Hence, Overload must be chosen closer to the range of 8.6-14.7. Thermal Overload Relay setting = 70%x Full Load Current(Phase) Min. Thermal Overload Relay setting = 120%x12.28 = 14.7A. In this tutorial, we will show the Star-Delta (Y-Δ) 3-phase induction AC Motor Starting Method by Automatic star-delta starter with Timer with schematic, power, control and wiring diagram as well as how star-delta starter works and their applications with advantages and disadvantages. How do star delta starters work for three phase induction motors and why do we use star delta starters. To enable a switch-over from star to delta, the six ends of the motor winding are connected onto terminals. It won't trip every time and when it does stay on it will run fine. The problem comes when I start the motor. On a star delta starter a motor overload or a motor going to ground and cause a short circuit will cause the overload protection to trip. Starting in star, the main contactor connects the mains to winding endings U1, V1, W1. Each starter is delivered assembled, bare, cabled by us and contains: – 1 KM1 "line" contactor, – 1 KM2 "star" contactor, – 1 KM3 "delta" contactor, – the hold-in contacts, – the electrical interlocking contacts for both the "star" and "delta" contactors, – the space for the thermal O/L relay (direct mounting). For this reason, the overload heater rating must be reduced from the full load current rating on the motor nameplate.In a delta connection, the phase current will be less than the line current by a factor of the square root of 3, or 1.732. Star Delta Starters Explained. Hi, I have a 90KW 3phase electrical motor. It is fine in star but when it switches into delta it will trip. Notice in Figure 39 – 12 that the overload heaters are connected in the phase windings of the delta, not the line. Automatic Star / Delta Starter with Timer for 3-Phase AC Motors. 'F2' detects the same current that flows through overload relay 'F1', and I don't see the reason for adding it. Overload Relay in Line: In the line is the same as just putting the overload before the motor as with a DOL starter. The star contactor shorts winding endings U2, V2, W2. Thermal Overload Relay setting = 120%x Full Load Current(Phase) Max. It is set up on the star/delta configuration for high current start ups. I've never seen a wye-delta starter with a second overload relay 'F2'. RA 6 That the starter is suitable for the operating environment. A star delta starter is a type of reduced voltage starter.We use it to reduce the starting current of the motor without using any external device or apparatus. Min. This is a big advantage of a star delta starter, as it typically has around 1/3 of the inrush current compared to a DOL starter. Most of the motor starter mfrs will publish diagrams on the 4 contactor arrangement, do an image search for "Closed Transition Star Delta Diagram". Size of each part of Star-Delta starter (1) Size of Over Load Relay: For a star-delta starter there is a possibility to place the overload protection in two positions, in the line or in the windings. And no, there is no option for fixing it without the resistors, that's what the 4th contactor is for. The setting of the overload has nothing to do with starting current or time. Overload Setting. The setting only changes for positioning in star delta because the current is split (as correctly stated by walden) but you need to know where the overload is in the circuit. The contactors of a star-delta starter switch over the windings accordingly. The "no resistor" option is to scrap the star-delta starter and put in a soft starter. That the setting range of the overload unit is suitable for the motor involved. 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