A new time-domain based power system frequency estimation algorithm Heresh Seyedi 1 * ,y and Majid Sanaye-Pasand 2 1 Faculty of Electrical and Computer Engineering, University of Tabriz, Iran 2 Control and Intelligent Processing Center of Excellence, School of ECE, University of Tehran, Iran SUMMARY Frequency stability is one of the most important features of power systems. It is closely dependent on the value of system frequency. In the present day modern power systems, fast and accurate frequency estimation has become quite vital. Any mistake in accurate estimation of frequency may threaten the frequency stability or at least lead to system operation problems. In this paper, a new time-domain based power system frequency estimation algorithm is proposed. Different abnormal events such as frequency decline due to load-generation mismatch are modeled and ability of the new frequency measurement technique to track the frequency is tested. Performance of the new method is evaluated and compared with an existing frequency estimation algorithm. Simulation results confirm advantages of the new approach over the existing method. Copyright # 2011 John Wiley & Sons, Ltd. key words: power system frequency measurement; frequency estimation algorithms; frequency tracking; wavelet transform 1. INTRODUCTION The fundamental frequency is one of the most important and sensitive parameters of a power system. Frequency stability of power systems is closely dependent on the value of system frequency. Any imbalance between the system load and generation directly affects the frequency and leads to frequency deviations. Grid frequency decline due to shortage of energy supply or disconnection of a generation plant should be detected by under-frequency load shedding relays. It is necessary to maintain frequency at its nominal value or as close as possible to that value within a narrow limit. Deviation of frequency from its rated value is an indication of imbalance between real power generation and load demand. Any mistake in accurate estimation of frequency could cause inadequate load shedding by frequency relays, which would eventually be resulted in a major grid collapse [1–3]. Various methods have been proposed for frequency estimation. These methods may be divided in two groups [4,5]:  Time-domain based methods: In these methods frequency calculation is performed in time domain. For example, zero-crossing algorithm is a time-domain based method.  Frequency-domain based methods: In these methods frequency calculation is performed in frequency domain. For example, Fourier algorithm is a frequency-domain based method. Most of the modern digital protective relays, using frequency-domain based methods, are based on digital phasor estimation algorithms [5]. When power system frequency is different from its rated value, accuracy of the phasor estimation algorithms is decreased. This could cause incorrect operation of the load shedding relays. *Correspondence to: Heresh Seyedi, Faculty of Electrical and Computer Engineering, University of Tabriz, Iran. y E-mail: hseyedi@tabrizu.ac.ir Copyright # 2011 John Wiley & Sons, Ltd. EUROPEAN TRANSACTIONS ON ELECTRICAL POWER Euro. Trans. Electr. Power 2012; 22:433–448 Published online 14 February 2011 in Wiley Online Library (wileyonlinelibrary.com). : 10.1002/etep.572 DOI