Zero-sequence current

Based on IEEE-80 recommendations, the following simplified formula may be used to determine the zero sequence current in the event of a phase to ground fault ... 

Setup for measuring sequence currents for a cross-bonded cable (a) zero-sequence current and (b) positive-sequence current. 

Figure 3.8a shows the setup for measuring the zero-sequence current for a cross-bonded cable. 

The zero-sequence current can be obtained from Equation 3.51 as follows ... 

After solving Equation 3.68 for and then eliminating from Equation 3.66, the zero-sequence current becomes... 

The phase angle of the zero-sequence current mentioned in Table 3.1 demonstrates that grounding resistance at substations in both cross-bonded and solidly bonded cables significandy affects the zero-sequence current. As a result, there is litde difference in the zero-sequence impedance of the cross-bonded cable and the solidly bonded cable. The results indicate the importance of obtaining an accurate grounding resistance at the substations to derive accurate zero-sequence impedances of cable systems. 

Solving (3.68) for Vs and eliminating Vs from (3.66), the zero sequence current is found as... 

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