Test On 110kV Power Cable After Installation - Part 2

General description of site test procedure

In previous part of this technical article first three procedures were explained. Now the rest will be explained in details:

1. Phase indication test (previous part)
2. DC conductor resistance measurement (previous part)
3. Capacitance test (previous part)
4. DC Sheath test on outher sheath
5. Insulation resistance measurement
6. Cross bonding check
7. Zero sequence and positive sequence impedance test (next part)
8. Earth resistance measurement at link boxes (next part)
9. Link box contact resistance measurement (next part)

4. DC sheath test on outher sheath

The test is applied when the cable sheath can be isolated from the earth to permit a voltage to be applied to the over-sheath to check the integrity of the covering.
This testing is generally applied at certain stages of cable system installation at specified parameter as follows:

1. When the cable is still on reel. The applied test voltage is 10 kV for 10 seconds, if a proper test lead is provided.
2. Once the cable are laid, dressed and tied together in trefoil configuration a test voltage of 10 kV for 30 seconds is applied.
3. Following backfilling sand beddind-2, a test voltage of 10 kV is applied for 1 minute on each cable. This is a formal testing with test records and signed by representatives of the responsible parties as witnesses.
4. Following completion of jointing activities between two cable sections in a joint bay and after backfilling of the joint bay, the jointed cable sections are then tested by applying 10 kV for 30 seconds.
5. Following the completion of cable system installation and prior to acceptance testing, as a pre-check testing a test voltage of 10 kV is applied for 1 minute.

Note – All above mentioned testing will be conducted in presence of project consultant.

References

• IEC 60840 – Power cables with extruded insulation and their accessories for rated voltages above 30 kV
• IEC 60229 – Electric cables // Tests on extruded oversheaths with a special protective function
• TES-P-104.08 – Bonding and grounding of insulated metallic sheath of power cable system

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Test On 110kV Power Cable After Installation - Part 1

Cable selection and application

It is essential to know cable construction, characteristics, and ratings to understand problems related to cable systems. However, to correctly select a cable system and assure its satisfactory operation, additional knowledge is required. This knowledge may consist of service conditions, type of load served, mode of operation and maintenance, and the like.

The key to the successful operation of a cable system is to select the most suitable cable for the application, make a correct installation, and perform the required maintenance.

In this technical article, discussion is based on the correct cable selection and application for power distribution and utilization.

General description of site test procedure

Site test procedure covers all necessary electrical testing for the 110 kV cable and accessories to be carried out during and after installation of the cable system.

This procedure is in line with the requirements of the contract suitable for 110 kV, XLPE cables and accessories and the tests are in accordance with TCSP-104.08, IEC 229, IEC 540 and IEC 840.

110 kV, 115 kV and 132 kV XLPE Cables

(Standard Reference is IEC 60840 and relevant SEC Transmission Specifications 11-TMSS-02, Rev. 0 and TCS-P-104.02, TCS-P-104.03, TCS-P-104.06 and TCS-P-104.08)

1. Mechanical Check and visual Inspection

ITEM	Description	Remark
1	Inspection for physical damage or defects
2	Check tightness of all bolted connections (torque wrench method)
3	Check for proper cable bolted connections
4	Check cable bends to ensure that bending radius is equal to or greater than the minimum bending radius specified
5	Check for proper cable support, clamping, trays arrangements
6	Link box tightness check
7	Verify that shields are terminated as specified (through link box or directly grounded)
8	Verify the exact route length as per approved drawings from terminations to terminations
9	Check that all grounding points are securely connected to ground grid as specified
10	Check that phases are identified and color coded
11	Single core cable connected between power transformer and switchgear shall be single point earthed as switchgear side and at floating side SVL (sheath voltage limiter) should be installed
12	Check single point or both ends, via voltage limiter as per approved design
13	Inspection of label inside link boxes and water proofing
14	Check cable entry path trench as ducts are properly sealed
15	Check irregularities of outer jacket formed by non-uniform shield wire distribution
16	Check/inspect the transposition of cable phases
17	Check the cable outer jacket for any physical damage during and after installation
18	Check for the cross connection of cable metallic sheath in cross bonding system
19	Check the rubber seal in cable clamps to avoid any damage to cable outer jacket
20	Check the insulating shrouds are installed at the base of the cable terminations
21	For accessories (sealing terminations, instrument panels and link boxes) check the following:
	a. Name plates installed and data is correct
	b. Danger signs
	c. Bolt tightness check and paint work conditions

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5 key factors to the correct cable selection and application

Cable selection and application

It is essential to know cable construction, characteristics, and ratings to understand problems related to cable systems. However, to correctly select a cable system and assure its satisfactory operation, additional knowledge is required. This knowledge may consist of service conditions, type of load served, mode of operation and maintenance, and the like.

The key to the successful operation of a cable system is to select the most suitable cable for the application, make a correct installation, and perform the required maintenance.

In this technical article, discussion is based on the correct cable selection and application for power distribution and utilization.

Cable selection can be based upon the following five key factors:

1. Cable installation
2. Cable construction
3. Cable operation (voltage and current)
4. Cable size
5. Shielding requirements

1. Cable installation

Cables can be used for outdoor or indoor installations depending upon the distribution system and the load served.

A good understanding of local conditions, installation crews, and maintenance personnel is essential to assure that the selected cable system will operate satisfactorily! Many times cable insulation is damaged or weakened during installation by applying the incorrect pulling tensions.

Designs of conduit systems not only should minimize the number of conduit bends and distances between manholes but also should specify the pulling tensions.

The inspection personnel should ensure that installation crews do not exceed these values during installations. It is also important that correct bending radius be maintained in order to avoid unnecessary stress points. Once a correct installation is made, routine inspection, testing, and maintenance should be carried out on a regular basis to chart the gradual deterioration and upkeep of the cable system.

Cable systems are the arteries of the electric power distribution system and carry the energy required for the successful operation of a plant. Following is a brief discussion on cable installation and maintenance.

There are several types of cable systems available for carrying electrical energy in a given distribution system. The selection of a particular system may be influenced by local conditions, existing company policies, or past experience.

No set standards or established guidelines can be given for the selection of a particular system.

2. Cable construction

Selection and application of cable involves the type of cable construction needed for a particular installation. Cable construction involves conductors, cable arrangement, and insulation and finish covering.

2.1 Conductors

Conductor materials such as copper and aluminum should be given consideration with regard to workmanship, environmental conditions, and maintenance. The requirements for aluminum conductors with regard to these factors are more critical than for copper conductors.

Cable conductors should be selected based upon the class of stranding required for a particular installation.

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Corrosion Types Encountered With Power Cables

Introduction

There are numerous types of corrosion, but the ones that are discussed here are the ones that are most likely to be encountered with underground power cable facilities.
In this initial explanation, lead will be used as the referenced metal. Copper neutral wire corrosion is not discussed here.

Anodic Corrosion (Stray DC Currents)

Stray DC currents come from sources such as welding operations, flows between two other structures, and –in the days gone by — street railway systems.

Anodic corrosion is due to the transfer of direct current from the corroding facility to the surrounding medium, usually earth. At the point of corrosion, the voltage is always positive on the corroding facility.

In the example of lead sheath corrosion, the lead provides a low resistance path for the DC current to get back to its source. At some area remote from the point where the current enters the lead, but near the inception point of that stray current, the current leaves the lead sheath and is again picked up in the normal DC return path.

The point of entry of the stray current usually does not result in lead corrosion, but the point of exit is frequently a corrosion site.

 

Clean sided corroded pits are usually the result of anodic corrosion. The products of anodic corrosion such as oxides, chlorides, or sulfates of lead are camed away by the current flow. If any corrosion products are found, they are usually lead chloride or lead sulfate that was created by the positive sheath potential that attracts the chloride and sulfate ions in the earth to the lead.
In severe anodic cases, lead peroxide may be formed. Chlorides, sulfates, and carbonates of lead are white, while lead peroxide is chocolate brown.

Cathodic Corrosion

Cathodic corrosion is encountered less fiequently than anodic corrosion, especially with the elimination of most street railway systems.

This form of corrosion is usually the result of the presence of an alkali or alkali salt in the earth. If the potential of the metal exceeds -0.3 volts, cathodic corrosion may be expected in those areas.

In cathodic corrosion, the metal is not removed directly by the electric current, but it may be dissolved by the secondary action of the alkali that is produced by the current. Hydrogen ions are attracted to the metal, lose their charge, and are liberated as hydrogen gas.

This results in a decrease in the hydrogen ion concentration and the solution becomes alkaline. The final corrosion product formed by lead in cathodic conditions is usually lead monoxide and lead / sodium carbonate. The lead monoxide formed in this manner has a bright orange / red color and is an indication of cathodic corrosion of lead.


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Industrial control wiring and cabling guide

Wires and preparation for control wiring

Electrical equipment uses a wide variety of wire and cable types and it is up to us to be able to correctly identify and use the wires which have been specified. The wrong wire types will cause operational problems and could render the unit unsafe.

Such factors include:

• The insulation material;
• The size of the conductor;
• What it’s made of;
• Whether it’s solid or stranded and flexible.

These are all considerations which the designer has to take into account to suit the final application of the equipment.

A conductor is a material which will allow an electric current to flow easily. In the case of a wire connection, it needs to be a very good conductor. Good conductors include most metals. The most common conductor used in wire is copper, although you may come across others such as aluminium. An insulator on the other hand is a material which does not allow an electric current to flow. Rubber and most plastics are insulators.

Insulation materials

Wires and cables (conductors) are insulated and protected by a variety of materials (insulators) each one having its own particular properties. The type of material used will be determined by the designer who will take into account the environment in which a control panel or installation is expected to operate as well as the application of individual wires within the panel.
As part of the insulating function, a material may have to withstand without failing:

• Extremes of current or temperature;
• A corrosive or similarly harsh environment;
• Higher voltages than the rest of the circuit.

Because of these different properties and applications, it is essential that you check the wiring specification for the correct type to use.

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