Low-Voltage Circuit Breaker Power Measurement With Phase Compensation
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Solution Overview
Problem
Rogowski coils used in low-voltage circuit breakers for current measurement suffer from phase errors due to stray field inductance and non-ideal components, leading to inaccurate power value calculations.
Innovation Solution
A low-voltage circuit breaker design that includes a Rogowski coil connected to an analog integrator and a microprocessor, with analog-to-digital converters for current and voltage sampling, where interpolated voltage values are used to compensate for phase errors, ensuring phase error-free power calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Rogowski coils are used to measure current, then potential isolation and high current stability are achieved, but phase errors occur due to stray field inductance and non-ideal components
Solution Approach 1:
The patent introduces an intermediary calculation process that uses the measured current and voltage values along with their phase angles to compute active power, reactive power, and apparent power. This intermediary mathematical processing compensates for the phase errors by explicitly accounting for the phase angle differences in the power calculation formulas, thereby resolving the contradiction between measurement stability and phase accuracy.
2Ease of operation
If Rogowski coils with integrators are used, then current measurement is achieved, but resultant phase errors distort all current measured values
Solution Approach 1:
The patent implements a feedback mechanism where the phase angles of both current and voltage are measured and fed into the power calculation process. By using these phase angle measurements in the calculation of active power (P = U×I×cosφ), reactive power (Q = U×I×sinφ), and apparent power (S = U×I), the system compensates for the phase errors introduced by the Rogowski coil and integrator, thereby improving current value accuracy while maintaining ease of operation.
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 provides accurate and phase error-free power measurements by compensating for phase errors in the voltage signal, minimizing distortions and improving the reliability of power value calculations.
Implementation Method 1
Rogowski coils output a voltage proportional to the differential current
Implementation Method 2
Following the signal derivation by the Rogowski transformer and the subsequent integration by an analog integrator
Data Source
AI summary
A power value for a low-voltage AC circuit, such as low-voltage circuit breaker, is derived. A voltage between conductors of the low-voltage AC circuit is ascertained and a current of at least one conductor is ascertained by a Rogowski coil, which outputs an analog voltage that is an equivalent to the level of the electric current. The analog voltage of the Rogowski coil is integrated and then digitized, and the level of the voltage is digitized. A power value is calculated in each case from a sample value of the current and an interpolated voltage value. The interpolated voltage value is in each case ascertained from two successive sample values of the voltage such that a phase error generated by the Rogowski coil or/and the integrator is compensated for in relation to the electric current in the conductor and a phase error-free power value is ascertained.