Medium-voltage distribution transformers can provide the final voltage conversion in the distribution system, thereby reducing the voltage used in the distribution line to the level used by customers.
The actual voltage level is usually called medium voltage, which means that the input voltage of the transformer is approximately 5 kV to 35 kV. Some distribution voltages may exceed 35 kV and are considered high voltage, but most distribution systems are in the medium-voltage range.
The inverters all adopt the pulse width modulation method, and the selected transformer should be able to be used with the pulse width modulation inverter. The AC output line voltage of the inverter is a power frequency sine wave, and the low-voltage side winding of the transformer needs to withstand a gradient voltage dU/DT of 500V/us to the ground.
When the inverter is in operation, the AC side is single-phased to the ground, and the maximum pulse voltage is ±1500V, and the corresponding root means square value can reach 800V. The low-voltage side winding of the selected transformer should be able to meet the requirements of this pulse voltage(wall-mounted transformer). At the same time, the maximum continuous working voltage of the lightning protection function of the low-voltage side winding of the transformer should be able to meet the requirement of this pulse voltage.
The line voltage on the low-voltage side of the transformer must match the line voltage output by the AC side of the inverter. Each inverter requires a low voltage winding that is electrically isolated. Ensure that the low-voltage winding and high-voltage winding of the transformer have good shielding isolation.
The line voltage output from the high voltage side of the transformer should be consistent with the grid voltage level at the installation site. In China, it is usually a 10kV/35kV medium-voltage grid. In foreign countries, it is usually a 15kV/22kV/25kV/27kV/30kV medium voltage grid. It is recommended to use a transformer with a tap changer on the high-voltage side, which can better adapt to different medium-voltage grid levels.
Ensure that the transformer core has one and only one reliable grounding; ensure that the transformer shell is reliably grounded. It is recommended that the low-voltage side winding and the high-voltage side winding of the transformer adopt different winding methods.