Petersen Coils:
§ A Petersen Coil is connected between the neutral
point of the system and earth, and is rated so that the capacitive current in
the earth fault is compensated by an inductive current passed by the
Petersen Coil. A small residual current will remain, but this is so
small that any arc between the faulted phase and earth will not be maintained
and the fault will extinguish. Minor earth faults such as a broken pin
insulator, could be held on the system without the supply being interrupted.
Transient faults would not result in supply interruptions.
§ Although the standard ‘Peterson coil’ does not
compensate the entire earth fault current in a network due to the presence of
resistive losses in the lines and coil, it is now possible to apply ‘residual
current compensation’ by injecting an additional 180° out of phase current into
the neutral via the Peterson coil. The fault current is thereby reduced to
practically zero. Such systems are known as ‘Resonant earthing with residual
compensation’, and can be considered as a special case of reactive earthing.
§ Resonant earthing can reduce EPR to a safe
level. This is because the Petersen coil can often effectively act as a high
impedance NER, which will substantially reduce any earth fault currents, and
hence also any corresponding EPR hazards (e.g. touch voltages, step voltages
and transferred voltages, including any EPR hazards impressed onto nearby
telecommunication networks).
§ Advantages:
1.
Small reactive earth
fault current independent of the phase to earth capacitance of the system.
2.
Enables high impedance
fault detection.
§ Disadvantages:
1.
Risk of extensive active
earth fault losses, High costs associated
No comments:
Post a Comment