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Home / Technical Articles / Detailed Overview of Power System Disturbances (Causes and Impacts)

Power Quality problems

To make the study of Power Quality problems useful, the various types of disturbances need to be classified by magnitude and duration.

Detailed Overview of Power System Disturbances (Causes and Impacts)
Detailed Overview of Power System Disturbances – Causes and Impacts (on photo: Fluke Three-Phase Power Quality and Energy Analyzer; credit: cetm.com.sg)

This is especially important for manufacturers and users of equipment that may be at risk. Manufacturers need to know what is expected of their equipment, and users, through monitoring, can determine if an equipment malfunction is due to a disturbance or problems within the equipment itself.

Not surprisingly, standards have been introduced to cover this field. They define the types and sizes of disturbance, and the tolerance of various types of equipment to the possible disturbances that may be encountered. The principal standards in this field are IEC 61000, EN50160, and IEEE 1159.

Standards are essential for manufacturers and users alike, to define what is reasonable in terms of disturbances that might occur and what equipment should withstand.

Table 1 provides a broad classification of the disturbances that may occur on a power system, some typical causes of them and the potential impact on equipment. From this Table, it will be evident that the electricity supply waveform, often thought of as composed of pure sinusoidal quantities, can suffer a wide variety of disturbances.

Table 1 – Power Quality issues

Category Causes Impacts
Voltage dips
  • Local and remote faults
  • Inductive loading
  • Switch on of large loads
  • Tripping of sensitive equipment
  • Resetting of control system
  • Motor stalling/tripping
Voltage surges
  • Capacitor switching
  • Switch off of large loads
  • Phase faults
  • Tripping of sensitive equipment
  • Damage to insulation and windings
  • Damage to power supplies for electronic equipment
Overvoltage
  • Load switching
  • Capacitor switching
  • System voltage regulation
  • Problems with equipment that requires constant steady-state voltage
Harmonics
  • Industrial furnaces
  • Non-linear loads
  • Transformers/generators
  • Rectifier equipment
  • Mal-operation of sensitive equipment and relays
  • Capacitor fuse or capacitor failures
  • Telephone interference
Power frequency
variation
  • Loss of generation
  • Extreme loading conditions
  • Negligible most of time
  • Motors run slower
  • De-tuning of harmonic filters
Voltage fluctuation
  • AC motor drives
  • Inter-harmonic current components
  • Welding and arc furnaces
  • Flicker in Fluorescent lamps
  • Flicker in Incandescent lamps
Rapid voltage change
  • Motor starting
  • Transformer tap changing
  • Light flicker
  • Tripping of equipment
Voltage
imbalance
  • Unbalanced loads
  • Unbalanced impedances
  • Overheating in motors/generators
  • Interruption of 3-phase operation
Short and long voltage
interruptions
  • Power system faults
  • Equipment failures
  • Control malfunctions
  • CB tripping
  • Loss of supply to customer equipment
  • Computer shutdowns
  • Motor tripping
Undervoltage
  • Heavy network loading
  • Loss of generation
  • Poor power factor
  • Lack of var support
  • All equipment without backup supply facilities
Transients
  • Lightning
  • Capacitive switching
  • Non –linear switching loads
  • System voltage regulation
  • Control system resetting
  • Damage to sensitive electronic components
  • Damage to insulation

Table 2 lists the limits given in Standard EN 50160 and notes where other standards have similar limits.

Table 2 – Power system disturbance classification to EN 50160

Type of disturbance Voltage level Limits from EN50160 Measurement period Typical duration Other applicable standards
Voltage Variation 230V +/- 10% 95% of 1 week
Voltage Dips 230V 10-1000/year 10ms –1sec IEEE 1159
Rapid voltage changes 230V 5% to 10% Several per day Short duration
1kV-35kV <6% Per day Short duration IEEE 1159
Short Interruptions 230V >99% 20-200 per day Up to 3 mins EN61000-4-11
Long Interruptions 230V >99% 10-50 per day >3 mins IEEE 1159
Transient Overvoltage 230V Generally <6kV Not specified <1ms IEEE 1159
Voltage unbalance 230V
Undervoltage 230V <-10% Not specified >1 min IEEE 1159
Voltage surge 230V <150% of nominal voltage Not specified >200ms IEEE 1159
Voltage fluctuations 230V 3% 10 min <200ms IEC 60827
Frequency variation +/- 1% 95% of 1 week Not specified Measured over 10s
+4%, -6% 100% of 1 week Not specified Measured over 10s
Harmonics THD<8% up to 40th 95% of 1 week Not specified

For computer equipment, a common standard that manufacturers use is the ITI (Information Technology Industry) curve, illustrated in Figure 1.

ITI (Information Technology Industry) curve for equipment susceptibility
Figure 1 – ITI (Information Technology Industry) curve for equipment susceptibility

Voltage disturbances that lie in the area indicated as ‘safe’ should not cause a malfunction in any way. However, some disturbances at LV levels that lie within the boundaries defined by EN50160 might cause a malfunction because they do not lie in the safe area of the ITI curve.

It may be necessary to check carefully which standards are applicable when considering equipment susceptibility.

What is Power Quality and Why It’s Important (Webinar)


Reference // Network Protection and automation Guide – Areva

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.

4 Comments


  1. vivek pandey
    Sep 05, 2015

    Good article


  2. nitin
    May 04, 2015

    Power quality ..need to create more awareness..in third world countries…


  3. Mohamed H. shwehdi
    Apr 18, 2015

    Need such power quality review and u tube for demonstrating to electrical engineering studentd


  4. SHUBHAJIT MANDAL
    Apr 18, 2015

    need more downloads

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