Transformer Insulation Can Be Divided into Internal Insulation and External Insulation
The insulation of the transformer can be divided into internal insulation and external insulation. The inner insulation is the insulation of the various parts in the fuel tank, and the outer insulation is the insulation between the upper part of the casing and the ground. The inner insulation can be divided into two parts: main insulation and longitudinal insulation. The main insulation is the insulation between the winding and the ground and between the windings.
In oil-immersed transformers, the main insulation is most commonly used as an insulating crepe paper barrier insulation structure. Longitudinal insulation is the insulation between the parts of the same winding, such as the insulation between different windings, between layers and between turns. Generally, the distribution of the impact voltage on the winding is used as the basis for the longitudinal insulation design of the winding, but the interturn insulation should also consider the influence of the long-term power frequency operating voltage.
The rectifier transformer may withstand the common mode voltage during operation. The common mode voltage generally refers to the voltage between the neutral point of the motor and the ground. Any frequency converter will generate a common mode voltage when the high frequency switch is working, and take certain measures on the output side of the inverter. The common mode voltage is transferred from the motor to the rectifier transformer, which no longer experiences the common mode voltage.
The common mode voltage has high du/dt and high amplitude voltage pulse characteristics, and the influence of common mode voltage should be considered when designing the low voltage winding insulation of the rectifier transformer. In order to ensure safe and reliable operation, the low voltage side of the rectifier transformer is generally required to increase an insulation level. Insulated crepe paper tubes can be used, and the low-voltage windings should be reinforced accordingly.