Self-power tripping relay with balanced power supply current and measurement current

摘要

A current induction arrangement develops a power supply voltage and a measurement signal from current flowing in a circuit path so as to optimize both the energy developed in the power supply and the fidelity of the sinusoidal signal used to measure the waveform in the circuit path. The arrangement includes a capacitor accumulating current to develop a positive voltage with respect to common, a current transformer inducing current from the circuit path and providing an output having a positive induced-current signal component and a negative induced-current signal component. A rectifier circuit is arranged to receive the output from the current transformer, and to produce the positive induced current signal component at a positive output terminal and the negative induced current signal component at a negative output terminal. A first zener diode is connected to receive the positive induced-current signal component, and the circuit permits the positive induced-current signal to charge the capacitor. The first zener diode also has a second terminal coupled to common. A second first zener diode is coupled between the negative output terminal and common via a burden resistor. For developing a measurement voltage corresponding to the current produced by the current transformer, the burden resistor is arranged in series with the second zener diode. The positive and negative induced- current signal components are returned to the current transformers via common.