Abstract: The invention provides a circuit to protect an AC motor powered by a Variable Frequency Drive (VFD) from overvoltages caused by reflected waves. A full wave bridge rectifier circuit across the lines of the motor to be protected provides rectified voltage output to a capacitor, across which a low resistance discharge resistor in series with one or more zener diodes is attached. When an overvoltage above the clamping voltage of the zener diode(s) occurs across the protected lines, the zener diode(s) will conduct, causing the excess charge across the capacitor to discharge through the resistor until the voltage drops below the clamping voltage of the diode(s).

Abstract: A method and device for detecting when a clipping component within a transient voltage surge suppressor (TVSS) or TVSS with high frequency electrical noise attenuation (both called surge suppression device or SPD) has failed open. The method comprises the steps of: collecting airborne debris and gases generated when the SPD fails open in a space; subjecting the space to a particle detector; diagnosing the detection of particles by the particle detector and communicating the diagnosis to an appropriate signal generator. The device comprises a container within which at least the clipping components of the SPD reside; an open air space within the container; particle detector associated with the space within the container; and an electronic control unit electronically associated with the particle detector to receive a message that airborne debris or gas particles are within the air space inside the container and then to communicate and, as required, act on such.

Abstract: This invention relates to a communication line filter for use in series with communication lines. The communication line filter provides for surge protection from voltage spikes and provides frequency filtering to remove selected interference signals from other radiating sources. The communication line filter comprises: two signal conductors linked together by a fuse; a common signal ground; and two shunts for shunting a surge current between the signal conductors and the common signal ground. The shunts provide protection from short duration voltage spikes while the fuse provides protection from longer duration overvoltages. The communication line filter functions effectively, independent of the direction of current flow along the communication line with respect the line filter. The two shunts and the fuse are selected to provide the required capacitance and impedance respectively, to form a suitable frequency notch filter.