A transformed current sensing relay (k2) with reduced AC impedance of the operating coil is accomplished by adding a shorted secondary winding (14) to an otherwise conventional current sensing reed relay The shorted secondary winding (14) is preferably implemented with a copper tube over the existing coil and inside the magnetic circuit This transformed current sensing relay (k2) is particularly advantageous for the line current sensing function in switched network communications equipment such as high speed modems, where the transformed relay (k2) exhibits substantially lower impedance at high frequencies than the conventional current sensing relay This transformed current sensing relay (k2) allows for the elimination of bypass capacitors and results in significant cost and space savings Moreover, the transformer nature of the transformed current sensing relay (k2) allows for the elimination of suppression resistors from the interface resulting in additional cost and space savings

Transformed current sensing relay for use in switched network modems and circuit incorporating same

An electronic overload relay connectable in series with the operating coil of a contactor for protecting a motor from overheating due to carrying greater than desired current. The disclosed overload relay includes a time delayed reset feature which does not require control power to provide the delayed reset. The delayed reset prevents an operator from restarting a motor before it has cooled off by interrupting power to the overload relay and then reapplying power. The time delayed reset includes means for transferring energy stored in the sensing and tripping portions during the overload period to an energy storage device which prevents power from being reapplied to the electric motor until a predetermined time after the overload relay has tripped. The transferred energy is discharged through a timing resistor until a predetermined point is reached at which time the overload relay can be again closed. A light emitting diode is provided to indicate that the overload relay is in the tripped mode and power cannot be applied to the protected motor. Operation of the overload trip relay is unaffected by connecting or disconnecting power to the motor during normal operation.

Solid state overload relay

A fault detector circuit for an electric vehicle control. The circuit is coupled to a power switching device for connecting a load, such as traction motor, to a source of DC voltage. When the conductivity of the power switching device remains high for an unduly long period of time the circuit produces a signal for disabling the control. If the switching device returns to a nonconductive condition within a subsequent predetermined period of time, the disabling signal ceases and a reset circuit is activated, causing it to change state. Should the switching device remain conductive for an undue period for a second time, a disable signal is again produced but the reset circuit, now in its changed state, renders it impossible to discontinue the disabling signal.

Fault detector circuit for electric vehicle control

A motor controller receives a signal proportional to motor current, integrates that signal during the high currents associated with starting, and holds a level during normal operation at speed within a maximum current limit. When an overload causes the motor to trip and there is a loss of power to the controller, a memory holds the level for a predetermined time to prevent an immediate restart of the motor.

Motor protector relay with memory of overload

In phase loss detection circuits a false indication can occur doing the starting, stopping and severe load transitions of a three-phase motor. The present phase loss detection circuit solves this problem by using a circuit (33) to detect the lost of a phase, a comparator (25), a changing capacitor (C5), a peak detection (21) and an overload voltage integrator (38), all of which provide a positive indication of either a phase loss or overload condition. The present phase loss circuit including transient protection which may be used with three-phase motors in a three-phase electrical system.

Phase loss detection circuit including transient protection

Overload and other excessive current conditions as regards an electric motor are sensed by current sensing loops which form the primary winding of respective transformers. The voltage developed across the secondary windings are rectified and supplied to a deenergizing circuit which additionally includes a holding circuit and a timing circuit. In the event of an overload condition, the current supply to the electric motor is interrupted and also a time delay is effected before reset occurs assuming that electric power is again available.

Walstad Dennis C Winfield

Papers

Solid state de-energizer having current sensing loops