First, the number of battery packs
“DC Design Regulations” has clearly defined various types of power projects. The principle is that from the standpoint of the reliability of DC load power supply, the power plant shall set up separate DC power systems in accordance with unit units and power and control loads. The network control part is set up independently and is set separately from the auxiliary workshops of the main plant. The power supply range of each battery DC system is reduced as far as possible and the independence of functions is guaranteed. 110kV important substations and substations of 220kV and above are starting from the importance and meeting the power supply requirements of relay protection and double-circuit breakers, and require the installation of 2 sets of batteries. Therefore, the number of battery packs should be based on the needs and reliability of the power supply load, reducing the power supply range as much as possible and considering the configuration from the importance of the project.
Second, the number of batteries to choose
The endless battery and the DC system without the pressure-reducing device simplify the wiring of the DC system, avoid the problem of vulcanization of the end battery and the trouble of the silicon pressure-reducing device, thereby improving the reliability. However, it is required that the operation of the battery pack must satisfy the normal busbar voltage of 105% of the nominal voltage during normal operation, the busbar voltage should not exceed 110% of the nominal voltage when the line charging voltage is equalized, and the bus voltage at the end of the accident discharge is its nominal voltage. 85% of the bus voltage of a DC system with a nominal voltage of 220V allows fluctuations between 187 and 242V. This float voltage is 2.23V, and the average charge voltage can be chosen between 2.28 and 2.33V. The voltage at the end of the accident discharge is chosen to be above 1.8V, which fully satisfies the fluctuation of the DC bus voltage within the permissible range. According to calculations, the number of 220V battery packs can only be selected for 103 or 104 batteries for a single 2V battery. However, the battery of most 220V DC systems in most small-scale power projects uses batteries below 200Ah. Most of them use 12V or 6V battery assemblies. For 12V assemblies, 18 are often used. This is equivalent to 108 single 2V batteries. This is normal operation. The DC bus voltage is higher, lowering the float voltage has an impact on the battery life. Because the DC bus voltage is higher during balanced charging during operation, it is more accustomed to using a silicon voltage regulator to regulate the voltage, increasing complexity and reducing reliability. Under the condition that the DC load is small and the battery capacity is guaranteed, the voltage at the end of the accident discharge can be increased by more than 1.83V, and a single 2V102 battery or 17 12V assemblies and 34 6V assembly batteries can be selected. At present, some battery factories can produce assembled batteries with a prosthesis, ie, a battery that produces a 10V assembly or a 4V assembly. If 14×12V+4×10V or 34×6V+1×4V is selected, it is equivalent to a single 2V battery. 104 battery packs. In short, the number of battery packs should be strictly controlled to simplify the wiring of the DC system.
Third, the choice of test discharge equipment
DL/T5044—2004 "Technical Specification for Design of DC System for Power Engineering" stipulates that "The test discharge device should use electrothermal device or active inverter discharge device." DL/T724-2000 "Technical specification for operation and maintenance of battery DC power supply device for power system It also specifies the battery's verification discharge method and discharge cycle.
What is the accident discharge capacity of a battery operated for a long time in a float charging mode, and the reliability is not high if only relying on a general capacity detection method. The level of the battery terminal voltage is not an indicator of the capacity. The only way is to check and charge the battery regularly to check the battery activation and capacity to ensure that the battery can always operate at more than 90% capacity. Satisfy the need for DC loads in the accident shutdown of power plants and the handling of accidents at substations in the event of a power outage during an exchange accident. This is also an important part of the reliability of DC power supplies.
Due to the backwardness of the equipment level of discharge equipment, the choice of discharge equipment is difficult and there is no good choice, which brings many difficulties to the operation and maintenance of the battery.