General principle
In order to ensure the safety of high-voltage electrical appliances under normal operation, maintenance, short-circuit and over-voltage conditions, high-voltage electrical appliances should be selected according to the following conditions:
1 According to normal working conditions, including voltage, current, frequency, mechanical load, etc.;
2 According to the short-circuit conditions, including short-time withstand current, peak withstand current, closing and breaking current;
3 According to environmental conditions, including temperature, humidity, altitude, earthquake, etc.;
4 Select according to the ability to withstand voltage, including insulation level;
5 According to the different characteristics of various types of high-voltage electrical appliances, including the operating performance of the switch, the protection characteristics of the fuse, the load of the transformer and the accuracy level.
2. Select according to normal working conditions
1 According to the working voltage, the selected high-voltage electrical appliance shall have its rated voltage in accordance with the nominal voltage of the system in which it is located. The maximum operating voltage Umax shall not be less than the maximum operating voltage Uy of the loop, ie Umax ≥ Uy.
2 According to the working current, the rated current In of the high-voltage electrical appliance should not be less than the continuous working current Ig of the circuit under various possible operating modes, ie In ≥ Ig.
3. Select according to short-circuit stability conditions
1 General requirements for short circuit stability check
2 Thermal effect of short circuit current
3 short circuit stability check
4. Select according to environmental conditions
1 Select the ambient temperature of the appliance
2 Select the environmental humidity of the appliance
3 High altitude impact on high voltage electrical appliances
4 Influence of earthquake on high-voltage electrical appliances 1 Selection of rated short-circuit breaking current
2 rated short circuit closing current selection
3 Selection of rated operation sequence
4 rated out-of-step breaking current selection
5 Rated out-of-phase ground fault current, developmental fault current and selection of breaking current
6 Rated near-zone fault breaking current selection
7 rated line charging breaking current, rated cable charging breaking current, rated electricity
Container group breaking current, rated capacitor bank closing current, rated induction electric
Machine breaking current, rated no-load transformer breaking current, rated reactor breaking
The choice of current, etc. In the standard, the breaking current and closing current for the above items are not
Provisions, but in use should be selected according to the test data given by the manufacturer.
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