Excitation Rectifier Fault Detection Using Field Current Harmonics
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Solution Overview
Problem
Existing methods for detecting faults in the power electronics devices of rotary rectifiers in brushless synchronous generators are inadequate, often requiring additional sensors or complex analogue circuits, which are not feasible for rotary rectifiers, leading to potential overloading and accelerated aging of the rotary exciter.
Innovation Solution
A method based on frequency analysis of the field current and rectified voltage signals to detect faults in rectifiers, using per-unit fault factors and threshold comparisons, without the need for additional sensors, applicable to both rotary and stationary rectifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage drop evaluation across power electronics devices is used for fault detection, then fault detection capability is improved, but device complexity increases due to complicated analogue circuits
Solution Approach 1:
The patent replaces complicated analogue circuits with a digital signal processing approach. A microprocessor-based system evaluates voltage and current signals through digital computation of RMS values and harmonics, substituting mechanical/electronic analogue circuitry with software-based analysis that achieves the same fault detection function with reduced hardware complexity
Solution Approach 2:
The patent introduces an intermediary computational layer that processes voltage and current signals through RMS calculation and harmonic analysis. This intermediary digital processing stage acts as a mediator between the raw electrical signals and the fault detection logic, enabling complex analysis without requiring complex analogue circuits
2Reliability
If current sensors are installed on AC side for continuous measurement, then fault detection capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent enables the existing control system to perform fault detection using signals already present in the system. The microprocessor utilizes voltage and current signals that are already being measured for normal control operations, allowing the system to self-diagnose faults without requiring additional dedicated sensors or measurement devices
Solution Approach 2:
The patent makes the existing voltage and current measurement systems serve multiple functions. The same sensors and signal acquisition channels used for normal generator control and protection are also utilized for rectifier fault detection, eliminating the need for separate dedicated fault detection sensors
3Reliability
If magnetic leakage field measurement is used for fault detection, then fault detection capability is improved, but cost increases due to special sensors
Solution Approach 1:
The patent enables the existing control system to perform fault detection using signals already present in the system. The microprocessor utilizes voltage and current signals that are already being measured for normal control operations, allowing the system to self-diagnose faults without requiring additional dedicated sensors or measurement devices
Solution Approach 2:
The patent introduces an intermediary computational layer that processes voltage and current signals through RMS calculation and harmonic analysis. This intermediary digital processing stage acts as a mediator between the raw electrical signals and the fault detection logic, enabling complex analysis without requiring complex analogue circuits
Data Source
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AI summary
In the method of detecting fault in excitation rectifier of synchronous generator (1), field current (3) on a stationary DC side of an excitation source (2), or voltage on a DC side of a. stationary rectifier (7), is measured. Further, a frequency analysis is used to determine from measured signal an amplitude of fundamental harmonic and amplitude of all non-zero integer multiples of fundamental harmonic frequency. A per-unit current fault factor X, or a per-unit voltage fault factor X u is calculated, a. reference fault-free per-unit current factor X i_ref or a reference fault- free per-unit voltage factor X u-ref is measured, and reference per-unit fault factor Xi_err or Xu_err is determined, and a. per-unit fault detection threshold Xi-threshold or X u threshold is determined. A. fault is signalled when determined values of the per-unit fault factor X i or X u are exceeded and/or the DC component of the measured field current (3) exceeds the permitted operation range and/or the rms value of the back EMF of the synchronous generator (1) is lower than the one corresponding to the minimum permitted operation field current (3).