Abstract—The objective of this paper is to investigate relationship between voltage and nondetection zone of OUV/OUF of local islanding detection techniques of distributed generation in electric power system network. This paper shows experimental results of inverter-based DG and synchronous-based DG with parallel RLC load that causes the most difficulty in detection. The experiments have shown that, case of inverter-based DG: variation of active power associated with variation of off-grid voltage at V PCC , case of synchronous-based DG: variation of off-grid voltage at V PCC was not associate with variation of active power but variation of off-grid voltage at V PCC associated with variation of reactive power. Nondetection zone of OUV of synchronous-based DG are very possibility that Q can more than -9.6 MVAR or Q can less than 3.6 MVAR which they can affect the V PCC to outside of normal voltage range when islanding condition is happen. Index Terms—Islanding detection, distributed generation, grid-connected. I. INTRODUCTION Distributed generation (DG) is the electricity generation at the distribution site. DG including photovoltaic (PV), fuel cell, wind turbine is growing larger and more complicated. Features of DG include secure of electricity supply to customers, liberalisation of the electricity market, reduced CO 2 emission by the introduction of renewable energy sources, increased power availability and reliability, increased standby capacity, improved power quality, grid support, combined generation of heat and power, and cost saving of adding more remote generating sources [1]. However, the advent of DG makes some problems to the stability and the power quality in the adjacent utility. Specially, most issued problem is islanding phenomenon which it is a condition in which a portion of the utility system, which contains both load and generation, is isolated from the remainder of the utility system and continues to operate. Generally, islanding is undesirable because it can cause safety problems to utility service personnel or related equipment [2]. When electrical energy transfer to electric power system network by utility system is isolated, islanding condition is formed. Anti to this condition, control system of DG must Manuscript received July 3, 2013; revised December 16, 2013. Authors would like to thank financial supports from the Energy Conservation Promotion Fund, Energy Policy and Planning Office, Ministry of Energy, Thailand and also Graduate School, Chiang Mai University. The authors are with the Department of Electrical Engineering, Faculty of Engineering, Chiang Mai University, Chiang Mai, 50200 Thailand (e-mail: manopyin@hotmail.com, suttic@gmail.com). have detection of islanding condition According IEEE Std. 1547, 2003 set the DG interconnection system shall detect the island and cease to energize the electric power systems network within two seconds of the formation of an island [3]. The DG connected to the power system is a growing trend [4]. To prevent islanding phenomenon, many anti-islanding methods have been studied until now. Islanding detection techniques can be divided into local and remote techniques. The local techniques can further be divided into passive, active and hybrid techniques. Remote islanding detection techniques: These detection techniques are based on some kind of communication between the grid and the DG. They are more reliable than the local techniques, but they are more expensive to implement. Local islanding detection techniques are based on the measurement of some parameters (voltage, current, frequency, among others on the distributed generator side. They are classified as passive, based exclusively on the monitoring of these parameters, and active techniques, which intentionally introduce disturbances at the output of the inverter and observe whether the parameters outlined above are affected. Hybrid methods employ both the active and passive detection techniques [5]. As, IEEE Std. 929, 2000 mentioned islanding condition, voltage will sudden variation when islanding condition is happen [2]. Comparison is measured voltage at PCC point (V PCC ) if V PCC > 110% or V PCC < 88% shown that islanding condition occurs [6]. Usually Nondetection Zone (NDZ) of islanding detection techniques is difficult evaluation but some techniques have effort such phase jump [7], active frequency drift (AFD) [8] and Sandia frequency shift (SFS) [9]. Especially OUV/OUF of islanding detection techniques can evaluation of NDZ by Inverter-based DG and evaluation of NDZ by Synchronous Distributed Generator (SDG) [7], [10]. Furthermore, over/under voltage (OUV) of islanding detection technique has been used in inverters such grid-connected inverter of Sunnergy Technology Co., Ltd., Thailand. Moreover, local islanding detection techniques interested in research and develop because they are suitable in used with small DGs. As remote islanding detection techniques are more expensive than local islanding detection techniques [5]. Therefore, investigation of relationship between voltage and nondetection zone of OUV/OUF of local islanding detection techniques will help to be more understanding in islanding phenomenon. Researchers can use this knowledge to develop new local islanding detection technique or adjust old local islanding detection techniques for increase efficiency and decrease disadvantages. Investigation of Relationship between Voltage and Nondetection Zone of OUV/OUF of Local Islanding Detection Techniques M. Yingram and S. Premrudeepreechacharn Journal of Clean Energy Technologies, Vol. 2, No. 4, October 2014 299 DOI: 10.7763/JOCET.2014.V2.144