Star delta start

The principle Learn the electrician will not star triangle how line. 1. When the load on the motor has no strict requirements and to limit the start torque motor starting electric fan motor parts current and motor can use 380 v/Δ connection condition star triangle boot method; 2. The method is: in the motor when the motor first starts, connect into the star connection, when the motor start again after successful will convert into triangular connection (via double-throw switch switch); 3. Because of the motor starting current is proportional to the power supply voltage, the power grid provided by the starting current is only 1/3 of the full voltage start current, but also start torque only 1/3 of the full voltage start torque. 4. Star triangle start, step-down starting at the expense of his power in exchange for a lower cost of starting current. So it defies and with the size of the motor power to determine whether to need to use the star triangle start, also depends on what kind of load, the general load when need to start the runtime negative light load can be used star triangle start, usually a squirrel-cage motor starting current is 5 to 7 times that of the running current, and voltage requirements for power grid is usually plus or minus 10%, in order not to form the impact to power grid voltage is too large to adopt star triangle start, general requirements in squirrel-cage motor power by more than 10% of the rated power transformer will be will use the star triangle. 5. 

In the process of actual use, found to be the star triangle step-down starting motor starting electricalmotor1.blogspot.com 11 kw are needed, such as fan, 11 kw electric current when it starts at about 7-9 times (100) A, according to the normal configuration of the thermal relay can't start, it's no use (the draft) thermal relay with big and does protect the motor, so suggest using step-down start. Two conditions 1, the capacity of 7.5 KW three-phase asynchronous motor. 2, motor in starting the instant power grid voltage fluctuation is less than 10%, for not often start the motor can be up to 15%; If there are special transformer S transformer or 5 p motor, motor asynchronous motor allows direct frequently. 3, meet the experience formula: Ist/IN < 0.75 + ST \ 4 pn ST - public transformer capacity, KVA; PN - motor rated power, KW; Ist / - IN the ratio of the motor starting current and the rated current. 4, star triangle step-down starting motor three-phase winding six external terminal: A - X, Y and C - B - Z (hereinafter with rated voltage 380 v motor as an example) A. start star: X - Y - Z, A, B, C three termination three-phase ac voltage 380 v, the voltage of each phase winding, 220, A 380 v directly start current is greatly reduced, to avoid the excessive starting current impact on grid form. At this time of the torque are relatively small, but the motor can reach a certain speed. B. angular run: star start the motor for a period of time (about) a few seconds after reaching a certain speed, electric switch connect six terminals into a triangle, and again from 380 v power supply when each phase winding voltage of 380 v, torque and rotational speed is greatly increased, the operation process of motor in the rated conditions.