A Computation and Metering Method for Harmonic Emissions of Individual Consumers

As the ratio of nonlinear loads fed from grids are increasing day by day, harmonic pollution problems seem to be more and more serious. Problems related to harmonics are the main sources of economic losses at power systems. In order to reduce economic losses and provide cleaner grids, utilities need to find new and reasonable ways to control harmonic pollution. A proper way of this is to enforce monetary sanctions to the consumers who are responsible for harmonic pollution. With this way, consumers are encouraged to take necessary actions for reducing their harmonic emissions. However, utilities still need a fair, reasonable, and applicable method for this aim to control harmonic emissions of costumers. In this context, a new method to compute the contribution of individual customers to harmonic pollution of grids is presented in this paper. For this aim, an index representing the harmonic emission level of loads is defined. In the development of the method, responsibilities of utilities and consumers, harmonic limits specified by standards and effects of each harmonic component on grid elements have been especially taken into account. Thus, it has been possible to form a fair, reasonable, and applicable method. Validity of the method is tested by simulations, and results are discussed. At the end of this paper, an experimental setup designed for real-time metering is also presented. This demonstrated the applicability of such a metering device that uses the proposed method.

I. Introduction

Nonlinear loads are the main source of harmonic emissions and pollutions in power grids. Depending on the increase of nonlinear loads, some power quality problems related to harmonics have been increasing. Some of these problems are the increase in the losses of grid elements, failures and false tripping of some sensitive equipment, malfunction of protection relays, and undesired noises in communication systems. These problems cause economic losses directly or indirectly [1]. Maintaining the quality of grid voltage at a desired level is in the responsibility of grid utilities. However, this level is affected by the currents of nonlinear loads that is in the responsibility of consumer. In addition, distorted grid voltages can distort the currents drawn by customers. This is a “chicken and egg” discussion. Thus, it is an important and difficult task to determine the source and amount of distortions. Determination of the sources and amount of economic losses due to harmonic pollution and its allocation is an emerging issue of academic community [2]–[4]. The most important methods developed until now for this aim are active power direction method [5], reactive power direction method [6], conforming–nonconforming current method [7], current–voltage superposition method [8], harmonic current/voltage method [9], critical impedance method [10], and nonfundamental apparent power method [11]. These techniques can also be classified as multipoint and single-point methods. Multipoint methods require synchronous measurement of voltages and currents at different points of grids. As these methods give more accurate and reliable information about the harmonic pollution, they are difficult to implement and require an extremely complex and expensive measurement instrumentation. On the other hand, single-point methods have many advantages, e.g., easy implementation, low cost, and low risk of failure [12], [13]. In almost of these methods, harmonic emissions of individual loads at the point of common coupling (PCC) are obtained by the use of harmonic impedance which is difficult to compute and its value changes in the dynamic conditions of grids [14], [15]. Ultimate goal of all these works is to develop a fair, reasonable, and applicable method. These methods can be only put in practice by implementing them in a digital board. Thanks to high-speed microprocessor technology developed in recent years, the real-time measurement of harmonics and billing the resulted economic losses to consumer have become a matter of interest to grid utilities besides academic community [16].