METREL MI 3399, Инструкция с упражнениями

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Power and Voltage Quality Trainer AD 2
– MI 3399
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time (s)
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Figure 2-4: voltage fluctuation
Origin
Origins of voltage fluctuation are arc furnaces, welding machines and similar heavy
loads that consume greatly varying currents. Flicker can arise in the presence of
interharmonics with a frequency close to the base frequency or harmonic.
Impact to customers’ equipment
Magnitude of voltage fluctuation is usually below 3% of supply voltage and does not
have any noticeable influence to equipment. Flickering caused by voltage fluctuation
of just 0.2% with frequency of 9 Hz is considered as annoying.
2.11 Inrush
Current needed to start a motor can be 10 to 15 times the normal operating current.
This initial surge of current can cause dips in voltage and can be hard to analyse with
normal test instruments, for this reason an analyser with a fast logging function is
required.
2.12 Transient overvoltages
Transient is a term for short, highly damped momentary voltage or current
disturbance.
There are two types of transient overvoltages:

impulsive overvoltage

oscillatory overvoltage
Origin
Impulsive transient overvoltages
are unidirectional disturbances caused by lighting
and have a high magnitude but low energy. Frequency range is above 5kHz with
duration 30-200 microseconds.
Oscillatory transient overvoltages are caused by switching, Ferro resonance or can
arise as a system response to an impulsive overvoltage. Switching overvoltages have