Investigation of stray currents and increase of the safety of electric blasting operations

Conclusions

The investigations made it possible to develop recommendations on increasing safety under conditions of constructing an underground hydroelectric station which pertain both to sources of stray currents and to the shot-firing circuits:

• 1. Prevention and maximum possible reduction of the duration of emergency operating regimes of electric power plants; maintenance of the insulation of all elements of the electric-supply system at the level required by the power plant regulations; elimination of the extension of a dangerous potential into the zone of conducting electric blasting operations through extended metal devices; monitoring of the level of stray currents by means of special stray-current signaling instruments.

• 2. Use of low-sensitivity electric detonators (type ÉD-1-8-T or ÉD-1-3-T), selection of the safest arrangement and optimal configuration of the shot-firing circuit; the area covered by the wires of the SFC should be minimum, the trunk lines should be twisted together, or special cables (for example, type KRPG KhL, etc,) should be used; maintenance of the normal (not less than 5 kΩ) insulation resistance of the SFC; checking of the insulation resistance of the SFC by means of special measuring instruments.

Strict observance of the requirements of the unified blasting regulations during blasting operations, the taking of measures to reduce the intensity of stray currents, and the elimination of their dangerous effect on the SFC will make it possible to considerably increase the safety of electric blasting operations during construction and to prevent premature firing of the ED.