Transmission Class Cables and Cable Accessories Failure Analysis
Powertech’s multidisciplinary team performs failure analysis on all types of electrical equipment, including transmission class cables and accessories. Our expertise in electrical, chemical and materials engineering, as well as system analysis, and protection and control allows us to evaluate all aspects of a failure.
Transmission class cable systems transfer large amounts of power between substations and operate at transmission level voltages, 69 kV and above. The majority of transmission cables are oil/paper insulated, either pipe type or self-contained fluid filled (SCFF), both of which have proven to be highly reliable and long lived. Many newer installations are using XLPE up to 500 kV, or EPR up to 138 kV.
Powertech performs qualification tests on new designs of transmission class cables, splices and terminations. Our third party, independent status enhances manufacturer’s credibility in their test reports. Many utilities specify independent testing of products in their specification. Powertech Labs is a trusted name with a worldwide reputation in the area of cables and cable accessories.
On older cables, our condition assessment services provide information about the near term risk of failure. We can also provide a replacement priority for securing optimum use of time and funds. Powertech offers a comprehensive, customized cable condition assessment program on transmission cables and accessories rated up to 500 kV.
Cable and Accessory Aging Tests
Powertech can provide specialized and standard accelerated aging tests for transmission class cables, terminations and splices. These tests provide both current cycling and elevated voltage application during the tests. Other specialized tests may include through fault current. Diagnostic evaluation, including partial discharge measurement, impulse and AC withstand can be provided. Standards include IEEE-40 or IEEE-48, as well as IEC and others.
Partial Discharge Measurements
We can measure partial discharge (PD) levels as well as inception and extinction voltages in cables and accessories. PD is often used as a pass/fail criterion in standard tests or as a diagnostic tool in the design process. Our experienced staff often locates sources of PD using modern phase resolved and ultrasound techniques.
Impulse and AC Withstand or Breakdown Tests
Powertech conducts both switching surge and lightning impulse tests on power cable and accessory samples. Thermal stresses can be incorporated into these tests if required. AC withstand or breakdown tests are conducted to levels in excess of 700 kV rms. We have water terminals for both AC and impulse tests if required.
Dissipation Factor Tests
Dissipation Factor (tan delta) can be measured at system voltages with the cable at either normal or emergency operating temperatures.
Cable and Accessory Failure Analysis
Powertech’s multidisciplined team performs failure analysis on all types of electrical equipment, including cables and accessories. The advantage of such a diverse group becomes evident as failures may result from various stresses. One may consider electrical stress on insulation as a common failure mode, but many factors may lead to the failure. These include thermal stresses, corrosion, operating conditions and design factors. Our expertise in electrical, chemical and materials engineering, as well as system analysis, and protection and control allow us to evaluate all aspects of a failure.
Examination of Samples Removed from Cables
Powertech can perform detailed dissection and microscopic examinations on cable and accessory insulation as well as:
- Tape tensile strength
- Degree of polymerization
- FTIP oxidation products
- Radial power factor and dielectric constant
- Dielectric Thermal Analysis
- AC breakdown
- Moisture content
Lead, aluminium and other metallic sheath, armor or pipe samples are evaluated for corrosion and fatigue damage.
Field Tests on Transmission Cable Systems
Using Powertech’s resonant test set or DC test set in the field, we can perform withstand tests on transmission class cable systems. We can also measure Dissipation Factor (tan delta), live line, on cable systems in the field.
One of the leading causes of failure in lead sheathed transmission cable is mechanical failure of the lead. We are developing new techniques for in-situ examination of lead sheaths that include the replica technique to examine the metallic grain size and eddy current measurement to locate corrosion and fatigue cracking.