Analysis and solution of common faults of DC power supply system

Mondo Technology Updated on 2024-02-20

1Introduction to the composition and function of DC power supply systemThe DC power supply system is widely used in various power plants, substations and other power system core hubs, and is composed of battery packs, charging devices, DC feeder screens, DC distribution cabinets, DC power monitoring devices, DC branch feeders, etc., to provide safe and reliable working power for relay protection devices, circuit breaker tripping, signal systems, DC chargers, UPS, communications and other subsystems.

As the core equipment of the substation, the DC power supply system of the substation supplies power to the control equipment of the substation, and if the power supply is stopped due to failure, it will directly affect the normal operation of the substation. At present, most of the chargers use high-frequency switching power supply type, and the battery has also been upgraded from the initial acid-proof lead-acid battery to the VRLA sealed lead-acid battery, and is equipped with a DC power supply microcomputer monitoring device.

The main functions of the battery pack in the operation of the DC power system:

1) When the mains power is interrupted or the DC charging equipment fails, the battery pack will supply power to the load separately to ensure that the power supply is not interrupted.

2) Under the short-circuit impact of the load or the initial impact of the normal load, the part exceeding the rated output of the charger shall be borne by the battery.

3) Smooth filtering. The battery pack has the same charging and discharging function as the capacitor, and the AC components are isolated, so that the AC components sent to the load are further reduced, and the voltage quality requirements of the load are guaranteed.

The battery pack is regularly inspected daily and common faults:

1) The VRLA battery pack operates in float charge mode during normal operation, and the single float charge voltage value should be 223-2.28V, equalization charge should be 23-2.35V, in operation, it is necessary to monitor the terminal voltage value, floating current value, single battery voltage value, ground resistance and insulation state of the battery pack and DC bus.

2) Daily regular inspection of the battery pack: terminal voltage measurement, internal resistance test, dynamic discharge test, AC input power switching test of charging device.

3) The function of the safety valve of the VRLA battery: the VRLA battery is in a sealed state under normal charging, and a safety valve that can be automatically opened and closed is installed. When the internal pressure exceeds the specified opening threshold, the safety valve will be automatically opened, and it will be automatically closed when the pressure is lower than the closing threshold. The safety valve is equipped with an acid filtration device, which will not discharge harmful gases such as acid mist, and will not leak electrolyte, which can prevent sparks from causing batteries**.

4) Common faults of VRLA batteries: abnormal VRLA shells and abnormal discharge voltages of VRLA batteries.

Charging device protection function and operation monitoring

The charger should have over-voltage, over-current, under-voltage, DC insulation monitoring, AC loss of voltage, AC phase loss and other protection and sound and light alarm functions. The daily inspection of the charger is essential, such as: whether the three-phase AC input voltage is balanced or missing, whether the operating noise is abnormal, whether the protection signals are normal, whether the AC input voltage value, DC output voltage value, DC output current value, etc. are correct, and whether the insulation state to the ground is good. If the AC power supply is interrupted, the battery pack will supply power to the load uninterruptedly, if there is no automatic voltage regulation device, manual voltage regulation should be carried out to ensure that the bus voltage is stable, and the AC power supply is restored, and the charging device should be started manually or automatically immediately.

Routine testing of DC power supply systems during overhaulAfter the installation of the DC power supply system, the handover acceptance test should be carried out before it is put into operation, and the test project must meet the technical requirements, and the trial operation shall be normal for 72 hours. The main content of handover acceptance:

Insulation monitoring and signal alarm device.

Withstand voltage and insulation test.

Battery pack capacity test.

Charging device current stabilization accuracy test.

Voltage regulation accuracy test of charging device.

Ripple coefficient test of charging device.

DC bus continuous power supply test.

FDT-220 110 DC System Comprehensive TesterAnd the supporting discharge load box integrates battery discharge, charger ripple coefficient, voltage and current stabilization accuracy characteristics test, and the main functions are as follows:

1. Charger characteristics test: as a DC charging device working characteristics tester, test its voltage stabilization accuracy, current stabilization accuracy, ripple coefficient and voltage and current setting error.

2. Battery discharge: As a battery pack load tester (discharge meter), test battery capacity and discharge curve, fully compatible with DC220V and DC110V battery packs.

3. Battery pack charging monitoring: monitor the charging process when the battery pack is charging, and test the charging curve of the whole group and a single section.

4. Wireless monitoring of a single battery: In the process of charging and discharging, the voltage and discharge curve of each battery can be monitored by wireless communication, and an automatic alarm will be given when any battery is lower than the lower limit.

In the actual operation process, a series of problems such as open circuit of the battery pack and loss of DC bus voltage are solvedMDC-1000G battery pack multi-function condition monitoring and voltage loss compensation systemProvide a set of multi-functional, modular comprehensive monitoring solutions with multi-state detection, open-circuit monitoring, voltage loss compensation, fault recording and automatic charging and discharging for battery packs.

MDC-1000G uses the battery pack self-compensation function to divide the battery pack into two sections, if one of the open circuit faults causes the bus to lose voltage, the other intact battery pack is used to provide short-term voltage loss compensation for the bus, so as to ensure the short-term operation of the relay protection and trip circuit. The real-time monitoring function of battery pack open circuit allows users to perform real-time data analysis, combined with historical data analysis, trend analysis and confirmatory analysis, to accurately and quickly determine open circuits. At the same time, the system also has the functions of single-cell battery monitoring, alternating direct monitoring, normally open and normally closed alarm node output, RS485 communication interface output, etc., which can communicate with the background to send alarm data. When the user needs to carry out the battery charge and discharge test, the optional energy feed discharge device is provided to carry out the battery pack charge and discharge and activation, charge and discharge curve and capacity monitoring. In addition to the routine test of the battery in the early stage of the construction of the DC power system, the MDC-1000G can also monitor the bus voltage after it is put into operation, and provide short-term voltage loss compensation for the bus when the battery pack is open.

Related Pages