2. Problems with Island Operation
If the utility cannot control the voltage and frequency on the island, there is a possibility of damaging the customer equipment (loads).
The islanded system may be inadequately grounded by the RES interconnection.
Reclosing into an island may result in re-tripping the line or damaging the RES equipment, or other connected equipment, because of out-of-phase reclosing.
The protection system may not be coordinated because of significant changes in the short circuit current.
The utility line workers and public safety cannot be guaranteed since the line remains energized because the utility does not have control.
The increment of power mismatch between the power generation and loads can vary the system frequency and voltage beyond acceptable limits and can lead to instability.
If there is a power mismatch between the RES generation and loads, the low frequency oscillation can be produced in the system voltage and current responses.
3. Islanding Detection Methods
There are two methods used for the detection of Island operation that are local and remote techniques.
3.1. Local Detection Methods
Local islanding detection methods use local measurements for island detection. It measures the system parameters such as voltage, frequency, active power, reactive power, phase angle, impedance, and harmonic distortion at the RES (locally) for island detection. Local islanding methods can be classified into two methods such as passive and active methods.
3.1.1. Passive Methods
In the passive methods, the system parameters are measured and compared with the predetermined threshold value to detect the island operation. The following system parameters can be measured.
The passive methods can be implemented with low cost, and it will not affect the power quality. Therefore, it is a widely used technique. The passive methods have a non-zero detection zone (NDZ). Fig. 2 shows the non-zero detection zone (NDZ). Here, OF – Overfrequency, UF – Underfrequency, OV – Overvoltage, and UV – Undervoltage. The island operation will not be detected if the power mismatch between RES and loads happens inside this region. Since the NDZ region is large, this method fails to detect the island operation inside this region.
