Generator neutral ground monitoring device utilizing direct current component measurement and analysis

Patent metadata

Field	Value
Publication number	US-2016266206-A1
Application number	US-201514644257-A
Country	US
Kind code	A1
Filing date	Mar 11, 2015
Priority date	Mar 11, 2015
Publication date	Sep 15, 2016
Grant date	—

Abstract

A device and method for detecting and analyzing faults in a generator stator are disclosed. The device and method include measuring a direct current component of a neutral ground current in a generator stator grounding conductor, analyzing the direct current flow and comparing it with other ground fault indicators, and providing diagnosis and recommended actions based on the analysis. The direct current flow is measured by a sensitive direct current sensor that may also measure AC components via oscillations in the current measurement, such as a Hall Effect sensor, placed on the generator stator grounding conductor. The analysis of the direct current signal includes consideration of the generator operating conditions and environmental conditions, and also includes comparison to historical data representing both normal and abnormal operation of the generator. Alarms and advisories are provided when generator faults are detected or predicted.

First claim

What is claimed is:

1 . A generator neutral ground monitoring device, said device comprising:
a direct current (DC) sensor placed on a stator neutral ground lead of a generator, said DC sensor measuring a direct current component of a generator neutral ground current and providing a DC neutral ground signal; an operating environment data module which provides generator operating environment data, where the operating environment data includes generator operating condition data and ambient condition data; and a monitor module including a processor and a memory, said monitor module being configured to receive the DC neutral ground signal and the operating environment data, analyze the DC neutral ground signal in consideration of the operating environment data to detect and predict faults in the generator, and issue an alarm or a diagnostic message if a fault is detected.

2 . The device of claim 1 wherein the monitor module includes an archive function for storing the DC neutral ground signal data and the operating environment data for later evaluation when a fault is identified in the generator.

3 . The device of claim 1 wherein the monitor module evaluates a magnitude and a rate of change of the DC neutral ground signal, and issues an alarm if the magnitude or the rate of change exceeds a predetermined threshold.

4 . The device of claim 1 wherein the monitor module performs fault detection and prediction using a two-part analysis, where a first part includes analyzing the DC neutral ground signal in consideration of the operating environment data for a current condition, and a second part includes analyzing the DC neutral ground signal in consideration of the operating environment data for historical conditions which represent both normal and abnormal generator operation.

5 . The device of claim 4 wherein the operating environment data includes generator load, dew point, terminal voltage, liquid detector alarm frequency, ambient temperature, generator temperatures, barometric pressure and ozone level.

6 . The device of claim 4 wherein the monitor module includes a learning feature, where the learning feature includes self-learning by identifying correlations between the DC neutral ground signal and the operating environment data for both normal and abnormal generator operation, and the learning feature also includes manually-programmed learning where inspection-confirmed faults in the generator or another generator of the same type are manually correlated to the DC neutral ground signal and the operating environment data during a time preceding the inspection-confirmed faults, and where output of the learning feature is used in the second part of the fault detection and prediction analysis.

7 . The device of claim 1 wherein the monitor module also receives an AC neutral ground signal that includes a DC component, either from the DC sensor or from another sensor capable of reading the DC component, converts the AC neutral ground signal to a frequency spectrum via a Fourier Transform (FT), and uses a zero hertz component of output from the FT as a supplemental indicator of generator neutral ground direct current flow to compare to the DC neutral ground signal.

8 . The device of claim 7 wherein the monitor module analyzes the AC neutral ground signal to detect and predict faults in the generator, and correlates faults detected and predicted through analysis of the AC neutral ground signal with faults detected and predicted through analysis of the DC neutral ground signal.

9 . A system for monitoring a generator neutral ground signal, said system comprising:
a Hall Effect direct current (DC) sensor placed on a stator neutral ground lead of a generator, said sensor measuring a direct current component of a generator neutral ground current and providing a DC neutral ground signal; a neutral grounding transformer (NGT), said transformer having a primary side coupled to the stator neutral ground lead and a secondary side which provides an NGT signal, where the NGT signal corresponds to an amount of alternating current (AC) on the stator neutral ground lead; an operating environment data module which provides generator operating environment data, where the operating environment data includes generator load, dew point, terminal voltage, liquid detector alarm frequency, ambient temperature, generator temperatures, barometric pressure and ozone level; and a monitor module including a processor and a memory, said monitor module being configured to receive the DC neutral ground signal, the NGT signal and the operating environment data, analyze the DC neutral ground signal and the NGT signal in consideration of the operating environment data to detect and predict faults in the generator, and issue an alarm if a fault is detected.

10 . The system of claim 9 wherein the monitor module evaluates a magnitude and a rate of change of the DC neutral ground signal, and issues an alarm if the magnitude or the rate of change exceeds a predetermined threshold.

11 . The system of claim 9 wherein the monitor module performs fault detection and prediction using a two-part analysis, where a first part includes analyzing the DC neutral ground signal in consideration of the operating environment data for a current condition, and a second part includes analyzing the DC neutral ground signal in consideration of the operating environment data for historical conditions which represent both normal and abnormal generator operation.

12 . The system of claim 11 wherein the monitor module includes a learning feature, where the learning feature includes self-learning by identifying correlations between the DC neutral ground signal and the operating environment data for both normal and abnormal generator operation, and the learning feature also includes manually-programmed learning where inspection-confirmed faults in the generator or another generator of the same type are manually correlated to the DC neutral ground signal and the operating environment data during a time preceding the inspection-confirmed faults, and where output of the learning feature is used in the second part of the fault detection and prediction analysis.

13 . The system of claim 9 wherein the monitor module also receives an AC neutral ground signal from a sensor capable of reading a DC component on the primary side of the NGT, converts the AC neutral ground signal to a frequency spectrum via a Fourier Transform (FT) or other method, and uses a zero hertz component of output from the frequency spectrum as a supplemental indicator of generator neutral ground direct current flow to compare to the DC neutral ground signal.

14 . A method for monitoring a direct current component of a generator neutral ground signal, said method comprising:
providing a DC neutral ground signal by a direct current (DC) sensor placed on a stator neutral ground lead of a generator, said DC sensor measuring a direct current component of a generator neutral ground current; providing generator operating environment data by an operating environment data module, where the operating environment data includes generator operating condition data and ambient condition data; and analyzing the DC neutral ground signal in consideration of the operating environment data to detect and predict faults in the generator, and issuing an alarm if a fault is detected, where analyzing the DC neutral ground signal is performed by a monitor module including a processor and a memory, said monitor module being configured to receive the DC neutral ground signal and the operating environment data.

15 . The meth

Assignees

• Siemens Energy Inc

Inventors

• Thompson Edward David
• Lau James F

Classifications

• G01R31/346

  Testing of armature or field windings · CPC title

• G01R31/343 Primary

  in operation · CPC title

• G01R31/52

  Testing for short-circuits, leakage current or ground faults · CPC title