Harmonics Problems in Distribution Systems Case Study AEP Texas Central Company Scott Lee, Reliability Engineer

SYMPTOMS OF A PROBLEM  Residential customer calls complaining of problems with electronics: TV, thermostat – AC, motors making strange noises  Serviceman and Operations Tech troubleshoot and have transformer replaced because of unusual humming and arcing sounds from coil  New transformer makes the same sound, customer still has problems – call the engineer  Tech goes to new pipe plant down the road and finds 2000kVA pad transformer making same noise

 Houston based company built a pipe coating and storage plant in George West to better serve the Eagle Ford Shale area  Two 1000kW induction furnaces to heat and coat 2 inch to 24 inch diameter casing with fusion bonded epoxy  Two solid state 6-pulse rectifiers and step up transformers provide variable frequency 4kV power to induction coils For more info... see texisle.com and ajaxtocco.com THE SOURCE

INSTALLATION  Previously during the plant planning stages, AEP provided system, line, and transformer impedances to drive manufacturer for design. Distance and PQ were discussed.  3 miles of distribution feeder was upgraded with 477MCM aluminum, with a total length of 6.4 miles  Drive manufacturer wanted two 1500kVA or one 3000kVA transformer, we supplied one 2000kVA. They were also very insistent on our transformer meeting their specs. Actual peak is 1380kW.  A 1000kVA pad was installed for other plant power that peaks at 600kW  AEP standard for three phase padmounts is wye-wye  IEEE-519 requirements were not discussed, customer did not tell us the inverter was a 6-pulse drive

George West Sub 138/12kV 9.4 MVA Plant  * Residence  Feeder upgraded to 477, 6.4 circuits miles from sub to customer

 1000kW  500 Hz  Variable Frequency  6-pulse rectifier  No filtering  Water cooled

 PMI recorders installed at plant transformer and at residential customer. Set to record harmonics and capture waveforms.  Voltage THD at pipe plant on secodary, 14%  Voltage THD at residential secondary, 5.1% PMI stands for Power Monitors Incorporated, see iVs-3 and Eagle 440www.powermonitors.com MEASUREMENTS

3rd 12.4% THD-Voltage 7th 11 th 13th 5th 23.4% THD-Amps 2000 kVA Padmount 6-Pulse Drive 5th 7th 11th Unfiltered, running at 1550kVA

12.4% THD-V 23.4% THD-A Unfiltered, 2000kVA Padmount, 6-Pulse Drive

THE FIX  Met with pipe company and drive manufacturer to request they install filtering and comply with IEEE-519 (5% THD limit on voltage)  Move other distribution customers in area to another feeder  Drive manufacturers said they would install passive filters (reactors and capacitors) but parts would have a 14 week lead time plus engineering and installation time  I countered to pipe company that this was unacceptable, and offered three filter manufacturers with on the shelf parts that offered active filtering and engineering support.  Recomended MTE Matrix Pure Sine active filters, Schaffner EMC ECOsine active filters, and TCI H5 active filters.

 There was a debate over passive versus active, but after some research, I pressed the customer to go with active filters because of the varying load and the possibility of hitting resonance with a passive unit, also recommend a 5% line reactor which is standard for 6 pulse drives  The customer chose a vendor, and we had several phone conferences about what to install, and what would be acceptable with AEP  The vendor chosen was Schaffner EMC and the ECOsine FN3420 filter with additional 5% reactors For more info... List location or contact for specification (or other related documents) THE FIX cont.

 Schaffner EMC ECOsine filter injects up to 300 amps of current  Compensates for harmonic currents  Compensates for reactive current  Can choose percentage of overall current dedicated to each harmonic  Two installed with 5% reactor ahead of each drive

 Before at 1850 amps of load:  Voltage THD 12.6% Current THD 23%  After at 2150 amps of load:  Voltage THD 5.5% Current THD 8.8%  After at 1320 amps of load:  Voltage THD 7% Current THD 5%  Adjacent Transformer Voltage THD 3.5%

Total Load 1800 amps HarmonicAmpsAmps with Filter 5 th th th th 6059 THD-V from 12.2% to 8.1%

2300A rms 5.9% THD-V 9.6% THD-A 8.4% THD-V 24.2% THD-A Neutral volts and amps Testing, filter on and off  Filter off

Waveforms showing commutation notching 6.9% THD-voltage 5% THD-current 1300 amps

UG Residence, one mile from pipe plant, plant running at 7% THD-V 3.5% THD-V 3 rd, 7 th, and 5th V I

 Not below 5% THD on voltage at meter  Filtering has done all it can do  Work with drive manufacturer to control commutation notching using saturating reactors on SCRs to speed gate closing

 Should have required drive manufacturer to meet IEEE 519 standard  Get a written proposal from drive manufacturer on how they will meet the standard  Use delta primary transformer to trap Triplen harmonics, this is 2.7% of total  Recommend active filtering  Recommend 12 pulse drives or technology to reduce commutation notching IN RETROSPECT