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NDT로 고전압 전력선 안전 전류를 유지하는 방법

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High-voltage insulators are used to attach electric power lines to utility poles and transmission towers without allowing dangerous electric current to flow through the tower to the ground. Porcelain, ceramic, and composite materials are used as insulators for power transmission lines and railroad traction power wires because of their high levels of electrical resistance.

Coatings Combat Contaminants

Over time, atmospheric contaminants, such as salt spray or chemical dust, can build up on an insulator, creating a conductive path that can cause a high-voltage electric discharge known as a flashover. Flashovers can be dangerous or even fatal if a person is too close to the insulator when it occurs. Construction, agriculture, and railway workers who operate machinery or work near power lines could all be at risk.

Silicone coatings are applied to high-voltage insulators to prevent flashovers caused by contaminant buildup. To be effective, the coatings must meet minimum thickness requirements and be securely bonded to the insulator. Because the coating is expensive, most manufacturers only apply the minimum required thickness.

Insulator manufacturers check coating thickness and bonding as part of quality control, and routine service inspections are required to ensure that high-voltage insulators continue to meet safety requirements. Two of our solutions are regularly used for these inspections—coating thickness measurement and silicone insulator bond testing.

Measuring Coating Thickness

Ultrasonic thickness gaging can quickly and nondestructively verify that silicone coatings meet the minimum required thickness. Ultrasound will reflect from the boundaries between materials of different acoustic impedances. Because silicone has an impedance lower than a ceramic or composite insulator, sound energy reflects from the silicone/insulator boundary. By calibrating a thickness gage to the sound velocity of silicone, you can quickly and repeatably measure the coating’s thickness without damaging the insulator.

You can measure the thickness of silicone coatings with a 38DL PLUS® or 45MG ultrasonic thickness gage with Single Element software. We recommend using an M1016 10 MHz contact transducer when there is sufficient access to permit coupling. A handle cable (LCMH-74-3) can be used to extend reach. When the insulator’s geometry doesn’t permit coupling with an M1016, we recommend using the M2055 handle-style 20 MHz delay line transducer. Measurements can be made over a thickness range of approximately 0.005 in. (0.12 mm) to greater than 0.050 in. (1.25 mm). Inspecting materials with a thicker or more attenuating coating may require the use of a lower frequency transducer, such as the M110-RM 5 MHz contact transducer.

Silicone coating measurement with an M1016 probe
Silicone coating measurement with an M1016 probe
Silicone coating measurement with an M2055 delay line probe
Silicone coating measurement with an M2055 delay line probe

Silicone-Insulator Bond Testing

The silicone coating and composite insulator must be bonded for proper electrical performance, and bond failures can result in flashovers. Using an ultrasonic flaw detector or thickness gage with a waveform display, it’s possible to quickly and nondestructively check the integrity of this bond.

For testing these bonds, we recommend an EPOCH® 650 or EPOCH 6LT ultrasonic flaw detector or 38DL PLUS or 45MG ultrasonic thickness gage with Single Element and Waveform software with a small-diameter contact transducer, such as the V112-RM 10 MHz probe. This probe’s small size enables it to fit between the insulator’s flared skirts.

Disbonded joint/ negative peak
Disbonded joint/ negative peak

Bonded joint/ positive peak
Bonded joint/ positive peak

Related Content

Bond Testing in Composite Power Line Insulators

Measurements of Silicone Coatings on Porcelain High Voltage Insulators

Phase Shift Test for Bond Integrity

Ringdown Test for Bond Integrity


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Sarah Williams는 거의 10년 동안 방송 산업에서 연구자 및 카피라이터로 일했습니다. 이제 Sarah는 작가 및 편집자로서 역량을 발휘하여 Evident의 다양한 비파괴 검사(NDT) 솔루션과 관련된 주제에 관해 흥미롭고 뛰어난 자료를 작성하고 있습니다. 그녀는 최신 원격 육안, 현미경, 초음파, 와전류 및 위상 배열 기술에 관한 글을 씁니다. 또한 이러한 기술의 응용 현황과 더불어 우리의 삶의 질과 세상의 안전을 향상하는 데 이러한 기술이 어떻게 기여하는지를 탐구합니다. Sarah는 파트너인 David 및 세 자녀 Sophie, Anouk 그리고 Éloi와 함께 퀘벡에 있는 사무실에서 근무하고 있습니다. 

8월 13, 2019
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