# Comparative Study of Different Approaches for Islanding Detection of Distributed Generation Systems
## 2 Literature Review
### Reduced NDZ Based Islanding Detection [67]:
#### 2.2.5 Remote Methods  
The remote method of islanding detection is the communication-based method between the utility and DG. The islanding is known through the status of the utility circuit breaker, and a trip signal is sent to the DG unit [69]. With no NDZ regions, no effect on the power quality and fast response time, the remote method of islanding detection provides a highly dependable scheme. However, the use of extra communication channels and high-cost software like Supervisory Control and Data Acquisition (SCADA) makes this method pricey to implement. The remote islanding detection can be divided into two schemes: transfer and trip scheme and power line signaling scheme [70].  
Transfer and trip scheme continuously monitor the status of all the reclosers and circuit breakers responsible for the islanded condition. Thus, a higher requirement of system interaction is essential. The SCADA system can be used for this scheme. Likewise, auto-ground is a low cost, scalable approach for anti-islanding protection of distributed generation, using a utility owned and operated system, installed just down-line of the utility protection device (substation breaker or inline recloser). In auto-ground, when the utility breaker opens, the auto-ground opens the substation side device called Sectionalizing Switch (SS) and closes the Auto-grounding Switch (AS) effectively applying a three phase to ground fault. In addition, based on online protection, all DGs connected on their anti-islanding protection will be forced to disconnect the breaker. However, in the power line signaling scheme, the power line communication scheme is used to broadcast a continuous signal from the transmission system to the distribution feeder using the transmission lines. DGs are provided with signal receivers which monitor the continuous signal and, in the case of the islanded condition, the signal disruption occurs. Some of the remote-based islanding detection methods are:  
A. A Remote Islanding Detection Photovoltaic-Based Distributed Generation Systems and Wind-Solar Hybrid Power Plants [49; 71]:  
Monitoring multiple parameters like changes in the current through circuit breakers, frequency and voltage at PCC on three sides of the PV system, this study compares them to a pre-defined threshold. This method uses continuous communication between the control system and on-field devices like the circuit breakers. This method is independent from the local loads and inverters and thus is independent from the power mismatch. This results in zero NDZ region. Circuit Breakers are tripped in case of islanding detection. With no NDZ, the islanding detection time is found to be 1.65 m-sec for the photovoltaic-based distributed generation systems.  
B. Wireless Communication-Based Islanding Detection [72]:  
With the introduction of an End Monitor Module (EMM) on the load side, generation side and distribution side, current, voltage, power, status of generators, and other required parameters are measured. These measured values are then communicated with the Local Area Monitor module (LAN) using the ZigBee module. The three EMs are provided with the capability of connecting and disconnecting loads and sources. This capability of EM is used to control various devices as required at the time of islanding. The use of wireless communication ensures the modular capability of the scheme and thus does not depend on the restrictions that would have risen when using a more conventional hard-wired based communication.  
A brief comparison of different islanding methods are presented in Table 1 below.