1.General principle
In order to ensure the safety of high voltage electrical appliances in normal operation, overhaul, short circuit and overvoltage, high voltage electrical appliances should be selected according to the following conditions:
① According to the normal working conditions, including voltage, current, frequency, mechanical load and other options
② short-circuit conditions, including short-term withstand current, peak withstand current, closing and breaking current selection;
③ According to environmental conditions, including temperature, humidity, altitude, earthquake and other options;
④ to withstand the voltage capacity, including the level of insulation and other options;
⑤ according to various types of high-voltage electrical appliances, including the characteristics of the switch, the protection of the characteristics of the fuse, the transformer load and the exact level of choice.
2. Select high voltage electrical appliances according to normal operating conditions
① Select the high voltage electrical appliance according to the working voltage. The rated voltage should be in accordance with the nominal voltage of the system where the circuit is allowed. The maximum operating voltage Umax should not be less than the maximum operating voltage Uy of the circuit, Umax ≥ Uy
② According to the working current selection of high voltage electrical current In should not be less than the loop in a variety of possible operating mode of continuous operating current Ig, that is, In ≥ Ig.
3. Select the high voltage appliance according to the short circuit stabilization condition
① general requirements for short-circuit stability check
② short-circuit current thermal effect
③ short circuit stability check
4. Select high voltage electrical equipment according to environmental conditions
① Select the ambient temperature of the appliance
② Select the ambient humidity of the appliance
③ high altitude on the impact of high voltage electrical appliances
④ earthquake on the impact of high-voltage electrical appliances
5. High-voltage electrical insulation level
6. According to the different characteristics of various types of high-voltage electrical appliances
① rated short circuit breaking current selection
② the choice of rated short-circuit closing current
③ the choice of the order of operation
④ rated out-of-step breaking current selection
⑤ rated out-of-phase fault fault current, development fault current and the choice of breaking current
⑥ Selection of rated breaking current
⑦ rated circuit charge breaking current, rated cable charging breaking current, rated power
Container group breaking current, rated capacitor group inrush current, rated induction electric
Circuit breaking current, rated no-load transformer breaking current, rated reactor breaking
Current and other options. The standard on the above-mentioned breaking current and closing current is not
Shall be used in accordance with the test data given by the manufacturer.
