Mounting of vertical grounding conductors
The mounting mode of vertical grounding conductors depends on dimensions of electrodes of grounding, character of soil and its state during mounting (thawed, frozen), season and climatic conditions, quantity of submersible electrodes, remoteness of objects from each other and on mechanization, availability and the possibility of receiving the mechanisms and devices necessary for mounting.
Also comparative characteristics of mechanisms and cost of their operation, volumes of the performed works and specific conditions of their performance are considered.
Rational mounting modes:
- for thawed, soft soil – cave-in and the vvertyvaniye of rod electrodes, blockage and cave-in of profile electrodes;
- for dense soil – blockage of electrodes of any section;
- for frozen soil – vibroimmersion;
- for rocky and frozen soil in need of deep immersion – the bookmark in the drilled well.
Resistance to spreading of the hammered electrode minimum; electrode resistance, mounted by the vvertyvaniye, 20-30% higher; electrode resistance, put to the ready well and filled up with friable soil, can be even higher that will not allow to put the electric unit into operation.
Resistance of electrodes increases slightly at cave-in in soil and at immersion by vibrators and exceeds resistance of the hammered electrodes only for 5-10%. In 10-20 days resistance of the electrodes submerged by vibrators, pressed and hammered begins to be leveled. Much more time it is required for recovery of structure of soil and reduction of resistance of the electrodes screwed in soil, especially at application of the expanded tip on the electrode that facilitates immersion, but loosens soil.
At blockage it is possible to apply steel electrodes of any profile – angular, square, round, however the smallest consumption of metal (at identical conductivity) and the greatest resistance to soil corrosion (in case of the equal consumption of metal) are reached when using rod electrodes from round steel.
At blockage in normal soil on depth up to 6 m it is economic to apply rod electrodes with a diameter of 12-14 mm. With the depth up to 10 m and also at blockage of short electrodes in especially dense soil, stronger electrodes with a diameter from 16 to 20 mm are necessary.
To chuck in electrodes more deeply, than 10-12 m, use mechanisms of shock and vibration action – vibrators by means of which it is easy to submerge electrodes even in the chilled soil.
Vibrators it is possible to submerge electrodes much more deeply, than at the vvertyvaniye and cave-in that is especially important for soil with the high unit resistance (about 1000 Ohms) and deep level of subsoil waters (more than 9 m), for example, for dry sands in which electrode resistance in process of burying very sharply decreases.
If at design soil was not probed and its electric characteristics are unknown, in order to avoid excess operation of deep grounding conductors it is recommended to install in the following sequence:
- To prepare electrode pieces, to accept their length according to the design of the used mechanism.
- To hammer the lower piece of the electrode.
- To measure resistance to spreading of the hammered piece.
- To weld the following piece of the electrode.
- To hammer the second piece and again to execute measurement.
- To continue work before achievement of the necessary conductivity.
As well as any other way, the vvertyvaniye of electrodes has the advantages and shortcomings defining its application in specific conditions. Undoubted advantage is comparative ease of development of the mechanized devices (manual electrodrilling machines, small petrolengines) which allow to bury electrodes only on rather small depth that in some cases increases number of electrodes and the consumption of metal.
Power of these devices small, and it is necessary to apply the tips on electrodes loosening soil that sharply increases the electrical resistance of soil by the period until its structure is recovered to simplification of the vvertyvaniye. The necessity of fast commissioning is caused by increase in number of submersible electrodes for achievement of the necessary conductivity of the grounding conductor and as a result, the additional consumption of metal.
But despite it, the way of the vvertyvaniye in many cases allows to mount quickly and economically grounding device.
Vertical deep grounding conductors provide good conductivity due to contact with the underground, especially if they have the increased resistance. Horizontal grounding conductors are irreplaceable because of lack of mechanisms for mounting of vertical electrodes in rocky, gravel and other soil. If rocky soil is closed by the earth layer, performance of the horizontal or beam grounding conductor can be less labor-consuming and rather cheap.
Horizontal grounding conductors lay also for connection of the mounted vertical electrodes in the general difficult grounding conductor or the ground loop.
Often use beam grounding conductors to lightning protection.
In summertime the horizontal grounding conductor laid in the peat or other well carrying out thawed upper layer of the earth can provide good conductivity. The same treats also the seasonal electric units working in summertime.
Structurally horizontal grounding conductors can be made of round, strip or any other steel. Preference should be given to round steel which at the same to the weight and conductivity has the smaller surface and big thickness owing to what has smaller corrosion vulnerability. Besides, round steel is cheaper and it is easier to mount it. Therefore for extended grounding conductors, as well as it is recommended to apply low-carbonaceous round steel to vertical electrodes at which device are not imposed special requirements for thermal stability, for amount of the carried-away metal, etc.
If near objects there are reservoirs, at the bottom of reservoirs stack extended grounding conductors, and from them lay connecting cable or air-lines to objects.Top