Automatic insulation test equipment for testing high voltage electrical equipment at the rated voltage level

• US 5,514,967 A
• Filed: 08/16/1994
• Issued: 05/07/1996
• Est. Priority Date: 08/16/1994
• Status: Expired due to Term

• Current Assignee: Richard J. Zelm
• Original Assignee: Richard J. Zelm
• Inventors: Zelm, Richard J.
• Primary Examiner(s): Regan, Maura K.
• Application Number:
  US08/291,411
• Time in Patent Office: 630 Days
• Field of Search: 324/510, 324/523, 324/527, 324/551, 324/772, 361/30, 361/33, 361/23, 361/42, 340/647, 340/648, 340/650
• US Class Current: 324/551
• CPC Class Codes: G01R 31/1227 of components, parts or materials G01R31/1209, G01R31/1218, G01R31/18 take precedence; circuits therefor G01R31/14; testing vessels of electrodes G01R31/16
• CPC Class Codes: G01R 31/14 Circuits therefor , e.g. for generating test voltages, sensing circuits G01R31/1209 - G01R31/1227 take precedence; for testing switches G01R31/327
• CPC Class Codes: G01R 31/346 Testing of armature or field windings

Abstract

Insulation test equipment for testing high voltage electrical equipment at rated voltage levels up to above 5 kV. A multistage rectifier-capacitor voltage multiplier ladder is used to boost the test voltage to the desired level, while keeping the current and load capacity to a safe, low level. If an appreciable amount of current is attempted to be drawn, such as might occur with accidental human contact, the rectifier--capacitor ladder breaks down to limit the voltage and current to safe levels. Two separate current limit resistors are provided for both outgoing and incoming voltages of the test equipment. One is installed in the test apparatus and the other is installed on the high voltage fuse at the contact point between the motor windings and the test lead. The voltages and insulation current generated by the test equipment are monitored indirectly through opto-coupler circuits to isolate and protect the monitoring circuits and the operator.

Claims

1. An insulation tester for measuring the insulation resistance of a high rated voltage motor or generator, the motor or generator having a chassis and at least one winding, the tester comprising:

a high voltage power supply having a first terminal for coupling to the winding and a second terminal for coupling to the chassis of the motor or generator, said high voltage power supply comprising;

means for generating a voltage signal having an intermediate voltage level; and

a voltage multiplier having a plurality of stages for converting said intermediate voltage signal to a high DC output voltage equal to or exceeding the rated voltage of the motor or generator and for providing said high output voltage between said first and second terminals, said voltage multiplier having a limited current capacity wherein said high output voltage collapses towards said intermediate level if a load across said first and second terminals causes the current provided to the load to exceed a predetermined maximum level, wherein said maximum current level is substantially safe for equipment and humans; and

sensing means coupled between said first and second terminals for determining the insulation resistance of the motor or generator by measuring the current flowing between said terminals.

2. The insulation tester of claim 1, wherein said intermediate voltage signal generating means comprises:

means for generating a low DC voltage;

a high impedance oscillator having an input and an output, wherein said oscillator input receives said low DC voltage; and

a transformer having a primary and a secondary, wherein said primary is coupled to said output of said high impedance oscillator,

wherein said oscillator switches said transformer to provide said intermediate voltage at said secondary of said transformer.

3. The insulation tester of claim 2, wherein said transformer is insulated to withstand said high voltage.

4. The insulation tester of claim 3, wherein said high DC output voltage is 5 kV.

5. The insulation tester of claim 1, wherein said voltage multiplier comprises:

a multistage rectifier-capacitor ladder.

6. The insulation tester of claim 5, wherein said multistage rectifier-capacitor ladder comprises:

a first set of capacitors coupled in series;

a second set of capacitors coupled in series; and

a set of rectifiers, coupled between said first and second sets of capacitors.

7. The insulation tester of claim 1, wherein said high DC output voltage is 5 kV.

8. The insulation tester of claim 1, further comprising:

a first current limit resistor connected between said high DC output voltage and said first terminal; and

a second current limit resistor connected between said first terminal and winding and located near the motor or generator.