Modeling of Rogowski Coil for Online PD Monitoring in CoveredConductor Overhead Distribution Network

1
Modeling of Rogowski Coil for On-line PD
Monitoring in Covered-Conductor Overhead
Distribution Networks

• G. Murtaza HASHMI
• Matti LEHTONEN, and
• A. ELHAFFAR
• Power Systems and High Voltage Engineering
• Helsinki University of Technology (TKK)
• Espoo-FINLAND

2
Introduction

• Use of CC lines in MV networks
• Trees fall on CC lines due to heavy storms
• On-line PD measurements to monitor falling trees
  on CC lines
• Automatic detection can reduce visual inspection
  work and improves reliability of the distribution
  network

3
Motivation

• Faling trees may damage TL components (e.g.
  insulators, clamps, ploes), if not removed
• PDs produced due to falling trees can damage
  insulation and may subsequently induce different
  faults
• The challenge for on-line PD measurements is to
  find the optimal locations for PD sensors
• Attenuation is an important parameter in order to
  estimate the maximum length of the line that can
  be monitored with a PD sensor

4
Rogowski coil as PD sensor

• Limitations of conventional PD detectors
• Influence of background noise
• Intrusive
• Limit in the detection frequency range
• Rogowski coil
• Non-intrusive
• Easy to install
• High detection frequency range
• Converted into a wireless one in next stage

5
Experimental Set-up
Rogowski coil responses for 5 nC calibrator pulse
at (a) point P1, and (b) point P2
6
Rogowski coil parameters
Rogowski coil is modeled in ATP as a saturable
current transformer having linear magnetizing
characteristics
7
CC line parameters

• The frequency-dependent CC line characteristics
  are calculated using theoretical model, and are
  used in simulation as resistance, 2 ?/m
  characteristic impedance, 350 ? and propagation
  velocity, 230 m/?s (average values for MHz range)
• The transmission lines are represented using
  distributed parameters Clarke model in ATP

8
ATP model of measuring system
ATP Draw circuit for the PD monitoring system
5 nC calibrator pulses (measured and simulated)
9
ATP simulation results
Rogowski coil response for 5 nC pulse calibrator
charge at point P2 in (a) time domain, and (b)
frequency domain
10
ATP simulation results-continued
Rogowski coil response for 5 nC pulse calibrator
charge at point P1 in (a) time domain, and (b)
frequency domain
11
Conclusions

• ATP simulations are performed to model the
  transient behavior of the Rogowski coil.
• The model can be used to estimate the length of
  the line at which the PDs due to falling trees
  can be detected thus, deciding the number and
  positioning of the sensors over a particular
  length of the CC line.
• The simulation results show that the CC line has
  very low attenuation, and the higher amplitude
  pulse measured by the Rogowski coil near the
  source of PD is due to the effect of its varying
  resonance frequencies at different distances.
• The Rogowski coil used in this study is not good
  for high frequency measurements beyond 5 MHz.
  Therefore, a higher bandwidth coil should be used
  for real time analysis of PDs produced by falling
  trees on the CC lines.

12
Future developments

• The proposed model can be used for different
  band-width Rogowski coils to observe the PD wave
  propagation
• It would be more practical and demanding if an
  on-line three-phase (instead single-phase) PD
  measuring system can be modeled.
• The simulated PD wave propogation can be
  investigated in an integrated network to analyze
  and resolve the real problems faced by the local
  utilities

13
Thanks

• For your attention