Hence, Overload must be chosen closer to the range of 8.6-14.7. 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. Starting in star, the main contactor connects the mains to winding endings U1, V1, W1. Notice in Figure 39 – 12 that the overload heaters are connected in the phase windings of the delta, not the line. 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. Hi, I have a 90KW 3phase electrical motor. How do star delta starters work for three phase induction motors and why do we use star delta starters. 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. 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). Overload Relay in Line: In the line is the same as just putting the overload before the motor as with a DOL starter. It is set up on the star/delta configuration for high current start ups. 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. 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. Thermal Overload Relay setting = 70%x Full Load Current(Phase) Min. It is fine in star but when it switches into delta it will trip. I've never seen a wye-delta starter with a second overload relay 'F2'. 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. 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. Thermal Overload Relay setting = 120%x Full Load Current(Phase) Max. It won't trip every time and when it does stay on it will run fine. The setting of the overload has nothing to do with starting current or time. Min. The contactors of a star-delta starter switch over the windings accordingly. Either overload relays were: placed in the mains line and set to motor full load current. To enable a switch-over from star to delta, the six ends of the motor winding are connected onto terminals. Star Delta Starters Explained. Thermal Overload Relay setting = 120%x12.28 = 14.7A. RA 6 That the starter is suitable for the operating environment. Selection of thermal overload. The star contactor shorts winding endings U2, V2, W2. Thermal Overload Relay setting = 70%x12.28 = 8.6A Max. The problem comes when I start the motor. 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 "no resistor" option is to scrap the star-delta starter and put in a soft starter. And no, there is no option for fixing it without the resistors, that's what the 4th contactor is for. Most of the motor starter mfrs will publish diagrams on the 4 contactor arrangement, do an image search for "Closed Transition Star Delta Diagram". Overload Setting. 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