Distribution Transformer Phasor Measurement via Vector Impedance
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Solution Overview
Problem
High-precision medium-voltage phasor measurements on distribution grids are challenging due to phase angle shifts within distribution transformers and the influence of uncontrolled loads, making accurate voltage phasor measurements on secondary windings impractical with existing technologies.
Innovation Solution
The method involves using current and voltage sensors on the secondary winding of a distribution transformer to measure phasors, combining these measurements with the transformer's effective ratio to calculate the phasor vector on the primary winding, and approximating the transformer's vector impedance by analyzing simultaneous changes in voltage and current, while minimizing external factor effects through threshold, statistical correlation, or intentional load changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If distribution transformers are used to step down voltage for measurement, then voltage reduction to measurable levels is achieved, but phase angle shifts within the transformer degrade measurement precision
Solution Approach 1:
The system continuously monitors secondary voltage and current phasors, calculates the transformer phase angle shift in real-time, and uses this feedback to correct primary phasor measurements. This closed-loop approach compensates for the transformer's phase angle shifts, maintaining measurement precision despite the transformer's inherent phase displacement
Solution Approach 2:
The patent introduces an intermediary calculation process that measures secondary phasors through the transformer, computes the phase angle shift, and uses this intermediate information to derive accurate primary phasors. This intermediary measurement approach allows the system to work around the transformer's phase shifting effect rather than being limited by it
2Ease of operation
If measurements are made on secondary windings of distribution transformers, then access to measurable voltage levels is achieved, but uncontrolled loads on the secondary side introduce measurement errors
Solution Approach 1:
The system uses feedback by continuously monitoring both voltage and current phasors on the secondary side, detecting changes caused by uncontrolled loads, and compensating for their effects through real-time calculation and correction of primary phasor measurements
Solution Approach 2:
The patent replaces direct primary voltage measurement (which would require high-voltage equipment) with secondary voltage measurement through the transformer, substituting a mechanically simple low-voltage measurement system for a complex high-voltage measurement system, while using computational methods to maintain accuracy
3Measurement precision
If traditional synchrophasor measurement standards (IEEE C37.118) are applied to distribution grids, then transmission grid measurement requirements are met, but the required angular resolution of ±0.5° is insufficient for distribution grid phenomena
Solution Approach 1:
The patent changes the measurement parameter from the standard ±0.5° angular resolution to a finer ±0.015° resolution specifically tailored for distribution grid applications. This parameter change enables the detection of subtle phase angle variations characteristic of distribution grid phenomena while maintaining compatibility with synchrophasor measurement frameworks
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 enables precise voltage phasor measurements on medium-voltage conductors with an angular resolution of ±0.015°, overcoming the limitations of existing technologies by accurately determining phasor vectors on distribution grids despite phase angle shifts and uncontrolled loads.
Implementation Method 1
The voltage and current on an a.c. power grid have a fundamental frequency... The measured fundamental angle can be combined with the measured fundamental magnitude to form a fundamental phasor measurement
Data Source
AI summary
A means and method for measuring precise voltage phasors on medium-voltage alternating current (AC) distribution grids, using existing distribution transformers as voltage sensors. The errors introduced by the distribution transformers are minimized by taking into account the transformer's vector impedance, combined with measuring the transformer secondary current phasor. The invention includes a means and a method of measuring the distribution transformer's vector impedance.