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Mai Da Insulation Coordination a Tattalin Kula ya kawo a tattalin kula don haɗa insulation levels daban-daban na binciken da ke tattalin kula mai suna electrical power system, ciki har da masana tattalin kula, haka don haka, idan failure of insulator yake faru, zai yi ne a wurin da za su iya aiki da ita, yana da muhimmanci a lura da wani abu a kan tattalin kula, da kuma yana da muhimmanci a lura da wani abu a kan tattalin kula, da kuma yana da muhimmanci a lura da wani abu a kan tattalin kula, da kuma yana da muhimmanci a lura da wani abu a kan tattalin kula.
Idan wani voltage mai yawa ta fitarwa a tattalin kula, akwai muhimmanci a yi failure of insulation. Muhimmancin failure of insulation, yana da muhimmanci a wurin da ke gaba da voltage mai yawa. A tattalin kula da masana tattalin kula, insulation an bayarwa zuwa duk binciken da abubuwan.

Insulators a wurare masu inganci a lura da sabon karfi, musamman har zuwa wurare masu karfi. Insulation a wurare ba a lura da sabon karfi ba, kuma sabon karfi ko lura zai iya kasance mafi girma da kuma zai iya buƙata tattalin kula. Saboda haka, yana da muhimmanci a yi failure of insulator, faɗa da insulator mai lura da sabon karfi. Dalilin mai yawa na insulation coordination shine koyar da cost da disturbance mai yawa daga insulation failure zuwa level mai yawa a tattalin kula da tattalin kula. A insulation coordination method, insulation of the various parts of the system must be so graded that flash over if occurs it must be at intended points.
Don samun fahimta da insulation coordination ba a yi, muna samun fahimta da wasu terminologies basic of the electrical power system. Bambanta.

Nominal System Voltage

Nominal System Voltage shine phase to phase voltage na tattalin kula da ke amfani da shi. Misali 11 KV, 33 KV, 132 KV, 220 KV, 400 KV systems.

Maximum System Voltage

Maximum System Voltage shine maximum allowable power frequency voltage wanda yake faru, domin a yi waɗannan voltage mai yawa a tattalin kula. Yana da shi a matsayin phase to phase manner.
List of different nominal system voltage and their corresponding maximum system voltage is given below for reference,

NB – It is observed from above table that generally maximum system voltage is 110 % of corresponding nominal system voltage up to voltage level of 220 KV, and for 400 KV and above it is 105 %.

Factor of Earthing

This is the ratio of the highest rms phase to earth power frequency voltage on a sound phase during an earth fault to the rms phase to phase power frequency voltage which would be obtained at the selected location without the fault.
This ratio characterizes, in general terms, the earthing conditions of a system as viewed from the selected fault location.

Effectively Earthed System

A system is said to be effectively earthed if the factor of earthing does not exceed 80 % and non-effectively earthed if it does.
Factor of earthing is 100 % for an isolated neutral system, while it is 57.7 % (1/√3 = 0.577) for solidly earthed system.

Insulation Level

Every electrical equipment has to undergo different abnormal transient over voltage situation in different times during its total service life period. The equipment may have to withstand lightning impulses, switching impulses and/or short duration power frequency over voltages. Depending upon the maximum level of impulse voltages and short duration power frequency over voltages that one power system component can withstand, the insulation level of high voltage power system is determined.
During determining the insulation level of the system rated less than 300 KV, the lightning impulse withstand voltage and short duration power frequency withstand voltage are considered. For equipment rated more or equal 300 KV, switching impulse withstand voltage and short duration power frequency withstand voltage are considered.

Lightning Impulse Voltage

The system disturbances occur due to natural lightning, can be represented by three different basic wave shapes. If a lightning impulse voltage travels some distance along the transmission line before it reaches to a insulator its wave shaped approaches to full wave, and this wave is referred as 1.2/50 wave. If during travelling, the lightning disturbance wave causes flash over across an insulator the shape of the wave becomes chopped wave. If a lightning stroke hits directly on the insulator then the lightning impulse voltage may rise steep until it is relieved by flash over, causing sudden, very steep collapse in voltage. These three waves are quite different in duration and in shapes.

Switching Impulse

During switching operation there may be uni-polar voltage appears in the system. The wave form of which may be periodically damped or oscillating one. Switching impulse wave form has steep front and long damped oscillating tale.

Short Duration Power Frequency Withstand Voltage

Short duration power frequency withstand voltage is the prescribed rms value of sinusoidal power frequency voltage that the electrical equipment shall withstand for a specific period of time normally 60 seconds.

Protection Level Voltage of Protective Device

Over voltage protective device like surge arrestors or lightning arrestors are designed to withstand a certain level of transient over voltage beyond which the devices drain the surge energy to the ground and therefore maintain the level of transient over voltage up to a specific level. Thus transient over voltage can not exceed that level. The protection level of over voltage protective device is the highest peak voltage value which should not be exceeded at the terminals of over voltage protective device when switching impulses and lightening impulses are applied.

Now let us discuss the insulation coordination methods one by one-

Using Shield Wire or Earth Wire

Lightning surge in over head transmission line may be caused due to direct hits of lightening strokes. It can be protected by providing a shield wire or earth wire at a suitable height from the top conductor of transmission line. If the conducting shield wire is properly connected to transmission tower body and the tower is properly earthed then direct lightning strokes can be avoided from all the conductors come under the protective angle of earth wire. Over head earth wire or ground wire or shield wire is also used to over the electrical substation to protect different electrical equipment from lightning strokes.

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