SYSTEM FOR MONITORING DISSOLVED GASES IN INSULATING OIL OF POWER TRANSFORMERS, REACTORS, ON-LOAD TAP CHANGERS, CURRENT TRANSFORMERS, POTENTIAL TRANSFORMERS, CONDENSIVE BUSHINGS AS WELL AS SIMILAR HIGH VOLTAGE EQUIPMENT IMMERSED IN OIL, wherein it has • a cylindrical rigid rod, endowed with a anchorage device for its fixing to an orifice which gives access to oil of the high voltage equipment, for the lower end of the rod to be inserted through the orifice until it reaches a place where there is a natural oil circulation, having such end of the rod two orifices (7, 8) diametrically opposed, one for oil inlet and the other for oil outlet; • these orifices (7, 8) being connected to tubing (7', 8') of oil circulation, that are axially placed inside the rod and parallel to each other; • the upper end of the rod being rigidly fixed to a main body, inside of which there are two oil chambers (10,11), each one connecting to the tubing (7', 8'), • both oil chambers (10, 11) being interconnected at their upper parts by means of a pump of oil circulation, which is controlled by a micro-processor, which switches it on and off according to a program present in a software; • the oil pump, when in operation, forcing the oil circulation, which enters through the inlet orifice, moving through the inlet tubing, entering into the first oil chamber, passing through the pump, entering into the second oil chamber, passing through outlet tubing and returning to the high voltage equipment after having left the discharge orifice; • each one of both oil chambers (10, 11) having one or more of their walls constituted by membranes (17, 18) made of semi-permeable material, that allow the in oil dissolved gas to permeated into the gas chambers (10', 11'), that are interconnected by channel; • the gas chamber having one or more sensors for the measurement of the concentration of the concerned gases intended to be monitored, being gas chambers (10', 11') hermetically sealed, making the gases concentration in its inside directly proportional to the in oil dissolved gases concentration, such a way that the concentration measurements made by the sensors may be used by the micro-processor for the calculation by its software of the same gases in oil concentration; • an air pump that, by means of the inlet and exhaust check valves obtains oxygen from the atmospheric air to assure oxygen presence in the gas chambers (10', 11'), being the air pump controlled by the micro-processor, that switches it on and off in an intermittent and cyclic manner, according to a program present in the software processed by the micro-processor. • a cylindrical rigid rod, endowed with a anchorage device for its fixing to an orifice which gives access to oil of the high voltage equipment, for the lower end of the rod to be inserted through the orifice until it reaches a place where there is a natural oil circulation, having such end of the rod two orifices (7, 8) diametrically opposed, one for oil inlet and the other for oil outlet; • these orifices (7, 8) being connected to tubing (7', 8') of oil circulation, that are axially placed inside the rod and parallel to each other; • the upper end of the rod being rigidly fixed to a main body, inside of which there are two oil chambers (10,11), each one connecting to the tubing (7', 8'), • both oil chambers (10, 11) being interconnected at their upper parts by means of a pump of oil circulation, which is controlled by a micro-processor, which switches it on and off according to a program present in a software; • the oil pump, when in operation, forcing the oil circulation, which enters through the inlet orifice, moving through the inlet tubing, entering into the first oil chamber, passing through the pump, entering into the second oil chamber, passing through outlet tubing and returning to the high voltage equipment after having left the discharge orifice; • each one of both oil chambers (10, 11) having one or more of their walls constituted by membranes (17, 18) made of semi-permeable material, that allow the in oil dissolved gas to permeated into the gas chambers (10', 11'), that are interconnected by channel; • the gas chamber having one or more sensors for the measurement of the concentration of the concerned gases intended to be monitored, being gas chambers (10', 11') hermetically sealed, making the gases concentration in its inside directly proportional to the in oil dissolved gases concentration, such a way that the concentration measurements made by the sensors may be used by the micro-processor for the calculation by its software of the same gases in oil concentration; • an air pump that, by means of the inlet and exhaust check valves obtains oxygen from the atmospheric air to assure oxygen presence in the gas chambers (10', 11'), being the air pump controlled by the micro-processor, that switches it on and off in an intermittent and cyclic manner, according to a program present in the software processed by the micro-processor.