Induction motors are widely used in industrial production processes. Use of an induction motor will result in increased lagging power factor. This power factor must be corrected by adding capacitors. If not, the result is the penalty of larger kVA burdens to the interconnected system. The synchronous machine, with the aid of an intelligent excitation controller, can control power factor to reduce the plant reactive loading to the connected system. This paper provides information regarding to the digital excitation system. In this system DSP320F2811 is used. Different modes like power factor control and var operation are also discussed. Simulation of the proposed topology is given. This paper will also address to the typical protections, which are included in this excitation system.
Keywords: Excitation System, Field Current, Power Factor Control, Synchronous Motor
[...] Since they are not built with slip electric contacts, avoiding sparking, synchronous brush less excitation motors are recommended for explosive atmosphere applications SYSTEM DESCRIPTION Block diagram of the proposed excitation system is shown in Fig As shown in block diagram, 3phase controlled rectifier is used to get the D.C. current, which is given to the field by changing the firing angle of SCR, the excitation current can change. Power Factor is sensed by monitoring the voltage across motor's two phases and current from third phase. [...]
[...] ARMATURE CURRENT - POWER FACTOR LEADING LAGGING UNDER EXCITED REGON OVEREXCITED REGION FIELD CURRENT Fig.1 Motor V Curves The relationship is more clearly illustrated for a typical case in Fig.2. This gives the relationship of power factor as a function of load at rated field current. When a 1.0 power factor motor is operating at rated field and rated torque output the power factor is unity ( 1.0 As the load decreases the motor's power factor becomes leading. Conversely, as the load increases beyond rated, the power factor becomes leading. [...]
[...] Different Protections are also provided in this controller AN OVERVIEW OF SYNCHRONOUS MOTOR Synchronous motors that have fixed stator windings that are electrically connected to the ac supply with a separate source of excitation connected to a field winding on the rotating shaft. Magnetic flux links the two windings when the motor is operating at synchronous speed. Synchronous motors consist of a fixed stator and a field that rotates concentric with the stator. The stator contains armature windings that are electrically connected to the ac supply system while the rotor contains field winding that is electrically connected to a source of excitation when the motor is at synchronous speed. [...]
[...] Bordeau, Senior Member, IEEE, Truman Hibbard and the Invention of Automatic Control for Synchronous Motors”, IEEE Transactions on Education, Vol. E-23, No August 1980, pp 163-169. Lawrence B. Farr and Mark Fanslow, “Power Factor control of synchronous motor powering large reciprocating compressors” Petroleum and Chemical Industry Conference Industry Applications Society 52nd Annual, 12-14 Sept pp 321- 325. Fig Waveforms for close loop simulation For low Excitation For High Excitation PROTECTIONS In this system various protections would be provided, like Field over voltage, Field over current, out of synchronism, pull out (power factor protection) protection, Field winding over temperature, Restart protection. [...]
[...] Simulation is carried out with under excitation and over excitation dc field voltage. Excitation requirement can be change by using the firing pulses. Waveforms of the speed power factor (Actual and programmed) are shown in the Fig field voltage field current are shown in the Fig Flow chart for the DLL program is shown in Fig Simulation parameters are as follow. Flowchart for the power factor is shown in Fig Input Power Rs (Stator) Ls (Stator) Ldm (d-axis mag. Ind.) Lqm (q-axis mag. [...]
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