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CASE STUDIES  OF HARMONICS PROBLEMS, ANALYSIS, & SOLUTIONS ON TRANSMISSION SYSTEMS
By Dave Mueller, Electrotek Concepts Dranetz-BMI Inc

​Analysis of harmonics on transmission systems


  • Large models are sometimes required
  • Different system configurations (contingencies)
  • Determining the harmonic loading
  • Determining the system damping
  • Evaluating solutions


Case Studies on Three Continents


  1. (Europe) Underground Transmission Connection to a Windfarm
  2. (Asia) Fifth Harmonic Filter Failures in China
  3. (North America) Capacitor Bank Resonance


Underground Transmission Connection to a Windfarm


Fifth Harmonic Filter Failures

Harmonic  Source


  • ​Transformer current under dc bias (monopole operation of the HVDC)
  • Similar to the effect of geomagnetic storms
HMagnitude
1825.213
2212.198
3141.465
494.3101
535.3663

Simulation Results

THD=169%, Irms=200%

(North America) Capacitor Bank Resonance

System Description


  • Four (4) identical 138kV, 52.8MVAr capacitor banks
  • On bank 4, during normal operation Vthd = 4-5%
  • During a line out contingency Vthd=10%
  • IEEE 519 Harmonics Limits
Bus VoltageMaximum Individual Harmonic Component
Maximum THD
69kV & below
3.0%5.0%
115kV to 161kV1.5%2.5%
Above 161kV
1.0%1.5%


Available Fault Levels (Normal)


Bus3 Phase MVAsc52.8 MVAr H resonant
147629.5
231897.8
344909.2
431177.7


System Model


  • 900 bus model, imported from system short circuit model
  • Capacitor banks at other locations
  • The figure on the right is a single line drawing of half of the network,  not including 36kV stations that were also modeled


Harmonic Trend Measurements


  • High harmonics coincided with the operation of an HVDC system in monopole operating mode

SuperHarm™ Modeling Software

www.pqsoft.com
Direct solution, admittance matrix approach
Constant harmonic current sources
Nonlinear load model automatically “adjusts” magnitudes and phase angle


Harmonic Source Assumptions

Harmonic NumberMagnitude (% of Load)
3

0.5 Balanced

3.0 Unbalanced

53.2
71.5
90.2
110.4
130.2

Frequency Scans (Various Contingencies)

Case List of Capacitor Bank Configurations

System Description


  • 525/242kV system
  • 750MVA autotransformer with a 34.5kV tertiary
  • 34.5kV busbar supplied reactive compensation
    • 40.08MVAr, 41.57kVAr, 16.5mH (144Hz)
    • 40.08MVAr, 38.11kVAr, 5.8mH (223Hz)
    • 40.08MVAr, 38.11kVAr, 5.8mH (223Hz)


Frequency Scan Analysis

Harmonic Simulation Results:

Case%THD%H3%H5
Existing1.360.21.1
New Cable2.390.31.7
Line 1 Out3.080.22.5
Line 2 Out4.140.73.9

Solution Alternatives

Capacitor Bank Current and Voltage

Windfarm Connection

  • 41 x 2MW turbines
  • 20km underground transmission connector


System Model:

Results


  • Capacitor bank sizes were reduced to allow for line out contingencies
  • 36kV capacitor banks were found not to have an important effect
  • A subsequent study for another network area showed that 69kV capacitor banks had important effects on the 138kV system