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1.3 Power Quality: All Power Quality Issues

 All the Power Quality Issues are comprised into following categories:

  1. Transient
  2. Long Duration Voltage Variation
  3. Short Duration Voltage Variation
  4. Voltage Imbalance
  5. Waveform Distortion
  6. Voltage Fluctuation
  7. Power Frequency Variation

1. Transients:

  • The term transient has long been used in the analysis of power system variation to demote an uneven, that is undesirable and momentary in nature motion of a damp oscillatory transient due to an RLC network is probably what most power engineers think of when they hear the work transient.

                                                    OR

  • Transients are power quality disturbances that involve destructive high magnitudes of current and voltage or even both.

Types of Transients:


a. Impulsive Transient:

Impulsive Transient


  • An impulsive transient is a sudden, non–power frequency change in the steady-state condition of voltage, current, or both and is unidirectional in polarity (primarily either positive or negative value).
  • It is mainly caused by lightning.


b. Oscillatory Transient:

Oscillatory Transient


  • Oscillatory Transient is described as a sudden, non–power frequency change in the steady-state condition of voltage, current, or both and is bidirectional in polarity (having both positive and negative polarity values).
  • They are mostly caused by frequent switching of capacitor banks.


2. Long Duration Voltage Variation:

  • When the rms value of voltage deviates for duration more than 1 minute, it is termed as long duration voltage variation.
  • It is caused due to Switching Off large load, energizing a capacitor bank or incorrect transformer tap setting.
  • Under Voltage, Over Voltage and Sustained Interruptions are the effect of these causes.

a. Under Voltage: 

  • It is decrease in the rms ac voltage, less than 90% at the power frequency duration longer than 1minute, which is caused by a Load Switching ON OR a capacitor Bank Switching Off over loaded switching.


b. Over Voltage: 

  • It is an increase in the rms ac voltage, greater than 110% at the power frequency duration longer than 1minute, which is caused by Switching Off Large load OR energizing capacitor Bank OR incorrect tap setting on Transformer.


c. Sustained Interruption:

  • When the supply voltage has been zero for a period of time more than 1-minute.
  • The long duration voltage variation is considered a sustained Interruption Voltage interruption longer that 1minute are often permanent and require human intervention to repair the system for restoration.
  • The term sustained Interruption refers to specific power system phenomena and in general has no relation to the usage of the term outage.

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