of 800Ω, coil current at 240v will be 300mA.

Connect both coils in series across 240v and the math becomes:-

1. Current in that circuit is now 98mA.

2. Voltage across KM3 is now 162v - that's just 39% of operating voltage.

3. Voltage across KM2 is now 78v - that's just 33% of operating voltage.

Voltage sag drop out figures for that size contactor are between 55 - 60% of normal operating voltage, and drop out times are between 5 -10 ms.

The timer will be in parallel with KM3, so that will also have just 162v or 39% across it.

No chance of either of these contactors or the timer remaining closed when the stop is pressed.

IMHO, it is the inductive reactance that matters. In Schneider Tesys contactors for example, the 230 V coil has a resistance of 595Ω and XL of 7854Ω. In the 415 V coil, the values are 1938Ω and 23248Ω respectively.

i repeat that the OP should buy a 400 V coil (or 415 V whichever is on the other two) and make it uniform. It is a better technical solution.

The total impedance of the coils will be higher if you include XL as well as R, but the relative voltages across both coils will remain very similar and the current through them will be around one third of their design values, so still way below hold in values when in series on 240v.

Adding your R & XL values together for individual impedances you get 60v (25%) across KM2 and 180v (43%) across KM3, but the calculations are more complex than that due partly to the lower XL in KM3 when on 240v caused by the lowering of the frequency (loss of 2nd phase). Therefore Z in KM3 will be lower, voltage across it will be lower, voltage across KM2 will be higher, and we come back to much the same figures as I posted.

Sure - it would be better to use the original voltage coil, but that wasn't the question. The OP wanted to know if he could use the 240v one as a quick fix and whether there were any dangers of doing so.

simple answer.. and I'm surprised you've not thought about it..

Measure the voltage between one phase and the neutral.....

oh, and make sure you have enough NO/NC contacts to control the new coil or you will end up feed 400volts into the 230 volt coil.

if you cant change all the contactors(for any reason ) just use a relay with 400vac coil voltage and careful to prevent the wiring mix of safety interlock contacts .

you can use what ever voltage ,you want.

A 230v contactor would work as long as the main contacts are rated for 400v. You will need to find a neutral supply (and terminal) for one end of the coil. You must check the effect of this reconnection on the rest of the control circuit.

I cannot see how phasing, loss of phase, reversal of phase, inductance of coils or any of that makes even the SLIGHTEST difference in whether or not a 230V coil will or will not work. If it is a Wye (Star) power source what is 400/230V, the coils can be 230 or 400. It will work fine. If a phase is lost, you can't run the motor anyway, if it somehow gets swapped, it makes absolutely no difference to the coil of the contactor, although your motor will run backward.

The only valid concern I see raised here that I agree with is the continuity and consistency of the records for future use. Use the 230V coil as a temporary fix and order the 400V coil to return the system to the original design of record when it eventually arrives.

So at the end of the day , the conclusion is that i can use the 230 vac coil contactor. the only issue being the uniformity of circuit and no othe technical issue ?