Circulating current

I One of the bearings should be insulated inside its housing by providing a layer of thin insulation as indicated at location 3 in Figure 10.8 to prevent circulating current through the motor bearings. 

Figure 15.22 A circulating current scheme to provide a phase and a ground fault differential protection...

This can be defined by the most severe external fault at which the schetne will remain inoperative. It should also remain inoperative in healthy conditions. That is it should be immune to the momentary voltage or current transients and normal harmonic contents in the circulating current. Series LC-filter circuits are generally provided with the relay coil to suppress the harmonics and to detect the fault current more precisely. 

Figure 15.27 Three-element high-impedance circulating current relay scheme...

This is a scheme introduced in the AVR circuit to adjust the reactive power (kVAr) of a machine during a parallel operation or when it is being used as a synchronous condenser. It prevents a reactive circulating current, l. ... 

E will cause a circulating current, 4, The circuit diagram is drawn in Figure 16.16(b) w here... 

All such CBCTs have to be identical in turns ratio and magnetizing characteristics to avoid circulating currents among themselves. To order a CBCT the following information will be essential ... 

The flow of circulating currents in the grounding conductors or ground of region two caused between two or more interconnected grounding stations, for a fault occurring in region one is termed the telluric effect. 

This should not be confused with AO ns used in Section 16.10 in connection with the paralleling of two generators. There it represented the electrical shift between the rotors of the two machines or supply buses. If ii is not eliminated, it will cause a circulating current between the two machines or the buses when running in parallel and will add to their healinc. 

Heat transfer by convection occurs as a result of the movement of fluid on a macroscopic scale in the form of eddies or circulating currents. If the currents arise from the heat transfer process itself, natural convection occurs, such as in the heating of a vessel containing liquid by means of a heat source situated beneath it. The liquid at the bottom of the vessel becomes heated and expands and rises because its density has become less than that of the remaining liquid. Cold liquid of higher density takes its place and a circulating current is thus set up. 

In forced convection, circulating currents are produced by an external agency such as an agitator in a reaction vessel or as a result of turbulent flow in a pipe. In general, the magnitude of the circulation in forced convection is greater, and higher rates of heat transfer are obtained than in natural convection. 

In most cases where convective heat transfer is taking place from a surface to a fluid, the circulating currents die out in the immediate vicinity of the surface and a film of fluid, free of turbulence, covers the surface. In this film, heat transfer is by thermal conduction and, as the thermal conductivity of most fluids is low, the main resistance to transfer lies there, Thus an increase in the velocity of the fluid over the surface gives rise to improved heat transfer mainly because the thickness of the film is reduced. As a guide, the film coefficient increases as (fluid velocity)", where 0.6 < n < 0.8, depending upon the geometry. 

Equation 10.4, which describes the mass transfer rate arising solely from the random movement of molecules, is applicable to a stationary medium or a fluid in streamline flow. If circulating currents or eddies are present, then the molecular mechanism will be reinforced and the total mass transfer rate may be written as ... 

Figure 3-3 Worst Way to Measure Anything—If Ground Clips Are at Different Grounds, this Can Create a Huge Loop Antenna of Circulating Current... 

---