Anti-islanding measures and frequency/voltage emergency control devices

(1) Inverter anti-islanding protection

        Inverters must possess anti-islanding protection functionality. The anti-islanding protection for inverters in photovoltaic power plants primarily employs detection methods such as frequency deviation, power variation, and voltage phase jumps, with response times ranging from 100ms to 1s. Islanding phenomenon protection is the most critical and highest-priority protection in grid-connected inverter systems. It is required that the photovoltaic system must cease supplying power to the grid within 2 seconds of grid voltage loss.

(2) Frequency/voltage emergency control device

During islanding phenomena, frequency and voltage undergo abrupt changes. For this phase, a set of frequency/voltage emergency control devices must be installed on the 10kV outgoing line side of the photovoltaic power plant. These devices should feature slip differential blocking functionality and short-circuit judgment capability.

        This frequency/voltage emergency control device is used for emergency grid frequency/voltage control under extreme conditions. It is required for scenarios where abnormal grid frequency/voltage necessitates urgent control measures, such as low-frequency/low-voltage separation or high-frequency generator tripping. The main functional requirements are as follows:

1. Low-frequency/low-voltage separation function: When grid frequency drops to the set value, the device should achieve separation to restore frequency to normal levels. In cases where severe faults or separations occur in grids with significant active power deficits, voltage may drop severely and fail to recover. Low-frequency separation might malfunction under conditions of system reactive power imbalance, making low-voltage separation functionality necessary.

2. High-frequency/high-voltage generator tripping function: When the system experiences over-frequency or over-voltage conditions, the device should be capable of generator tripping, separation, or rapid steam valve control.

3. Out-of-step oscillation separation function: When the power plant loses synchronization with the main system and out-of-step oscillations occur, the device must simultaneously trip all parallel connections between the generating units and the main grid, separating the primary outgoing section of the power plant (i.e., disconnecting both lines; during maintenance, only the operational tie lines are disconnected).

4. Measurement function: The device should simultaneously measure three-phase voltage, three-phase current, frequency, active power, reactive power, and phase angle from two bus sections or two tie lines, serving as the basis for judgment.

5. Remote function: The device must reserve communication interfaces or remote trip contact inputs for executing remote trip commands or load reduction commands; it should also be capable of transmitting load reduction or separation commands remotely.

6. The device should record essential information (such as fault waveform data) and transmit it through interfaces; recorded information must not be lost and should be reproducible. The recorded data is primarily used to determine whether all parts of the device are functioning normally and whether operations are correct.

7. The device should possess automatic time synchronization functionality.

        Jiangsu Mangzhong Construction Co., Ltd. is a comprehensive energy service provider specializing in the photovoltaic field, dedicated to being a smart energy enterprise engaged in photovoltaic power plant investment, development, design, construction, intelligent operation and maintenance, professional consulting services, and photovoltaic equipment recycling.

Company Name: Jiangsu Mangzhong Construction Co., Ltd.

Business Scope: Photovoltaic power plant EPC and solar power station investment

Company Landline: 025-5888 3737

Mobile Number: 159 5163 4545

Company Website: http://www.mangz.cn