Neutral-Line Capacitor Precharge in Y-Connected Battery Strings
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Solution Overview
Problem
In three-phase four-wire alternating-current power sources using battery strings, short-circuit and inrush currents occur due to the connection of battery strings to a neutral line, degrading power factor and requiring measures to mitigate these issues.
Innovation Solution
A power source system configuration that includes Y-connected battery strings connected to a neutral line with a neutral line capacitor, a neutral line switch in series, and an electric resistance element in parallel, where the neutral line switch is initially interrupted to pre-charge the capacitor, reducing inrush and short-circuit currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If battery strings are connected to a neutral line in a three-phase four-wire configuration, then power factor is improved and phase control is enabled, but short-circuit current and inrush current occur
Solution Approach 1:
The neutral line capacitor is pre-charged through the electric resistance element before the neutral line switch is closed. This preliminary charging action reduces the inrush current that would otherwise occur when the capacitor is suddenly connected to the battery strings. The resistance element serves as a current limiter during the pre-charging phase.
Solution Approach 2:
The electric resistance element acts as an intermediary component between the neutral line capacitor and the battery strings. It temporarily limits the current flow during the pre-charging phase, mediating the connection to prevent harmful inrush current while still enabling the capacitor to be charged to the appropriate voltage level.
2Object-affected harmful factors
If a capacitor is provided on the neutral line to block direct current, then short-circuit current is reduced, but inrush current occurs during starting power supply
Solution Approach 1:
The neutral line capacitor is pre-charged through the electric resistance element before the neutral line switch is closed. This preliminary charging action reduces the inrush current that would otherwise occur when the capacitor is suddenly connected to the battery strings. The resistance element serves as a current limiter during the pre-charging phase.
Solution Approach 2:
The electric resistance element acts as an intermediary component between the neutral line capacitor and the battery strings. It temporarily limits the current flow during the pre-charging phase, mediating the connection to prevent harmful inrush current while still enabling the capacitor to be charged to the appropriate voltage level.
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 configuration effectively reduces short-circuit and inrush currents, improving the power factor and operational stability of the three-phase four-wire alternating-current power source by pre-charging the neutral line capacitor and utilizing the resistance element to manage current flow.
Implementation Method 1
a neutral line capacitor for blocking a direct current
Implementation Method 2
an electric resistance element disposed in parallel to the neutral line switch
Data Source
Figure 1
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AI summary
A power source system includes a first battery string, a second battery string, and a third battery string. Each of the battery strings includes a plurality of batteries capable of outputting direct-current power. The battery strings are Y-connected so as to output three-phase alternating-current power to three-phase output terminals (alternating-current output terminals) as well as connected to a neutral line. On the neutral line, a neutral line capacitor for blocking a direct current, a neutral line switch disposed in series to the neutral line capacitor, and an electric resistance element disposed in parallel to the neutral line switch are provided.