Self-Powered Numeric Controlled Relay Current Sensing
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Solution Overview
Problem
Existing self-powered relays for electrical systems face challenges in providing accurate phase and earth over-current protection with optimal VA-capacity and linearity range, often resulting in bulky current sensors due to power extraction methods that introduce distortion and require auxiliary power supplies, limiting their flexibility and reliability.
Innovation Solution
A self-powered numeric controlled relay that derives its operating power from current sensing transformers, using MOSFET and Darlington pair circuits with control algorithms for power control, allowing for accurate current measurement and protection without auxiliary power, with features like internal or external earth current measurement, trip energy release, and fault indication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If power is extracted from the current sensor to supply the relay electronics circuit, then the relay can operate without auxiliary power supply, but the current sensor waveform becomes distorted and the sensor size increases
Solution Approach 1:
The patent divides the power supply function from the current sensing function by using separate current transformers: one dedicated to current measurement and another (or the same transformer with separate winding) dedicated to power generation. This segmentation allows the measurement CT to operate without power extraction distortion while the power CT provides energy to the electronics circuit.
Solution Approach 2:
The patent introduces a power factor correction (PFC) circuit as an intermediary between the current sensor and the relay electronics. The PFC circuit efficiently converts the AC current from the sensor into regulated DC power, minimizing the impact on the original current waveform and reducing distortion while providing stable power to the electronics.
2Adaptability or versatility
If current sensors with greater VA capacity are used to provide power for control electronics, then the relay can function as self-powered, but the current sensors become bulky
Solution Approach 1:
The patent separates the power supply function from the current sensing function by using dedicated power factor correction circuits and separate current transformer windings. This allows the measurement CT to be small and precise while power is drawn efficiently through PFC from a dedicated power winding, eliminating the need for oversized sensors.
Solution Approach 2:
The patent employs power factor correction technology to change the electrical parameters of power extraction, achieving high efficiency power conversion from the current transformer output. This allows minimal VA capacity to be used from the sensor while providing sufficient power to the electronics, thereby keeping sensor size small.
3Reliability
If power MOSFETs are used to control load current with bypass sensing, then over-current protection is achieved, but phase and earth fault protection is not provided
Solution Approach 1:
The patent implements a universal protection scheme using current transformers and microprocessor-based control that can detect and respond to multiple fault types including over-current, phase faults, and earth faults. The same sensing infrastructure supports multiple protection functions, making the system versatile while maintaining reliable over-current protection.
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 solution enables compact, reliable phase and earth over-current protection with optimal VA-capacity and linearity range, supporting a wide current range from 7.2A to 8960A, and adaptable for various applications, including Ring Main Units, with enhanced fault detection and response capabilities.
Implementation Method 1
The relay senses the current flowing through the circuit using current sensing transformers
Implementation Method 2
MOSFET and Darlington pair circuits with control algorithms for power control
Implementation Method 3
The relay senses the current flowing through the circuit using current sensing transformers and rectifier circuitry to convert the sensed current into voltage to power the relay electronics
Data Source
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AI summary
The invention relates to a process of configuring a standalone self-supplied numeric controlled relay for providing phase and earth over current protection to electrical systems by accurate current measurement. The arrangement for current measurement with control algorithms is provided for power control by providing amplified and conditioned current for optimization between the current necessary to power an electronic circuit and the fidelity of a measured current waveform so that they both are at the acceptable levels at the same time. This invention disclosure describes the current sensing and associated algorithm for power control in a truly self- powered relay.