Modular Coupling Circuit for Ungrounded Power Supply Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing solutions for coupling insulation monitoring devices to unearthed power supply systems face challenges in safely isolating high voltages, leading to complex and costly circuit designs, especially when nominal voltages exceed 1.5 kV, and current solutions are not suitable for AC systems or are overly expensive.
Innovation Solution
A modular coupling circuit composed of identical coupling modules, each with a switching unit and a transformer, allowing for series connection to bridge potential differences and provide electrical isolation, enabling safe operation and cost-effective potential separation across varying voltage ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-voltage switches from the power supply field are used to switch high voltages in conjunction with high currents, then the switching capability is sufficient, but the switches are very large and complex in construction, making them oversized and significantly too expensive
Solution Approach 1:
The patent divides the high-voltage switching task into multiple stages by introducing a multi-stage coupling circuit with series-connected coupling impedances and switches. Instead of using a single high-voltage switch, the circuit segments the voltage isolation task across multiple lower-voltage switching stages, each handling a portion of the total voltage difference, thereby avoiding the need for oversized high-voltage switches.
Solution Approach 2:
The patent introduces coupling impedances as intermediary elements between the semiconductor switch and the high-voltage ungrounded power supply system. These coupling impedances act as mediators that limit current during switching operations and enable the use of lower-voltage-rated semiconductor switches by reducing the voltage stress across them during transient states.
2Reliability
If the nominal voltage of an ungrounded power supply system exceeds the rated voltage of the insulation monitoring device, then a coupling impedance must be used to protect the device, but this requires additional circuit components and complexity
Solution Approach 1:
The coupling circuit serves multiple functions simultaneously: it provides voltage isolation to protect the insulation monitoring device, enables switching of the insulation monitoring device connection, and can be integrated with the insulation monitoring device itself. This multi-functionality reduces overall system complexity despite the added coupling impedance.
Solution Approach 2:
The patent merges the coupling impedance function with the insulation monitoring device by integrating the coupling circuit directly into the device structure. This combination eliminates the need for separate external coupling components and simplifies the overall system architecture while maintaining device protection.
3Ease of operation
If a switch forms a series circuit with the coupling impedance, then the switch can control connection, but when open it causes voltage drop across the switch leading to destruction risk and high costs for potential isolation
Solution Approach 1:
The patent applies beforehand cushioning by introducing RC circuits (resistor-capacitor networks) in parallel with the switches and coupling impedances. These RC circuits provide pre-established discharge paths and voltage limiting mechanisms that prevent dangerous voltage spikes before they can occur, cushioning the switch from destructive voltage stress during opening and closing operations.
4Speed
If semiconductor switches are used in AC systems, then switching speed is improved, but additional circuit modifications are required since semiconductor switches are predominantly unipolar
Solution Approach 1:
The patent employs dynamically controllable switching arrangements where semiconductor switches are controlled through RC circuits that adapt the switching characteristics to the AC waveform. The RC circuits enable the unipolar semiconductor switches to effectively handle bipolar AC currents by providing appropriate gate control signals and current paths during different phases of the AC cycle.
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 modular design simplifies the actuation of semiconductor switches and reduces costs by allowing easy adaptation of coupling impedance to different nominal voltages, ensuring safe and reliable operation of insulation monitoring devices in unearthed power supply systems, even at high voltages.
Implementation Method 1
the transformer performs the function of galvanic isolation between a semiconductor switch potential and a control potential of the semiconductor switch
Implementation Method 2
exactly one transformer, which supplies the control circuit(s) with a voltage
Implementation Method 3
When the switch is open, it has a very high resistance relative to the coupling impedance, causing the voltage of the ungrounded power supply system to drop almost completely across the switch
Implementation Method 4
Each switching unit comprises a series connection of a coupling impedance and a semiconductor switch, with the semiconductor switch being controlled by a control circuit
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a coupling circuit (20) with a switching function for coupling an insulation monitoring device (6, 6a, 6b) to an ungrounded power supply system, consisting of a coupling module (22) or several identical coupling modules (22) connected in series, wherein the coupling module (22) comprises at least one switching unit (25) comprising a coupling impedance (26), a switch (24) arranged in series with the coupling impedance (26) for mains isolation and a control circuit (28) for controlling the switch (24), as well as exactly one transformer (30) for voltage supply and galvanic isolation.