1. Operating temperature of the transformer:
During operation, transformers generate copper losses and iron losses, both of which are converted into heat. This heat causes the temperature of the transformer to rise. Most transformers in China use Class A insulation. In the process of heat transfer during transformer operation, there is a significant temperature difference between different parts. The winding temperature is the highest, followed by the core temperature, and then the insulation oil temperature. Additionally, the temperature of the oil in the upper layer is higher than that in the lower layer. The allowable temperature during transformer operation is determined by the temperature of the oil in the upper layer. For transformers with Class A insulation, under normal operating conditions, when the ambient temperature is 40°C, the maximum temperature of the oil in the upper layer of the transformer shouldn't exceed 85°C.
2. Temperature rise during transformer operation:
The temperature difference between the transformer temperature and the surrounding medium temperature is called the temperature rise of the transformer. Due to the significant temperature difference between different parts of the transformer, this will affect the insulation of the transformer. Moreover, as the temperature of the transformer increases, the losses in the winding will also increase. Therefore, it is necessary to specify the temperature rise of each part of the transformer under rated load conditions. For transformers with Class A insulation, when the ambient temperature is 40°C, the allowable temperature rise of the upper layer oil is 55°C, and the allowable temperature rise of the winding is 65°C.
3. Voltage variation range during transformer operation:
In the power system, due to voltage fluctuations in the grid, the voltage applied to the transformer winding will also fluctuate. When the grid voltage is lower than the rated voltage of the tap used by the transformer, there is no damage to the transformer. When the grid voltage is higher than the rated voltage of the tap used by the transformer, it will cause the winding temperature of the transformer to rise, increase the reactive power consumed by the transformer, and distort the waveform of the secondary coil. Therefore, it is generally advisable for the power supply voltage of the transformer not to exceed 5% of the rated voltage of the tap.
4. Requirements for parallel operation of transformers:
Parallel operation of transformers refers to connecting the primary windings of two or more transformers to a common power source and connecting the secondary windings in parallel to supply power to the load. In today's power system, as the system capacity increases, parallel operation of transformers is essential.
The parallel operation of power transformers must meet the following requirements:
(1) The transformation ratios of each transformer should be equal, with an allowable difference within +0.5%.
(2) The short-circuit voltages of each transformer should be equal, with an allowable difference within +10%.
(3) The connections of each transformer should be the same.