Solid state over-current protective apparatus for a power circuit
US4345288A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 4, 1981 |
| Grant date | Aug 17, 1982 |
| Priority date | — |
| Expiry date | May 4, 2001 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH02H7/09
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
A solid state overload relay protective apparatus for electric motors which includes not only the overload feature, but the additional features of underload and single phase protection. Small current transformers for sensing the current flow in each phase of the motor are utilized, like those found in the ground fault sensing art because a current-to-voltage converter circuit reflects a short circuit back to the secondary of the transformers. The signal from the current transformers which is proportional to the sensed current in the motor is fed through the converter, a scaling and summing amplifier adjustable for a wide range of motor full load currents, an ideal diode peak detector, a time integrator amplifier, to one input of a comparator circuit having a trip reference voltage signal at another input. The comparator provides an output signal to a transistorized trip level circuit that deenergizes a coil of an overload relay opening its contacts and interrupting power to the motor.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.