Current Transformer Hot Socket Detection in Electric Meters
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Solution Overview
Problem
Existing electric meter systems face issues with detecting degradation in connections, leading to increased resistance and temperature increases due to wear or corrosion, which can result in a 'hot socket' condition, affecting accuracy and reliability.
Innovation Solution
The system employs a current transformer with a primary and secondary bifilar winding, where a DC voltage signal is applied to determine temperature through a sense resistor, allowing for frequent and accurate temperature measurements without requiring a separate temperature sensor, and enabling continuous bias voltage application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate temperature sensor is added to measure temperature frequently and accurately, then temperature measurement accuracy and frequency improve, but device complexity and cost increase
Solution Approach 1:
The patent makes the existing current transformer serve a dual function: its primary function of current measurement is maintained while its secondary function is used for temperature measurement. By applying DC voltage to the transformer windings and measuring the resulting current through sense resistors, the same hardware component performs both current sensing and temperature detection, eliminating the need for separate temperature sensors and reducing overall device complexity
Solution Approach 2:
The current transformer uses its own internal components (windings and core) to perform temperature measurement. The magnetic properties of the transformer's core, which inherently change with temperature, are exploited to detect temperature without requiring external sensing elements. The transformer essentially measures its own temperature through changes in its electrical characteristics
2Measurement precision
If intermittent bias voltage is applied to the transformer, then saturation and distortion are avoided, but measurement frequency and continuity decrease
Solution Approach 1:
The patent implements periodic sampling of the transformer's electrical characteristics by applying DC voltage in controlled intervals. The system measures the current through sense resistors at specific moments when DC voltage is applied, then uses these periodic measurements to continuously track temperature. This periodic action prevents continuous saturation while providing sufficient measurement data for accurate temperature determination
Solution Approach 2:
The system applies DC voltage only partially (intermittently) rather than continuously, which is sufficient to obtain temperature measurements without causing continuous saturation. The DC voltage is applied just enough to generate measurable current through the windings, and the measurement is taken during this partial application period, avoiding the need for continuous voltage that would cause distortion
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 allows for more frequent and accurate temperature measurements, reducing the risk of hot socket conditions and maintaining measurement accuracy, while enabling constant bias voltage application without saturation or distortion.
Implementation Method 1
a current transformer with a primary and secondary bifilar winding
Implementation Method 2
A temperature coefficient of the first sense resistor is less than a temperature coefficient of a resistivity of a material of the first bifilar winding and the second bifilar winding
Data Source
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AI summary
Techniques for hot socket detection are disclosed. In an example, a meter includes a current transformer with a secondary bifilar winding. The meter is in proximity to a current coil. The secondary bifilar winding includes a first bifilar winding and a second bifilar winding. A start lead of the first bifilar winding is connected to a start lead of the second bifilar winding. The meter further includes a voltage source configured to generate a direct current (DC) voltage signal. The DC voltage signal is provided to a finish lead of the first bifilar winding. A first sense resistor is connected between a finish lead of the second bifilar winding and ground. A processing circuit receives a signal indicating a voltage across the first sense resistor and determines a temperature associated with the current coil. The processing circuit is further configured to detect a hot socket condition based on the temperature.