Appx.5
Explanation of Power Quality Parameters and Events
Voltage dip (Sag)
Waveform and event
Most dips are caused by natural
phenomena such as lighting.
Short-term voltage drops occur under the
following conditions:
• An equipment fault is detected and the
power supply is switched off, due to the
occurrence of a power system ground
fault or short-circuit
• When there is a inrush current with a
large load, such as when a motor starts.
Primary fault Power supply voltage dips may cause the following events:
• Equipment stops operating or is reset
• Lamps turn off
• Speed uctuation or stopping of motors
• Synchronized motors and generators lose synchronization
Event to be detected Dip
Interruption
Waveform and event
Interruptions are caused by momentary,
short/long-term power supply outages,
mainly under the following circumstances:
• Fault at the power company (interruption
of power due to lightning strikes, etc.)
• Circuit breaker tripping due to power
supply short-circuits
Primary fault Interruptions may cause the device to stop operating or to reset.
Event to be detected Interruption
Frequency uctuations
Waveform and event
Occurs due to line separation caused by
changes in the supply/demand balance
of active power, the shutdown of a high-
capacity generator, or circuit issues.
Primary fault Changes in the speed of synchronized motors may cause product defects.
Event to be detected Frequency: 200 ms (Freq), frequency 1 wave (Freq_wav)
Measurement Items IEC61000-4-30 Average frequency of frequencies obtained for 10-s periods (Freq10s)
Harmonics
Waveform and event
Harmonics are caused by distortions of
the voltage and current waveforms when a
device’s power supply uses semiconductor
control devices.
Primary fault Larger harmonic components may cause any of the following major failures:
• Abnormal heat or increased noise of motors and transformers
• Fire of reactor connected to phase advance capacitor
Event that may be
detected
Total harmonic distortion (THD) (voltage)
Measurement Items Harmonic voltage, harmonic current, harmonic power
10
9
8
7
6
5
4
3
2
1
Appx. Ind.
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