Photovoltaic Direct-Flexible System Anti-Islanding Measures and Frequency/Voltage Emergency Control Device

Anti-Islanding Measures and Frequency-Voltage Emergency Control Devices

(1) Inverter Anti-Islanding Protection

Inverters must have anti-islanding protection functions. The anti-islanding protection for inverters in photovoltaic power stations primarily includes detection methods such as frequency deviation, power variation, and voltage phase jumps, with an operating time between 100ms and 1s. Islanding phenomenon protection is the most critical and highest-priority protection in grid-connected inverter protection. It is required that the photovoltaic system must cease supplying power to the grid within 2 seconds after grid voltage loss.

(2) Frequency-Voltage Emergency Control Device

During an islanding event, frequency and voltage will undergo abrupt changes. For this phase, a frequency-voltage emergency control device must be installed on the 10kV outgoing line side of the photovoltaic power station. This device should feature slip differential blocking functionality and the ability to detect short circuits.

This frequency-voltage emergency control device is used for emergency control of grid frequency and voltage under extreme conditions. It is applicable in scenarios where abnormal grid frequency or voltage requires 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 and low-voltage separation function: When the grid frequency drops to the set value, the device should be capable of initiating separation to restore frequency to normal levels. In cases where a grid with a significant active power deficit experiences severe faults or separation, voltage may drop critically and fail to recover. Under such conditions, low-voltage separation should be employed if low-frequency separation fails to operate or in situations of reactive power imbalance.

2. High-frequency and high-voltage generator tripping function: When the system experiences over-frequency or over-voltage conditions, the device should be able to perform generator tripping, separation, or rapid steam valve control.

3. Out-of-step oscillation separation function: If a power plant loses synchronization with the main system and experiences out-of-step oscillations, the device must simultaneously trip all parallel connections between the generating units and the main grid, isolating the plant's primary output section—meaning both lines are separated (during maintenance, only the operational tie-line is separated).

4. Measurement function: The device should be capable of simultaneously measuring three-phase voltage, three-phase current, frequency, active power, reactive power, and phase angle across two bus sections or two tie-lines, serving as the basis for decision-making.

5. Remote function: The device must include reserved communication interfaces or remote trip contact inputs for executing remote trip commands or load shedding commands. It should also be able to send load shedding or separation commands to remote locations.

6. The device should record essential information (such as fault waveform data) and transmit it via interfaces. The recorded information must not be lost and should be reproducible. The content of the recorded data is primarily used to verify whether all parts of the device are functioning correctly and whether operations are performed as intended.

7. The device should feature an automatic time synchronization function.

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 station investment, development, design, construction, intelligent operation and maintenance, professional consulting services, and photovoltaic equipment recycling.

Company Name: Jiangsu Mangzhong Construction Co., Ltd.

Business Scope: EPC for photovoltaic power stations and investment in solar power stations

Company Landline: 025-5888 3737   

Mobile Number: 159 5163 4545

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