How can you maintain power system protection and stability during islanding?

1 Detect islanding

The first step is to detect islanding as soon as possible, and either reconnect or disconnect the islanded area from the grid. There are different methods for islanding detection, such as passive, active, hybrid, or communication-based. Passive methods rely on measuring changes in frequency, voltage, or harmonics that indicate islanding. Active methods inject disturbances or signals into the system and monitor the response. Hybrid methods combine passive and active methods. Communication-based methods use data from sensors, smart meters, or relays to identify islanding. You should choose the most suitable method for your system, considering factors such as speed, accuracy, reliability, and cost.

2 Control frequency

The second step is to control the frequency of the islanded area, which may deviate from the nominal value due to the imbalance between generation and load. Frequency control is essential for maintaining the stability and integrity of the islanded area, as well as for facilitating the reconnection with the grid. There are different strategies for frequency control, such as droop control, isochronous control, or secondary control. Droop control adjusts the output of generators based on the frequency deviation. Isochronous control maintains a constant frequency by matching the generation and load. Secondary control restores the frequency to the nominal value by coordinating the generators. You should select the most appropriate strategy for your system, considering factors such as the number, type, and size of generators, the load characteristics, and the operational constraints.

3 Control voltage

The third step is to control the voltage of the islanded area, which may fluctuate due to the changes in reactive power demand and supply. Voltage control is important for maintaining the power quality and performance of the islanded area, as well as for preventing overvoltage or undervoltage conditions. There are different techniques for voltage control, such as reactive power compensation, tap changing transformers, or voltage regulators. Reactive power compensation injects or absorbs reactive power to maintain the voltage level. Tap changing transformers adjust the voltage ratio between the primary and secondary windings. Voltage regulators regulate the output voltage of generators or converters. You should implement the most effective technique for your system, considering factors such as the location, capacity, and type of reactive power sources, the load profile, and the voltage limits.

5 Monitor power quality

The fifth step is to monitor the power quality of the islanded area, which may degrade due to the harmonic distortion, the flicker, or the unbalance. Power quality monitoring is essential for ensuring the reliability and efficiency of the islanded area, as well as for complying with the standards and regulations. There are different tools for power quality monitoring, such as power analyzers, power meters, or power quality recorders. Power analyzers measure and display the parameters and waveforms of the power system. Power meters measure and store the energy and power data of the system. Power quality recorders capture and analyze the power quality events and disturbances. You should use the most suitable tool for your system, considering factors such as the accuracy, resolution, memory, and functionality.

6 Plan reconnection

The sixth step is to plan the reconnection of the islanded area with the grid, which may require synchronization and coordination. Reconnection planning is important for restoring the normal operation and service of the power system, as well as for avoiding transients or instability. There are different requirements for reconnection, such as the frequency, voltage, phase angle, and active and reactive power matching. You should meet these requirements by using synchronization devices, such as synchronizing relays, synchronizing check relays, or automatic synchronizers. Synchronization devices compare and control the parameters and signals of the islanded area and the grid, and close the circuit breaker when the conditions are met. You should also coordinate with the grid operator and follow the procedures and protocols for reconnection.