Current Transformer Temperature Estimation for Phase-Shift Compensation
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Solution Overview
Problem
Current transformers in electric meters introduce phase shifts that cause measurement inaccuracies, which are not adequately compensated by existing temperature sensors, failing to meet stringent accuracy requirements of 0.5% or lower.
Innovation Solution
An electricity meter that uses internal temperature measurements from a thermistor and current measurements to estimate the winding temperature of current transformers, applying a low-pass filter to improve accuracy, and compensates for phase shifts using a processing unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a temperature sensor is integrated into the meter's casing to measure internal temperature, then the device complexity is reduced and manufacturing cost is lowered, but the measurement precision of winding temperature is insufficient
Solution Approach 1:
The current transformer itself serves as the temperature sensing element by utilizing its own electrical parameters (current, impedance) to infer winding temperature through self-heating characteristics, eliminating the need for separate temperature sensors
Solution Approach 2:
The patent replaces the mechanical/physical temperature sensor system with an electrical measurement system that uses current and impedance measurements to calculate winding temperature through mathematical models
2Measurement precision
If a temperature sensor is mounted directly on each transformer winding, then the measurement precision of winding temperature is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The current transformer uses its own electrical characteristics (current flow, impedance changes) to determine its winding temperature without requiring external sensors, making the system self-diagnostic
Solution Approach 2:
The processing unit performs multiple functions: it measures current for energy calculation, measures impedance for temperature estimation, and compensates phase shift, eliminating the need for dedicated temperature sensing hardware
3Measurement precision
If additional temperature sensors are integrated into each transformer, then the measurement precision of winding temperature is improved, but the manufacturing cost increases
Solution Approach 1:
The system uses existing electrical measurements (current and impedance) to infer temperature, making the manufacturing process simpler and less costly by eliminating additional sensor components
Solution Approach 2:
The patent creates a virtual model of the winding temperature based on electrical parameter measurements, replacing the need for physical temperature sensors and reducing manufacturing complexity
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
Accurately compensates for phase shifts in current measurements, achieving high accuracy in energy consumption measurements without additional hardware, meeting stringent accuracy requirements.
Implementation Method 1
A temperature sensor is typically integrated into the meter's casing. This is, for example, an NTC thermistor (for Negative Temperature Coefficient).
Implementation Method 2
We know that a current transformer generates a phase shift Δφ(t) on current measurements
Implementation Method 3
the processing unit is arranged to apply a low-pass filter to the first measurements to obtain the estimated current
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Electric meter (1) comprising: - a current transformer (17) arranged to produce first measurements of a current (Iph) flowing in a winding (20) of the current transformer; - a temperature sensor; - a processing unit (8) arranged to evaluate an estimated current (Ie) and an internal temperature (Ti), to evaluate an estimated temperature (Te) of the winding (20) from the estimated current and the internal temperature, and to evaluate, from the estimated temperature, a measurement phase shift (Δφ) produced by the current transformer on the first measurements, the measurement phase shift being intended to be used to measure the electrical energy consumed.