An Investigation on the Validity of Power Direction Method for Harmonic Source Determination

Abstract

Abstract-The power-direction method has been used widely to identify the locations of harmonic sources in a power system. A number of utility-customer disputes over who is responsible for harmonic distortions have been settled with the help of the method. A closer examination of the method, however, reveals that it is unable to fulfill the task of harmonic source detection. Case studies can easily show that the method yields incorrect results. In this paper, problems associated with the method are investigated using case studies and mathematical analysis. The results show that the power direction method is theoretically incorrect and should not be used to determine harmonic source locations. The main cause of the problem is that the direction of active power flow is a function of the phase-angle difference between the two sources. The direction of reactive power flow, on the other hand, has a better correlation with the source magnitudes.

A Single-Point Method Based on Distortion Power for the Detection of Harmonic Sources in a Power System

“…The obtained value for P H in Table 2 shows that this value in some situation gives incorrect information about the location of the source of harmonic pollution as claimed in [12]. Namely, the waveforms of currents and calculated THD I clearly indicate the level of nonlinearity for each particular load.…”

“…Table 1 summarizes the state of the art of single-point methods that are used for harmonic source detecting or sharing harmonic responsibility between utility and consumer. One of the most common used single-point strategies from Table 1 (APD) is based on monitoring the sign of the harmonic active power P H [1,11,12]. According to this method a consumer represents a source of harmonic pollution just in case when P H < 0.…”

“…This identification of the nonlinear consumer is widespread and has been used in the industry for many years [1,12]. Many manufactures present this possibility as a key feature of their equipment despite the proofs that it is not 100% accurate [12]. RPD proposes tracking the sign of the harmonic reactive power, Q H .…”

“…It is a complement to APD. Which one will be applied depends on the balance of resistances and reactances of the loads [1,12]. However, determining the character of impedance is, in most cases, a difficult problem.…”

“…Unlike some other approaches, this method does not require spectral analysis of voltage and current [1,11,12]. All required values of U, P, and Q can be easily calculated using measured samples of voltage and current obtained from an analog/digital converter.…”