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 19 - 21 September 2011, Chiang Mai, Thailand

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 14,089.58 MW of peak load 89,602.24 millions of KWhr of sales electricity ยังไม่ Update Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

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 19 - 21 September 2011, Chiang Mai, Thailand

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 19 - 21 September 2011, Chiang Mai, Thailand

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

Parallel Resonance (cont’) At resonance point : Current Amplification Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

Easy evaluation of resonance H5 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 19 - 21 September 2011, Chiang Mai, Thailand

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 19 - 21 September 2011, Chiang Mai, Thailand

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

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

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 1036-1992. Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

Capacitor Limitation IEEE Std 1036-1992 indicates that the capacitor can be applied continuously within the following limitations, including harmonic components: a)       180% of rated rms current b) 120% of rated peak voltage c) 110% of rated rms voltage d) 135% of rated reactive power Provincial Electricity Authority, Thailand

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

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

Single line diagram of system Is Measuring Point Ic Provincial Electricity Authority, Thailand Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand 15

Measurement Location Ic Is Is Ic Provincial Electricity Authority, Thailand

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 1000.20 20.00 0.15996792 0.008268257 12.68 2 707.25 14.14 0.1131144 0.008289018 6.34 3 577.47 11.55 0.09235752 0.00830988 4.23 4 500.10 10.00 0.07998396 0.008330845 3.17 5 447.30 8.95 0.07153983 0.008351911 2.54 6 408.33 8.17 0.06530663 0.008373081 2.11 7 378.04 7.56 0.06046219 0.008394355 1.81 8 353.62 7.07 0.0565572 0.008415734 1.59 Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

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 19 - 21 September 2011, Chiang Mai, Thailand

Harmonic Assessment with Standard Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

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

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

Magnified Current Ic Is Vs Vc Provincial Electricity Authority, Thailand

Result : VTHD (Capacitor) THD Fund Normalized Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

Result : VTHD (System/Transformer) THD Fund Normalized Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

Result : ITHD (Capacitor) THD Fund Normalized Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

Result : ITHD (System/Transformer) THD Fund Normalized Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

Capacitor Switching Switching of Capacitor (Switch off for 1 step) Ic Is Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

Capacitor Switching Switching of Capacitor (Switch in for 1 step: step 4 to 5) Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

Capacitor Switching Vpeak of 230V. System = 325.26 V. Vpeak = 455.2 V. equal to 1.4 Vpk (exceed to the limit of rated Vpk, IEEE1026-1992 : 1.2 Vpk) Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

All of 8 Capacitors Steps are switched into the system. Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

Harmonic Assessment with Standard Provincial Electricity Authority, Thailand 19 - 21 September 2011, Chiang Mai, Thailand

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 19 - 21 September 2011, Chiang Mai, Thailand

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 19 - 21 September 2011, Chiang Mai, Thailand