Static Transfer Switch Parallel Branches for Inrush Current Limiting
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Solution Overview
Problem
Conventional static transfer switches (STSs) are vulnerable to damage from inrush current during start-up and voltage source transfer, and existing solutions like circuit breakers incur downtime and are costly due to the need for matching current ratings.
Innovation Solution
Incorporating parallel circuit branches with passive elements and auxiliary switches in STSs to mitigate inrush current, using resistors or inductors in conjunction with semiconductor or electromechanical switches to divert current during start-up and transfer, eliminating the need for circuit breakers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a circuit breaker is positioned upstream of the thyristor switches to protect against inrush current, then the switches are protected from damage, but the system becomes costly and incurs downtime when the breaker trips
Solution Approach 1:
A current limiting reactor (inductor) is introduced as an intermediary component in series with each thyristor switch. This reactor limits the rate of rise of inrush current (di/dt) without requiring a circuit breaker, thereby protecting the thyristors while avoiding the cost, complexity, and downtime associated with breaker systems. The reactor acts as a passive current-limiting element that operates continuously without tripping or resetting.
Solution Approach 2:
The current limiting reactors are pre-installed in series with each thyristor switch before operation. These reactors continuously limit the inrush current from the moment the thyristor is triggered, preventing damage before it can occur. This preliminary protective action eliminates the need for reactive circuit breaker intervention after inrush current damage has been permitted to occur.
2Power
If high-power solid-state switches (thyristors) are used in the STS, then the switching capability and power handling are improved, but the vulnerability to inrush current damage increases
Solution Approach 1:
Current limiting reactors are inserted in series with each high-power thyristor switch to act as intermediaries that limit the harmful di/dt of inrush current while allowing the thyristor to handle full power during normal operation. The reactor's inductance naturally limits the rate of current rise without restricting the maximum current capability of the thyristor.
Solution Approach 2:
The electrical parameters of the circuit are modified by adding series inductance through the reactors. This changes the current waveform characteristics, specifically limiting the rate of rise (di/dt) parameter while maintaining the overall current magnitude capability. The reactor transforms the harsh inrush current profile into a controlled, gradual current rise that the thyristor can withstand.
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 effectively prevents damage from inrush current while maintaining reliability and reducing costs by using compact, cost-effective components, eliminating downtime associated with circuit breakers.
Implementation Method 1
a first passive element and a first auxiliary switch coupled in parallel to the first switch
Data Source
AI summary
Disclosed herein is a static transfer switch and methods of operating the same. The static transfer switch includes a first switch between a first voltage source and a load, and a second switch between a second voltage source and the load. The first switch and the second switch are configured to alternate power to the load between the first voltage source or the second voltage source. The static transfer switch also includes a first parallel circuit branch coupled in parallel to the first switch, the first parallel circuit branch comprising a first passive element and a first auxiliary switch.