Microprocessor Overload Relay with Rogowski Transformer
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Solution Overview
Problem
Current industrial control systems for electrical motors require numerous overload relay sizes to accommodate varying current ranges, leading to costly inventory and potential errors in sizing due to limited adjustment ranges and manual calibration, which can result in inadequate protection and safety issues.
Innovation Solution
An automatic protection and control system using a microprocessor-based overload relay with self-calibration and wide-range line-powered electronics that can measure and adjust to various current and voltage ranges, reducing the need for multiple relay sizes and manual calibration, and incorporating a Rogowski current transformer for improved accuracy and immunity to saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal overload relays with heater and detector elements are used, then small amperage increments can be measured, but the current adjustment range is limited to 1.5:1 requiring numerous sizes
Solution Approach 1:
The patent changes the fundamental measurement parameter from thermal heating effects to magnetic field detection using a Rogowski current transformer. This allows the system to measure wide current ranges (0.1A to 40A) with high precision without being constrained by thermal time constants or saturation effects, eliminating the need for multiple relay sizes.
Solution Approach 2:
The patent replaces the mechanical thermal overload relay system with an electronic measurement and control system. The Rogowski transformer provides electrical measurement without mechanical contact, and the microprocessor-based relay provides electronic control instead of mechanical operation, enabling wide current range adaptation.
2Adaptability or versatility
If electronic overload relays with current transformers are used, then wider current ranges can be measured, but accuracy degrades due to magnetic saturation
Solution Approach 1:
The patent extracts the magnetic core from the current transformer design, using an air-core Rogowski transformer instead of a ferromagnetic core. This eliminates magnetic saturation entirely, allowing accurate measurement of wide current ranges from 0.1A to 40A without the accuracy degradation that plagues conventional current transformers.
3Adaptability or versatility
If multiple overload relay sizes are maintained in inventory, then various current ranges can be accommodated, but inventory costs increase and sizing errors occur
Solution Approach 1:
The patent creates a universal overload relay design that can accommodate any current range from 0.1A to 40A through software configuration and automatic calibration. The single device replaces multiple specialized relays, eliminating inventory complexity and sizing errors while maintaining full adaptability to different motor loads.
Solution Approach 2:
The patent implements automatic self-calibration functionality where the relay automatically determines the motor's full-load current and sets appropriate protection parameters without manual intervention. This eliminates the need for field calibration and ensures correct sizing every time, removing the human error factor in relay selection.
4Reliability
If manual field calibration is performed, then proper overload settings can be established, but labor costs increase and human error occurs
Solution Approach 1:
The patent implements automatic self-calibration where the relay autonomously measures motor current characteristics during startup and operation, then automatically sets the appropriate overload protection thresholds. This eliminates manual field calibration entirely, reducing installation time and eliminating human error in setting protection parameters.
Solution Approach 2:
The patent uses continuous current monitoring and feedback to automatically adjust and verify protection settings. The system continuously monitors motor current and compares it against calibrated thresholds, automatically adjusting parameters based on actual motor performance and providing feedback on protection status.
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 system provides reliable, cost-effective protection and control for electrical devices by reducing inventory needs, minimizing manual calibration errors, and enhancing accuracy and safety through automatic detection and adjustment of load parameters across a wide range of conditions.
Implementation Method 1
incorporating a Rogowski current transformer for improved accuracy and immunity to saturation
Implementation Method 2
An indication of overcurrent conditions is provided by a thermal element which may be, for example, a bimetallic strip
Data Source
AI summary
An electrical device protection apparatus, such as an overload relay, can include a microprocessor 102 that can receive a wide range of current signals from a current transformer or other current sensor. Also microprocessor 102 can employ a voltage sensor 112 to measure line voltage, for representing true power, and as a power supply 114 source for the microprocessor 102. The microprocessor can then generate annunciation signals 118, control signals 120, and/or communication signals 122 as necessary for the control and/or protection of an attached electrical device.