| 摘要 |
An alarm system for warning of unbalance or failure of one or more phases of a multi-phase load circuit which is convenient and practical to use even where the load circuit is drawing a large current and where the flow of power to the load may be controlled by various devices, said alarm system including a three-phase resistance bridge circuit with a phantom neutral point at the common juncture of three similar resistances connected in a Y-pattern and each shunted across a secondary winding of transformers having magnetic cores encircling the power leads to the load circuit and with the outer terminals of these resistors connected through resistance elements to the adjustable taps of three potentiometers included in the respective legs of a second Y pattern having the outer ends of these legs connected to the respective load phases for defining a second neutral point at their common junction. An unbalance sensing resistor is connected in circuit between the phantom neutral point and the second neutral point with an alarm circuit connected across said unbalance sensing resistance element. The alarm circuit includes adjustable amplifier means, time-delay means, adjustable threshold responsive means, alarm means for giving a warning signal, operating means for the alarm means and actuating means connected to said operating means and controlled by said threshold means with a hysteresis feedback circuit for preventing fluctuation of said threshold responsive means after it has responded to an unbalance signal. The alarm circuit also provides warning if the input power fails in one or all phases due to a blown fuse or any other cause.
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