Abstract: As distributed generators increase their importance on the electric power system, more and more parameters have to be controlled in order to assure the proper operation of the utility. One of the main problems encountered with this kind of generation is the potential formation of islands which could keep working in a normal way even if the utility grid has failed. There are several power generation units connected to the grid such as hydel, thermal, solar etc to supply power to the load. These generating units need to supply power according to the rules of the grid. These rules involve maintaining a voltage variation within limits and also the frequency. As per CENTRAL ELECTRICTY AUTHORITY OF INDIA Regulations 2010, variation of the system voltage should be of +- 5 % and make all efforts to operate at a frequency close to 50 Hz and shall not allow it to go beyond the range 49.2 to 50.3 Hz or a narrower frequency band specified in the Grid Code, except during the transient period following tripping. If any deviation from the acceptable limit of the grid it is mandatory that the same feeder should automatically get disconnected from the grid which by effect is termed as islanding. This prevents in large scale brown out or black out of the grid power. So it is preferable to have a system which can warn the grid in advance so that alternate arrangements are kept on standby to avoid complete grid failure. A large number of methods for detecting the islanding condition are used. Requirements for the performance of these methods have been spelled out by the International Electro technical Commission (IEC), the Underwriters Laboratories Inc. (UL), the Institute of Electrical and Electronics Engineers (IEEE) and several other “National Standards”. Currently, the anti-islanding methods are clearly grouped into three categories as a function of their operating mode. These three categories are: • Passive methods resident in the grid tied inverter. • Active methods resident in the grid tied inverter. • Methods not resident in the DG but communicating the DG and the utility. The paper is based on passive method to detect the synchronization failure of any external supply source to the power grid on sensing the abnormalities in frequency and voltage.

Keywords: Islanding, Grid, voltage variation, frequency variation, Active method, Passive method.