Monitoring of internal partial discharges in a power transformer

• US 5,903,158 A
• Filed: 12/06/1996
• Issued: 05/11/1999
• Est. Priority Date: 05/02/1995
• Status: Expired due to Term

• Current Assignee: ABB Research Ltd. (ABB Ltd.)
• Original Assignee: ABB Research Ltd. (ABB Ltd.)
• Inventors: Eriksson, Thomas, Leijon, Mats
• Primary Examiner(s): Regan, Maura K.
• Application Number:
  US08/750,592
• Time in Patent Office: 886 Days
• Field of Search: 324/142, 324/547, 324/536, 324/72, 174/143
• US Class Current: 324/536
• CPC Class Codes: G01R 15/142 Arrangements for simultaneous measurements of several parameters employing techniques covered by groups G01R15/14 - G01R15/26
• 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 31/62 Testing of transformers

Abstract

In a method for monitoring of partial discharges in an electric power transformer (1) under normal operating conditions, the magnetic field at a high-voltage bushing (2) on the power transformer is sensed with an inductive sensor (6) comprising at least one coil (6a, 6b) arranged at the bushing, and the electric field at the bushing is sensed with a capacitive sensor (5). The output signals from said sensors are supplied to a signal processing unit (3) in which each one of the output signals is filtered in a separate bandpass filter (101, 102), whereupon the filtered output signals from said sensors are multiplied by each other. An output signal (PDI) from the signal processing unit is formed in dependence on the result of said multiplication for the purpose of detecting internal partial discharges in the transformer.

Claims

1. A method for monitoring partial discharges in an electric power transformer under normal operating conditions, comprising:

sensing a magnetic field at a high-voltage bushing on the power transformer with an inductive sensor that includes at least one coil arranged at the bushing;

sensing an electric field at the high-voltage bushing with a capacitive sensor;

supplying output signals from the inductive sensor and the capacitive sensor to a signal processing unit in which each output signal is filtered in a separate bandpass filter;

multiplying the filtered output signals by each other;

forming with the signal processing unit a PDI output signal corresponding to the amount of internal partial discharge in the transformer in dependence on the result of the multiplication to detect internal partial discharges in the transformer.

2. The method according to claim 1, wherein the capacitive sensor includes a capacitive test tap on the high-voltage bushing.

3. A device for monitoring partial discharges in an electric power transformer under normal operating conditions, comprising:

an inductive sensor including at least one coil arranged at a high-voltage bushing on the power transformer;

a capacitive sensor arranged at the bushing; and

a signal processing unit for receiving output signals from the inductive sensor and the capacitive sensor and forming a PDI output signal corresponding to the corresponding to the amount of internal partial discharge in the transformer, the signal processing unit including bandpass filters for filtering the output signals from the inductive sensor and the capacitive sensor, the signal processing unit also including a multiplier for multiplying signals from the respective bandpass filter by each other and producing the PDI output signal in dependence on the output signal from the multiplier.

4. The device according to claim 3, wherein the inductive sensor includes two mutually series-connected coils arranged opposite to each other at the high-voltage bushing.

5. The device according to claim 3, wherein the capacitive sensor includes a capacitive test tap on the high-voltage bushing.

6. The device according to claim 3, wherein the signal matching unit includes a peak value detector for receiving a signal from the multiplier and for transmitting signals only with a preselected polarity.

7. The device according to claim 3, wherein the signal matching unit includes a conversion circuit for converting a signal from the multiplier into a direct current corresponding to the signal.