![]() ![]() 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 generator#When 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. If the delta-connected system has the same resistance R on its three sides, then the same star resistance will be r.You can’t have short circuit set for both the motor breaker and the upstream breaker, that’s why both are tripping. The same star resistance connected to the given terminal is equal to the product of two delta resistances connected to the same terminal divided by the sum of the resistances connected to the delta. The relation of delta-star change can be shown as follows: Subtracting Equations (I), (II), and (III) from Equation (IV), Similarly, the resistance between points C and A will be the same.Īdding the equations we get (I), (II), and (III), Just as the resistance between A and B is the same, so is the resistance between B and C. ![]() ![]() Since the star and delta systems are similar, the resistance measured between terminals A and B of these two systems must be the same. Now if we measure the resistance value between points A and B we get this. In this star system the resistances RA, RB, and RC are connected to A, B, and C respectively. The resistance between points A and B is named R1 just as the resistance between points B and C is named R2 and the resistance between A and C is named R3.Īs shown in the figure the star connection is connected to a point named A, B, and C. The triangles are named A, B, and C respectively as shown in the figure. This means that the value of impedance remains the same whether it is measured between any two pairs of lines whether it is connected between delta lines or its equivalent star connected between those lines. If a barrier is measured between any pair of barrier lines then the two connections are equal to or equal to each other.
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