Page 79 - Practical Power System and Protective Relays Commissioning

76 Practical Power System and Protective Relays Commissioning

6.4.6 Verification of Cross Bonding Test of Metallic Sheath of
Cable

Cross-bonding is used to reduce the induced currents and eddy currents in
the metallic sheath. This cross-bonding is made at link boxes. Transposition
between phases is also made through the cable length. The test is undertaken
by injecting an AC current of 100 A at the three phases of the cable with the
other end of phases shorted. Then a measurement of the current passing
through the cable sheath is made. This current should not exceed 3% of the
injected current as shown in Fig. 6.10.

6.4.7 Measurements of Cable Positive Sequence Impedance
This test can be done by injecting a three-phase power supply on the cable with
shorting the three-phase conductors of the cable at the remote end of the cable
as shown in Fig. 6.11.where Z 1 5 Z 2 5 V/I and Z 1 is the positive sequence
impedance of the cable, Z 2 is the negative sequence impedance of the cable
V V
R 1 5 cosΦ; X 1 5 sinΦ
I I

6.4.8 Measurements of Cable Zero Sequence Impedance
This test can be done by using single phase power supply as shown in
Fig. 6.12.where Z 0 5 3 V/I and Z 0 is the Zero sequence impedance of the
cable sequence impedance of
V V
R 0 5 3 cosΦ; X 0 5 3 sinΦ
I I

FIGURE 6.10 Verification of cross-bonding test of metallic sheath of cable.