PROCEDURE
6a IR Test
The Insulation resistance (IR) test measures the dc resistance of the insulation of the cable
installation using an Insulation Resistance Tester. It involves measuring both the ph-ph & ph-earth insulation resistances. Because of cable capacitance, the IRT shall be applied until a stable reading is obtained.
IR tests shall be performed after laying and prior to jointing each section of cable.
The Insulation resistance (IR) test measures the dc resistance of the insulation of the cable
installation using an Insulation Resistance Tester. It involves measuring both the ph-ph & ph-earth insulation resistances. Because of cable capacitance, the IRT shall be applied until a stable reading is obtained.
IR tests shall be performed after laying and prior to jointing each section of cable.
Acceptable IR values are:
Screen to Earth test will record an IR after one (1) minute. This test shall be performed first to assist in the reconnection process of the screen to earth connection.
Phase to Screen and Phase to Phase testing requires the measurement of IR at 1kV after one (1) minute duration.
Note : IR tests shall be applied for a period of 1 minute for cables less than 100m and 3 minutes for cables greater than 100m in length.
6b Conductor Resistance Test
This is carried out to determine the effectiveness of the conductor joints and terminations by
measuring the dc loop resistance. Results are compared with the manufacturer’s conductor
resistance usually expressed in ohms/km in the cable specification.
6c Phase Identification
Screen to Earth test will record an IR after one (1) minute. This test shall be performed first to assist in the reconnection process of the screen to earth connection.
Phase to Screen and Phase to Phase testing requires the measurement of IR at 1kV after one (1) minute duration.
Note : IR tests shall be applied for a period of 1 minute for cables less than 100m and 3 minutes for cables greater than 100m in length.
6b Conductor Resistance Test
This is carried out to determine the effectiveness of the conductor joints and terminations by
measuring the dc loop resistance. Results are compared with the manufacturer’s conductor
resistance usually expressed in ohms/km in the cable specification.
6c Phase Identification
Phase identification should be checked by the use either of the phasing resistors or a continuity check of each individual core wherever possible after all jointing work has been completed. Alternatively, the current injection phasing method may be used. Phase identification checks must be carried out by jointing staff to ensure cables have been
connected correctly in line with the system phasing diagrams. Phase identification relates to both conductors and sheaths.
6d Cross Bonding Test
connected correctly in line with the system phasing diagrams. Phase identification relates to both conductors and sheaths.
6d Cross Bonding Test
Cross bonding tests on the cable sheaths shall be performed to verify the integrity of the cross bonding system. This test ensures circulating sheath currents generated by induced voltages at full load will not adversely affect the cable rating.
This test involves injection of a 3 phase currentinto the cores of the cable, and measuring of
voltages and currents induced into the sheaths at each cross bonding point along the complete cross bonding section. An injection current of greater than 50A shouldbe used. Sheath currents and voltages are to be measured at each cross bonding point, earth point and termination. The cross bonding connections shall be rearranged to prove incorrect connection, and checked again after correct restoration.
The procedure shall be repeated for each complete cross bonding section of the cable run.
Current and voltage measurements are to be scaled up to the rated load current. Voltage values at isolated (not solidly earthed) cross bonding pointsshall be less than the rated load current scaled voltages of the installation design.
6e Sequence Impedance Measurements
These tests are carried out for protection settings, earth potential rise and fault analysis. The tests are circuit dependent. The cable measurements shall include DC resistance, positive, negative and zero sequence impedances, and shall be expressed at a reference temperature of 20deg C. The measured values shall be compared with the calculated theoretical values or those provided by the cable manufacturer.
This test involves injection of a 3 phase currentinto the cores of the cable, and measuring of
voltages and currents induced into the sheaths at each cross bonding point along the complete cross bonding section. An injection current of greater than 50A shouldbe used. Sheath currents and voltages are to be measured at each cross bonding point, earth point and termination. The cross bonding connections shall be rearranged to prove incorrect connection, and checked again after correct restoration.
The procedure shall be repeated for each complete cross bonding section of the cable run.
Current and voltage measurements are to be scaled up to the rated load current. Voltage values at isolated (not solidly earthed) cross bonding pointsshall be less than the rated load current scaled voltages of the installation design.
6e Sequence Impedance Measurements
These tests are carried out for protection settings, earth potential rise and fault analysis. The tests are circuit dependent. The cable measurements shall include DC resistance, positive, negative and zero sequence impedances, and shall be expressed at a reference temperature of 20deg C. The measured values shall be compared with the calculated theoretical values or those provided by the cable manufacturer.
6f Serving Tests
A high voltage DC test between the metallic sheath to earth is performed to test the integrity of the outer sheath. An IR test is performed to and after the high voltage test to assess the insulation integrity of the cable.
The test voltage level and test period for serving tests on subtransmission cables are :
33kV & 66kV – 10kV/1min.
132kV – 15kV/1min.
6g Sheath or Screen Resistance Test
The dc resistance of the metallic sheath and connections is measured and compared with the manufacturer’s sheath resistanceusually expressed in ohms/km in the cable specification.
6h Sheath Voltage Limiters (SVL) SVL’s are connected to the cable sheaths to limit the transient voltage rises to avoid puncturing the cable servings under fault conditions.
The units are tested to ensure their compliance with their original characteristics. The test shall be carried out in accordance with the manufacturer’s recommendations.
6i HV Tests
The requirement is to complete the prescribed tests as specified. All cables must be fully discharged for a time duration equal to the test time upon completion of each testby means of discharge function on test equipment or an independent earth. HV tests shall be carried out after laying & bedding has been completed. The following table shows the test voltages and times required for cable system voltage.
A high voltage DC test between the metallic sheath to earth is performed to test the integrity of the outer sheath. An IR test is performed to and after the high voltage test to assess the insulation integrity of the cable.
The test voltage level and test period for serving tests on subtransmission cables are :
33kV & 66kV – 10kV/1min.
132kV – 15kV/1min.
6g Sheath or Screen Resistance Test
The dc resistance of the metallic sheath and connections is measured and compared with the manufacturer’s sheath resistanceusually expressed in ohms/km in the cable specification.
6h Sheath Voltage Limiters (SVL) SVL’s are connected to the cable sheaths to limit the transient voltage rises to avoid puncturing the cable servings under fault conditions.
The units are tested to ensure their compliance with their original characteristics. The test shall be carried out in accordance with the manufacturer’s recommendations.
6i HV Tests
The requirement is to complete the prescribed tests as specified. All cables must be fully discharged for a time duration equal to the test time upon completion of each testby means of discharge function on test equipment or an independent earth. HV tests shall be carried out after laying & bedding has been completed. The following table shows the test voltages and times required for cable system voltage.
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