Technical reference · English
Introduction to new energy industry applications
OVERVIEW
Global solar energy utilization has become a mature and effective new energy development direction. In western China, Inner Mongolia, Xinjiang, Qinghai and other places are rich in solar energy resources and are suitable for the construction of larger-scale photovoltaic power generation projects. The rooftop photovoltaic power generation project plans to use crystalline silicon photovoltaic modules. According to the building layout, the photovoltaic modules are arranged on the roofs of 40 buildings or factories. Each building is planned to lead to an AC output. The inverter capacity is based on the installed power of the panel, using non-transformer isolated inverter equipment of 10 kilowatts to 30 kilowatts. The total photovoltaic installation capacity is 1000KWP. Based on the characteristics of the building and mainly considering the fire protection requirements, it is proposed that online insulation monitoring and fault location protection measures should be implemented for the photovoltaic system. In view of the particularity of the photovoltaic system that is different from the power grid, it is particularly pointed out that the measurement method of actively injecting low-frequency AC signals should be used.
Introduction to online insulation monitoring
BRIEF INTRODUCTION OF ONLINE IMD
The insulation monitoring device superimposes measurement signals onto the ungrounded system to observe the system's insulation against the ground. The distributed capacitance and insulation status of the photovoltaic system will affect the measurement conditions. A device suitable for the corresponding voltage, loop structure and capacitance range should be selected.
Fault location system
BRIEF INTRODUCTION OF IFLS
After the system issues an insulation alarm, the fault location device identifies the abnormal branch through the test signal and the measurement transformer of each circuit. The test current, access location and supporting equipment should be configured according to the corresponding model instructions and system design.
Residual current monitoring
BRIEF INTRODUCTION OF RCM
The photovoltaic system contains AC and DC links, and the residual current monitoring type should match the load waveform, harmonics and DC components. Type B monitoring can be used for corresponding AC and DC current detection. The actual frequency range is subject to the model data; monitoring alarm and protection actions need to be planned separately.
Implementation plan
ARETEK'S PV SOLUTION
The layout of the rooftop photovoltaic power station is shown in Figure 2 below. Each photovoltaic array represents the installed capacity of a rooftop. The roof module is connected to the DC power distribution cabinet through the combiner box, and then inverted into AC by a 30kW inverter. It is first connected to the AC combiner box, and then connected to the corresponding AC power distribution cabinet according to actual needs. Finally, it is raised to the corresponding voltage level by the step-up transformer, and finally connected to the grid. Install an insulation online monitoring system for the entire photovoltaic power generation system to monitor the operation of the system. The layout of the monitoring system in the photovoltaic system is shown in Figure 4 below. It is set as a grid-connected access point, that is, the power generated on the forty rooftops will be connected to the step-up transformer from two AC distribution cabinets. Then our insulation monitoring system adopts the following methods:
This solution is based on multiple rooftops and a centralized grid-connected structure, and is equipped with insulation monitoring, fault location and loop measurement devices. The number of monitoring access points, evaluation devices and transformers should be determined based on the actual loop grouping, number of equipment channels and system diagram. The same quantity list should not be directly applied to different branches.
Fixed monitoring installations can use insulation monitors such as the ATK-IMDPV. Configure system connections, monitoring points and associated equipment according to the design drawings and the installation requirements of the selected model.
Simple installation and debugging
INSTALLATION AND COMMISSIONING
The monitoring and positioning device can be arranged in the corresponding distribution cabinet or independent cabinet according to the system design, taking into account the installation space, maintenance access and line organization. Transformers, signal lines and communication lines are connected to the project drawings according to the complete equipment description. During debugging, the corresponding relationships between measurement, alarm and fault loops are checked according to the prescribed process.
Benefits for PV plants and operations
BENEFITS FOR PV PLANTS
Continuous insulation monitoring and fault location help operators identify abnormal changes, clarify the scope of troubleshooting and arrange maintenance. Monitoring information should be used in conjunction with on-site inspections and project protection measures, and cannot alone ensure that personnel, equipment or power stations will not malfunction.
Products related to the plan
DEVICES INFORMATION
§Insulation monitoring and monitoring device
§Fault location monitoring device
§Residual current monitoring device
§Multi-circuit full-current fault analysis and determination device
§Daily operation monitoring device