Transformer Inrush Current Control via Point-on-Wave Switching
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Solution Overview
Problem
In power systems, the existing methods for controlling transformer energization fail to effectively mitigate magnetizing inrush currents due to unsymmetrical residual fluxes, especially in transformers without voltage transformers, and are exacerbated by interphase coupling, leading to heavy magnetic inrush currents.
Innovation Solution
A method and system that uses a point on wave controller to acquire current waveforms, determine peaks, calculate correction factors based on symmetry and apparent magnetic properties, and adjust switching instances to minimize inrush currents, eliminating the need for voltage measurements and transformer modeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional deenergization and energization methods are used at peak voltage waveform, then switching control is simplified, but heavy magnetic inrush currents occur due to residual flux and interphase coupling
Solution Approach 1:
The system performs preliminary measurement of current waveform peaks during closing operation, calculates correction factors based on apparent magnetic properties and residual flux, and adjusts the switching instance before actual energization occurs. This preliminary analysis of current characteristics enables proactive compensation for residual flux effects without requiring complex voltage measurements or transformer modeling.
2Object-generated harmful factors
If voltage transformers and transformer modeling are required for residual flux estimation, then accurate inrush current mitigation is achieved, but device complexity and cost increase
Solution Approach 1:
The system uses the transformer's own current waveform characteristics during closing operation to estimate residual flux and calculate correction factors. By analyzing the peaks and symmetry of current waveforms already present in the system, the method enables the transformer to provide its own diagnostic information without requiring external voltage transformers or complex modeling, thus achieving self-service for inrush current mitigation.
Solution Approach 2:
The current waveform acts as an intermediary that carries information about residual flux and magnetic state. Instead of directly measuring voltage or magnetic flux, the system uses current waveform characteristics (peaks, symmetry, timing) as an intermediate indicator to infer the magnetic state and determine appropriate switching corrections, simplifying the measurement requirements.
3Ease of operation
If switching instance is not adjusted for residual flux compensation, then switching control is simpler, but asymmetric flux causes heavy inrush currents
Solution Approach 1:
The system measures the actual current waveform peaks during closing operation, compares them against expected symmetric patterns, and uses the observed asymmetry to calculate correction factors. This feedback from actual current characteristics enables dynamic adjustment of switching instances to compensate for residual flux, creating a closed-loop control that adapts to the transformer's actual magnetic state without requiring predetermined models.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces magnetizing inrush currents by adjusting switching instances based on current waveforms, reducing electrical disturbances and eliminating the requirement for voltage transformers, thus improving transformer energization control.
Implementation Method 1
The point on wave controller detects the opening or closing actuation time (also referred to as operating time) of the circuit breaker and calculates a time for switching in respect of the opening or closing command of the circuit breaker to ensure switching on a particular point on the voltage waveform.
Implementation Method 2
However, due to improper deenegisation and due to magnetic hysteresis, flux is often retained or left in transformer core.
Implementation Method 3
The method comprises acquiring electrical current waveform in the first phase of the transformer from a current measuring device during a closing operation of the first circuit breaker at an instance for switching determined by the controller, determining a first peak in the current in the first phase within a first predetermined window, calculating a first correction factor for adjusting the instance for switching in the first phase, based on the first peak
Data Source
AI summary
In aspects, the present invention provides a method for controlled energizing of a transformer (150) being connected to a first electrical subsystem (110) through a first circuit breaker (140). The method comprises acquiring electrical current waveform in a first phase of the transformer during a closing operation of the first circuit breaker at an instance for switching determined by a controller (130), determining a first peak (310) in the current in the first phase within a first predetermined time window (Tpw), calculating a first correction factor for adjusting the instance for switching in the first phase, and adjusting the instance for switching based on the calculated first correction factor for performing a next controlled energization at the adjusted instance of switching in the first phase.