1. PQSynergy TM 2011
Harmonic Assessment of PEA North1, Chiangmai’s Customers in North Industrial Estate
Chotepong Pongsriwat. M.Eng(EE) Chief of Power Quality Section
PEA (Chiang Mai, THAILAND)
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

2. Provincial Electricity Authority
PEA North Area 1, ChiangMai, Thailand
Distribution System: 22, 33 kV 289,328 cct-km
Transmission System: 115 kV 8,701 cct-km
99.98% of electrified villages
14.60 millions of customer
14, MW of peak load
89, millions of KWhr of sales electricity
ยังไม่ Update
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

3. Problems created by harmonics
Capacitor Problems
Due to its lower impedance, capacitors are even more susceptible to higher order harmonics. If not protected from harmonic stress, a capacitor may fail pretty soon.
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

4. When capacitor banks are installed for power factor improvement, the power system will exhibit one or more nature frequencies due to a RLC network system formed by the capacitor bank and the remaining power distribution system.
-If one of the harmonic currents produced by the non-linear load is close to one of the nature frequencies, resonance conditions will occur . a
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

5. Parallel Resonance Typical industrial circuit topology
Simplified Network
Harmonic Source
PCC
We used to have voltage sources. Harmonic generators are often current Sources
Provincial Electricity Authority, Thailand

6. Parallel Resonance (cont’)
At resonance point :
Current Amplification
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

7. Easy evaluation of resonanceH5 H7
14.2%
13%
* If the harmonic spectrum exhibits abnormal magnitudes, it is abad sign of harmonic resonance.
* Typically caused by interaction with Power Factor Correction capacitors.
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

8. Resonance Frequency :
At this frequency where the inductive and capacitive reactances are equal, harmonic resonance occurs and the total effective impedance can be very high (parallel resonance) or very low (series resonance) depends on the system configuration.
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

9. Capacitor Size (% of Transformer Size)
From Simulation
Resonance Point
Case 3:
Case 2:
Case 1:
Case
Capacitor Size (% of Transformer Size) 1
30% 2
20% 3
10%
In the past of Thailand, most medium/low voltage transformer in distribution system have delta/wye ground winding configuration installed with low voltage fixed capacitor which has defined the reactive power rating (kVAR) equal to 30% of transformer size (kVA) on secondary side of the transformer .
From this action, harmonic resonance from this capacitor can possibly occur.
Provincial Electricity Authority, Thailand

10. Current Amplification
From Simulation
Current Amplification
Case 2:
Case 3:
Case 1:
Case
Capacitor Size (% of Transformer Size) 1
30% 2
20% 3
10%
Provincial Electricity Authority, Thailand

11. Changing for 30% rule.
For a low voltage distribution system with capacitor installed, system response evaluation is useful method in order to get an approximation of the resonance frequency for the system.
During the resonance condition, some of the capacitor indices may over the limitation if the resonance frequency has the same value or very close to some harmonic order of harmonic current source.
Noticeably, capacitor installation at 30% of distribution transformer size may lead to have higher rms current in capacitor and exceed the maximum allowable limit recommended by IEEE Std
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

12. Capacitor Limitation
IEEE Std indicates that the capacitor can be applied continuously within the following limitations, including harmonic components:
a)       180% of rated rms current
b) % of rated peak voltage
c) % of rated rms voltage
d) % of rated reactive power
Provincial Electricity Authority, Thailand

13. Harmonic Standard IEEE Std 519-1992 Purpose: Ensure that the network
distortion does not exceed
permissible levels that
guarantee proper operation of
connected equipment.
Typical levels & tendencies:
-THDV <5% and limit for each harmonic component
-Derive current limits to obtain voltage limits
-Take into account high order harmonics
Provincial Electricity Authority, Thailand

14. Customer Story
Customer specializes in desiging, manufacturing and servicing high quality galleys, galley & cargo equipment
-Magnetic contactor of switching capacitor used to explode and they would like to check the quality of power system.
-They would like to eliminate harmonic, if it exists.
After checking, Major problems are
-Most loads are Electronic Ballast,
ASDs(Adjustable Speed Drives), including with anodizing & electropolishing process which run frequently during production process.
-The harmonics are higher than standard
-Capacitor Switching cause high current rate and current magnification
Provincial Electricity Authority, Thailand

15. Single line diagram of systemIs
Measuring Point Ic
Provincial Electricity Authority, Thailand
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand 15

16. Measurement Location Ic Is Is Ic
Provincial Electricity Authority, Thailand

17. Harmonic Resonance Point Assessment
Resonance frequency corresponding to the parameters of the system.
C Bank Step#
f(Hz)
Resonance Order
XL Resonance
XC Resonance
System Impedance at Fundamantal Frequency (Ohm)
System Impedance at Resonance Frequency (Ohm) 1
20.00
12.68 2
707.25
14.14
6.34 3
577.47
11.55
4.23 4
500.10
10.00
3.17 5
447.30
8.95
2.54 6
408.33
8.17
2.11 7
378.04
7.56
1.81 8
353.62
7.07
1.59
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

18. Frequency Scan Resonance at 7th Harmonic From 400V System
Capacitors & reactors(transformers) will always create resonance for some frequencies.
Resonance is impossible to avoid
Resonance is not a problem if not excited
From 400V System
System frequency response as capacitor size is varied in relation to transformer
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

19. Harmonic Assessment with Standard
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

20. Result from MDB Spectrum Current Waveform Voltage Waveform
Provincial Electricity Authority, Thailand

21. Result from Capacitor Spectrum Current Waveform Voltage Waveform
Provincial Electricity Authority, Thailand

22. Magnified Current Ic Is Vs Vc
Provincial Electricity Authority, Thailand

23. Result : VTHD (Capacitor)
THD Fund Normalized
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

24. Result : VTHD (System/Transformer)
THD Fund Normalized
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

25. Result : ITHD (Capacitor)
THD Fund Normalized
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

26. Result : ITHD (System/Transformer)
THD Fund Normalized
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

27. Capacitor Switching Switching of Capacitor (Switch off for 1 step) IcIs
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

28. Capacitor Switching
Switching of Capacitor (Switch in for 1 step: step 4 to 5)
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

29. Capacitor Switching Vpeak of 230V. System = 325.26 V.
Vpeak = V. equal to 1.4 Vpk
(exceed to the limit of rated Vpk, IEEE : 1.2 Vpk)
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

30. All of 8 Capacitors Steps are switched into the system.
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

31. Harmonic Assessment with Standard
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

32. Suggestions
Replace the original magnetic contactor to new type Magnetic contactor with insertion of damping resistor (With Unlimited Peak Current)
Detuned Filter Bank 8x50 kVar, 400V. 50Hz. 3 phase.
Reconsideration, for individual harmonic loads , when new harmonic loads are installed to the system because customer has oftenly add the load without concerning to harmonic.
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand

33. Thank you very much for your attentions.
Chotepong Pongsriwat
PQ Chief
Suwipa Kittithanapisan PQ Assistant Chief
Nat Songkram PQ Engineer
Narusorn Jan-ngern PQ Engineer
Satid Sriwong Technician
Chinaruk Kumprom Technician
Power Quality Team : Chiangmai THAILAND
Provincial Electricity Authority, Thailand
September 2011, Chiang Mai, Thailand