Current transformers must be specified according to the load to be connected to their secondary. In this way, NBR 6586/92 standardizes secondary loads.
For a current transformer, the secondary load represents the ohmic value of the impedances constituted by the different apparatus connected to its secondary, therein including the interconnecting conductors.
By definition, nominal secondary load is the impedance connected to the secondary terminals of the TC, whose value corresponds to the power for the guaranteed accuracy, under rated current.
It should be noted that when the nominal secondary current is different from 5A, the values of the loads shall be multiplied by the square of the relation between 5A and the corresponding nominal secondary current in order to obtain the desired values of said parameters.
The load of the devices to be connected to the current transformers must be carefully dimensioned to choose the compatible standardized load current transformer. However, since the devices are connected to the CTs by means of wires, usually of great length, it is necessary to calculate the power dissipated in these conductors and to add it to the power of the corresponding apparatuses.
Some actions that directly operate in the world of electric motors that everyone should know what they are and what they serve, and this should be considered in order to ensure the improvement of performance and extend its useful life. Among these procedures is balancing, which basically consists of a procedure whereby the mass distribution of a body is accounted for and, if necessary, is also adequate to warrant that residual imbalance or vibrations and forces in the bearings in the frequency of mechanical rotation, and within the limits specified in the international standards.
The balancing intensity has the important task of recommending the peak amplitude of the vibration velocity, which will be reported in mm / s, of a rotor that rotates freely in space, being a specific unbalance item and the rotor angular velocity at maximum speed of operation. 3B58SD Browning
The grounded part is metal parts electrically connected to the grounding system and the live part is incident on a conductor or a conductive part, which is to be energized in normal use and may include the neutral conductor.
In the case of electric motors that will not be used soon, they must be stored in appropriate environments, such as dry places with an average air humidity of 60%, with a temperature ranging between 5 ° C and 40 ° C, preserved from dust, vibrations, gases and corrosive agents.
Engines that have heating resistance must be energized whenever the engine is not operating. This is also useful for cases where the engine is already installed but not used for a long time. In these situations, depending on the ambient conditions, water condensation may occur inside the engine, which may result in the insulation resistance being reduced. reelcraft D8800 OLP
Engines must be carefully stored in such a way that drainage is facilitated. The heating elements must never be energized when the engine is running.
Electric motors need to be kept at constant temperature and in the original position, preventing any object from being supported on them. Remove the pulleys from the shaft end and keep them free and with protective grease to prevent corrosion.
The electric motors are commanded by means of starters and the most applied are the direct, reversing starter, which works in the drive of small motors; Star triangle starter, which acts on the drive of large motors that have no load; compensating start-up that drives the big engines with load; and starting with frequency inverter, which acts in the drive of FD84000 OLP small and large motors.
Starters include protection devices such as fuse, thermal relay, circuit breaker, control devices such as buttons, contactors and timers. And there are also signaling devices, such as signal, voltmeter and ammeter.
All of these starting switches have a main circuit and a control circuit, where the main or power circuit, as it is also called, acts on the motor supply, in this way it ends up having the function of connecting the terminals and wires of the motor the power grid. In turn, the control circuit, as its name says, has the function of controlling the power circuit, thus determining when the motor can be turned on or off.
The magnetic cores of electric motors, which are stators and rotors, with rare exceptions, are constructed from thin metal sheets (low carbon steel plates) with a thickness of less than 1 mm, grouped in sheet metal packages. Magnetic nuclei surrounded by coils (windings), where alternating currents circulate, cause a magnetic flux also alternating and for that reason, these nuclei are subject to the action of parasitic currents. These currents are known as Foucault currents, which are responsible for appreciable loss of power in these nuclei.
Some higher performance motors are designed with silicon steel plates, with a percentage of approximately 3% silicon. The total process for making these cores consists essentially of lamination, stamping, a treatment for electrical insulation, packaging and fixing. With regard to low carbon steel plates, the process for insulation is based on a heat treatment, where the packages of plates are placed in kilns for a certain time, there being oxidation of the surface of the plates, and as a consequence, the formation of an insulating layer of iron oxide between the adjacent sheets. Some types of silicon steel sheets are provided by manufacturers with a paint based oxide on one of the surfaces.
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