Discharge Method Of Dry Type Power Transformer
The discharge methods of dry type power transformer include constant current discharge, constant load discharge, pulse discharge and constant power discharge. The discharge of lithium-ion dry-type transformers mainly adopts the method of constant load, because the internal resistance of the dry-type transformer will change during discharge. Therefore, when testing the discharge performance of dry-type transformers, constant current discharge is often used. When the dry-type transformer group is discharged, the dry-type transformer protection board is set to a low protection voltage to prevent the dry-type transformer from failing due to overdischarge.
The discharge voltage of the single dry type power transformer is usually controlled at 2.75V, and the voltage is controlled at 2.5V during low-temperature or high-rate discharge; when the dry-type transformer group is used, the general discharge voltage is n·3V (n is the number of dry-type transformer groups). When the discharge voltage is lower than the lower limit of discharge, the dry-type transformer is over-discharged.
The size of the discharge current will affect the discharge performance of the dry-type transformer. Under the high current, the discharge voltage platform of the dry-type transformer will decrease, and the discharge capacity will decrease, especially during constant power discharge due to the decrease of the discharge voltage platform, the working current increases, and If the current exceeds 2C, the capacity of the dry-type transformer will be greatly affected. Therefore, various dry-type transformer manufacturers generally recommend that the dry-type transformer discharge within 2C, unless a dry-type transformer produced by a special process (such as a power-type dry-type transformer) is adopted.
The working temperature range of lithium-ion dry type power transformer is wide, ranging from -40 to +60 °C, and the working environment temperature of ordinary lithium-ion dry-type transformers is -25 to +55 °C. If you want to meet the performance of dry-type transformers at low temperature (-40°C) or high temperature (60°C), the materials and design of dry-type transformers are different from ordinary dry-type transformers, so the cost of high-temperature dry-type transformers and low-temperature dry-type transformers are both higher than ordinary dry-type transformers.
When the lithium-ion dry-type transformer is discharged at low temperature, the internal resistance of the dry-type transformer increases a lot, and there will be a large voltage drop in the initial stage of discharge, and then the dry-type transformer voltage rises and begins to discharge smoothly. However, the discharge capacity is lower than that at room temperature, and the lower the temperature, the less the discharge capacity. The low operating temperature and discharge capacity of Li-ion dry-type transformers are closely related to the design of dry-type transformers and the materials used.
In a high temperature environment, the discharge capacity of dry type power transformer is slightly higher than that at room temperature, but similar. Studies have shown that long-term operation at high temperature (40°C) reduces the cycle life of dry-type transformers.
