Bus-Tie Link Capacitor Layout for DC Bus Zonal Selectivity
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Solution Overview
Problem
Existing electric power systems face challenges in maintaining zonal selectivity and efficient fault current distribution due to high dependency on power flow via interconnected direct voltage busses, particularly in marine vessels, where fault currents can overwhelm overcurrent protection devices, necessitating high capacitance on busses for activation.
Innovation Solution
Incorporating capacitors between bus-tie links and overcurrent protection devices to form a distributed capacitor storage, providing fault currents to operate overcurrent protection devices and achieve zonal selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single bus-tie link is used to interconnect direct voltage busses, then the system structure is simple, but fault current distribution becomes unmanageable and zonal selectivity cannot be maintained
Solution Approach 1:
The patent divides the single bus-tie link into multiple parallel bus-tie links (at least two links between the same busses). Each link is equipped with its own overcurrent protection device. This segmentation allows independent protection and selective disconnection of individual links, maintaining zonal selectivity while distributing fault current across multiple paths.
2Power
If high power rated bus-tie link is used, then fault current capacity is sufficient, but high amount of capacitance is required on direct voltage busses to activate overcurrent protection devices
Solution Approach 1:
The patent merges multiple bus-tie links in parallel between the same direct voltage busses. This combination increases the overall fault current capacity of the interconnection without requiring excessive capacitance on the busses, as the fault current is distributed across multiple links rather than concentrated in a single high-power link.
Solution Approach 2:
The patent introduces capacitors as intermediary elements connected to each bus-tie link. These capacitors provide the necessary energy to activate overcurrent protection devices during faults, reducing the capacitance burden on the main direct voltage busses while still enabling reliable protection operation.
3Reliability
If overcurrent protection devices are placed on bus-tie link, then fault protection is enabled, but each device carries only a part of fault current making protection coordination difficult
Solution Approach 1:
The patent places overcurrent protection devices on each individual bus-tie link rather than sharing a single protection device. This segmentation allows each protection device to independently detect and respond to faults on its specific link, simplifying coordination and maintaining zonal selectivity even though multiple devices are used.
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 capacitors enable effective separation of faulty bus-tie links and direct voltage busses by supplying sufficient fault currents to overcurrent protection devices, ensuring rapid disconnection and maintaining system operability.
Implementation Method 1
each of the bus-tie links comprises at least one capacitor between first and second poles of the bus-tie link
Data Source
AI summary
An electric power system includes direct voltage buses (101, 102) and at least two bus-tie links (103-105) each being connected between the direct voltage buses. Each bus-tie link has at least one capacitor (106-111) between positive and negative poles of the bus-tie link. At least one pole of each bus-tie link is connected via overcurrent protection devices (112-117), such as fuses, to respective poles (118, 119) of the direct voltage buses. The capacitors of the bus-tie links form a distributed capacitor storage that is capable of providing fault currents to the electric power system to operate overcurrent protection devices so that zonal selectivity is achieved. The electric power system can be for example an electric power system of a ship or another marine vessel.