Apparatus for and method of ground fault detection

• US 20040145842A1
• Filed: 01/09/2004
• Published: 07/29/2004
• Est. Priority Date: 01/09/2003
• Status: Active Grant

• Current Assignee: Safran Power UK Ltd.
• Original Assignee: Goodrich Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Rice, Kevin Edward
• Granted Patent: US 7,233,464 B2
• Time in Patent Office: Days
• US Class Current: 361/42
• CPC Class Codes: H02H 3/006 Calibration or setting of parameters
• CPC Class Codes: H02H 3/28 involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus for transformers H02H7/045
• CPC Class Codes: H02H 7/06 for dynamo-electric generators; for synchronous capacitors

Abstract

A ground fault detection system is provided where one current sensor is used to calibrate a second sensor in order to provide automatic zeroing of the difference measurement. The calibration is done gradually in order to differentiate between sensor drift and a transition in current due to a differential fault.

Claims

1. A ground fault protection system, comprising:

a first current measuring device for measuring current flow to a load;

a second current measuring device for measuring current flow from a source of electrical power;

and a controller arranged to compare measurements from the first and second current measuring devices when there is no ground fault condition;

to derive a relationship between the measurements; and

on the basis of the relationship to compare the current flow to the load and the current flow from the source of electrical power and to disconnect or de-energise the source of electrical power if the currents differ by more than a predetermined value.

2. A ground fault detection system as claimed in claim 1, wherein the first current measuring device is used to calibrate the second measuring device.

3. A ground fault protection system as claimed in claim 1, wherein the source of electrical power is a generator and the second current measuring device is a winding within the generator.

4. A ground fault protection system as claimed in claim 3, wherein the winding within the generator is an interpole winding.

5. A ground fault protection system as claimed in claim 3, wherein the controller estimates the resistance of the winding.

6. A ground fault protection system as claimed in claim 3, wherein the controller measures the voltage occurring across the winding.

7. A ground fault protection system as claimed in claim 1, in which the outputs of the first and second current measuring devices are filtered.

8. A ground fault protection system as claimed in claim 1, in which the controller applies a time varying correction to a measurement of current difference such that under no fault conditions the measurement of current difference tends to approach a reference value.

9. A ground fault protection system as claimed in claim 8, in which a ground fault is indicated when the measurement of current difference differs from the reference value by more than a first threshold.

10. A ground fault protection system as claimed in claim 1, in which the relationship derived when a first current is flowing allows the current measuring devices to be used to compare current flow at values different to the first current.

11. A ground fault protection system as claimed in claim 1, in which the first and second current measuring devices have dissimilar impedances.

12. An aircraft including a ground fault protection system as claimed in claim 1.

13. A method of providing ground fault protection, comprising the steps of:

measuring a first current supplied to a load;

measuring a second current supplied from a generator;

on the assumption that no ground fault condition exists, applying a correction, scaling or mapping function to the measurements so as to substantially equate the measurements, and then to compare the measurements of the first and second currents and to indicate a fault condition if the difference exceeds a predetermined value.

14. A method as claimed in claim 13, in which the correction, scaling or mapping varies as a function of time so as to maintain the current measurements in substantial equally.

15. A method as claimed in claim 14, in which the variation has a time constant such that short term difference are detectable as a fault condition.