Motor protection device

• US 3,950,675 A
• Filed: 07/12/1974
• Issued: 04/13/1976
• Est. Priority Date: 07/12/1974
• Status: Expired due to Term

• Current Assignee: Sycon Corporation
• Original Assignee: Diversified Electronics, Inc.
• Inventors: Normet, Henno, Weber, Clement J.
• Primary Examiner(s): Goldberg, Gerald
• Assistant Examiner(s): Moose, Harry
• Application Number:
  US05/488,162
• Time in Patent Office: 641 Days
• Field of Search: 317/36 TD, 317/22, 317/141 S, 317/13 R, 317/13 A, 317/33 SC, 317/31
• US Class Current: 361/29
• CPC Class Codes: H02H 3/24 responsive to undervoltage or no-voltage H02H3/207 takes precedence
• CPC Class Codes: H02H 7/09 against over-voltage; against reduction of voltage; against phase interruption

Abstract

Electrical and electronic circuitry offering protection to motors, compressors and the like, from conditions of low energizing voltage or momentary voltage interruptions resulting in excessive mechanical load (locked rotor). When the undesirable condition is present, an internal relay prevents the equipment from being energized - transient conditions being allowed for by means of suitable time delay circuitry. The protection device provides significant improvement in safety and economy by preventing equipment from burning up.

Claims

1. Apparatus for use in combination with an electrical load and an electrical power supply having a pair of output terminals, comprising:

normally open switch means connecting said load to said power source to the closed position, and disconnecting said load from said source in the open position;

first and second input terminals connectable to said pair of output terminals;

a first impedance element connected between said first input terminal and a circuit node;

a second impedance element connected between said second input terminal and said node;

a relay coil for closing said switch means when energized, being connected between said first and second input terminals and in series with a gated semi-conductor switching device having a gate terminal;

a voltage sensitive break-down device connected between said node and said gate terminal for applying a gate control signal to said gate terminal when the voltage level at said node exceeds a predetermined value;

said semi-conductor switching device being responsive to said gate control signal to energize said relay coil only in the presence of said signal;

an inhibit circuit connected to said gate terminal for preventing said semi-conductor switching device from responding to said signal for a predetermined period of time after said switch means is changed from the open to the closed position;

a third impedance element connected between said node and said second input terminal; and

switch means connected in series with said third impedance element and responsive to energization of said coil to open the current path through said third impedance element.

2. Apparatus for use in combination with and connectable to an electric motor requiring a specified minimum voltage level for proper operation, and an electrical power supply for selectively interconnecting said motor and said power supply, comprising:

a voltage level detector circuit connected to said power supply and responsive to the voltage level occurring at output terminals of said power supply to generate a control signal only when said voltage level at said output terminals is greater than or equal to said specified minimum voltage level;

relay means having a relay coil and a set of normally-open contacts for interconnecting said motor and said power supply when said relay coil is energized;

switch means connected to said coil and responsive to said detector circuit control signal for energizing said coil;

said switch means being operative to prevent the flow of current through said coil in the absence of said control signal, whereby said first set of contacts are opened and said motor is disconnected from said power supply in the absense of said control signal;

an inhibit circuit for preventing said switch means from responding to said control signal for a predetermined period of time after opening of said contacts.

3. Apparatus in accordance with claim 2 wherein said relay further comprises a set of normally-closed contacts and wherein said voltage level detector circuit comprises a first impedance element connected in series with a second and third impedance elements connected in parallel, said third impedance element being connected in series with said normally-closed contacts, whereby the current path through said third impedance element is opened when said coil is energized.

4. Apparatus in accordance with claim 2, wherein said relay further comprises a set of normally-closed contacts and wherein said inhibit circuit comprises a capacitor having a discharge path including said normally-closed contacts, and a gate circuit connected to said capacitor and said switch means and responsive to charge on said capacitor when said normally-closed contact is in the closed position to inhibit activation of said switch means.