Commissioning and Test Procedure of Power Cable and Equipment

Testing methods for power cable insulation depend basically on the type and material of cable insulation. Cross-linked Polyethylene (XLPE) is now spreading widely for power cable insulation at the rated voltage of 66 to 500 kV worldwide.

Quick and easy understanding of commissioning tests for transmission lines and major equipment. Here specially focused on the underground power transmission line, underground cable megger testing, cable fault location and main causes of cable fault, and some manufacturing faults. You also find some megger test procedures for transformer or circuit breakers, or common methods for insulation tests and megger tests.   

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Commissioning and Test Procedure of Power Line

Typical Electrical Test for Power Cable

01. Resistance measurements through bolted connections with a low-resistance ohmmeter;

02. Insulation-resistance test individually on each conductor with all other conductors and shields grounded. Apply voltage in accordance with the manufacturer’s published data;

03. Shield-continuity test on each power cable;

04. In accordance with ICEA, IEC, IEEE, and other power cable consensus standards, testing can be performed by means of direct current, power frequency alternating current, or very low-frequency alternating current. These sources may be used to perform insulation-withstand tests and baseline diagnostic tests such as partial discharge analysis, power factor, or dissipation factor.

HVDC or HVAC, Which Test is the best for XLPE Power Cable?

Sponsored:

We propose to take the HVAC test-1.            

HVAC Soak Test is also a suitable way for testing insulation as per IEC 62067. There are 2 ways of HVAC Test mentioned in IEC 62067

(1.7 U0 HVAC Test / U0 HVAC Soak Test)

 2.    HVAC Soak Test doesn’t require additional cost for equipment and complex testing progress, It is the way to keep the testing cost as the HVAC Soak Test does.  
We do not recommend taking the HVDC test

There are several reports that DC Testing is ineffective and could even be dangerous for the system under test.

v IEC 62067: The clause regarding HVDC Test for insulation is changed to HVAC Test for insulation after it is revised

v IEEE 400: HVDC is not effective in detecting certain types of insulation defects in a cable system when compared with the AC Test.

              doesn’t need the equipment to make 1.7 U0 for testing

1. The DC test can’t detect some problems that can be detected during the HVAC Test.

ü  AC Electrical stress is influenced by capacitance in insulation instead DC Electrical stress is influenced by resistivity

ü  So, the problems in the AC system can be different from the DC system because of the Electrical stress difference.

ü  The reason for some problems in the AC system can’t be detected in the DC test.

2. DC test can’t detect some problems regarding partial discharge, which can be the worst problem in the Cable system.

ü  AC voltage makes many kinds of partial discharge pulses in 1 cycle of AC current, and it’s repeated

ü  But, DC voltage makes a constant value, so the number of partial discharge pulses and the value are very normal as compared with AC voltage.

ü  So, even a big defect can’t be detected in the DC voltage test.

3. Space Charge

ü  In the case of applying DC voltage, normally, Space charge is accumulated in the insulation layer.

ü  However, when there is a defect, more charges get into the insulation layer and will be accumulated more than in a normal situation because of unequal electrical stress as compared with equal electrical stress.

ü  Because of space charge, unequal electrical stress caused by a defect can be released, so we can’t detect even a big problem when we take a DC Test

How can you benefit from IEC 62067 for Commissioning and Testing of Power Cables?

     For Commissioning and Testing of Power Cables, IEC 62067 provides a formal, internationally accepted methodology for the final quality check. It essentially answers the question: "Is the system we just installed free from defects and safe to put into service for the next 40 years?"

The primary benefit comes from the section on "Tests after installation," often called commissioning tests or site acceptance tests.

Here is how you get direct benefits from IEC 62067 during this phase:

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1. The Benefit of a Standardized "Final Quality Gate"

The core benefit is that the standard provides a rigorous, non-destructive procedure to find hidden problems before they cause a catastrophic failure. These problems are almost always introduced during the final stages of a project:

• Damage during transport or pulling: Scrapes, kinks, or crushing of the cable.

• Workmanship errors during accessory installation: This is the #1 cause of new cable failures. A tiny speck of dust, a misplaced semiconducting screen, or moisture in a joint can lead to failure.

The "After Installation Test" is your last line of defense. By specifying this test in your contract, you gain:

• Massive Risk Mitigation: You find the flaw during a controlled test, not during a thunderstorm a year later when it causes a city-wide blackout. The cost of a commissioning test is minuscule compared to the cost of an in-service failure.

• Clear Contractual Handover: A successful test provides a clear, objective milestone. It formally proves that the installation contractor has delivered a sound system, allowing for project sign-off, final payments, and the official transfer of the asset to the owner.

2. The Benefit of Using the Right Test Method (And Avoiding the Wrong Ones)

IEC 62067 doesn't just say "test it." It provides expert guidance on how to test, which protects your very expensive asset.

• It Recommends the Best Practice: AC Voltage Testing: The standard's preferred method is an AC voltage withstand test, often using resonant test sets.

  • Benefit: This test subjects the cable insulation to the same type of electrical stress (alternating polarity) it will see in service. It is the most effective way to find critical defects without harming healthy insulation.

• It Incorporates Advanced Diagnostics: Partial Discharge (PD) Measurement: Modern best practice, supported by the standard, is to perform Partial Discharge (PD) measurements during the AC voltage test.

  • What it is: PDs are tiny electrical sparks or discharges in a defect within the insulation. You can't see them, but specialized equipment can hear them.

  • Benefit: This is like a stethoscope for the cable system. It can detect minuscule defects (like a void in a joint) that might pass a simple voltage "hold" test but would grow over time and cause a failure months or years later. It provides incredible insight into the "health" of the installation.

• It Protects the Asset from Harmful Tests: The standard explicitly warns against using high-voltage DC tests on extruded insulation systems like XLPE.

  • Benefit: This is a crucial piece of guidance. DC testing can be destructive to modern cables. It creates "space charges" within the insulation that don't dissipate quickly. When the cable is later energized with AC, these trapped charges can create points of extreme electrical stress, leading to a failure that would not have otherwise occurred. Following IEC 62067 prevents you from inadvertently damaging your brand-new cable system.

3. The Benefit of Clear Roles and Responsibilities

During commissioning, a lot can go wrong, and "finger-pointing" is common. A successful test performed according to IEC 62067 provides clarity for everyone.

• For the Asset Owner (Utility):

  • You receive a "birth certificate" for your cable system.

  • You have documented proof that the asset you are accepting is free from installation defects.

  • You get a baseline PD measurement, which is invaluable for future condition monitoring. If you test the cable again in 10 years, you can compare the PD levels to see if any degradation has occurred.

• For the Installation Contractor:

  • You have objective, third-party proof that your workmanship (especially on the critical joints and terminations) was performed correctly.

  • This protects you from liability if a problem arises years later that is traced back to a manufacturing defect in the cable itself. The successful site test proves the installation was sound.

• For the Cable Manufacturer:

  • It protects them from being wrongly blamed for installation errors. If the system passes the site test, it confirms that its components were installed correctly.

Practical Example in Commissioning:

1. Contract: Your contract with the installer specifies, "The completed 400 kV cable system shall be tested on-site in accordance with the After Installation test requirements of IEC 62067, consisting of a 24-hour soak test at operating voltage followed by a 1-hour AC voltage withstand test at 1.7 U₀ combined with Partial Discharge measurement."

2. Execution: After the cable and all joints are installed, a specialized testing company brings a mobile AC resonant test set to the site.

3. The Test: They apply the specified AC voltage for one hour. During this time, sensitive sensors listen for any Partial Discharge activity along the entire length of the cable and at every joint.

4. The Result: The system holds the voltage, and the PD measurements are below the specified acceptable limits.

5. The Benefit: The asset owner, contractor, and consultant all receive a formal report. The contractor gets their final payment. The owner energizes the multi-million dollar line with a very high degree of confidence that it is sound, safe, and ready for decades of reliable service.