Differential Current Transformer Self-Test for SSPC Protection
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Solution Overview
Problem
Existing solutions for monitoring and protecting power circuits with solid state power controllers (SSPCs) fail to distinguish between different levels of earth leakage currents and do not provide a means to verify the proper functioning of current detection circuits, especially in scenarios where individuals may be in contact with the devices.
Innovation Solution
A monitoring and protection device with a current measurement circuit and a test module that includes a current injection channel, allowing for the measurement and testing of differential currents, and a self-test sequence to ensure correct operation, using multiple windings for current measurement and control of SSPC switches based on predefined thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current detection transformer is used to detect phase leakage or insulation faults, then fault detection capability is improved, but the ability to distinguish between different levels of earth leakage currents is insufficient
Solution Approach 1:
The patent divides the current measurement function into multiple independent measurement channels, each equipped with its own current detection transformer and measurement circuit. This segmentation allows each channel to independently measure and distinguish different levels of leakage currents, resolving the contradiction by providing both reliable fault detection and precise current level differentiation through parallel measurement paths.
Solution Approach 2:
The patent introduces a new dimension of measurement capability by implementing multiple measurement channels with different measurement ranges and characteristics. Instead of relying on a single measurement dimension, the system uses multiple dimensional measurement channels that can simultaneously detect and distinguish various levels of leakage currents, thereby achieving both reliable detection and precise measurement.
2Device complexity
If only measurement channels are provided without testing capability, then the device structure is simpler, but the ability to verify correct operation of measurement circuits is lost
Solution Approach 1:
The patent implements preliminary testing actions through self-test sequences that are executed automatically during system initialization or operation. The test module performs preliminary verification of measurement channel functionality before normal operation begins, ensuring that measurement circuits are functioning correctly without requiring complex external testing equipment or procedures.
Solution Approach 2:
The measurement and test module is designed to perform self-verification through integrated test functions. The system uses its own internal resources to test and verify the operation of its measurement channels, eliminating the need for external testing equipment. This self-service approach maintains measurement reliability while avoiding excessive structural complexity.
3Measurement precision
If multiple measurement channels with different ranges are implemented, then leakage current measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent designs the measurement and test module with universal functionality that can handle multiple measurement channels through a single integrated controller. The module uses common components such as the controller, communication interface, and power supply across all measurement channels, allowing the system to achieve multi-range measurement precision while minimizing the increase in overall device complexity through shared resources.
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 detection of earth leakage currents at various levels and ensures the proper functioning of the measurement circuit, providing reliable protection by controlling SSPC switches in response to measured currents, enhancing safety and reliability in power circuit monitoring.
Implementation Method 1
a current measuring transformer receiving at the primary at least the three phases of a three-phase power supply to the equipment or the phase and neutral of a single-phase power supply to the equipment and provided at the secondary with at least one winding for measuring the current in the primary
Implementation Method 2
said path comprising a current generator Iinj driven by an output of the controller and connected to an injection winding on said transformer, said injection winding comprising a number of turns Ninj adapted so that the current Iinj produces in said measuring winding a current Im testing said secondary in the absence of current in the primary
Data Source
Figure 1~2A
Figure 2B~3
AI summary
The invention relates to a device for monitoring and protecting equipment supplied by at least one solid state power controller (SSPC) (5, 6, 7), said device comprising at least one current measuring circuit comprising: a current measuring transformer (8) receiving at the primary at least the three phases (1, 2, 3) of a three-phase supply to the equipment or the phase and neutral of a single-phase supply to the equipment and provided at the secondary with at least one winding (10, 11) for measuring the primary current, a measuring and testing module (9) comprising a controller (9a) provided with at least one analogue input (10a, 11a) connected to said measurement winding (13, 14) by a measurement channel (10, 11) for measuring a secondary current lm, representative of a differential current ld at the primary, and provided with a measurement program and a digital communication channel (16) with said SSPC for controlling a switch of said SSPC in the event that said current ld exceeds a given threshold; wherein said module (9) comprises a current injection path in said transformer, said path including a current generator Iinj driven by an output of the controller (9a) and connected to an injection winding (15) on said transformer, said injection winding comprising a number of turns Ninj suitable for the current Iinj to produce in said measurement winding (13, 14) a test current lm of said secondary in the absence of primary current and comprises a test program suitable for driving a current injection in parallel with a current measurement.