Impulse Current Generator Crowbar Circuit for Surge Protection Testing

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Solution Overview

Problem

Existing surge protection device testing methods face challenges in simulating lightning-related surge currents effectively, leading to excessive electrical and thermal stress on SPDs, particularly varistors, and requiring calibration for different types of SPDs.

Innovation Solution

A novel impulse current generator system with a crowbar circuit that bypasses the impulse current after a specified time, using a thyristor triggered by a voltage threshold, to simulate a 10/350µs current waveform without excessive stress, and includes a current and voltage rate limiter to manage the current and voltage rates.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional high current generators are used to produce current waveforms simulating lightning related surges, then the required charge transfer Q and specific energy W/R can be achieved, but excessive electrical and thermal stress is applied to the SPD being tested

Engineering Contradiction:

Improvecharge transfer Q and specific energy W/RVSAvoidelectrical and thermal stress on SPD

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The harmful tail portion of the current waveform is extracted and removed from the test circuit using a crowbar circuit. The crowbar circuit bypasses the excess current that would otherwise continue flowing through the SPD after the required Q and W/R have been delivered, thereby eliminating the source of excessive thermal and electrical stress while preserving the essential test parameters.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The crowbar circuit rapidly activates to bypass the harmful tail current, effectively skipping through the dangerous phase of the waveform. This allows the test to complete the necessary charge and energy transfer quickly without lingering in the excessive stress region, thus protecting the SPD from damage while achieving test objectives.

Inventive Principle:

Principle #21Skipping (Rushing through)

2Stability of the object's composition

If critical and/or overcritical damping of the RLC circuit is used to obtain unidirectional current, then the current waveform meets testing standards, but higher peak currents for the same generator energy cannot be achieved

Engineering Contradiction:

Improveunidirectional current waveformVSAvoidpeak current

Core Design Contradiction:

Stability of the object's compositionVSPower

Solution Approach 1:

The damping parameter of the RLC circuit is changed from critical/overcritical to undercritical by adjusting the resistance value. This parameter change allows the circuit to generate higher peak currents for the same generator energy, while the crowbar circuit subsequently removes the harmful effects of the resulting oscillatory tail, thus achieving both high power and waveform control.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the full 10/350μs current waveform is applied to SPDs, then testing standards are met, but excessive electrical and mechanical stress corresponds to the tail of the waveform

Engineering Contradiction:

Improvetesting standard complianceVSAvoidelectrical and mechanical stress on SPD

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of applying the full 10/350μs waveform, only the necessary portion delivering the required charge Q and specific energy W/R is applied to the SPD. The crowbar circuit prevents excessive action by bypassing the remaining tail current, thus achieving test compliance with adequate safety margin.

Inventive Principle:

Principle #16Partial or excessive action

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 system allows for testing surge protection devices according to IEC standards without excessive electrical and thermal stress, reducing the need for calibration and ensuring accurate peak value, charge transfer, and specific energy measurements.

Implementation Method 1

direct impulse current (DIC) (discharge of capacitors through an RL circuit)

Methodology Applied

Scientific EffectCapacitor discharge: Capacitance

Implementation Method 2

using a thyristor triggered by a voltage threshold

Methodology Applied

Scientific EffectThyristor triggering:

Data Source

PatentEP2843428B1Devices and methods for providing an impulse current

Publication Date: 2021.03.17 RAYCAP INTELLECTUAL PROPERTY LTD

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AI summary

Devices include an impulse current generator that is configured to provide a direct impulse current (DIC) that includes a specified waveform to a test load during a test duration, a continuous power supply that is configured to provide a continuous power to the test load during the test duration, a trigger circuit that is configured to determine a trigger condition that corresponds to the DIC and to generate a trigger signal responsive to determining the trigger condition, and a current bypass circuit that is configured to receive the trigger signal generated by the trigger circuit and to conduct a majority portion of the DIC being conducted by the load responsive to the trigger signal.