DC Busbar Fault Isolation With Precharged Switch Reclosing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
DC distribution grids face challenges in protection against short-circuits and fault sources due to the fast self-protection functions of power electronics, leading to potential damage from voltage reversal and high current peaks, which conventional electromechanical switches are unable to handle quickly enough.
Innovation Solution
An electrical grid equipped with a device that includes an electrical switch, a fault current identification mechanism, a trip unit, a pre-charging device, and a control unit to automatically close the switch after pre-charging, allowing for rapid disconnection of feeders and isolation of faults within microseconds, enabling the use of semiconductor switches for high-power applications and smaller electromechanical switches for the rest of the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional electromechanical switches are used for protection, then device complexity is reduced, but the switching speed is too slow to handle fast fault currents and voltage reversal
Solution Approach 1:
The protection system is segmented into two distinct parts: semiconductor switches (fast-acting) for rapid fault current interruption, and electromechanical switches (slow-acting) for feeder disconnection and isolation. This segmentation allows each component to operate within its optimal performance range, resolving the contradiction between speed and complexity.
Solution Approach 2:
The semiconductor switches perform preliminary action by quickly interrupting fault currents before they can cause damage to the electromechanical switches or other system components. This preliminary protection enables the slower electromechanical switches to then safely disconnect feeders without being exposed to harmful fault conditions.
2Reliability
If semiconductor switches are used throughout the system, then switching speed and protection capability are improved, but power losses and costs increase
Solution Approach 1:
Semiconductor switches are applied locally only at critical positions where fast fault current interruption is essential (e.g., at the DC busbar and near sensitive equipment), while electromechanical switches are used for less critical feeder disconnection. This localized application of high-performance components improves protection reliability where needed while minimizing overall power losses and costs.
Solution Approach 2:
The system uses inexpensive electromechanical switches for applications where high speed is not critical (feeder disconnection), accepting that these components are less durable under fault conditions. The expensive semiconductor switches are reserved for critical protection functions, optimizing the overall cost-effectiveness and energy efficiency of the protection system.
3Stability of the object's composition
If AFE devices are used to stabilize the AC side, then grid quality is improved, but freewheeling diodes remain vulnerable to voltage reversal and high current peaks
Solution Approach 1:
The semiconductor switch acts as an intermediary protective element positioned between the AFE device and the freewheeling diode. When voltage reversal or high current peaks occur, the semiconductor switch quickly interrupts the fault current, preventing damage to the diode while allowing the AFE device to continue stabilizing the AC side without interference.
Data Source
AI summary
An electric grid includes feed-ins, loads, and a distribution grid, which is arranged therebetween. The distribution grid comprises at least one busbar and at least one device for opening or closing a DC circuit. The at least one device includes an electric switch for opening or closing the DC circuit, a fault current detector, a trigger unit, a precharging device, and a control unit for automatically closing the electric switch after the precharging process. The electric switch opens the DC circuit via the trigger unit if a fault current is detected by the fault current detector, and the precharging device restores the voltage on the busbar prior to closing the electric switch.