Impulse Current Generator Crowbar Circuit for Surge Protection Testing
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Solution Overview
Problem
Conventional surge protection device testing methods apply excessive electrical and thermal stress due to higher Q and W/R values than specified, particularly affecting varistors, and require calibration for different types of SPDs.
Innovation Solution
A device comprising an impulse current generator with a crowbar circuit that bypasses the impulse current after a specified time, using a thyristor triggered by a voltage pulse, to limit the stress and achieve the required Q and W/R values within the IEC 61643-11 standard without excessive stress on the SPD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional high current generators are used to produce current waveforms for surge testing, then the required Q and W/R values can be achieved, but excessive electrical and thermal stress is applied to the SPD being tested
Solution Approach 1:
The current waveform is segmented into two distinct parts: an initial surge portion that delivers the required Q and W/R values to the SPD, and a subsequent tail portion that is bypassed through a crowbar circuit. This segmentation allows the beneficial testing parameters to be delivered while eliminating the harmful excessive stress from the tail portion.
Solution Approach 2:
A crowbar circuit acts as an intermediary component that selectively bypasses the tail portion of the current waveform. The crowbar circuit includes a thyristor that is triggered at a specific time to create a low-impedance path, diverting the harmful tail current away from the SPD while allowing the initial surge to pass through for proper testing.
2Manufacturing precision
If crowbar devices are used to produce current waveforms according to testing standards, then the waveform shape can be controlled, but calibration and synchronization are required for different types of varistor based SPDs
Solution Approach 1:
The testing system is designed with a universal crowbar circuit configuration that can be used with different types of varistor-based SPDs without requiring recalibration. The fixed timing of the crowbar trigger and the standardized waveform generation approach make the system adaptable to multiple SPD types while maintaining consistent testing parameters.
Solution Approach 2:
The system uses fixed parameter settings for the crowbar trigger timing and waveform generation that work across different SPD types. By establishing standardized parameter values for the current waveform (such as the trigger time relative to the waveform crest), the system eliminates the need for individual calibration while maintaining waveform accuracy.
3Manufacturing precision
If the full 10/350 μs waveform is applied to the SPD, then the complete Q and W/R are delivered, but excessive stress is applied during the tail portion of the waveform
Solution Approach 1:
The crowbar circuit effectively skips or rushes through the tail portion of the waveform by creating a bypass path. This allows the current to quickly transition from the SPD to the bypass path, minimizing the duration of exposure to excessive stress while ensuring the initial charge transfer and energy delivery are complete.
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 solution allows for testing surge protection devices according to IEC standards without excessive electrical and thermal stress, avoiding the need for calibration and ensuring accurate peak value, charge transfer, and specific energy measurements.
Implementation Method 1
an impulse current generator that is configured to provide a direct impulse current (DIC) (discharge of capacitors through an RL circuit)
Implementation Method 2
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
Implementation Method 3
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
Data Source
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.