The present article of review of the
Norma IEC 60071-1 and IEC 60071-2, aims to be a tool for determining tensions
of coordination of overvoltages
Front fast using the method
Simplified described in Annex F of the
It is important to mention that the estimation of the ray current or the amplitude
wave’s front will be subject to a
wide range of variables as a ceramic level of the geographical place in the
which is located the project, resistivity of the
Land, Return Periods, Polarity
Positive or negative lightning, among others.
In turn, aspects such as the level
Ceráunico are variable statistics dependent on the precision of the monitoring plants
environmental and a good
Management of the data history.
Therefore, the norm raises a method
Simplified for the estimation of the
overvoltages due to lightning, which in
general terms assumes that the
Line entry bays and the main electrical equipment of the substation will be protected
by surge and lightning dischargers, properly selected low
The IEC 60099-4 standard.
Before performing the calculation of the amplitude of the representative voltage of the beam
Some hypotheses should be assumed as it should be:
The wave front slope is
cushioned mainly by the
Crown effect of the lines of
transmission, it is worth saying that for rays far from the substation
Amplitude of the wave will be less.
Investment primed do not occur in the tower closest to the
substation due to proximity
of the grounding of the substation.
Therefore, the norm raises the expression
(URP) Amplitude of the representative voltage of the ray (KV).
(A) Lightning behavior factor
Depending on the type of transmission line.
(UPL) Level of protection of the type wave
Lightning Ray (KV).
(L) Distance of separation from the lightning rod and the equipment to be protected (M).
(n) Minimum number of lines connected to the substation (n = 1 or n = 2).
(Lsp) Length of the average vain (M).
(Lt) Portion of the airline that has
A rate of defects equal to the rate
of established return (M).
(Rt) Return rate of overvoltage,
Established (1 / year).
(Rkm) Annual defects rate of the corresponding transmission line
to the first kilometer of line from
of the substation, (1/100 km / year).
Incorporating the expression F.18 It has:
Obtaining the supported tension of
Coordination for the ray impulse:
La Portion of the airline whose rate
Default is equal to the Acceptable Established failure rate.
Ra Acceptable fault rate of equipment.
Factor A for different types of lines
For electrical equipment the rate of
Acceptable failure RA due to overvoltages are in the range of 0.001 / year
up to 0.004 / year.For electric transmission lines Acceptable fault rates due to rays are
in the range of
0.1 / 100 km / year Up to 20/100 km / year.
In Bolivia it is a common practice assign for lines at 115 kV and 230 kV, two
(2) Net departures 100 km / year and for lines at 500 kV, one (1) Net departure 100
Km / year.
It is important to indicate that the protection characteristics of a lightning rod are
only valid in its location, in
that sense, the greater the separation distance between the lightning rod and
The protected team, the lower the effectiveness
protector for this team and could
Exceed the level of protection of the lightning rod.
Below is the elements that must be taken into account to determine the distance of
From the resort to the protected equipment (L).
It is pertinent to make a comparison
of the calculation of the protection distance
of a lightning lights made by the simplified method with respect to the method of
Simulation with software.
According to the graph, with the method
Simplified more values are obtained
conservatives, being able to overcome the bearable tension for atmospheric discharge at 40 meters from
Distance from the resort to the protected equipment.
However, the simulation method
By software usually requires introducing parameters such as amplitude
of the current of the atmospheric discharge that will be subject to studies
Middle environmental statisticians or reports of similar characteristics projects.It is common to find
atmospheric discharge current
of the order of 150 kA, 200 kA and 250 kA,
However, the choice of one or the other
value will depend on the information available for each project and finally
of the proper selection of the engineer
Electric design, since each parameter will offer different results.
Also, the behavior of the front
of wave once it is entered the
Substation will depend on aspects
such as the contact state of the
Power switches (open / open
Closed), the capacitance of electrical equipment, the type of conductors
Electric bar and grounding
of the substation among others.
Below you can see the
Atmospheric when the switch is in an open position:
As can be seen for the curve
of tension there is a reflection of the wave by having a discontinuity that
produces an overlap and elevation
On the other hand, the electrical equipment
of the substation will also play an important role regarding attenuation
Wave front as can be seen below:
Effect of tension transformer
Capacitive and lightning rod in an electrical substation
In the graph you have the results of
The voltage measured in the power switch for a wave amplitude of
2000 kV, as can be observed
lowest level of overvoltage happens
In the case of closed switch, Bay
line with lightning and transformer
capacitive stress, as long as,
Situation more criticism happens with open switch and line bay without lightning or transformers
of capacitive tension.
Capacitive voltage transformers have a capacitance between 4-8 NF
and the power transformers of 2-4 nf.
Finally, it is important to indicate that
for the range I (1 kv & lt; um≤ 245 kV)
Standard supported tensions include short-term supported voltage at frequency
Industrial and tension
supported at ray impulse, therefore,
the proper selection by the designer of the supported tensions and
Normalized for the ray impulse
They will grant reliability to electrical installations by guaranteeing electrical distances phase-earth
Internal and external isolation.