Power monitoring

• US 5,754,421 A
• Filed: 07/07/1995
• Issued: 05/19/1998
• Est. Priority Date: 05/10/1994
• Status: Expired due to Fees

• Current Assignee: Load Controls Incorporated
• Original Assignee: Load Controls Incorporated
• Inventors: Nystrom, Robert W.
• Primary Examiner(s): Hecker, Stuart N.
• Assistant Examiner(s): Han, Y. J.
• Application Number:
  US08/499,749
• Time in Patent Office: 1,047 Days
• Field of Search: 363/1, 363/2, 363/148, 363/152, 363/153, 363/64, 363/155, 363/156, 323/212, 323/213, 323/215, 323/216, 323/332, 323/355, 323/356, 323/361
• US Class Current: 363/155
• CPC Class Codes: G01R 21/08 by using galvanomagnetic-effect devices, e.g. Hall-effect devices

Abstract

Electrical power monitoring apparatus comprises a loop and a first conductor. A current sensor coupled to the first conductor provides a current signal that is representative of the current in the first conductor. A voltage sensor coupled at least to the first conductor provides a voltage signal that is representative of the voltage on the first conductor relative to that on a reference terminal. A multiplier coupled to the current sensor and voltage sensor has a power output which provides a power signal that is proportional to the instantaneous value of electrical power carried by the first conductor. A calibration circuit in the loop has an input coupled to the power output and has an adjustable output. A current regulator in the loop has an input coupled to the adjustable output to maintain the current in the loop between predetermined minimum and maximum loop current values.

Claims

1. A dual primary transformer comprising:

a core,

first, second and third input terminals,

first and second primary windings on said core connected in series between said first and said third terminals at said second terminal,

first and second output terminals,

a secondary winding on said core connected between said first and second output terminals,

a source of a three-phase supply having first, second and third phases coupled to said first, second and third input terminals respectively,

said transformer constructed and arranged so that voltage between said first and second output terminals is in phase with the signal on said second input terminal.

2. A single primary transformer circuit comprising,

a core,

first, second, and third input terminals,

a primary winding on said core having first and second ends,

said first end coupled to said first input terminal,

a first resistor connected between said second input terminal and said second end of said primary winding,

a second resistor connected between said third input terminal and said second end of said primary winding,

a source of a three-phase supply having first, second and third phases coupled to said first, second and third input terminals respectively,

first and second output terminals,

and a secondary winding on said core connected between said first and second output terminals,

said transformer circuit constructed and arranged so that the voltage between said first and second output terminals is in phase with the signal on said first input terminal.

3. A transformer circuit comprising,

a core,

first, second and third input terminals,

primary winding structure on said core connected between said first and third input terminals and to said second input terminal,

first and second output terminals,

a secondary winding on said core connected between said first and second output terminals,

a source of a three-phase supply having first, second and third phases coupled to said first, second and third input terminals, respectively,

said transformer circuit constructed and arranged so that voltage between said first and second output terminals is in phase with the signal on a selected one of said first and second input terminals.

4. A transformer circuit in accordance with claim 3 wherein said primary winding structure comprises first and second primary windings connected in series between said first and third input terminals at said second input terminal,

said transformer circuit constructed and arranged so that voltage between said first and second output terminals is in phase with the signal on said second input terminal.

5. A transformer circuit in accordance with claim 3 wherein said primary winding structure comprises a primary winding on said core having first and second ends,

said first end coupled to said first input terminal,

and further comprising a first resistor connected between said second input terminal and said second end of said primary winding,

a second resistor connected between said third input terminal and said second end of said primary winding,

said transformer circuit constructed and arranged so that the voltage between said first and second output terminals is in phase with the signal on said first input terminal.