Power Cable – is a cable user for transmission of Electrical energy – Power cable used for High Voltage electrical power Transmission – Power cable is an assemble of one or more electrical conductor together within the sheath.
Any wire or cable plays a critical role in the functioning of our infrastructure assets and tools. As lives and equipment is dependent on the cables and wires, it will be in your best interest to conduct thorough inspection on a regular basis.
Electric power can be transmitted or distributed either by overhead transmission systems or by underground cables. Cables are mainly designed for a specific requirement. Power cables are mainly used for power transmission and distribution purposes. It is an assembly of one or more individually insulated electrical conductors, usually held together with an overall sheath. The assembly is used for transmission and distribution of electrical power. Electrical power cables may be installed as permanent wiring within buildings, buried in the ground, and run overhead or exposed. Flexible power cables are used for portable devices, mobile tools, and machinery.
Construction of Power Cable
There are various parts of a cable to be taken care of during construction. The power cable mainly consists of
- LAY for Multicore cables only
- Beading/Armouring (if required)
- Outer Sheath
Mainly above 6 square mm cables are called power cables but it depends upon the use of a cable. For PVC power cables we use IS:1554 and for XLPE power cables we use IS:7098 and for Rubber-based power cables, we use IS:9968 and other relevant specifications. Power cables are defined by voltage grade and nominal cross-sectional area.
Defects in Power Cable
Core rupture – A core rupture is the failure of the cable’s electrical conductivity due to broken copper wires. This is as a result of the mechanical loads on the individual core due to constant bending stress.
Corkscrew – A corkscrew is an externally visible helical deformation of the entire cable due to broken copper strand wires. This is caused by subjecting the individual cores to mechanical loads during the bending process. A corkscrew is usually due to a faulty cable structure. Cores wound in layers with an outer jacket extruded like a hose or a missing core can cause problems here. In addition, an application outside of defined parameters (too tight a bend radius, too long travel) can lead to corkscrews.
Insulation damage – With electric cables, core insulation damage can lead to short circuits. The cause can be material fatigue under constant bending stress or material abrasion within the cable structure. Single strand wire breakage of the conductor or the shield braiding result in perforation of the insulation.
Jacket damage – Jacket swelling or jacket breakage describes damage of a cable’s outer jacket. The jacket becomes soft and deformed or breaks until the cores or shield can be seen. The cause can be the incorrect selection of materials with respect to the oils or other chemical substances being used. Too low an ambient temperature can also lead to jacket breakage, when the temperature is below the minimum stated in the data sheet. As soon as a jacket swelling or jacket breakage occurs, the cable needs to be changed immediately.
Shield wire breakage – A shield wire breakage occurs when the shield braiding, designed to protect a cable from EMC, breaks down. The consequences of a breakage range from reduced shielding effects up to short circuits whenever the sharp wire ends penetrate through the fleeces or foils into the cores. The cause is often an incorrect braiding angle. If after the insulation has been stripped off the shield can be easily pushed back over the jacket, it is an indication that the shield is unsuitable for use in energy supply systems.
Inspection of Power Cable
Third Party Inspection for power cable is a sample procedure for power cable testing and power cable inspection in the manufacturing facility. All power cable inspection and testing is done against the approved drawings, purchase order specifications, purchasers or company standards, and within the practices and rules of the country, state or province and any government decrees, laws, ordinance or regulation as may apply.
The applicable codes and specifications for a power cable that is under the construction process are:
- Design code
- Purchase order specification
- Purchaser’s standards
- Approved drawings
Required Documents for Third Party Inspection review of Power cable
These are the list of documents that are normally agreed upon to be presented at the time of inspection –
- Cable Purchase Order or Contract
- Cable Quality Control Plan
- Cable Inspection and Test Plan
- Cable Data Sheet
- Cable Approved Drawings
- Cable Fittings Drawings and/or Parts Lists
- Cable Material/parts Certificates
- Cable FAT Test Procedure (Electrical Test)
- Cable Special Procedures
- Cable Special Qualifications
- Cable Calibration Records for Testing and Measuring Equipment
- Preservation, packing and Shipping Procedure
- Cable Packing List
Power Cable – Material Inspection
The review includes checks on:
- Maker’s name and location
- Certificate number, grade
- Heat or cast number
- Chemical composition
Then the inspector witnesses the materials identification on the certificates against the materials marking. It is also necessary to check these with the power cable drawing datasheet, material list and other specifications as appropriate.
Visual inspection for surface finish and probable defects is done and dimensional compliance with specification need to be controlled, as well.
When the third party inspector carries out the material inspection, then provides the inspection visit report (IVR), the report contains the following items:
- Confirmation of satisfactory document review
- Record of the endorsement of certification reviewed/witnessed
- Record of all non-conformities
- Record of any tests witnessed and the result
Power Cable – Construction Check
The third-party inspector checks the following items in the power cable casing inspection process:
- Check of paint using specified colour swatch, measure thickness, if specified
- Check of name plate
- Check of outline dimensions, interface dimensions
- Power Cable General Arrangement Check
The inspection scope is determined in the inspection and test plan (ITP), which has already been agreed upon between the purchaser and the power cable manufacturer.
Inspection and Test Plan for Power Cable – Important Points
- Witnessing voltage and insulation resistance tests or alternative spark tests.
- For 33Kv cable, witness dielectric power factor voltage test.
- Dimensional checking on sample off-cut i.e. construction consistency, insulation thickness, external sheath screen, armours and mans of main components.
- Visual checking in respect of cable formation, core and external sheath colors, marking legibility.
- Testing on material sample i.e. conductor coating, insulation external jacket for elongation, heat stroke blending and characteristics of armour, metal and sheath components including zinc coating.
Power Cable – Configuration
Following items is taken in account:
- Cable type
- Number of conductors
- Conductor size
- Conductor color coding
- Insulation type and size
- Water stoppers
- Outer diameter
- Other specified elements/dimensions
- Cable identification
Power Cable – Drum
For cable already drummed the third-party inspector controls following items:
- Drum quantity
- Conformance of quantity listings on drums to documented declarations
Power Cable – Conductor Resistance Test
It is done by “Kelvin’s Double Bridge” or “Wheatstone Bridge” and checks the result against acceptance criteria specified in the purchase order.
Power Cable – Withstand Voltage Test
The AC and DC withstand voltage test is witnessed for each length of completed cable as below:
- AC Withstand Voltage Test: The test voltage is applied between the conductor or conductors and metallic shield, metallic armour, or water. The duration is 5 minutes and the test would be acceptable if withstand the specified test voltage.
- DC Withstand Voltage Test: All cables rated 5001 volts and above is tested by the DC withstand voltage test and would be acceptable if withstand specified test voltage
Power Cable – Insulation Resistance Test
Reading of the insulation resistance is taken for one minute and obtained value would be acceptable if they are above the specified value in the requirement.
Power Cable – Discharge Test
The partial discharge test is made prior to the AC voltage test as per the appropriate test method specified in the code and standard. The AC test voltage is applied between conductor and the metallic component of insulation shield. If the existence of discharge is not evident after the voltage has been raised to a value 20% above the specified minimum extinction value, the cable is considered to have met the requirements.
Power Cable – Tensile Strength and Elongation Test
Physical tests are made at room temperature and the test specimens are kept at room temperature for not less than 30 minutes prior to the test.
The specimen is stretched until it breaks. Elongation at rupture is determined simultaneously with the test for tensile strength and on the same specimen.
The tensile strength is calculated on the area of the unstretched specimens. The percentage of elongation at rupture is divided by the original gauge length and multiplied by 100. They would be acceptable if meet the requirements.
Power Cable – Aging Test
The test specimens are heated at the required temperature for the specified period in air oven or immersed in oil hot oil.
The kind of oil, temperature and duration is in accordance of applicable standards.
Physical tests on both the aged and unaged specimens are made at the same time and the result of the test would be acceptable if comply with the requirement.
Power Cable – Heat Shock Test
Samples of the cables are wound around a mandrel, held firmly in place and subjected to the specified temperature for 1 hour. Diameter of mandrel is specified in the standard.
The test specimen would be acceptable if show no cracks visible to the normal unaided eye.
Power Cable – Heat Distortion Test
The test is made in accordance with appropriate method specified in the standard (ICEA). The test would be acceptable if obtained value is not exceeding the maximum percentage of unaged value specified in ICEA.
Power Cable – Flame Resistance Test
Flame resisting test is made in accordance with respective code, standard. (IEC, IEEE) and after the test, the test would be acceptable if specimens meet the requirement of applicable code, standard.
The third-party inspector provides an Inspection Visit Report (IVR) after each visit, as well as a final report summarizing the activities carried out during the power cable production in accordance with the contract requirements and circulated within the time limits specified in the contract.
The report is in the format required by the client and clearly indicates final acceptance or rejection of the power cable.
When required by the contract or purchase order, a release note is issued by the third-party inspection agency and given to the manufacturer when the power cables have been accepted.
Packing and Marking
The following points are checked for packing inspection:
- Drum marking and tagging.
- Cable end secured.
- The reel is lagged or covered with suitable material to provide physical protection for the cables during transit.
- Cable end sealed against moisture.
- Verify that the packing materials conform to specifications and accepted practice for the mode of transport.
- Check protection against humidity, abrasion, distortion and other damage.
- Check shipping marks with marking instructions and record. Check handling marks.
Third Party Inspection of Power Cable
As we know that Power cable pay very much important role in supply of Electrical energy. So, the Quality and reliability of Power cable pay very much important role.
Any failure of Power cable in transmission in power supply could create the Black out and even cause to life of Huma beings and infrastructures etc.
So, Quality and performance of Power cable is very much important.
Third Party Inspection Agency – who perform the Inspection of Power cable -should have the sound knowledge on Technical aspects of Power cable – Including – Construction, Routine Test, Type Test and endurance Test of Power cable.
Third Party inspection Services
The Third-Party inspection services is an Independent activity of the organization- who are not a manufacturer or Buyer of the product. Third Party Inspection agency are an independent organization performing the Third-party inspection services as professional organization conducting the Inspection services based on competency of the organization and Team – Perform the Third-Party Inspection services independent and provide the Inspection report which gives the actual / correct findings of Inspection which is generated on factual findings.
There are many professional Third-Party Inspection agency in India performing Third Party Inspection service based on their expertise, we are also one of Leading Third-Party Inspection agency in India – Providing Third Party Inspection services in many industrial sectors.