Star delta problem pdf10/29/2022 ![]() ![]() If it doesn't work the first time, do it once more, but of course doing it a 3rd time puts you back to the beginning. The motor rotation stays the same, all you have done is shift the relative position of the phases with regard to the line side. So to try to take advantage of that, you move the three phases over by one for example U1 to V1, V1 to W1, W1 to U1, then U2 to V2, V2 to W2, W2 to U2 (assuming IEC connection terminologies here because you said "star-delta" instead of "wye-delta"). Part of the problem spades describes is due to the phase shift that takes place in the transition from star to delta, and the current spike that happens as a result can sometimes be mitigated naturally by the inherent differences in natural resistance of the motor windings. It's called "rolling" your phase connections to the motor. Soft Starters are only a few percent more expensive than star-delta now, yet come with so many less problems that it makes no sense to continue with the old ways.īut if you are stuck with this, there is a cheap trick you can try. Spades has correctly described what is a VERY common problem with star-delta starting schemes and is the main reason I stopped using them over a decade ago in favor of solid state soft starters. #Star delta problem pdf installThe only really satisfactory solution is to go to a solid state starter which is likely cheaper than a closed transition unit in any case, and certainly simpler to install and maintain. The resistors have to be suitably sized to achieve this. The resistors, together with a fourth contactor, allow a current to flow in the windings during transition with the aim being to overcome the induced voltage and thus maintain phase relationship. Moving to a Closed transition type starter can overcome the problem, but has its own disadvantages with resistors etc. The reason that you are having success when there is no load attached is likely because the motor is not slowed sufficiently to produce a phase difference of such magnitude that will cause the current spike to trip the safeties.Įxtending the star time period does nothing to alleviate this problem.Īltering transition time - if you could - is problematic as the phase relationship can vary with motor load. ![]() #Star delta problem pdf generatorWhen the power is now reconnected in the Delta form, you are effectively connecting mains power to an unsynchronised generator - resulting in a very high current spike and torque transient which, depending on the instantaneous phase difference, can be high enough to trip overloads or breakers, and even damage equipment. The instant that the transition begins, the motor loses torque and begins to slow down, the frequency of the induced voltage is now controlled by the speed of the rotor, which will necessarily be out of phase with the supply voltage. In this condition, power is applied to one end only of the motor windings and, although there is no current flow, the motor now behaves like a generator due to the residual magnetism in the rotor core. ![]() I assume that the starter is an open transition type where there is a short period during transition from Star to Delta where the main contactor is closed but both the star and delta contactors are open. like this repeat this for all the three windings. if the multimeter makes negative kick then the assumed connections become reverse like c2 anc1. connect multimeter to other leftout terminal,multimeter makes positive kick the assumed terminal is c1 and c2. same way connect battery positive to b1 and negative to b2 just touch battery terminals. observe multimeter makes a positive kick,then assumed polarity b1 and b2 is correct,make permanent marking. Just touch 12 v battery positive to a1 and negative to a2,dont connect permenant. ![]() Take one winding mark a1 and a2,take 6v or 12 v nnect multimeter in dc v smaller range to other winding terminals,assume b1 and b2.Ĭonnect multimeter to b1 and b2. qu estions/144747/ident ify-coils-end-in-3-p hase-ac-induction-mo tor-for-star-delta-c onfiguration You may need to re-identity the winding connections, using maybe this method: Upstream breakers cannot have instantaneous elements active, unless there is a current limiting element between the breakers.Īs to the starter problem, your starter is likely wired to the motor incorrectly, likely incorrect identification of motor leads. The upstream 250A breaker may need to be replaced unless you can deactivate the short circuit trip setting. You can’t have short circuit set for both the motor breaker and the upstream breaker, that’s why both are tripping. ![]()
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