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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General considerations when choosing power cable

Copper or Aluminium?

Thousands of cable types are used throughout the world. They are found in applications ranging from fibre-optic links for data and telecommunication purposes through to EHV underground power transmission at 275 kV or higher.

Certain design principles are common to power cables, whether they are used in the industrial sector or by the electricity supply industry. For many cable types the conductors may be of copper or aluminium.

 

The initial decision made by a purchaser will be based on price, weight, cable diameter, availability, the expertise of the jointers available, cable flexibility and the risk of theft.

What to choose?

Once a decision has been made, however, that type of conductor will generally then be retained by that user, without being influenced by the regular changes in relative price which arise from the volatile metals market.

For most power cables the form of conductor will be solid aluminium, stranded aluminium, solid copper (for small wiring sizes) or stranded copper, although the choice may be limited in certain cable standards.

Solid conductors provide for easier fitting of connectors and setting of the cores at joints and terminations. Cables with stranded conductors are easier to install because of their greater flexibility, and for some industrial applications a highly flexible conductor is necessary.

Where cable route lengths are relatively short, a multi-core cable is generally cheaper and more convenient to install than single-core cable.

Single-core cables are sometimes used in circuits where high load currents require the use of large conductor sizes, between 500 mm² and 1200 mm².

 

In these circumstances, the parallel connection of two or more multi-core cables would be necessary in order to achieve the required rating and this presents installation difficulties, especially at termination boxes.

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Hybrid Servo Cables Do More For Less

If you design servo systems, you may not pay much attention to the cost of the cabling. But you should.

The upfront and lifetime costs associated with power and signal cables can represent a significant portion of the total outlay for a servo system. And the smaller the servo system, the more the cable costs matter.

Fortunately, there’s an up-and-coming control architecture that can reduce the lifetime costs of servo cabling by more than 35%.

Called HIPERFACE DSL®, this digital servo architecture uses a single hybrid servo cable for both power and signal. This cable contains a shared signal pair for the motor feedback and temperature signals, both of which are modulated for transmission. This streamlined approach to cabling eliminates the need to buy, install and maintain standalone encoder and resolver cables.

Selecting Hybrid Servo Cables

In addition to its cabling advantages, HIPERFACE DSL® offers performance benefits from a servo control standpoint, and it has already gained support from the world’s leading drive manufacturers. So you may soon find yourself in the market for a cable compatible with HIPERFACE DSL.

When you do specify these hybrid power and signal cables, keep the following design considerations in mind to minimize cost while maximizing performance:

    •       Look for a tight bend radius. Many hybrid cables will see use in cable tracks. In these applications, look for cables with a tighter bend radius, which may allow you pick smaller, more economical cable tracks.

    •       Pay attention to the cable insulation. Hybrid servo cables tend to use either PVC or —about 20% smaller for this type of cable.

polypropylene core insulation systems. Each has advantages. PVC, for example, supports a slightly higher temperature rating. But polypropylene offers much better electrical properties. These include low capacitance and a relatively low dielectric constant, which limits leakage current to the shield and screen. The superior electrical properties mean that polypropylene insulation can be substantially thinner than PVC for a given characteristic impedance level. And thinner insulation means smaller cable diameters

    •       Go for durability. Hybrid servo cables vary widely in their durability. So it’s important to evaluate the resistance to temperature extremes, oil, UV light and flame. When using servos in cable tracks, add wear resistance and maximum travel length to the list of factors to consider. In general, you should lean toward polyurethane jacketed products for use in cable tracks and in harsh environments.

Single Cable Solutions

To serve the fast-growing HIPERFACE DSL market, we have developed two new hybrid servo cables:

•   OLFLEX® SERVO FD 7DSL features a polyurethane jacket for use in cable tracks.

•   OLFLEX® SERVO 7DSL is PVC jacketed for fixed installations.

Both products meet HIPERFACE DSL standards and have UL and AWM approvals. Download the full specifications here.