Current Transformer Winding Temperature Estimation for Phase Correction
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Solution Overview
Problem
Current transformers in electricity meters introduce a phase offset that causes significant inaccuracy in energy measurement, which cannot be compensated by conventional temperature sensors due to their imprecision in estimating winding temperatures, especially in polyphase meters where additional sensors increase cost and complexity.
Innovation Solution
An electricity meter that uses internal temperature measurements and current measurements to estimate winding temperatures accurately, employing a processing unit to evaluate phase offsets with low-pass filtering and a Butterworth filter, without requiring additional hardware, thus achieving precise energy consumption measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a temperature sensor is integrated into the meter box (NTC thermistor), then the device complexity is reduced, but the measurement precision of winding temperature is insufficient
Solution Approach 1:
The patent uses current measurements as an intermediary parameter to indirectly determine winding temperature. Instead of directly measuring temperature with a sensor, the system measures current flowing through the winding and uses the known relationship between current and temperature rise to calculate the winding temperature. This mediator approach resolves the contradiction by achieving precise temperature measurement without adding temperature sensors.
Solution Approach 2:
The patent replaces the physical temperature sensing mechanism (NTC thermistor) with an electrical measurement approach. By substituting the mechanical/thermal sensing system with an electrical current measurement system, the invention achieves both reduced device complexity and improved measurement precision, as the same current transformer already present in the meter can be used for this purpose.
2Measurement precision
If a temperature sensor is mounted directly on each transformer, then the measurement precision of winding temperature is improved, but the device complexity and cost increase
Solution Approach 1:
The patent makes the existing current transformer serve multiple functions: it not only measures current for energy calculation but also provides temperature information through the same current measurements. This multi-functionality eliminates the need for separate temperature sensors on each transformer, reducing device complexity while maintaining measurement precision.
Solution Approach 2:
The current transformer serves itself by providing temperature measurement capability through its primary function of current measurement. The system uses the current data already being collected for energy calculation to simultaneously determine winding temperature, eliminating the need for additional dedicated temperature sensing components.
3Measurement precision
If multiple temperature sensors are integrated in polyphase meters, then the measurement precision of each transformer temperature is improved, but the manufacturing cost increases
Solution Approach 1:
The patent merges the temperature measurement function with the existing current measurement function. By combining these two functions into a single measurement process using the current transformer, the invention eliminates the need for separate temperature sensors in polyphase meters, thereby reducing manufacturing cost while maintaining precision.
4Device complexity
If temperature sensors are positioned on the plastic sheath, then the device complexity is reduced, but the measurement precision of winding temperature is insufficient
Solution Approach 1:
The patent uses current measurements as an intermediary that provides direct information about winding temperature without requiring physical contact with the winding or proximity to it. This intermediary measurement approach overcomes the limitation of external temperature sensors that cannot accurately capture the temperature at the winding location.
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
The solution allows for precise estimation of phase offsets, meeting stringent accuracy requirements of 0.5% to 0.1% in energy measurement without additional components, simplifying implementation and reducing costs.
Implementation Method 1
a current transformer generates a phase offset Δφ(t) on the current measurements
Implementation Method 2
A temperature sensor, arranged to produce second measurements representative of the internal temperature present inside the meter
Implementation Method 3
evaluate an estimated temperature of the winding on the basis of the estimated current and the internal temperature
Implementation Method 4
evaluate, on the basis of the estimated temperature, a measurement phase offset produced by the current transformer during the first measurements
Data Source
AI summary
An electricity meter includes a current transformer arranged to produce first measurements of a current flowing in a winding of the current transformer; a temperature sensor; and a processing unit arranged to evaluate an estimated current and an internal temperature, to evaluate an estimated temperature of the winding on the basis of the estimated current and internal temperature, and to evaluate, on the basis of the estimated temperature, a measurement phase offset produced by the current transformer on the first measurements, the measurement phase offset being intended to be used to measure the electrical energy consumed.