Capacitive Reference Potential Coupling for Flashover Prevention

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Solution Overview

Problem

In household appliances, the direct connection of the reference potential to the protective conductor can lead to undefined voltage buildup between the electronics unit and the device housing due to parasitic capacitances, causing flashovers and potential destruction of components, and can also interfere with the functionality of residual current circuit breakers (RCDs) due to direct current leakage.

Innovation Solution

A capacitor is used to couple the reference potential to the protective conductor, forming a capacitive voltage divider that limits the voltage between the electronics unit and the protective conductor, while a resistor in parallel with the capacitor prevents excessive direct current flow, ensuring the proper functioning of RCDs without significant additional cost or space requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the reference potential is directly connected to the protective conductor, then the voltage between the electronic unit and device housing is limited, but voltage buildup due to parasitic capacitances causes flashovers and component destruction

Engineering Contradiction:

Improveprotection against voltage buildupVSAvoidvoltage buildup and flashover risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A capacitor is introduced as an intermediary component between the reference potential and the protective conductor. This capacitor provides a low-impedance path for high-frequency discharge currents while blocking DC leakage currents, thereby preventing voltage buildup without causing harmful DC current flow that would trigger RCDs

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the reference potential is directly connected to the protective conductor, then protection against voltage spikes is improved, but DC leakage currents interfere with RCD functionality

Engineering Contradiction:

Improveprotection against voltage spikesVSAvoidDC leakage current

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The capacitor acts as a frequency-selective intermediary that allows high-frequency transient currents to pass through to ground while blocking low-frequency or DC leakage currents. This resolves the contradiction by providing protection against voltage spikes without generating harmful DC leakage currents that would interfere with RCD operation

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If a direct connection is made between reference potential and protective conductor, then the insulation requirements are simplified, but the risk of undefined flashover increases

Engineering Contradiction:

Improveinsulation design simplicityVSAvoidundefined flashover

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The capacitor provides beforehand cushioning by offering a controlled discharge path for parasitic capacitances before voltage can build up to dangerous levels. This prevents undefined flashovers by continuously maintaining the reference potential at a safe voltage level relative to the protective conductor, while the insulation design remains simple

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 solution effectively reduces the voltage between the electronics unit and the protective conductor, preventing flashovers and ensuring the correct operation of RCDs, while maintaining low impedance for capacitive switches and avoiding excessive current flow that could damage components or impair RCD functionality.

Implementation Method 1

a capacitor through which the reference potential (9) is coupled to a protective conductor PE

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

Methodology Applied

Scientific EffectCapacitive voltage divider: Capacitance

Implementation Method 3

a resistor in parallel with the capacitor prevents excessive direct current flow

Methodology Applied

Scientific EffectElectrical Resistance: Electrical Resistance

Implementation Method 4

an undefined voltage could build up between the reference potential on the one hand and the protective conductor – and thus also the device housing – on the other, even during normal operation. This electrical voltage would arise due to leakage currents and parasitic capacitances between the mains connections on the one hand and the electronic unit on the other

Methodology Applied

Scientific EffectParasitic capacitance: Parasitic Capacitance

Data Source

PatentEP2602895B1Circuit arrangement for a household appliance and household appliance with a circuit arrangement

Publication Date: 2019.01.09 BOSCH SIEMENS HAUSGERATE GMBH

Figure 1~2
Figure 3~4

AI summary

The circuit device (101) has an input circuit (102) which is provided with alternating voltage terminals (103,104) between which an electric alternating voltage (UN) is applied. One of alternating voltage terminals is coupled to the direct current (DC) voltage generating unit (105) attached with input circuit. An electrical DC voltage (UG) is applied between the direct voltage terminal (108) and reference potential (109). The reference potential is coupled with a protective conductor (PE) via capacitor (116). A resistor (117) is arranged parallel to the capacitor.