Petersen coil grounding

Petersen coil grounding in a power system

1. P ETERSEN C OILS Authorized By: Muhammad Imran Channa 2012-SECR-45

2. Introduction The arc Suppression coil invented in 1917 by Waldemar Petersen , so that’s why it is referred as Petersen coil. An arc suppression is device that is connected to the neutral to limit the capacitive earth fault current flowing when earth fault occurs in a high or medium voltage network. This method grounding is called resonance grounding , it has been used in Central &Eastern Europe as well as Scandinavian countries for many decades. The Petersen coil chokes fault current below the level of self extinction for overhead networks. By this action all transient faults in overhead networks can be cleared without tripping the feeder. The basic principle of Petersen coil remained unchanged since 1917 & it is excellent properties have been mirrored by low outage rates where it has been used.

3. Basic Principle When a phase-to-earth fault occur in underground 3 phase system , the phase voltage of the faulty phase is reduced to earth potential as capacitance of faulty line is discharged at the fault location, the phase-to-earth voltages of other two phases rises by √3. A charging current “IC” occurs between these phase to earth capacitances, which will continue to flow via the fault path while it remains. IC is three times the charging current of each phase to earth.

4. Diagrams Circuit Diagram Vector Diagram

5. Application When a phase to earth fault occur in underground 3 phase systems, the phase voltage of faulty phase is reduced to ground potential . This cause the phase voltage in the other two phase to rise by √3 times. This increase in voltage causes a charging current, Ic between the phase-to-earth capacitances.

6. Advantages & Disadvantages Advantages: The Petersen coil is completely effective in preventing any damage by an arcing ground. This coil has the advantages of undergrounded neutral system. Disadvantages: Due to varying operational conditions, the capacitances of the networks changing from time to time. Therefore inductance “L” of the Petersen coil required readjustment. The line should be transposed.