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With cable diagnostic testing becoming more common, the need for fault locating will rise. If a cable cannot withstand the test voltage, failure will occur, requiring fault locating. If you’re in the market for a thumper, why not get one with a VLF hipot built-in to test the AC integrity of the cable following repair. The VT33 incorporates a powerful VLF hipot, a VLF Burner that rapidly reduces a faults impedance (arc-over voltage), TDR/radar capability, and continuous discharge for pinpointing the fault. Suitable for cables up to 25 kV. HVI puts all the tools needed in one box.
HVI produces some of the most powerful and full featured fault locators available. All the features needed for efficient fault finding can be found in our thumpers, don’t settle for less:
• Three full joule output voltage settings
• Three fully variable hipot output voltages
• The highest Burn current available
• Internal Arc Reflection and Current Impulse filter
• Compatable with nearly all TDR/radar models
• The most rugged and reliable design
• World’s only VLF Thumper combination
5 kV – 25 kV Cable Systems
The VT33 VLF Thumper Combination is the best approach: VLF test cables, use VLF output for diagnostic cable testing, use VLF Cable Burner to reduce fault voltage, fault locate with 13 kV @ 760 joules, use TDR/radar for sectionalizing and for pre-locating faults.
• VLF test cables per IEEE400.2, VDE 0276, CENELEC, etc.
• Pre-locate faults using a connected TDR/radar
• VLF Burn faults to lower arc-over voltage
• Pinpoint fault with continuous thumping
VLF stands for Very Low Frequency. VLF is generally considered to be 0.1 Hz and lower. VLF testing is used for any application requiring AC testing of high capacitance loads. The major application is for testing solid dielectric cable (per IEEE400.2), followed by testing large rotating machinery (per IEEE 433-1974), and occasionally for testing large insulators, arrestors, and the like. One of the best reasons to use VLF is to check installation quality and accessories, like splices. Many failures are due to damage during installation and/or defective workmanship. At the very least, every newly installed or repaired cable should be VLF tested before re-energizing.
The IEEE/EPRI/CEA and other world engineering bodies recommended test level for solid dielectric cable is up to three times (3Vo) line to ground voltage for 15 + minutes. For a 15 kV cable, which ordinarily carries from 7.2 to 8 kV line-ground voltage, the test is usually performed at 22 kV. A 25 kV system is tested up to 33 kV and a 69 kV cable system is VLF tested up to 120 kV. VLF hipoting is not destructive to good insulation and does not lead to premature failures like with DC voltage testing. Using VLF does not cause degradation of the insulation. It does cause existing cable defects, like water trees and splice defects, to break through during the test. If a cable can’t hold 2 – 3 times normal voltage, it is not a good situation. Cause failure at defect locations during a controlled outage or prior to energizing newly installed or repaired cables, find the fault, make the repair, and be left with a good cable. It is AC voltage; what the cable is designed for and experiences during service. Cable is factory tested with AC voltage at levels higher than the field test voltage.
VLF testing is not a diagnostic test. It is an AC stress test. There are no leakage current readings to take. (DC leakage currents tell little about the cable quality.) A cable either holds the test voltage or fails. If a cable can’t hold 2 – 3 times normal voltage, it’s not going to last long. You want it to fail during the test, when you are ready to repair or replace it. The surest way to weed out bad cables and accessories is to just perform a simple AC hipot test, just like we do with vacuum bottles, arrestors, hot sticks, switchgear bus and insulators, etc. Yes the cable may fail under test if it has a severe defect, but that’s the point of the test. If a cable can’t withstand three times normal voltage for 10 or 15 minutes, it’s bound to soon fail. Fail it when convenient, rather than waiting for it to fail on its own, often at the worst possible time.
高压 VT33 组合 VLF AC Hipot 和 Thumper 13kV
随着电缆诊断测试变得越来越普遍，故障定位的需求将会增加。如果电缆不能承受测试电压，就会发生故障，需要进行故障定位。如果您在市场上购买重击器，何不购买一个内置 VLF 高压测试器来测试维修后电缆的交流完整性。 VT33 集成了一个强大的 VLF 耐压、一个 VLF 燃烧器，可快速降低故障阻抗（电弧过电压）、TDR/雷达功能以及用于精确定位故障的连续放电。适用于高达 25 kV 的电缆。 HVI 将所有需要的工具放在一个盒子里。
HVI 生产一些最强大、功能最齐全的故障定位器。高效故障查找所需的所有功能都可以在我们的 thumpers 中找到，不要满足于更少：
• 三个完整焦耳输出电压设置
• 三个完全可变的耐压输出电压
• 可用的最高烧伤电流
• 内部电弧反射和电流脉冲滤波器
• 与几乎所有 TDR/雷达型号兼容
• 最坚固可靠的设计
• 世界上唯一的 VLF Thumper 组合
5 kV – 25 kV 电缆系统
VT33 VLF Thumper 组合是最好的方法：VLF 测试电缆，使用 VLF 输出进行电缆诊断测试，使用 VLF Cable Burner 降低故障电压，使用 13 kV @ 760 焦耳进行故障定位，使用 TDR/雷达进行分段和预定位故障。
• 符合 IEEE400.2、VDE 0276、CENELEC 等标准的 VLF 测试电缆。
• 使用连接的 TDR/雷达预先定位故障
• VLF 燃烧故障以降低电弧电压
• 通过连续重击来精确定位故障
VLF 代表极低频。 VLF 通常被认为是 0.1 Hz 或更低。 VLF 测试用于任何需要对高电容负载进行交流测试的应用。主要应用是测试固体电介质电缆（根据 IEEE400.2），其次是测试大型旋转机械（根据 IEEE 433-1974），偶尔也用于测试大型绝缘体、避雷器等。使用 VLF 的最佳理由之一是检查安装质量和配件，如接头。许多故障是由于安装过程中的损坏和/或工艺缺陷造成的。至少，每条新安装或维修的电缆在重新通电之前都应进行 VLF 测试。
IEEE/EPRI/CEA 等世界工程机构推荐的固体介质电缆测试级别为高达三倍（3Vo）线对地电压，持续 15 分钟以上。对于通常承载 7.2 至 8 kV 线对地电压的 15 kV 电缆，测试通常在 22 kV 下进行。 25 kV 系统的测试电压高达 33 kV，69 kV 电缆系统的 VLF 测试电压高达 120 kV。 VLF Hipoting 不会破坏良好的绝缘，也不会像直流电压测试那样导致过早失效。使用 VLF 不会导致绝缘性能下降。它确实会导致现有的电缆缺陷，如水树和接头缺陷，在测试过程中突破。如果一根电缆不能承受正常电压的 2-3 倍，就不是一个好情况。在受控停电期间或在为新安装或维修的电缆通电之前在缺陷位置引起故障，找出故障，进行维修，并留下良好的电缆。它是交流电压；电缆的设计用途和使用过程中的体验。电缆在出厂时使用高于现场测试电压的交流电压进行测试。
VLF 测试不是诊断测试。这是一个交流压力测试。没有泄漏电流读数。 （直流泄漏电流几乎不能说明电缆质量。）电缆要么保持测试电压，要么失效。如果电缆不能承受正常电压的 2-3 倍，它就不会持续很长时间。当您准备修理或更换它时，您希望它在测试期间失败。清除不良电缆和附件的最可靠方法是执行简单的交流耐压测试，就像我们使用真空瓶、避雷器、热棒、开关设备总线和绝缘体等一样。是的，如果电缆在测试中失败一个严重的缺陷，但这就是测试的重点。如果电缆不能承受 10 或 15 分钟的三倍正常电压，它很快就会失效。在方便的时候失败，而不是等待它自己失败，通常是在最糟糕的时候。
