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Test On 110kV Power Cable After Installation (1)

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Test On 110kV Power Cable After Installation
Test On 110kV Power Cable After Installation – Part 1 (on photo: Kyoritsu 4102A digital earth resistance tester)

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

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

2. Electrical Test

(Standards Reference is IEC 60840, and relevant SEC Transmission specifications 11-TMSS-02, TCS-P-104.08).

ITEMDescriptionRemark
1Check Phasing for Conductor and sheath bonding
2Sheath DC high voltage test (10 kV DC for 1 min.) and 5 kV DC insulation test before and after high voltage/24 hour soaking test
3Conductor resistance, capacitance and inductance measurement test
4Conductor insulation resistance test
5Cross-bonding verification testThe sheath current should be <3% the current due to induction neighboring circuits should be considered and limit should be 3%+current due to external circuits
6Zero and positive sequence impedance measurement
7SVL (Sheath/Surge voltage Limiter) test by 2.5 kV DC insulation tester
8Measure the ground resistance at all link box positions as per SEC standards TES-P-104.08)
9Contact resistance test on link boxes (less than 20 μΩ)
10Metallic sheath continuity test
11Cable profile test- during jointing
12In case of Double Circuit (110 kV and above), check the separate grounding pit
13AC High voltage test for all new cables, but if old portion are involved then soaking for 24 hours at rated voltage

1. Phase indication test

After complete installation, the cables are to be identified with respect to their phases and are to be reconfirmed whether they are correctly marked or not.

Phase Identification Test diagram
Phase Identification Test diagram

Equipment / Instruments Used

Battery operated KYORITSU, High Voltage Insulation Resistance Tester, and MODEL-3125

Kyoritsu 4105A - Digital Earth resistance tester
Kyoritsu 4105A – Digital Earth resistance tester

Instructions

  1. The screens of all cables at one end are to be shorted and grounded.
  2. The conductor of the cable under test is to be connected to the negative pole of the meter.
  3. The positive pole of the meter is to be grounded.
  4. Through a switch ground the other end of this conductor of the cable under test and measure the resistance.
  5. If the resistance becomes zero, the phase identification is ok and checks whether the correct color coding is applied or not.
  6. To cross check, open the switch, the meter shall read high resistance (Tending to infinity).
  7. Similarly repeat the test for other phases and verify the correctness of color coding.

2. DC Conductor Resistance Measurement

The DC resistance of conductors of the cables, to be measured at ambient temperature before conducting any other test, and the values are to be computed for 20ºC.

Schematic layout for measurement of DC resistance for long cable
Schematic layout for measurement of DC resistance for long cable

Reference

  • IEC 60228 – Conductors of insulated cables

Equipment / Instruments used

  1. Any wheatson bridge, micro Ohm-Meter.
  2. Any industrial type thermometer to measure the ambient temperature.

Instructions

  1. The conductors are short circuited at the far end by minimum 95 mm2 cable.
  2. The other ends of the cable are connected to the bridge according to equipment instructions.
  3. Note down the measured value.
  4. The resistance of conductor at 20ºC/km is obtained by substituting the measured value in the formula.
Formula for Temperature Correction:

For Copper R20 = R/L (1 + 0.00393*(T-20)) Ω/KM

Where,

  • R20 – Conductor resistance at 20ºC *(ohm/km
  • R – Measured resistance of one phase (ohm)
  • L – Exact length (km)
  • 0.00393 – Temperature coefficient at 20ºC for copper (K)
  • T – Temperature of conductor when measured in ºC


3. Capacitance Test

The capacitance shall be measured between conductor and metallic screen. According to IEC, the measured value shall not sxceed the normal value specified by the manufacturer by more than 8%.

Schematic layout for capacitance measurement
Schematic layout for capacitance measurement

Reference

  • IEC 60840 – Applies to cable voltage ratings between 30 kV and 150 kV. It includes a regular type test sequence for cables and a separate sequence for the cable accessories.

Equipment / Instruments used

Any RLC bridge capable of measuring capacitance up to 0.01 micro-farad (μF)

Omicron - for zero positive sequence test and capacitance measurements
Omicron – for zero positive sequence test and capacitance measurements

Instructions

  • Connections are made as per below schematic.
  • Connect the instrument cable between conductors and metallic screen and take the measurements.
  • The capacitance is measured between each individual conductor and sheath. A capacitance bridge is used for this measurement.
  • The value obtained can be converted to μF/km
Formula for Capacitance:

C = Cm/L (μF/km)

Where:

  • C – Capacitance in μF/k
  • Cm – Measured Capacitance in μF
  • L – Length of Cable in km.

To be continued soon…

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About Author

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Zafar Iqbal

Zafar Iqbal - Electrical engineer with more then 5 year experience in Electrical Transmission and Distribution Field. Highly specialized for design, installation and testing of HV/MV T&D lines and Power Substations.