The control circuit should time the trip pulses from the last zero value of the waveform, both voltage and current. The sensor can be installed in a single phase and in this case the system measures only the one-point or one-point crossing point for each phase.
The soft-starter operates by means of the microprocessor, which controls the thyristors and adjusts the voltage sent to the motor stator. In this way, it is possible to smooth the activation of the high induction motor acceleration conjugates and to protect the mains from the high starting currents.
In order for the motor to start smoothly, the initial voltage (Vp) must be parameterized so that it assumes the smallest possible value and is sufficient to initiate the movement of the load. From this point, the voltage rises linearly according to a time also parameterized (tr) until it reaches the nominal value.
In braking, the voltage is instantly reduced to an adjustable value (Vt), which must be parameterized at the level at which the engine starts to reduce the speed. Thus, the voltage decreases linearly (adjustable ramp, tr) to the final voltage (Vz), when the motor stops rotating. At that time, the voltage is switched off.
During the operation of the transformer, the oil undergoes an aging process, a result of the request for temperature increase, oxygen action and contact with materials in its constitution, such as metals (copper and iron). As a consequence, it occurs to the deterioration of the insulating properties of the oil.
In addition, by-products from IMO degradation lead to the acceleration of the degradative process of solid insulation and the formation of sludge. The process that governs the oxidation of hydrocarbons is the mechanism of peroxidation, leading to the formation of hydroperoxides.
After formation of these compounds, many oxidation by-products are formed, which differ according to the species that gave rise to them. The by-products formed, also called intermediates, are alcohols, aldehydes and ketones, which, in the presence of oxygen, generate carboxylic acids.
Because of their polar and acid nature, carboxylic acids are aggressive agents to the insulation paper and other materials present in the transformer. The insoluble, acidic sludge deposits on the windings, damaging the transfer of heat from the copper to the oil, increasing the temperature of the insulating paper and attacking it chemically.