| 摘要 |
When short circuits occur in the operation of electricity supply systems (predominantly medium-voltage systems in this case), it is attempted to find the source of the fault as quickly as possible. To find the fault quickly, short-circuit indicators are used. The short-circuit indicators hitherto used in practice could only be used in radial systems with one feed point. The indicator of the direction of power flow is capable of finding and indicating the power flow in a power system. This makes it possible to monitor ring systems and parallel systems having one or more feed points. The operation of the indicator of the direction of power flow is determined by the phase angle of the alternating voltage from a generator (Figure 1) being picked up and stored for a short period in the case of a short circuit (the alternating voltage drops to zero volts). Thus, the phase angle of the alternating voltage can be compared with the phase angle of the alternating current at the instant of the short circuit. The displacement in the phase angle between alternating current and alternating voltage allows the direction of power flow to be determined. <IMAGE>
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