Basic Electrical Engineering

  Rotating Magnetic Field Rotating magnetic field is magnetic field which rotates in space about some point or axis. The North and South poles continuously rotates with a specific speed, called  synchronous speed . To understand the generation of the magnetic field  we will first imagine one stator of an electric motor where three-phase winding is physically distributed in the stator core in such a manner that winding of each phase is separated from other by 120 o in space. Although the vector sum of three currents in a balanced three-phase system is zero at any instant, but the resultant of the magnetic fields produced by the currents is not zero rather it will have a constant non-zero value rotating in space in respect to time. The magnetic flux produced by the current in each phase can be represented by the equations given below. This is a similar representation of current is a three-phase system as the flux is cophasial with the current . Where, φ R , φ Y and ...

  There are two methods to connect three-phase windings. Star connection Delta connection Star Connection The connection diagram of the three-phase star connection is shown in the figure below. In star connection, one terminal of all three windings is connected and makes a star point or neutral point. Neutral terminal is taken from this point. The second terminal of all windings is taken out, and supply is given to these terminals. Due to the shape of this configuration, it is known as star connection or Y-connection, or Wye-connection.   Delta Connection In delta connection, all three windings are connected in series and make a triangular shape. The supply is given to three junction points. The shape of this configuration looks like Delta (∆). Therefore, it is known as delta connection or ∆-connection. In some cases, this connection is also known as a mesh connection.   Factors Affecting Choice of Connection The factors affecting the choice of connection are listed below...