Self-Calibrating Capacitor Voltage Sensor for Transformer Systems
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Solution Overview
Problem
Capacitor voltage sensors in medium voltage applications, such as in loop circuits with transformers, have limited accuracy (±10%), making it difficult to determine if the system has returned to normal voltage post-fault isolation and restoration, and existing calibration methods require either memory transfer or manual interface, which is impractical for field setup.
Innovation Solution
A method for self-calibrating capacitor voltage sensors by measuring a control voltage on a secondary coil and determining a calibration factor to adjust the measured voltage on the capacitor sensor, allowing accurate voltage measurements without requiring primary voltage knowledge, enabling the sensors to operate accurately when the switch is open or closed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitor voltage sensors are used in medium voltage applications, then the system can measure voltage on the line, but the measurement accuracy is limited to ±10%, which is not sufficient for determining normal voltage return post-fault
Solution Approach 1:
The capacitor voltage sensor performs self-calibration by utilizing the transformer's secondary voltage as a reference. The system automatically determines a calibration factor by comparing the sensor's voltage reading with the known secondary voltage ratio, eliminating the need for external calibration equipment or manual intervention. This self-service approach resolves the contradiction by achieving high measurement precision without increasing device complexity.
Solution Approach 2:
The system implements a feedback mechanism where the controller continuously monitors the voltage measurements from the capacitor sensor and compares them against the calibrated reference value. Based on this feedback, the controller applies the calibration factor to correct subsequent measurements, ensuring sustained measurement accuracy. This feedback loop resolves the contradiction by maintaining high precision through automatic correction rather than complex calibration systems.
2Measurement precision
If traditional calibration methods are used in manufacturing facilities, then sensor accuracy can be calibrated, but the application voltage is unknown and requires memory transfer or manual interface for field setup
Solution Approach 1:
The calibration process is designed to be self-executing in the field without requiring external equipment or manual data transfer. The controller automatically obtains the calibration factor by processing the relationship between primary and secondary voltages through the transformer, eliminating the need for memory devices or manual interfaces. This resolves the contradiction by maintaining calibration accuracy while dramatically simplifying field setup operations.
Solution Approach 2:
The transformer itself serves as an intermediary that provides the calibration reference. By utilizing the known turns ratio between primary and secondary coils, the system obtains a reliable calibration reference without requiring external calibration equipment. This intermediary approach resolves the contradiction by enabling accurate calibration in the field without complex setup procedures.
3Adaptability or versatility
If the control unit is transported separately from the capacitor voltage sensors, then assembly flexibility is improved, but calibration becomes impractical without memory transfer or manual interface
Solution Approach 1:
The calibration system is designed to be self-configuring after assembly, regardless of whether the control unit and sensor were transported separately. The controller automatically determines the calibration factor by measuring the secondary voltage and calculating the appropriate multiplication factor. This self-service capability resolves the contradiction by maintaining assembly flexibility while eliminating complex calibration procedures that would otherwise be required.
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
Enables accurate voltage measurements and reliable fault isolation and power restoration by calibrating capacitor sensors within the system, allowing the controller to determine normal voltage configurations and apply over/under voltage limits effectively.
Implementation Method 1
capacitor voltage sensor that measures voltage on a power line
Implementation Method 2
transformer... primary coil... secondary coil
Data Source
AI summary
A system and method for calibrating a capacitor voltage sensor that measures voltage on a power line coupled through a switch to a primary coil of a transformer. The method includes measuring a control voltage on a secondary coil of the transformer and measuring voltage on the capacitor sensor when the switch is known to be closed. The method identifies a calibration factor that when multiplied by the measured voltage on the capacitor sensor when the switch is closed makes the measured voltage on the capacitor sensor substantially equal to the control voltage. The method subsequently measures voltage on the capacitor sensor when the switch is open or closed during operation of the transformer, and multiplies the subsequently measured voltage on the capacitor sensor when the switch is open or closed by the calibration factor to obtain a measured voltage.