Solid-State Breaker Pulse Chopping for Selective Coordination
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Solution Overview
Problem
Achieving selective coordination in electrical distribution systems where a solid-state circuit breaker (SSCB) is upstream of a conventional thermal/magnetic circuit breaker is challenging due to the SSCB's inability to carry sustained high currents, which contradicts the concept of selective coordination and is cost-prohibitive to replace all breakers with SSCBs.
Innovation Solution
A circuit breaker distribution system where a SSCB with a microcontroller allows repeated pulses of current to a downstream thermal/magnetic breaker, setting a 'chop level' higher than its rated current but low enough to prevent damage, and optimizing pulse intervals based on the system voltage waveform to effectively trip the downstream breaker, ensuring selective coordination without damaging the SSCB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a solid-state circuit breaker (SSCB) is used as the upstream breaker, then the short-circuit interrupting capacity is improved, but the ability to achieve selective coordination with downstream thermal/magnetic breakers deteriorates due to the SSCB's inability to carry sustained high currents
Solution Approach 1:
The patent applies periodic action by implementing a pulse-chopping control strategy where the SSCB allows repeated pulses of high current to pass through to the downstream thermal/magnetic breaker. The controller periodically opens and closes the SSCB, creating a series of current pulses that accumulate thermal energy in the downstream breaker's magnetic actuator, eventually causing it to trip. This periodic pulsing resolves the contradiction by enabling the SSCB to achieve selective coordination without requiring sustained high current carrying capability.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the pulse width, pulse frequency, and duty cycle of the SSCB based on real-time monitoring of downstream breaker status and system conditions. The controller modifies these parameters to optimize the thermal accumulation effect in the downstream breaker while preventing excessive heat stress on the SSCB. This dynamic parameter adjustment enables selective coordination to be achieved under varying load and fault conditions.
2Reliability
If the SSCB allows repeated high current pulses to trip the downstream breaker, then selective coordination is achieved, but heat stress on the SSCB increases which may damage the semiconductor junctions
Solution Approach 1:
The patent applies partial action by allowing the SSCB to pass only the minimum necessary current pulses required to trip the downstream breaker, rather than continuously carrying full fault current. The pulse-chopping strategy delivers just enough thermal energy to the downstream magnetic actuator to cause tripping, while keeping the total energy exposure to the SSCB's semiconductor junctions within safe limits. This partial action approach achieves selective coordination without excessive heat stress.
Solution Approach 2:
The patent uses the downstream thermal/magnetic breaker's bimetal and magnetic actuator as an intermediary that converts the pulsed current from the SSCB into a mechanical tripping action. The thermal/magnetic breaker absorbs the heat stress and mechanical wear from high current interruption, protecting the SSCB's semiconductor junctions. This intermediary mechanism enables the SSCB to achieve selective coordination while avoiding direct exposure to damaging thermal and mechanical stresses.
3Reliability
If all breakers are replaced with SSCBs to achieve selective coordination, then the coordination reliability is improved, but the system cost increases significantly
Solution Approach 1:
The patent applies this principle by using a single expensive SSCB as the upstream breaker while allowing downstream thermal/magnetic breakers to serve as sacrificial protective devices. The downstream breakers are designed to be replaced after tripping, while the SSCB remains in service providing intelligent control. This approach achieves selective coordination reliability with minimal use of expensive SSCB technology, significantly reducing overall system cost compared to replacing all breakers with SSCBs.
Solution Approach 2:
The patent applies universality by designing the SSCB with multi-functionality: it serves as both the primary protective device for upstream protection and as an intelligent controller that enables selective coordination for downstream breakers. The SSCB's controller performs multiple functions including pulse-chopping control, fault detection, communication with downstream breakers, and system monitoring. This multi-functionality eliminates the need for separate selective coordination devices, reducing overall system cost while maintaining high reliability.
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
This solution allows only the downstream breaker to trip, limiting power interruption to the faulty circuit, reducing heat stress on the SSCB, and potentially extending the life and reliability of conventional breakers by avoiding high short circuit currents, while being cost-effective by not requiring all breakers to be SSCBs.
Implementation Method 1
This reverse voltage is produced via a so-called pinching effect at the solid-state junction.
Implementation Method 2
the magnetic actuator in the downstream breaker has sufficient force to actuate tripping in the downstream device
Implementation Method 3
They typically contain overload and short-circuit trip actuators in the form of bimetals and electromagnets, respectively.
Data Source
AI summary
A circuit breaker distribution system is configured to provide selective coordination. The system comprises a solid-state switch disposed as a main or upstream breaker and a switch with an over current protection disposed as a branch or downstream breaker. The solid-state switch comprises a microcontroller to: allow repeated pulses of current through to the branch or downstream breaker in an event of an overload or short circuit, choose a maximum current limit for the solid-state switch as a “chop level” such that the chop level is chosen higher than a rated current of the solid-state circuit breaker but low enough that the solid-state switch is not damaged from repeated pulses over a period of time needed to switch OFF the branch or downstream breaker, and add a pulse interval which is optimized to a system voltage waveform in that chopped pulses tend to be longer and more effective for de-latching the branch or downstream breaker when they occur in vicinity of a zero crossing of the system voltage waveform and chopped pulses are shorter and less effective near peaks of the system voltage waveform.