Overload Relay Power Management via Periodic Burden Resistor Switching
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Solution Overview
Problem
Smaller overload relays face challenges in providing sufficient power for microprocessor-based control circuitry, often requiring more costly and inflexible ASICs when power scavenging from current transformers is insufficient.
Innovation Solution
A processor-based power management scheme that periodically switches measurement and power supply circuitry, utilizing capacitors for power storage and including a burden resistor for voltage measurements proportional to current, allowing for operational and trip/reset power supplies, and optional add-on modules for additional power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If power scavenging from current transformers is used to power microprocessor-based control circuitry, then device size can be reduced, but power availability becomes insufficient
Solution Approach 1:
The patent implements periodic switching of the burden resistor between measurement mode and power generation mode. During measurement periods, the burden resistor enables accurate current measurements. During power generation periods, the burden resistor is switched out and power is scavenged from the current transformer to charge energy storage capacitors. This periodic action allows the system to achieve both accurate measurement and sufficient power availability in a compact device.
2Measurement precision
If more sophisticated processing capabilities are implemented, then measurement and control accuracy improve, but power consumption increases
Solution Approach 1:
The system performs preliminary action by charging energy storage capacitors in advance during periods when measurement accuracy is not critical. This stored energy is then available to support sophisticated processing operations when needed, allowing high-precision measurements and control without continuous high power consumption from the current transformer.
3Measurement precision
If continuous power supply is provided to measurement circuitry, then measurement accuracy is maintained, but power consumption increases
Solution Approach 1:
The measurement circuitry operates periodically rather than continuously. The burden resistor is switched into the circuit only during measurement intervals to maintain measurement accuracy, while remaining switched out during power generation intervals to minimize power consumption. This periodic operation allows accurate measurements to be taken when needed while significantly reducing overall power consumption from the current transformer.
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 the use of microprocessors in small devices by efficiently managing power scavenged from current transformers, reducing the need for costly ASICs and enhancing processing capabilities in overload relays.
Implementation Method 1
The power supply circuitry may include power storage devices, such as capacitors
Implementation Method 2
The measurement circuitry may include a burden resistor that is switched into an out of the power supply line from sensors in order to make periodic voltage measurements that are proportional to current
Data Source
AI summary
A sensing and switching device, such as an overload relay, is provided which includes a processor configured to make measurements and control operation (e.g., tripping) of the device. The processor regulates measurement of voltage and/or current, and the supply of power to power supplies. The power supplies store charge to provide operational power for the processor and that can be used for tripping and resetting contacts within the device. The processor opens a burden resistor measurement circuit when charge is being stored in the power supplies, and opens switches in the power supplies while closing the burden resistor switch to permit measurements. By alternatively switching for charging of the power supplies and making of measurements, the processor is able to reliably make measurements, control the device, and store sufficient power for operation of the device despite a demanding power budget.