Power System Internal Overvoltage and External Voltage
by Starlight Generator dieselgeneratortechOvervoltage refers to
the phenomenon that the rms value of the AC voltage rises at the power
frequency, exceeding 10% of the rated value, and the long-term voltage fluctuation
phenomenon lasts longer than 1 minute; the occurrence of overvoltage is usually
the result of load switching. Occurs when the inductive or capacitive load is
turned on or off during normal use.
The abnormal voltage
rise over the working voltage in the power system under certain conditions
belongs to a kind of electromagnetic disturbance phenomenon in the power
system. The insulation of electrical equipment is tolerant to the operating
voltage for a long time, and must be able to withstand a certain range of
overvoltage, so as to ensure the safe and reliable operation of the power
system.
Overvoltage is divided
into external overvoltage and internal overvoltage.
External overvoltage is
also called lightning overvoltage and atmospheric overvoltage. Caused by the
discharge of thunderclouds in the atmosphere to the ground.
Internal overvoltage: An
overvoltage caused by a change in the internal operating mode of the power
system. There are power frequency overvoltage, operating overvoltage and
resonant overvoltage.
1.
Atmospheric overvoltage
Caused by direct
lightning strike, it is characterized by short duration and strong impact,
which is directly related to the intensity of lightning stroke, and has nothing
to do with the voltage level of the equipment. Therefore, the insulation level
of systems below 220KV is often determined by preventing atmospheric
overvoltage.
2.
Power frequency overvoltage
It is caused by the
capacitive effect of the long lines and the sudden change of the operation mode
of the power grid. It is characterized by long duration, low overvoltage
multiple, and generally not dangerous to the equipment insulation, but it plays
an important role in determining the insulation level of ultra-high voltage and
long-distance transmission. Common power frequency overvoltage can be divided
into the following types:
a. No-load long-line
capacitance effect
b. Asymmetric short
circuit grounding
c. Load rejection
overvoltage
3.
Operating overvoltage
The voltage caused by
line fault, no-load line switching, isolating switch operating no-load bus,
operating no-load transformer or other causes in the system, can be prevented
by high-performance arrester.
Operating overvoltage
occurs during system operation and fault, which is characterized by randomness.
In the most unfavorable case, the overvoltage multiple is high. The insulation
level of 330kv and above ultra-high voltage system depends on the operating
overvoltage.
4.
Resonant overvoltage
It is the overvoltage
caused by the resonance of power supply, capacitance and other energy storage
components with power supply frequency in some wiring modes. The generation is
related to the operation state, parameters, or magnetic circuit with iron
equipment. It is characterized by high overvoltage multiple and long duration.
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Created on Nov 8th 2019 00:32. Viewed 295 times.