Voltage Estimation in Medium Voltage Circuits
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Solution Overview
Problem
Existing methods for monitoring medium voltage electrical circuits face challenges in accurately estimating phase voltages due to variability in capacitor values and temperature effects, leading to unreliable voltage measurements and imbalances between phases.
Innovation Solution
A method for estimating periodic voltage in two-phase electrical circuits using voltage sensors that supply signals representative of the periodic voltage, allowing for normalization of voltages across phases without additional measurements, and incorporating recursive low-pass filtering and vectorization to account for high-frequency noise and phase shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage measurement is performed using crossing capacitors in medium voltage circuits, then voltage information can be obtained, but measurement precision deteriorates due to capacitor variability with temperature and aging
Solution Approach 1:
The patent introduces an intermediary approach by using current measurements (which are stable and accurate) combined with a modeling technique that indirectly estimates voltage. Instead of directly measuring voltage with unreliable capacitors, the system uses reliable current sensors and a mathematical model (Thevenin equivalent circuit) to compute voltage, thereby mediating between reliable measurements and the need for accurate voltage information.
Solution Approach 2:
The patent replaces the physical voltage measurement mechanism (crossing capacitors) with an alternative approach based on electrical circuit modeling and calculation. Instead of relying on the physical capacitor voltage division method, the system uses a Thevenin equivalent circuit model combined with current measurements to computationally determine voltage, substituting a mechanical/physical measurement system with an analytical calculation system.
2Loss of information
If crossing capacitors are used for voltage measurement, then voltage information is obtained, but device complexity increases due to the need for additional correction mechanisms
Solution Approach 1:
The patent makes the monitoring equipment multi-functional by integrating both current measurement and voltage estimation capabilities into a single system. The same monitoring device that measures current for protective relay functions also estimates voltage using the Thevenin model, eliminating the need for separate voltage measurement equipment and reducing overall system complexity.
Solution Approach 2:
The system performs self-calibration and self-correction by using its own current measurements and the known circuit topology to automatically compute accurate voltage values. The monitoring equipment serves itself by generating the voltage information it needs through calculation rather than requiring external calibration or additional hardware components.
3Ease of manufacture
If traditional voltage measurement methods are used in medium voltage circuits, then measurement can be performed, but manufacturing precision deteriorates due to temperature and aging effects on capacitor values
Solution Approach 1:
The patent changes the measurement parameter from direct voltage measurement (which is sensitive to capacitor parameter variations) to current measurement combined with computational voltage estimation. By measuring current instead of voltage directly and using circuit models to derive voltage, the system becomes insensitive to capacitor aging and temperature effects, maintaining manufacturing precision without complex temperature compensation mechanisms.
Data Source
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AI summary
The invention relates to a method for estimating a periodic voltage, such as an input voltage, of one of the phases of at least a two-phase electrical circuit comprising, for each of its phases, a voltage sensor, each voltage sensor being capable of providing a representative signal (VAr, VBr, VCr) of at least a portion of the period of the periodic voltage (VA, VB, VC) of said phase. The method comprises the following steps: measuring the representative signal (VAr, VBr, VCr) from the voltage sensor; amplifying the representative signal (VAr, VBr, VCr) by a gain determined in the absence of an electrical fault in the electrical circuit (1) and based on a reference voltage common to all phases of the electrical circuit (1); estimating, from the amplified representative signal (VAc, VBc, VCc), the periodic voltage (VA, VB, VC). The invention further relates to a device for estimating a voltage (10) and an electrical circuit comprising such a device (1).