Usage of lightning arrester line to feed light electrical loads

American Journal of Applied Sciences, Jan, 2009 by Hani Bani Odeh, Yousif El-Tous

INTRODUCTION

There are scattered loads everywhere which lay in the field of high voltage lines specially those is close (adjacent) to transportation roads like petrol stations, restaurants ... etc). Supplying these loads in the traditional methods is too expensive while these are only low power-consuming loads and lying in the field of high voltage lines (220KV and above) which are fed from substations (220/0.4 KV). This will lead to the investment in big transformers but on the other hand, the complete power of these transformers is not utilized (1). Nowadays, the rating of power transformers which operates on 220 KV is not less than 2.5 MW. Reducing the nominal power of these transformers based on the used power will cause an increase in the unit price (cost of one kilowatt compared to transformer cost). Therefore, we should search for new ways that are feasible from the economical point of view. (It should be noted the possibility of using Voltage Dividers to feed agricultural loads located within the High Voltage lines and far from the main Distribution Centers 11-0.38KV. Some Capacitive Dividers were used to feed the indication lamps at High Voltage lines crossing rivers and rough areas.

In the sixties of last century the use of such Dividers (to supply remote villages) appears in some American Scientific magazines and since then, no considerable developments were recorded in this field due to the lack of such subjects in the scientific libraries. In the other hand, most remote industrial areas were fed by electricity (1), (2), (3).

During the construction of such plants, many problems faced those who were dealing with this subject, such as the possibility of having three phase Dividers, the possibility of lines protection during short Circuit at those power plants, the effect of these Dividers on the Network's operation and the resonance at some parts of the sub-station etc. All of the above factors slowed down the scientific researches on the voltage dividers.

In 1980, in the Scientific Research Center in Moscow, a single Phase Voltage Divider Station was built to supply the Train Indication lamps at the cross-section of Railway with roads, that station was called Capacitive Voltage Divider where Capacitors were used to divide the voltage. Since then, many scientific articles were discussing the possibility of using Voltage Dividers to feed the protection elements of electrical Networks and the possibility of building a special Reactor (Air Transformer) as a voltage Divider to feed some loads at country sides) (4).

This paper studies the possibility of using lightning arrester line as a source of power to such loads while keeping the main function of this arrester.

CALCULATIONS OF INDUCED VOLTAGE AND CAPACITANCE BETWEEN THE HIGH VOLTAGE LINES AND LIGHTNING ARRESTER LINE

As it is well known, lightning arrester line is always installed at the top of high voltage lines. It usually consists of single line or double lines depending on the operating voltage of the high voltage lines. Figure 1 shows two samples.

[FIGURE 1 OMITTED]

When hanging the lightning arrester line in the field of high voltage lines, it becomes a capacitive divider because there is capacitance between it and the high voltage lines from one side and the ground (earth) from the other side (5) .

While calculating the capacitive dividing stations, it is better to follow the computation in two stages:

First Stage: By means of the initial data and the voltage of high voltage line [U.sup.l.n], it is possible to determine the location of lightning arrester with reference to the high voltage lines as in Fig. 2. Then by using the formulas in Table 1, we indicate the coefficients of voltage difference which represents the matrix [alpha]. Also, by solving the set of Eq. 1 and 3 we indicate the nominal values for the electrical charges [q.sub.1], [q.sub.2], [q.sub,3].

[FIGURE 2 OMITTED]

In order to find the induced voltage on the lightning arrester line by the Mirror Reflection Method, considering that the induced voltage on the lightning arrester line is the linear voltage, it could be found as a result of the mutual affect between all the lines as follows (6):

[U] = [[alpha]].[q (1)

Where: [] = Matrix of voltage coefficients

[q] = Vertical matrix of linear charges

We symbolize the voltage self coefficients as [[alpha].sub.nn] and the reciprocal as [[alpha].sub.nm]. They could be found as follows:

Table 1: Equations for calculating voltage coefficients

[[alpha].sub.11] = [[alpha].sub.22] = [[alpha].sub.33] =
  K.Ln D/[r.sub.un] = K.ln 2[h.sub.B]/[r.sub.un]
[[alpha].sub.44] = [[alpha].sub.55] = K.ln [2h + 2x]/[r.sub.T]
[[alpha].sub.41] = [[alpha].sub.53] = [[alpha].sub.42] =
  [[alpha].sub.52] = K.ln[[squate root of[(2[h.sub.B] + X).sub.2] +
  [y.sub.2]]/[square root of[[x.sub.2]+[y.sub.2]]
[[alpha].sub.43] = [[alpha].sub.51] = K.ln[square root
  of[(2[h.sub.B]+X).sub.2] + [y.sub.2]
[X.sub.12] = [X.sub.23] = K.ln[square root of([X.sub.2] + 3[y.sub.2])]
[X.sub.45] = K.ln[square root of([2X+2[h.sub.B]).sub.2] + [y.sub.2]]/2y
Where: K = const=2.3 x [10.sup.5]
[[alpha].sub.nn] = [K.sub.eq].ln [[2[h.sub.n]]/[r.sub.n]]
[[alpha].sub.nm] = [K.sub.eq].lnSpace[[B.sub.nm]/[a.sub.nm]] (2)
where, [K.sub.eq] = Electrostatic coefficient and it equals
  18.[10.sup.6] km/F.
[R.sub.n] = Radius of line n.
[h.sub.n] = Height of line n hanging from earth surface
nm = Distance between the lines n, m.
nm = Distance between line n and the reflection of line m on the earth.