The advantages of FFT application in frequency domain and wavelet theory in time domain were studied

and an Embedded System for Power Quality Detection (ESPQD) based on radix-4 FFT and Wavelet Transform is developed. The ESPQD uses the wavelet theory to monitor the transient power qualityincluding voltage dip

voltage swell and so on.FFT is applied to analysis harmonics of electrical signals in steadystate. Three different states including steady-state

voltage dip and transient interference were tested with both the ESPQD hardware system and Matlab simulation for verification. The results show that the amplitude error of fundamental wave is within 0.3%

meeting the A level standard of the utility grid standards GB/T 14549-93 about harmonic measuring instruments. The system can also precisely and quickly detect the abrupt changes of the electrical signals during voltage dip and transient interference. The time difference between ESPQD and simulation is within 1.6 ms and the system can be used in real time measurement.