Test On 110kV Power Cable After Installation 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 InspectionITEM

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

4Check 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

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

10 Check 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

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

15Check irregularities of outer jacket formed by non-uniform shield wire distribution

16 Check/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

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

2. Electrical Test

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

ITEM

Description Remark

1 Check 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

3 Conductor resistance, capacitance and inductance measurement test

4 Conductor insulation resistance test

5 Cross-bonding verification test

The sheath current should be

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

Equipment / Instruments Used

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

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 20C.

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 20C/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)) /KM

Where,

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

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

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 (F)

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 F/km

Formula for Capacitance:

C = Cm/L (F/km)

Where:

C Capacitance in F/k Cm Measured Capacitance in F L Length of Cable in km.

Test On 110kV Power Cable After Installation (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

Equipment / Instruments used

The DC HV 25kV Tester, Model No. PGK 25 manufactured by BAUR Germany. The test is applied only to cables covered with conductive layer over outer sheath. (Read more about Hipo Testing)

DC Hipo Tester, BAUR PGK 25

Instructions

1. The covering under sheath is exposed about 2 cm length at one end of the cable so that the negative polarity shall be applied to it.

2. The conductive layer on outer sheath shall be removed about 20 cm wide at a distance of 30 cm from both ends of the cable.

3. The positive terminal of the DC source is connected to a copper band wound on the conductive layer of the sheath at one end of the cable (60 cm away from the end).

4. The 25 kV tester can be operated by choice either from the power supply source of 220/110 v- 50/60 Hz supply or can be charging its in-built battery set-up.

5. Switch on the timer in clockwise direction, a lamp indicator will be indicated ON position to a desired test period.

6. Select the voltage selector switch to 5 kV or 25 kV.7. Select the range of current measurement to position corresponding to the current value intended

for charging the test cable.8. Slowly rotate the voltage selector to the desired voltage value on the scale (1 kV per second

in intervals). Watch carefully the voltmeter while charging. If required re-adjust voltage selector before the desire test voltage is reached.

9. Set range switch for current measurement to the desire range after charging has been completed.

10. After the time has elapsed the high voltage bring down to zero, switch off the timer and discharge the cable through ground wire.

DC Sheath Test diagram

Requirements

The cable is considered to have passed if it withstands the required voltage (10 kV) during the test for 1 minute without break down. During the test, the leakage current shall be recorded. During the testing, safety regulations on electric hazards should be strictly observed. The measurements / reading are recorded in the available format in company.

5. Insulation resistance measurement

The insulation resistance shall be measured between conductor and metallic screen according to IEC 60840.

References

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

Equipment / instruments used

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

KYORITSU High Voltage Insulation Resistance Tester

Instructions

1. Cable should be free from all system connections2. Connect the cables between conductor and metal sheath.3. Measure the resistance at the required voltage and charging time (1 minute).

Insulation resistance test diagram

The insulation resistance (Ri) measured between each individual conductor and metal sheath. The insulation resistance per kilometer is calculated from:

Rl = Ri x L (G Km)

Where:

Rl Insulation resistance in G Km.Ri Measured insulation resistance in G.L cable length in Km.

6. Cross bonding check

With the cross bonding checks, the right connection of the cables can be checked and when correctly bonded, no current may flow in the metal sheath of the cable in case of an ideal situation.

Ideal case is only the case when all cable sections have the same length and the spacing between the cables is constant along the cable route. But in practice, some induction current will always flow as the configuration of the cable system is never ideal.

The actual site requirements and situation dictate what the actual cable section lengths that may differ from section to section.

Equipment / Instruments used

380 V Generator 3-Phase Current Transformer Clamp Meter

Instructions

1. Screen is to be grounded at both ends.2. The conductors are short circuited at the far end firmly by minimum 95 mm2 cable.3. The conductors under test are connected as shown in figure below.4. Increase the current gradually insteps by balancing the phases individually to desired value.5. Note down the current induced in all the link boxes.6. Reduce the current gradually and switch off the breaker.

Cross bonding check diagram

Home / Technical Articles / Test On 110kV Power Cable After Installation (3)

Test On 110kV Power Cable After Installation (3)

Posted Jan 2 2015 by Zafar Iqbal in Cables, Testing and Commissioning with 7 Comments

Test On 110kV Power Cable After Installation (Part 3)

General description of site test procedure

In previous two parts of this technical article first six procedures were explained. Now the last three (7, 8 and 9) will be explained in details:

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

7. Zero sequence and positive sequence impedance test

Positive sequence impedance are calculated assuming that there are no metallic elements that are placed within an influential distances of cable (Railway lines, pipe lines or buried equipments etc.).

The presence of other metals or metallic objects influences the sequence impedance. Because of influence of other unknown factors, it is recommended that the impedance should be measured in the field after the circuits are installed. Positive and negative sequence impedance for cables is same value, because the impedance of these in uncharged if a symmetrical voltage system with reverse sequence is applied to them.

Zero sequence impedance of the cable is not a fixed parameter and depends on the kind of transmission and electrical conductivity of the soil (environment). Measurements on installed cables have to be carried out, in order to obtain the exact value.

Usually the zero sequence impedance can be assumed as 3 times the positive sequence impedance value as a practice for initial approximation.

The three currents of zero sequence system, equal in magnitude and direction, are opposed by an impedance that is determined by the loops formed by the three cable cores and returned by the metallic sheaths and earth in parallel. The effective AC resistance of the zero sequence system includes both the effective resistance of the line conductor as well as that of earth return.

The zero sequence impedance can be determined by measurement or calculation when the three phase of the system are connected in parallel and single phase AC current is applied to them.

Instruments / Equipment used

3-phase variable transformer (up to 100 Amps supply capacity). Impedance measurement equipment Digital.

CP-CU1 Omicron for Zero positive sequence test and capacitance measurements

Instructions

Measurement of positive/negative sequence impedance:

1. The measurement is done between two phases of the circuit once the complete circuit is installed, cable may be transposed and cross bonded between the terminations. There should be electric accessibility to the cable cores at terminations.

2. The connections should be made as per Figure 1A.

3. Turn up the power with the variable transformer until 25 Amps of current starts flowing. Switch the impedance measurement equipment and record the voltage, current and angle (power factor).

4. Switch off after the measurement and turn the variable transformer down.5. The measurement is to be repeated three times: between R & Y, between R & B and between

Y & B phases.

Measurement of zero sequence impedance

1. The measurement is done by connecting the three phases of circuit connected in parallel and a single phase AC voltage is applied to them.

2. The connections should be made as per Figure 1B.3. Turn up the power with the variable transformer until 25 Amps of current starts flowing.

Switch the impedance measurement equipment and record the voltage, current and angle (power factor).

4. Switch off after the measurement and turn the variable transformer down.5. Repeat for each phase.

Precautions: safety precautions should be taken prior to switching by putting up warning tapes and stationing personnel at critical point to ensure that no one is within reach of system parts where high current are applied.

Schematic diagrams

Figure 1A Schematic layout for measurement of Positive/Negative Sequence Impedance

Figure 1B Schematic layout for measurement of Zero Sequence Impedance

8. Earth resistance measurement at link boxes

The measurement of earth resistance is mainly intended for the purpose of grounding the links of bonding system of high voltage cable screen.

Equipment / Instruments used

Analogue Earth tester Model-04102A, Make-KYORITSU.

Analogue Earth tester Model-04102A, Make-KYORITSU

Instructions

1. Check the battery voltage, set the range switch to battery check position and press test button and make sure the indicator is at right of BATT GOOD position.

2. The connections as per the figure bellow.3. Check the earth voltage by setting switch to earth voltage position, make sure the voltage is

10V or less. If the earth voltage is higher, the result may be with excessive high errors.4. Measure the earth resistance by setting the switch to resistance range position and press

test button.5. The earth resistance must not exceed 5 for outside substation and 3 for inside substation.

Schematic diagram

Earth resistance measurement at link boxes

9. Link box contact resistance measurement

This test is basically carried out after installation of link boxes and connecting leads.

Equipment / Instruments used

Megger DLRO-200 for contact resistance and DC resistance measurements

Megger DLRO-200 for contact resistance and dc resistance measurements

Instructions

1. All the bolts are to be tightened firmly2. Connect the micro-ohmmeter with the link box as shown in figure below.3. The micro-ohmmeter shall be applied between earth copper bar and each disconnect

able copper bars.4. Test shall be repeated for individual connections.5. The values should bein micro-ohm range.

Schematic layout

Link box contact resistance schemetic layout

110 kV, 115 kV and 132 kV XLPE Cables1. Mechanical Check and visual Inspection2. Electrical Test

1. Phase indication testEquipment / Instruments UsedInstructions

2. DC Conductor Resistance MeasurementReferenceEquipment / Instruments usedInstructions

3. Capacitance TestReferenceEquipment / Instruments usedInstructions

General description of site test procedure4. DC sheath test on outher sheathReferencesEquipment / Instruments usedInstructionsRequirements

5. Insulation resistance measurementReferencesEquipment / instruments usedInstructions

6. Cross bonding checkEquipment / Instruments usedInstructions

Test On 110kV Power Cable After Installation (3)General description of site test procedure7. Zero sequence and positive sequence impedance testInstruments / Equipment usedInstructionsSchematic diagrams

8. Earth resistance measurement at link boxesEquipment / Instruments usedInstructionsSchematic diagram

9. Link box contact resistance measurementEquipment / Instruments usedInstructionsSchematic layout