harmonics problems in distribution systems case study aep texas central company scott lee,...
TRANSCRIPT
Harmonics Problems in Distribution SystemsCase StudyAEP Texas Central CompanyScott 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 www.powermonitors.com, iVs-3 and Eagle 440
MEASUREMENTS
3rd12.4% THD-Voltage
7th11th 13th
5th
23.4% THD-Amps
2000 kVA Padmount6-Pulse Drive
5th7th
11th
Unfiltered, running at 1550kVA
12.4% THD-V23.4% 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 ampsHarmonic Amps Amps with Filter
5th 427 497th 225 6011th 113 5213th 60 59
THD-V from 12.2% to 8.1%
2300A rms5.9% THD-V9.6% 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-voltage5% THD-current1300 amps
UG Residence, one mile from pipe plant, plant running at 7% THD-V
3.5% THD-V3rd, 7th, and 5thV
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