Transcript Diapositiva 1

Evaluation of the Ground Operating current in Industrial
Systems with Network Distribution through MV cables
Jorge Cardenas
GE Digital Energy
Email: [email protected]
Introduction
Oil and Gas Industrial installations have facilities that
involve extent areas where the different loads are
located several kilometres away from the generating
points. In Oil and Gas Industry there is the particularity
that the distribution of the energy is made through
relatively long underground cables (Energy
transmission is made through MV cables with lengths
that goes in the range of 500 m. to 10 Km.
approximately) and in the design frequently it is not
taken in consideration the influence of the capacitive
currents provided by the underground cables on the
protective elements. This situation has a significant
effect, mainly on the directional ground relays in MV,
because the neutral frequently is grounded through a
Zigzag transformer + a limiting resistor, that reduces
the short circuit current, during ground faults, at levels
similar that the ones produced by the capacitance of
the MV cables.
Results
Direction of the Fault Currents during a Real
Fault
Phasor Analysis in Phase-to-Ground fault.
.
ANALYSIS
Neutral Directional Element Performance in
Generators
Conclusions
Phase-to-Ground Fault in a Typical Large Industrial Network
Direction of Polarization and Fault Currents.
·Neutral direction element applied in
Industrial Systems need to be analyzed
with a network model detailed in all the
main parameters as resistance,
inductance and capacitance, in order to
find the optimal forward and reverse
covering areas.
·Neutral directional can be applied in
Industrial Systems with relative long
cables to optimize the protection not
only on the feeders, also on the
grounding transformer and Generators
operating in parallel.
Direction of the Fault Currents
Current distribution during a phase-to-ground fault.
Neutral Directional Element Performance
·Majority of Industrial Installations use
high impedance grounding and as a
consequence low phase-to-grounds
currents in the range of the capacitance
currents are usual during faults. This
can produce a big change in the fault
direction. As a consequence a detailed
analysis is needed to determine the
optimal setting of the directional
element.