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What are Overvoltages and its Causes in the Electrical Power Systems

In today’s article, we are getting to realize the overvoltages and its causes. There are numerous sources concerned with overvoltages like generators, transformers, and transmission lines. These overvoltages are often caused by lightning, a gap of circuit breakers, the grounding of a conductor, etc. These overvoltages might not be huge in magnitude but its effect can interrupt the protection system or devices connected within the system. Engineers always trying to limit and control the effect of overvoltages on operating sorts of equipment. Now we try to seek out out the most causes of overvoltages. How they will be generated and may affect the OS.

“A sudden rise in voltage for a really short duration on the facility system is understood as overvoltages or transients”

these transients or surges are of temporary nature and short duration (a few hundred µs) but they cause overvoltages on the facility system. They originate from switching and from other causes but the foremost important transients are those which are generated from the natural lightning strokes on transmission lines. When lightning strikes a line, the surge rushes along the road and a flood of giant voltages rushes into the system which is capable of damaging every single protective and electrical appliances.

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The above figure shows the lightning surge waveform. The voltage build-up along the x-axis and therefore the time along the y-axis. It seems quite clear that the surge generates a really steep forward wave during a very short time which is named wavefront. This buildup is extremely rapid, being of the order of 1-5µs. While the rear side called wave tail passes slowly compare to the wavefront. It takes a touch longer than a steep wave.

Causes of overvoltages

The overvoltages on the facility system are often broadly divided into two main categories.

A) Internal causes B) External causes

Internal causes don’t produce surges of huge magnitude. Experience shows that internal surge hardly increases the system voltage to twice of the traditional voltage.

Switching surges: the primary sort of internal overvoltage is switching surges. The overvoltages produced on the facility system thanks to switching operations are referred to as switching surges.1) It is often caused when an unloaded line is connected to the voltage source. 2) Also, it is often caused when a loaded line is connected. Suppose a loaded is suddenly interrupted. this may find out a voltage of transients.3) the foremost important explanation for overvoltages in switching surges is current chopping. Current chopping leads to the assembly of high voltage transients across the contacts of the air blast breaker.
Insulation failure: the foremost important case of insulation failure during a power grid is that the grounding of the conductor. Suppose a conductor grounds in the middle. It produces negative voltages which follow each side.

Arcing ground: The phenomenon of an intermittent arc happening within the line to the bottom fault of the three-phase system with consequent production of transients is understood as arching ground. These transients are cumulative; they will be very dangerous and may cause some serious damage to the facility system by causing insulation failure. Arcing ground is often prevented by earthing the neutral.
Resonance: Resonance is that situation within the power grid when the inductive reactance of the circuit becomes adequate to the capacitive reactance. Under resonance, the impedance and resistance become equal and therefore the power factor is unity. Resonance causes high voltages within the transmission lines.

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