DC Bus Protection Using Transformer Impedance Current Limiting
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Solution Overview
Problem
Conventional DC power distribution systems with current-limitation circuits to manage short-circuit currents increase in cost and size due to the need for high current-carrying capacities in resistors and reactors.
Innovation Solution
A DC power distribution system design that includes a transformer with a specific inductance value for short-circuit impedance, allowing for shorter interrupting-operation times in DC interrupting portions, eliminating the need for a current-limitation circuit by limiting short-circuit currents within the rectification device's capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current-limitation circuit composed of a resistor and a reactor is implemented to limit short-circuit current, then short-circuit current can be limited, but the cost for and the size of the DC power distribution system increase
Solution Approach 1:
The patent extracts the current limitation function from a separate resistor-reactor circuit and integrates it into the transformer's inherent short-circuit impedance. By setting the transformer's inductance value appropriately, the transformer itself limits the short-circuit current without requiring additional current-limitation components, thereby reducing system cost and size while maintaining reliability.
Solution Approach 2:
The transformer is given a dual function: it not only performs voltage conversion but also serves as the current-limitation element through its short-circuit impedance. This multi-functionality eliminates the need for dedicated current-limitation circuits, resolving the contradiction between reliability and device complexity.
2Reliability
If the interrupting-operation time for DC interrupting portions is set to be shorter than for AC interrupting portion, then short-circuit current can be limited within rectification device capacity, but the DC interrupting portions must operate faster which may increase their complexity
Solution Approach 1:
The patent changes the inductance parameter of the transformer to an specific value that naturally limits the short-circuit current to within the rectification device's capacity. This parameter adjustment allows for shorter interrupting times without requiring excessively complex high-speed interrupting mechanisms, as the current is already limited by the transformer's impedance.
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 design suppresses increases in cost and size by ensuring short-circuit currents do not exceed the rectification device's capacity, maintaining system reliability without additional components.
Implementation Method 1
a transformer (11) configured to convert an AC power inputted to the transformer (11) into an AC power at a different voltage and output the AC power obtained by the conversion
Implementation Method 2
a rectification device (12) configured to convert the AC power outputted from the transformer (11) into a DC power and output the DC power
Data Source
AI summary
A DC power distribution system includes: a transformer; a rectification device; a DC bus through which DC power flows; a plurality of DC branch lines branching off from the DC bus; an AC interrupting portion connected to an input side of the transformer; a first DC interrupting portion connected between the rectification device and the DC bus; and a plurality of second DC interrupting portions respectively provided to the plurality of DC branch lines. An interrupting-operation time for each second DC interrupting portion is set to be shorter than interrupting-operation times for the AC interrupting portion and the first DC interrupting portion. An inductance value of a short-circuit impedance of the transformer is set to a value at which short-circuit current can be limited to take a value not larger than a maximum current value permitted for the rectification device.