The DC system is a very important part of the photovoltaic power station, and its main task is to provide power for relay protection devices, circuit breaker operations, and various signal paths. The normal operation of the DC system is related to the correct operation of the relay protection and circuit breaker, which will affect the safe operation of the photovoltaic power station and even the entire power grid.
1. The composition of the DC system
The DC system consists of charging equipment, battery, DC screen, insulation monitoring device, load, etc.
(1) Rectifier module system.
The power rectifier module is a stand-alone module that rectifies alternating current into direct current. It is usually nominally based on the size of the passing current (such as 2A module, 5A module, 10A module, 20A module, etc.). According to different design concepts, it can also be divided into: air cooling module, independent air duct module, self-cooling module, self-energy air-cooling module and self-energy self-cooling module. Multiple rectifier modules can be used in parallel to achieve N+1 redundancy. The output of the module is a stable and adjustable DC voltage of 110V and 220V. The module itself has relatively complete protection functions such as: input overvoltage protection, output overvoltage protection, output current limiting protection and output short circuit protection.
(2) Monitoring system.
The monitoring system is the control and management core of the entire DC system. Its main tasks are: long-term automatic monitoring of each functional unit and battery in the system, acquisition of various operating parameters and states in the system, and timely processing according to the measurement data and operating states. , and control the system based on this, realize the automatic management of the power system, and ensure the continuity, reliability and safety of its work. The monitoring system is divided into two types: one is the button type; the other is the touch screen type. The monitoring system provides man-machine interface operation to realize system operation parameter display, system control operation and system parameter setting.
(3) Insulation monitoring unit.
The DC system insulation monitoring unit is a device that monitors the insulation condition of the DC system. It can monitor the line-to-ground leakage resistance in real time, and this value can be set according to specific conditions. When the line-to-ground insulation decreases to the set value, an alarm signal will be issued. The DC system insulation monitoring unit includes busbar insulation monitoring and branch circuit insulation monitoring.
(4) Battery inspection unit.
The battery inspection unit is a device that cyclically detects the online voltage of the battery. The voltage of each battery can be detected in real time. When the voltage of a battery is higher or lower than the setting, an alarm signal will be issued, and the monitoring system can display which battery is faulty. The battery inspection unit can generally detect 2~12V seedling batteries and cyclically detect 1~108 batteries.
(5) Switch quantity detection unit.
The switch quantity detection unit is a device for online detection of switch quantity and output of alarm dry nodes. For example, when a circuit breaker trips or a fuse is blown in the whole system, the switching value detection unit will send an alarm signal, and the monitoring system can display the location of the circuit breaker tripping or the fuse being blown. . The switch value detection unit can collect 1~108 channels of switch value and multi-channel passive dry node alarm output.
(6) Power distribution unit.
The power distribution unit is mainly the devices used in the DC panel to realize AC input, DC output, voltage display, current display and other functions, such as: power cord, terminal block, AC circuit breaker, DC circuit breaker, contactor, lightning protection device, Shunts, fuses, transfer switches, push-button switches, indicator lights, and current and voltmeters, etc.
2. DC system operation and maintenance specifications
In order to ensure the safe and stable operation of the DC system, the DC system should be checked and maintained regularly:
(1) The insulation value of the DC bus to ground should be checked every day. If there is a grounding phenomenon, it should be searched and dealt with immediately.
(2) For the DC power supply device in operation, it mainly monitors whether the AC input voltage value, the voltage value and current value output by the charging device, the battery pack voltage value, the DC bus voltage value, the float current value and the insulation voltage value are normal.
(3) Check whether the high-frequency rectifier switch works normally. If it is not normal, exit the fault rectifier and notify the on-site operation and maintenance personnel to deal with it.
(4) Check whether the working state of the microcomputer monitoring device is normal, if it is not normal, it should be out of operation, and the on-site operation and maintenance personnel should be notified for maintenance.
(5) The operating temperature of the battery should not be too high or too low. In normal operation, the room temperature is generally required to be 10~30 °C, the maximum should not exceed 35 °C, and the minimum should not be lower than 5 °C.
(6) The battery should be placed in a cool and dry place, and should avoid direct sunlight.
(7) When the battery is in normal operation, the full floating charging operation mode is adopted.
(8) The battery should be regularly charged in a balanced manner; after large-scale operations, the whole station loses pressure, and the float charger fails, it should also be charged equally.
(9) Overcharge or overdischarge should be avoided when the battery is used, otherwise it will affect the life of the battery.
(10) The battery is not allowed to connect to any other load.
(11) Regularly remove dust and check whether the battery is leaking, damaged, bulging and whether the connection parts are loose.