It is important to analyze that up to two basic categories of transformers can be found. They are the voltage, which aims to ensure the reduction of the high voltages present in the lines, allowing their routing to the places frequented by operators and their reading in common voltmeters. The other type is the current one, which makes it possible to carry out the main functions of the measurement process of high value electrical quantities, ensuring the galvanic isolation between the high voltage or current network and the measuring circuit.

Thus, transformers of measurement have as main function to reduce the high voltages or electrical currents in networks of transport and distribution of electric energy, namely for the purpose of its measurement process or, still, of safe detection in devices of reduced dimensions and high precision motor accessories. As an example of the use of this type of transformers, it is possible to stand out the equipment of measurement of the voltage, current and electrical power in networks of energy, the phasimeters, the frequencmeters and the relays of protection, the counters of electrical energy, the insertion of signals high frequency transmission lines, namely for communication between exchanges, substations and the telecontration of energy consumed by users.

Due to the fact that they only present one feeding phase, this category of machine does not present a rotating field, as it happens in three-phase motors. However, they have a pulsating magnetic field, which can prevent them from obtaining starting torque, since in the rotor magnetic fields are properly induced in line with the stator field. To solve the problem, we use auxiliary windings, sized and positioned in a way capable of creating a second phase, allowing the formation of the rotating field necessary for starting.

Single-phase electric motors are called this way due to their field windings, which are connected directly to a source known as single-phase. Single-phase induction motors are seen as a natural option compared to three-phase induction motors in places where three-phase power is not available, such as in rural areas, workshops, offices and homes, for example. Its use is only indicated for reduced power, on average of one to two kw. Amongst the various types of single-phase electric motors, the cage-type rotor can be highlighted, considering its simplicity, ease of projection, reduced maintenance and robust body. https://www.mrosupply.com/motors/ac-motors/general-purpose-motors/26523_vm3546_baldor/