On-Load Tap Changer Switching Device Inductive Transition Path
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Solution Overview
Problem
Existing tap changers face challenges in safely performing frequent switching operations due to heat loss issues in transition resistors, which can lead to overheating and damage.
Innovation Solution
A switching device for on-load tap changers featuring a main switch as a compact-break switch, such as a vacuum interrupter or semiconductor switch, with a transition path having mainly inductive impedance, allowing for safe and frequent tap changing operations without additional equipment for current-zero creation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transition resistor is used in traditional tap changers to avoid circulating currents, then the switching operation is safe, but heat loss increases and frequent switching causes overheating
Solution Approach 1:
The patent changes the impedance parameter of the transition path from primarily resistive to primarily inductive. This parameter change allows the transition path to limit circulating currents during switching while significantly reducing heat loss, as inductive impedance stores and releases energy rather than dissipating it as heat. The inductive transition path maintains switching safety while enabling frequent tap changes without overheating.
2Ease of operation
If the main switch is opened during tap changing, then the load current can be commutated to the transition path, but a transient recovery voltage is produced across the main switch
Solution Approach 1:
The patent introduces a compact-break switch as an intermediary device that can withstand the transient recovery voltage produced when the main switch is opened. This compact-break switch acts as a mediator that bridges the gap between the main switch and the transition path, allowing current commutation to proceed while blocking the harmful transient voltage from damaging the main switch.
3Reliability
If additional equipment is added to create current-zero for commutation, then the transient recovery voltage can be managed, but the device complexity increases
Solution Approach 1:
The patent employs a compact-break switch that is self-capable of withstanding transient recovery voltage without requiring external current-zero creation equipment. The compact-break switch inherently provides the necessary voltage blocking capability, making the system self-sufficient and eliminating the need for additional complexity in the form of external current-zero creation devices.
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
Significantly reduces heat losses during tap-changing operations, enabling more frequent switching while ensuring complete commutation of load current despite transient recovery voltage, without the need for additional equipment.
Implementation Method 1
The main switch is a vacuum interrupter or a semiconductor switch, which are switch types that can block a high transient recovery voltage over a short isolation distance
Implementation Method 2
when the main switch is opened and parts of the load current starts to flow in the transition path, the transition inductor will produce a transient recovery voltage across the main switch
Implementation Method 3
By providing the main switch in the form of a compact-break switch, complete commutation of the load current to the transition path can be ensured despite the transient recovery voltage
Data Source
Figure 1
Figure 2~10
Figure 3
AI summary
A switching device (115, 300) for an on-load tap changer (100) is disclosed. The switching device is designed for providing electrical connection between a fixed contact (135) and an external output (155) of the tap changer. The switching device provides: a main current path comprising a main switch (140) which is series-connected in the main current path; and a transition current path comprising a transition inductor (400) and a transition switch (145). The transition switch and the transition inductor are connected in series. The impedance of the transition current path is higher than the impedance of the main current path, the impedance of the transition current path being mainly inductive. The main switch and the transition inductor are connected in parallel, so that upon opening of the main switch, a load current flowing through the main current path will be commutated to the transition current path.