The Working Principle Of High Frequency Spark Tester

The high-frequency spark tester is a fast and continuous withstand voltage test method. It is mainly used for the withstand voltage test of rubber and plastic insulated wires, or the rubber and plastic insulated cores of sheathed wire and cable products. Suitable for products with voltage levels of 1000V and below. Because of its simple equipment and high speed, the high-frequency spark tester is widely used in manufacturing plants.

The working principle of the spark withstand voltage test is that the conductive core of the product is grounded, and the product passes through the high-voltage electrode at a certain speed, so that the insulating layer can withstand the high-voltage test. There are two types of high voltage electrodes: contact type (the electrode is in contact with the insulating surface of the product) and non-contact type. Most of them use contact type electrodes (bead chain or brush type). When the product passes through the high-voltage electrode, on the one hand, the insulating surface is in contact with the densely distributed electrodes.


On the other hand, the air that the electrode occupies part of the space is freed by the high voltage. When the electrode voltage of the high-frequency spark tester reaches a certain value (above several thousand volts), it can be approximated that the air voltage on the insulating surface of the product is the electrode voltage. Therefore, the free air around the electrode is equivalent to the composition of the product. An external electrode. According to the selected spark withstand voltage test value, it has been proved in long-term production practice that it can basically achieve the same effect as the water immersion withstand voltage test.　There are many types of power sources used in the spark withstand voltage test. The main ones used are power frequency (50Hz) voltage, high frequency (3kHz) voltage and DC voltage.

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What is a spark test?

A spark test is an inline voltage test used either during cable manufacturing or during a rewinding process. Spark testing is primarily for low voltage insulations and medium voltage non-conducting jacket or sheaths. The test unit generates an electrical cloud around the cable which in high frequency AC units appears as a blue corona around the cable. Any pin holes or faults in the insulation will cause a grounding of the electrical field and this flow of current is used to register an insulation fault.

Spark testers are usually fitted with counters indicating the number of faults. Different spark test voltages are applied which are determined by the cross-sectional area of the conductor and insulation material, with the appropriate voltage specified in the relevant cable standard.

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Spark tester for Cables, DC or AC?

Edwin Cheow
Senior Product and Business Development Manager at Pan-International Wire and Cable


Advantages of AC Spark Testing: • AC creates a field of ionized air (a blue-colored glow called corona) around the product. Corona is electrically conductive and provides a good test even when the bead chains are not making physical contact. Corona is caused in part by the AC voltage changing from positive to negative with each cycle. For this reason high frequency spark testers generate more corona than 60 cycle testers. • A byproduct of corona is heat. If you were to leave a grounded cable stationary in an energized high frequency electrode for a while, you would notice that the insulation is noticeably warmer where it made contact with the corona field. This heating helps to break down weak spots in the dielectric that otherwise might pass through the electrode undetected, only to fail during a later spark or hipot test. Disadvantages of AC spark testing: • In wires with very weak insulation (such as telecommunication and Datacom wires having a foamed dielectric), the AC voltage ionizes the air inside the foam cells, reducing the overall dielectric strength of the insulation. The insulation may then fail, damaging the product. This is particularly true with high frequency spark testers, which should not be used with foamed insulation. • When the capacitance of the product in the electrode is very high, a "leakage current" forms. Because capacitance is a more a function of the ratio of conductor size to insulation thickness than to overall size, products that produce high capacitance can include cables with large conductors and thin insulation, small wires with very thin dielectric, or multiple conductors going through the same electrode (tape and ribbon cables, for instance). For safety reasons, the spark tester's current output is limited to 4 to 6 milliamps. When the leakage current reaches this level, there is no more available supply current to generate a greater test voltage. The maximum possible voltage attainable with that product may not be high enough to provide a good test. Advantages of DC spark testing: • DC generates practically no corona and no heat and is therefore a gentler test. DC can be used on foamed insulation and thin insulation. • DC has no problem with capacitance. Very large wires and multiple conductors can be tested with one power supply. DC is often used in cabling operations, sometimes testing 25 twisted pairs within a single electrode. Disadvantages of DC spark testing: • THE PRODUCT MUST BE GROUNDED! The center conductor or shield should be grounded for reasons of safety and efficacy. If the product is not grounded and a fault passes through the electrode, the spark tester will count, but the entire reel will become charged to high voltage and will maintain this potential until something discharges it. Subsequent faults may not be detected because the center conductor will be nearly the same potential as the electrode, and detection circuits require differentiation. • A different test voltage must be used, compared with AC (1.414 x AC RMS Voltage = DC Peak voltage). This is not really a disadvantage but a difference in the way the two types of voltage are measured. AC is measured in RMS (root means squared) while DC is measured as Peak Voltage.

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