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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.
| Device | DC subway substation, electrochemical, etc. | Alternating-current electric railway vehicle | General-purpose inverters, elevators, refrigeration and air conditioners, etc. |
| UPS, Power supply for communication, distributed device for grid connection | Reactive power compensator (SVC), lighting device, heater | Electric motors (for rolling, cement, AC railway vehicles) | |
| For steelmaking | etc. (LED, induction, Electric vehicle charging device) | ||
| Types of circuits | 3 phase bridge | Single phase bridge | 3 phase/Single phase bridge |
| 3 phase/Single phase bridge (PWM control) | rnating current power controller | Cyclone 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 term | Resonance caused by voltage and current | Power factor reduction | Decrease in power generation |
| Neutral over current | Overcurrent of cables, transformers, generators, power capacitors | Unpredictable shutdown of the protection system | |
| Malfunction of precision control device | Increased facility noise and vibration | Current and voltage distortion | |
| Induced disturbance of telephone and communication lines | Overdesign (wires, transformers, power capacitors) | ||
| Mid · Long-term | Reduce motor and transformer life | Acceleration of deterioration of dielectric materials and insulation materials | Rising economic costs |
| Transformer | Power quality technology | Overheating, increased noise | Capacity reduction |
| Insulation breakdown | |||
| Wires and conductors | Overheating | Corona outbreak | Neutral over current |
| Capacity reduction | Insulation breakdown | Skin Effect | |
| Rotating machine | Overheating | Decrease in efficiency | Shortened device lifespan |
| Tog uneven | Vibrational torque | ||
| Capacitor for power | Overheating | Over-resonance | Overcurrent |
| Overvoltage insulation explosion | |||
| Overcurrent | Abrupt stop | Inaccurate measurement | Non-integer harmonic generation |
| Malfunction | Frequent part failure | ||
| Circuit breaker · Other | Ampacity reduction | Noise, Vibration | Acceleration of life deterioration |
| Drop in power factor | Decreased fuse capacity | Signal, 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)
· Criteria : Building electrical equipment design standards (KDS 31 60 10 : 2019)
· Review : Public announcement
· Notification : October 11, 2019 (molit Notice No. 2019-549)
| Field | Before mendment | After mendment |
|---|---|---|
| Incoming transfer facility | Transformers 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)
· 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 | ||||
| 3 | 2.30 | 3.45 | 30 X Power factor | 2.30 |
| 5 | 1.14 | 1.71 | 10 | 1.14 |
| 7 | 0.77 | 1.155 | 7 | 0.77 |
| 9 | 0.40 | 0.60 | 5 | 0.40 |
| 11 | 0.33 | 0.495 | 3 | 0.33 |
| 13 | 0.21 | 0.315 | 3 | 0.21 |
| 15 ≤ n ≤ 39 | 0.15 × 15/n | 0.225 × 15/n | 3 | 0.15 × 15/n |
| Even Harmonics | ||||
| 2 | 1.08 | 1.62 | 2 | - |
| 4 | 0.43 | 0.645 | - | - |
| 6 | 0.30 | 0.45 | - | - |
| 8 ≤ n ≤ 40 | 0.23 × 8/n | 0.345 × 8/n | - | - |
IEEE Std. 519 Standard for Harmonic
Table 1—Voltage distortion limits
| Bus voltage V at PCC | Individual harmonic (%) | Total harmonic distortion THD (%) |
|---|---|---|
| V ≤ 1.0 kV | 5.0 | 8.0 |
| 1 kV ＜ V ≤ 69 kV | 3.0 | 5.0 |
| 69 kV ＜ V ≤ 161 kV | 1.5 | 2.5 |
| 161 kV ＜ V | 1.0 | 1.5a |
※ 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 / 𝐼𝐿 | 3 ≤ ℎ＜11 | 11 ≤ ℎ＜17 | 17 ≤ ℎ＜23 | 23 ≤ ℎ＜35 | 35 ≤ ℎ ≤ 50 | TDD |
| ＜20c | 4.0 | 2.0 | 1.5 | 0.6 | 0.3 | 5.0 |
| 20＜50 | 7.0 | 3.5 | 2.5 | 1.0 | 0.5 | 8.0 |
| 50＜100 | 10.0 | 4.5 | 4.0 | 1.5 | 0.7 | 12.0 |
| 100＜1000 | 12.0 | 5.5 | 5.0 | 2.0 | 1.0 | 15.0 |
| ＞1000 | 15.0 | 7.0 | 6.0 | 2.5 | 1.4 | 20.0 |
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
where
𝐼𝑆𝐶 = maximum short-circuit current at PCC
𝐼𝐿 = maximiun demand load current (fundamental frequency component) at the PCC under normal load operating conditions
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
where
𝐼𝑆𝐶 = maximum short-circuit current at PCC
𝐼𝐿 = maximiun demand load current (fundamental frequency component) at the PCC under normal load operating conditions