Electrical load transfer control system

• US 3,971,957 A
• Filed: 05/30/1975
• Issued: 07/27/1976
• Est. Priority Date: 05/30/1975
• Status: Expired due to Term

• Current Assignee: Alfred Max Hase
• Original Assignee: Alfred Max Hase
• Inventors: Hase, Alfred Max
• Primary Examiner(s): Hohauser, Herman
• Application Number:
  US05/582,200
• Time in Patent Office: 424 Days
• Field of Search: 307/64, 307/66, 307/60, 307/61, 307/62, 307/63, 307/80, 307/43
• US Class Current: 307/64
• CPC Class Codes: H02J 9/062 for AC powered loads

Abstract

In an electrical system having two power sources, one being an inverter and the other being a commercial power souce, where the load is critical and is normally connected to the inverter, a load transfer control system is provided to assure uninterrupted power supply to the load in the event of inverter failure. The load transfer control system includes a fault detector connected to the inverter, a fast-acting and normally open switch connected to the commercial power source and the load, and a slower acting and normally closed switch connected to the inverter and the load. When an inverter fault is sensed, there is a momentary make-before-break switch action of the two switches. A ferroresonant circuit is in the inverter circuit, and has a storage element with enough energy storage capacity to carry the load during the period that it takes for the fault detector to operate and the first switch to close. The switches are contactors or similar devices, so that there is complete voltage and current isolation of one power source from the other when the respective switch is open.

Claims

1. For use in an electrical power system having two power sources, where the first power source is an ordinarily available aternating current source and the second power source is an inverter having an output synchronized to said first power source, and where the load is an alternating current load which is normally connected to the output of said second power source;

a control system for providing an essentially uninterrupted power flow to said load in the event of failure of said second power source by transferring said load to said first power source, and for isolating said second power source from said first power source when said first power source is connected to said load, comprising;

first controllable and normally open switch means having a first operating period to close, and being connected to said first power source and to said load;

second controllable and normally closed switch means having a second operating period to open, and being connected to said second power source and to said load;

each of said first and second switches being such that the respective power source is both current and voltage isolated from said load when that switch is open;

fault sensing means connected to said second power source for sensing any fault therein while said second power source is connected through said second switch means to said load;

said fault sensing means being connected to said first switch means so as to emit a first control signal to cause said first switch means to close when a fault in second power source is sensed, and being connected to said second switch means so as to emit a second control signal simultaneously with said first control signal to cause said second switch means to open;

and a ferroresonant circuit having an energy storage element connected between said second power source and said load so as to be connected to said load even after any failure of said second power source for at least the length of time of said second operating period;

3. The control system of claim 1 where said energy storage element is connected between said second switch means and said load.

4. The control system of claim 1 where said energy storage element is connected to the output of said second power source and to said load.

5. The control system of claim 3 where said first switch means is a controllable contactor.

6. The control system of claim 3 where said first switch means is a fast-acting motor-operated switch.

7. The control system of claim 3 where said second switch means is a controllable contactor.

8. The control system of claim 3 where said second switch means is a shunt trip breaker in said inverter.

9. The control system of claim 3 where said first and second switch means are each solid state switch devices.

10. The control system of claim 3 where, when at least said first switch means is a solid state switch device, it has isolating means associated therewith so as to assure both voltage and current isolation of said load when said first power source is non-operative.

2. said first operating period being shorter than said second operating period so that said first switch means is closed before said second switch means is opened after a fault in said second power system has been sensed;

said energy storage element having at least sufficient energy storage capacity substantially to provide the energy requirement of said load for the length of time of said first operating period plus the operating period of said fault sensing means.