Three-phase ac motor star row and delta connection?
Three-phase winding delta connection Three-phase asynchronous motor winding delta connection, when the power of a phase (L3) circuit, by the winding with cz series and winding ax again after parallel hybrid circuit of stator current whether meet the phase condition, the need to be calculated to determine. Because of the three-phase symmetric winding structure, the three-phase excitation impedance is equal, namely, Zma = Zmb = Zmc = Zm < Φ, the three phase stator current are: A = 0 12 / (Zm < Φ) = < - Φ, 0 = 0 c = 12 b/(2 Zm < Φ) = / 2 < - Φ. The current in the three-phase winding is visible, but the current phase is the same, and the current is not satisfied with the phase condition. Three-phase winding delta connection, three-phase asynchronous motor open phase, not only unable to start, lacks when starting the stator current is very big, if not in time to cut off the power supply, motor will be destroyed immediately. This is quite different from normal starting and must be taken seriously.
Three-phase squirrel-cage asynchronous motor adopts - delta Y step-down starting advantage: Y connection of the stator winding, the starting voltage for direct using delta connection, a third of the 1/3 of the starting current to delta connection, thus features good starting current, the circuit is simple, less investment. The drawback is that the torque is reduced to a third of the triangular method, and the torque characteristics are poor. So the line is suitable for light or no-load start. In addition, note that the consistency of the rotation direction should be noted when the y-delta joins
Three-phase squirrel-cage asynchronous motor adopts - delta Y step-down starting advantage: Y connection of the stator winding, the starting voltage for direct using delta connection, a third of the 1/3 of the starting current to delta connection, thus features good starting current, the circuit is simple, less investment. The drawback is that the torque is reduced to a third of the triangular method, and the torque characteristics are poor. So the line is suitable for light or no-load start. In addition, note that the consistency of the rotation direction should be noted when the y-delta joins
The design of this circuit is still controlled by the principle of time. The difference is that when starting the motor stator windings into star, each phase winding withstand voltage of power supply phase voltage (220 v), reduces the starting current impact on power grid. In its late starting, it according to the setting time for pick up in advance to delta connection, each phase winding withstand voltage of the power line voltage (380 v), into the normal operation of the electric motor. This kind of circuit is available for the squirrel-cage asynchronous motor, which is connected to a triangle in normal operation
