Development Of Asynchronous Motor Protection Based On Dsp

The asynchronous motor, which is one of the most popular kinds of motors, iswidely used in the power stations and corporate enterprises. According to statistics,power drive, most of which are three-phase AC asynchronous motors, accounts forabout 60 percent of the total load in the power networks. So, it's greatly significant toprotect well the three-phase AC asynchronous motor.In order to protect the asynchronous motor sensitively and reliably, it is necessaryto learn of the characteristics of the asynchronous motor first. This thesis analyzes thestatic and dynamic characteristics of the asynchronous motor, simulates the dynamiccharacteristics using MATLAB, entirely analyzes the fault causes and fault features,and designs the comprehensive protect schemes for the asynchronous motor. Thecomprehensive protect schemes are as follows. The protection of quick-break for thecurrent is used to protect the interphase short-circuit faults of the stator winding in themotor and the inlet wire. The quick-break protection for the negative-sequence currentis used to protect the faults of the opposite operation and the asymmetric short circuitof the motor. The protection of overload is used to prevent damages because of theoverheating of windings under the condition of the long time overload. The inversetime-lag current protection of positive-sequence is used to protect the faults ofthree-phase short circuit and symmetry overload during the proper operation ofmotors. The inverse time-lag current protection of negative-sequence is used toprotect the faults of interphase asymmetric short circuit, loss of phase, turn-to-turnshort circuit and asymmetric overload. The zero-sequence current protection is used toprotect the ground faults. The protection of starting time is used to prevent damagescaused by long-time big starting current on the condition of all types of motors'unsuccessful starting. In order to support the protection schemes discussed above, thisthesis presents an advanced Fourier algorithm fit for the asynchronous motor andinverse time-lag algorithm fit for the microcomputer protection, and puts forward aprotection method to distinguish the fault area, which is important for improving thesensitivity of zero-sequence and negative sequence protection.This protecting equipment is a microcomputer asynchronous motorcomprehensive protecting equipment based on DSP. The hardware performance of theequipment can be improved by the use of DSP. With a wide applicability, theequipment can be used as a universal platform of microcomputer protection. At thesame time, the use of DSP chips brings much convenience such as software designingand programming. In addition, the equipment can not only implement the protectionfunction, but also fulfill measurement, control and data communication functions, thatis, integration of protection, control, measurement and communication.