Configurable Circuit-Breaker Single Setting Element Coordination
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Solution Overview
Problem
Current circuit-breakers require multiple setting elements and parameters for current limit values and delay times, which can lead to complex settings and potential intersections with fuse characteristic curves, causing incorrect tripping of protective elements.
Innovation Solution
A circuit-breaker with a single setting element for the second current limit value, where the first current limit value is set between 8 and 16 times the rated current, and the delay time is proportional to the inverse fourth power of the current, simplifying the graduation of current limit values and matching the behavior to fuse/circuit-breaker combinations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple setting elements are provided for current limit values and delay times, then the circuit-breaker can be adjusted to different protection characteristics, but the device complexity and setting complexity increase
Solution Approach 1:
A single setting element is designed to perform multiple functions: it sets both the second current limit value Ir and indirectly determines the first current limit value Ii (which is fixed at 8-16 times Ir) and the delay time characteristic (fixed at inverse fourth power relationship). This multi-functionality reduces the number of setting elements from multiple to one, simplifying the device while maintaining full adjustability of protection characteristics.
2Manufacturing precision
If multiple current limit values are set independently, then precise protection control is achieved, but the risk of intersection with fuse characteristic curves increases causing incorrect tripping
Solution Approach 1:
The patent establishes a fixed mathematical relationship between current limit values (Ii = 8-16 × Ir) and a fixed functional relationship for delay time (t ∝ I^-4). This parameter linkage ensures that the circuit-breaker characteristic curve maintains proper positioning relative to fuse curves, preventing intersections that would cause incorrect tripping while preserving precise protection control through the adjustable second current limit value Ir.
3Speed
If delay time is reduced for higher currents, then short-circuit protection is improved, but the complexity of coordinating with fuse characteristics increases
Solution Approach 1:
The circuit-breaker automatically achieves proper coordination with fuse characteristics through the fixed inverse fourth power relationship between delay time and current. When the current exceeds the set limit, the system self-adjusts the delay time according to the formula t ∝ I^-4, eliminating the need for manual coordination calculations or additional setting elements. This self-service mechanism simplifies coordination while ensuring fast interruption for high currents.
Data Source
AI summary
A circuit breaker is disclosed for interrupting an electrical circuit when current limit values are exceeded. The circuit-breaker includes a current sensor for determining the electrical current flow and a control device. When current limit values are exceeded, the electrical circuit is interrupted. A first current limit value, when exceeded, results in an immediate interruption and a second current limit value, when exceeded, results in a time-delayed interruption, such that the second interruption time reduces as the current increases. Only one control element is included for setting a current limit value. The element defining the second current limit value is included for the time-delayed interruption of the electrical circuit. The other parameters are either set in a fixed manner and/or are related to the settable second current limit value.