Bidirectional DC Switching Apparatus Arc Interruption
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Solution Overview
Problem
Existing bidirectional direct current electrical switching apparatus, such as relays and circuit breakers, are inadequate for effectively interrupting arcs at high DC voltages with low forward currents and high reverse currents, particularly in photovoltaic power systems where fuses are ineffective for protecting against forward feed faults and bus faults.
Innovation Solution
A direct current electrical switching apparatus featuring a dual arc chamber design with oppositely directed magnetic fields and a movable contact system that allows for arc extinction at varying current magnitudes, enabling effective arc interruption across a wide range of currents by directing arcs into specific chambers based on current flow direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single arc chamber design is used, then the device structure is simple, but it cannot effectively interrupt arcs at high DC voltages with varying current magnitudes and directions
Solution Approach 1:
The arc chamber is divided into two separate chambers (first arc chamber and second arc chamber), each optimized for different current directions. The first arc chamber handles arcs generated when current flows from first contact to second contact, while the second arc chamber handles arcs when current flows from second contact to first contact. This segmentation allows each chamber to be specifically designed for its intended current direction, improving arc interruption reliability without requiring a single complex universal chamber.
Solution Approach 2:
The two arc chambers are designed with asymmetric characteristics - the first arc chamber has a first width optimized for forward current arcs, while the second arc chamber has a second width optimized for reverse current arcs. The magnetic fields in the two chambers are also oppositely directed, creating an asymmetric configuration that efficiently handles bidirectional currents of different magnitudes.
2Reliability
If fuses are used for over current protection, then conductor protection is provided, but they are ineffective for forward feed faults and bus faults in PV systems
Solution Approach 1:
The electrical switching apparatus provides universal protection capability for both forward and reverse current directions, unlike conventional fuses that only protect against reverse over current. The device can detect and interrupt faults occurring in either direction (forward feed faults and bus faults), making it a multi-functional protection device suitable for all fault conditions in PV systems.
Solution Approach 2:
The switching apparatus automatically detects the direction of current flow and activates the appropriate arc chamber without external control. When a fault occurs, the device self-adjusts by directing the arc into the appropriate chamber based on current direction, providing automatic adaptive protection without requiring external sensing or control circuitry.
3Reliability
If arc chambers with uniform width are used, then manufacturing is simplified, but arc extinction effectiveness varies with current direction and magnitude
Solution Approach 1:
Each arc chamber is designed with specific local characteristics optimized for its intended function. The first arc chamber has a first width optimized for arcs generated during forward current flow, while the second arc chamber has a second width optimized for arcs during reverse current flow. This local optimization ensures effective arc extinction for each current direction without requiring complex variable-width structures throughout the entire device.
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 reliable arc interruption and circuit disconnection at high DC voltages with low forward currents and high reverse currents, providing effective protection against faults in photovoltaic systems while minimizing back-striking and arc flash risks.
Implementation Method 1
a magnet assembly cooperating with the first and second arc chambers to establish generally oppositely directed magnetic fields normal to the first and second longitudinal axes, normal to a first direction of a first arc between the first contact and the first portion of the movable contact as the movable contact moves away from the closed contact position toward the open contact position, and normal to an opposite second direction of a second arc between the second contact and the second portion of the movable contact as the movable contact moves away from the closed contact position toward the open contact position
Implementation Method 2
one of the first arc plates at the first end of the first arc chamber being proximate the first arc runner, another one of the first arc plates at the opposite second end of the first arc chamber being proximate the second arc runner
Data Source
AI summary
A direct current electrical switching apparatus includes a first contact in electrical communication with first and third arc runners, a second contact in electrical communication with second and fourth arc runners, a movable contact, a first arc chamber including first arc plates having a first width, a second arc chamber including second arc plates having a greater second width, an operating mechanism, and a magnet assembly cooperating with the arc chambers to establish generally oppositely directed magnetic fields. The magnetic fields cause one of a first arc and a second arc to enter one of the arc chambers depending upon a direction of current flow between the contacts. The electrical switching apparatus is rated for a first magnitude of current flowing from the first contact to the second contact and for a greater second magnitude of opposite second current flowing from the second contact to the first contact.