Selective estimation of harmonic components in noisy electrical signals for protective relaying purposes

• A new method to estimate harmonic components in noisy electrical signals is presented.
• Selective estimation is allowed to match the requirements of the digital relay.
• A new parameter (sample slip) is defined in order to reduce the influence of noise.
• The value of the optimal sample slip to estimate each specific harmonic is justified.
• Stability and accuracy of the method are analysed through a series of tests.

Digital filters used in protection relays must comply with a series of requirements. Among its most important features are: low computational load, good behaviour in the presence of harmonic and decaying dc components, accuracy against noise in the input signal and good behaviour in the transition from steady state to fault period.Before implementing a digital filter in a protection relay, it is necessary to subject it to stringent tests simulating a large array of real fault conditions. Electrical signals undergo a series of transformations before reaching the digital filter. As a result of this, the analysed signal carries errors and noise with it. The filter will only be apt for use in a digital relay if it rapidly and precisely responds to these types of signals. The objective of this paper is to present a new digital filter for selective estimation of harmonic components in noisy electrical signals for protective relaying purposes.