ESS String Protection Using Contactor-Disconnector Isolation
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Solution Overview
Problem
Conventional protection devices for medium-voltage DC switchgear and fuses are not scaled to high voltage levels without a commensurate increase in size, cost, and complexity, posing challenges for the protection of energy storage systems (ESS) in power grids with high renewable energy penetration.
Innovation Solution
An energy storage system (ESS) incorporating a protection arrangement with derated contactors and disconnectors, where contactors interrupt current flow and disconnectors provide galvanic insulation, allowing for safe and cost-effective disconnection of strings in ESS systems, using a contactor with a voltage rating less than the total string voltage and a disconnector with a rating similar to the total string voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional protection devices are scaled to high voltage levels, then voltage rating is improved, but size, cost, and complexity increase commensurately
Solution Approach 1:
The protection device is divided into two separate functional components: a contactor responsible for current interruption and a disconnector responsible for voltage isolation. This segmentation allows each component to be optimized independently, with the contactor rated for lower voltage but higher current, and the disconnector rated for higher voltage but operating at zero current, thereby reducing overall system complexity and cost while maintaining high voltage capability
Solution Approach 2:
The contactor acts as an intermediary component that interrupts current flow before the disconnector opens. By introducing this intermediate current-interruption step, the disconnector only needs to handle voltage isolation at zero current, allowing it to be rated for high voltage without requiring high current capability, thus reducing complexity and cost
2Reliability
If conventional protection devices are scaled to high voltage levels, then voltage rating is improved, but cost increases commensurately
Solution Approach 1:
The protection device is divided into two separate functional components: a contactor responsible for current interruption and a disconnector responsible for voltage isolation. This segmentation allows each component to be optimized independently, with the contactor rated for lower voltage but higher current, and the disconnector rated for higher voltage but operating at zero current, thereby reducing overall system complexity and cost while maintaining high voltage capability
Solution Approach 2:
The contactor is designed as a lower-cost component with reduced voltage rating that performs the temporary function of current interruption. By accepting that the contactor operates under more stressful conditions (higher current, lower voltage rating), it can be manufactured more cheaply, while the disconnector, though rated for high voltage, only operates at zero current and can be simpler in design
3Device complexity
If a contactor with voltage rating less than total string voltage is used, then device complexity and cost are reduced, but voltage stress on contactor increases during operation
Solution Approach 1:
The contactor is designed to interrupt current flow in advance before the disconnector opens. By performing this preliminary current-interruption action, the arc duration is limited to the brief period between contactor opening and disconnector opening, preventing excessive voltage stress accumulation on the contactor despite its lower voltage rating
Solution Approach 2:
The contactor acts as an intermediary component that interrupts current flow before the disconnector opens. By introducing this intermediate current-interruption step, the disconnector only needs to handle voltage isolation at zero current, allowing it to be rated for high voltage without requiring high current capability, thus reducing complexity and cost
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 provides reliable and cost-effective protection for ESS systems by derating contactors and disconnectors, ensuring safe operation and reducing complexity and cost, while maintaining high voltage levels without significant voltage stress on the contactors.
Implementation Method 1
a contactor arranged in series with the one or more electrical energy storage units, configured to interrupt current flow through the string
Implementation Method 2
a disconnector switch arranged in series with the one or more electrical energy storage units, configured to open after the contactor has interrupted current flow
Data Source
Figure 1
Figure 2~3
AI summary
There is disclosed herein an energy storage system, ESS, (100) adapted for incorporation with a medium-voltage static compensator (STATCOM), the ESS comprising a plurality of strings electrically connected in parallel, each string comprising one or more electrical energy storage units (104) electrically connected in series. At least one string comprises a protection arrangement (102a-c, 106), the protection arrangement comprising a contactor (106) arranged in series with the one or more electrical energy storage units, configured to interrupt current flow through the string during a fault response, and a disconnector switch (102a-c) arranged in series with the one or more electrical energy storage units, configured to open after the contactor has interrupted current flow through the string. The contactor has a voltage rating substantially less than the total string voltage; and the disconnector switch has a voltage rating at least substantially similar to the total string voltage. There is further disclosed herein a STATCOM device connected to such an ESS, and a method for controlling such an ESS. Fig. 1