| 摘要 |
<p>For safeguarding an alternating current electrical power supply system against a blackout due to overloading, particularly on a system which is not strongly interconnected, each consumer (20, 21, 22) is provided with means sensing when the supply frequency falls below a predetermined frequency, these means controlling switching devices (36) for interrupting the power to at least part of the load taken by each consumer. The sensing means conveniently comprises a control unit (50) responsive to the loss in phase lock of an oscillator (40) locked to the incoming supply frequency and forming for example part of an energy metering device. Provision is made for automatic restoration of the supply to loads when the frequency increases to another predetermined value.</p> |
