Increase in


Types of damage
caused by harmonics


Strengthen standards
for harmonics

Increase in harmonics

Harmonic generation is increasing as rectifiers, inverters, LEDs, landscape lighting, PCs, motors, and automation facilities with high harmonics in the power system increase. These harmonics cause damage in various forms, including increased loss of electrical equipment, reduced efficiency, malfunction, shorter life expectancy, and heat generation.

DeviceDC subway substation, electrochemical, etc.Alternating-current electric railway vehicleGeneral-purpose inverters, elevators, refrigeration and air conditioners, etc.
UPS, Power supply for communication, distributed device for grid connectionReactive power compensator (SVC), lighting device, heaterElectric motors (for rolling, cement, AC railway vehicles)
For steelmakingetc. (LED, induction, Electric vehicle charging device)
Types of circuits3 phase bridgeSingle phase bridge3 phase/Single phase bridge
3 phase/Single phase bridge (PWM control)rnating current power controllerCyclone converter
Alternating current arc furnace

Types of damage caused by harmonics

Harmonics cause various forms of damage to the power system and various electrical installations, such as increased losses, increased temperature, and breakdown of insulation.

Immediately · Short termResonance caused by voltage and currentPower factor reductionDecrease in power generation
Neutral over currentOvercurrent of cables, transformers, generators, power capacitorsUnpredictable shutdown of the protection system
Malfunction of precision control deviceIncreased facility noise and vibrationCurrent and voltage distortion
Induced disturbance of telephone and communication linesOverdesign (wires, transformers, power capacitors)
Mid · Long-termReduce motor and transformer lifeAcceleration of deterioration of dielectric materials and insulation materialsRising economic costs
TransformerPower quality technologyOverheating, increased noiseCapacity reduction
Insulation breakdown
Wires and conductorsOverheatingCorona outbreakNeutral over current
Capacity reductionInsulation breakdownSkin Effect
Rotating machineOverheatingDecrease in efficiencyShortened device lifespan
Tog unevenVibrational torque
Capacitor for powerOverheatingOver-resonanceOvercurrent
Overvoltage insulation explosion
OvercurrentAbrupt stopInaccurate measurementNon-integer harmonic generation
MalfunctionFrequent part failure
Circuit breaker · OtherAmpacity reductionNoise, VibrationAcceleration of life deterioration
Drop in power factorDecreased fuse capacitySignal, communication failure

Effects on Transformers

Increased Iron loss Hysteresis loss and eddy current loss increase due to harmonic current

Iron loss increase rate

Copper loss increase Skin Effect-Induced Copper Loss Increase

Copper loss increase rate

Capacity reduction 64% reduction in output due to reduced capacity

Three-phase load

Winding temperature increase The winding temperature increased by about 39% compared to the temperature rise due to the fundamental wave current

Transformer winding temperature rise

Strengthen Standards for Harmonics

To prevent electrical damage from harmonics, harmonics standards are being enforced globally.

Korean Standards

MOLIT - Incoming transfer facility design criteria

Revision of building electrical equipment design standards

· Legislation : Article 44 of the Construction Technology Promotion Act and Article 65 of the Enforcement Decree of the same Act
· Criteria : Building electrical equipment design standards (KDS 31 60 10 : 2019)
· Review : Public announcement
· Notification : October 11, 2019 (molit Notice No. 2019-549)
FieldBefore mendmentAfter mendment
Incoming transfer facilityTransformers are selected in consideration of the place of use, economic feasibility, and electrical characteristics, but when installed inside a building, a transformer with more than standard consumption efficiency should be used.When selecting a transformer, the place of use, load characteristics, efficiency, safety, etc. must be considered, and a standard efficiency transformer is used. However, in the case of facilities with a high harmonic generation load ratio, a transformer with harmonic attenuation function or a transformer with equivalent or better performance can be used to improve power quality and reduce power loss.

KEPCO - Regulations on the use of electric facilities for transmission and distribution

KEPCO harmonic regulation

· Regulation : Regulations on the use of electric facilities for transmission and distribution (July 01, 2019) and enforcement rules (December 16, 2019)
· Content : Harmonics (THD) acceptance criteria and protection device installation
· Subject : Users of electric furnaces and electric railways (mandatory application)

International Standards

IEC 61000 Harmonic Standard

Table. Allowable current ampacity by equipment

Harmonics (n)Equipment Classification
Balanced 3-phase equipment, Tools, sound equipment, Household appliances (A)Portable device, Arc welding machine (A)Lighting equipment (A)PC, Monitor, TV, Refrigerator, Freezer (Under 600W) (A)
Odd Harmonics
X Power factor
15 ≤ n ≤ 390.15 × 15/n0.225 × 15/n30.15 × 15/n
Even Harmonics
8 ≤ n ≤ 400.23 × 8/n0.345 × 8/n--

IEEE Std. 519 Standard for Harmonic

Table 1—Voltage distortion limits

Bus voltage V at PCCIndividual harmonic (%)Total harmonic distortion THD (%)
V 1.0 kV5.08.0
1 kV < V ≤ 69 kV3.05.0
69 kV < V ≤ 161 kV1.52.5
161 kV < V1.01.5a
aHigh-voltage systems can have up to 2.0% THD where the cause is an HVDC terminal whose effects will have attenuated at points in the network where future users may be connected.

Table 2—Current distortion limits for systems rated 120 V through 69 kV

Maximum harmonic current distortion in percent of 𝐼𝐿
Individual harmonic order (odd harmonics)a,b
𝐼𝑆𝐶 / 𝐼𝐿3 ≤ <1111 ≤ <1717 ≤ <2323 ≤ <3535 ≤ ≤ 50TDD
aEven harmonics are limited to 25% of the odd harmonic limits above.
bCurrent distortions that result in a dc offset, e.g., half-wave converters, are not allowed.
CAll power generation equipment is limited to these values of current distortion, regardless of actual 𝐼𝑆𝐶 / 𝐼𝐿
𝐼𝑆𝐶 = maximum short-circuit current at PCC
𝐼𝐿 = maximiun demand load current (fundamental frequency component) at the PCC under normal load operating conditions
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