3-Phase Electronic Tap Changer Commutation via Single SCR
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Solution Overview
Problem
Existing 3-phase AC electronic tap-changing voltage regulators face challenges in minimizing load current discontinuity and inter-tap short circuit currents during commutation, which can damage SCRs and transformer windings, and current solutions are costly and complex due to the need for additional components and control complexity.
Innovation Solution
A novel commutation method using a single commutation resistor and associated SCR, where the commutation SCR is fired to maintain current flow through a commutation resistor, allowing the old SCR's current to naturally fall to zero before activating the new SCR, and then removing the gating signal from the commutation SCR to cease current flow, thereby reducing component count and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a commutation resistor and SCR pair are added to each tap winding to enable safe commutation, then inter-tap short circuit current is limited and SCR damage is prevented, but device complexity and cost increase substantially
Solution Approach 1:
The patent merges the commutation function from multiple distributed components into a single centralized commutation resistor and SCR pair. Instead of having protection components at each tap winding, the invention uses one commutation circuit that handles commutation for all phases, substantially reducing component count while maintaining protection functionality
Solution Approach 2:
The single commutation resistor and SCR pair serves multiple functions: it limits inter-tap short circuit current, provides a controlled commutation path for all phases, and enables safe SCR switching. This universal commutation circuit replaces what would otherwise require multiple specialized components distributed throughout the system
2Speed
If the new tap SCR is fired before the old tap SCR current falls to zero, then commutation is faster, but inter-tap short circuit current flows and may damage SCRs
Solution Approach 1:
The commutation resistor serves as an intermediary element that provides a controlled path for commutation current. When the commutation SCR is fired, it creates a controlled current path through the commutation resistor, allowing the old SCR current to transition safely to the new SCR while limiting any potential short circuit current through the resistor's impedance
Solution Approach 2:
The commutation SCR is fired in advance to establish a controlled commutation path before the old SCR current naturally falls to zero. This preliminary action creates a safe transition path that prevents harmful short circuit currents while enabling faster commutation than waiting for natural current zero
3Reliability
If a delay is used to allow the old tap SCR to turn off before activating the new SCR, then SCR damage from short circuit current is avoided, but load current discontinuity causes voltage transients
Solution Approach 1:
The commutation resistor provides a continuous current path during the transition between old and new SCRs. By keeping the commutation SCR fired throughout the commutation process, the circuit maintains continuous current flow, preventing load current discontinuity and the associated voltage transients that would occur with delayed commutation
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 approach maintains continuous current through the series transformer during tap changes, minimizing voltage transients and reducing costs and complexity while achieving similar performance to schemes with multiple commutation resistors and SCR pairs.
Implementation Method 1
firing a commutation silicon controlled rectifier (SCR), removing a gating signal from a first SCR connected to a first of the plurality of taps, firing a second SCR connected to a second of the plurality of taps
Implementation Method 2
This current overload is potentially damaging to the SCRs and transformer windings... provisions must be made to avoid both load current discontinuity and high inter-tap circulating current when commutating
Data Source
AI summary
The invention provides a novel 3-phase electronic tap changer commutation and related device. In one embodiment, the invention includes firing a commutation silicon controlled rectifier (SCR), removing a gating signal from a first SCR connected to a first of the plurality of taps, firing a second SCR connected to a second of the plurality of taps, and removing a gating signal from the commutation SCR.