What are circulating currents?
Circulating currents are a result of an asymmetry in the motor and the voltage it creates between the stator and rotor iron, but not related to the motor drive or method used to drive the motor. Specifically, the asymmetry in a motor comes from imbalanced windings, the differences in the iron core, and air gaps.
Why are circulating currents detrimental to good motor operation?
Circulating currents cause problems in power supplies when the large output currents cause a difference between the actual output voltage and the feedback voltage as well as when the large output-ground currents move the power-supply chip’s analog ground off its true ground.
What is circulating current in generator?
During the operation of electrical generators that generate alternating current, as opposed to direct current, current can circulate. This current circulates in much the same way as a current would in a river or water situation, moving back and forth between the two generator fields.
What are shaft currents?
Shaft circulating currents are caused from “dissymmetries” in the magnetic paths through the stator and rotor iron. As the rotor rotates within the stator and as the stators magnetic field rotates, small differences in the magnetic “reluctance” of the core parts generate small voltages between the ends of the shaft.
How much circulating current can be tolerated for parallel operation of transformer?
For satisfactory operation, the circulating current for any combinations of ratios and impedances probably should not exceed ten percent of the full-load rated current of the smaller unit. Generally, electrical power transformer gives the maximum efficiency at full load.
What is the effect of circulating current in a circuit having two transformers in parallel?
When two transformers are connected in different/opposite polarities, they will get shorted. Because of this short circuit a huge circulating current will flow through the windings of the transformers but no load will be fed from these transformers as load voltage and current will become zero.
How much circulating current can be tolerated for parallel operation of transformers?
How is circulating current measured?
Conceptually, it really is as simple as Ohm’s Law: I = V/R. Of course that is an over simplification, but it is the same concept applied to three phase AC systems.
What is neutral circulating current?
The total circulating current in the common neutral will be the sum of the circulating current in each phase. Since the zero phase sequence impedance of the cables is normally quite small relative to that. of the sources, it can typically be ignored.
How is shaft current measured?
You can indirectly measure bearing current by looking for sudden collapses in shaft voltage. These indicate a discharge (arc) through the bearings. You can measure shaft voltage with an oscilloscope like the AEGIS Shaft Voltage Tester, or any scope with bandwidth greater than 100 MHz.
What is shaft grounding?
Shaft groundings stop the energy from causing harm to vulnerable motor parts. These devices redirect electrical current away from sensitive motor parts with weaker resistances—such as motor bearings—and provide a better route to the ground.
What are the conditions to be met before two transformers can be connected in parallel?
The mandatory conditions conditions are: Same Phase Angle Shift, Same Polarity, Same Phase Sequence and Same Frequency. When the convenient conditions are not met paralleled operation is possible but not optimal.
Why is tertiary winding used?
A “Tertiary” is a third winding added to a two winding transformer. Also called “Stabilizing” winding – stabilizes neutral point voltage. Stabilizing winding also helps in reduction of third-harmonic voltages in the line, thus reducing harmonic related issues, e.g. telephonic interference or heating.
What happen if two transformer are connected in parallel with wrong polarity?
when two transformer are connected in parallel condition,and the polarity of transformer are opposite to each other then a large circulating current flow through out the winding,therefore a very small current flow thro, the load . therefore lifespan of transformer will be reduced.
What is the formula for circulating voltage?
Voltage for each circuit element in a series circuit can be calculated by applying Ohm’s law: V=R*I. Also, if the element’s resistance is unknown, the Kirchhoff loop rule helps to calculate the voltage across such a circuit element.
How do you measure bearing current?
What type of meter is used to test for shaft voltages?
The BPK-Probe™ uses (2) propriety silver graphite brushes to directly contact the motor shaft. One brush is used to measure shaft voltage, the other is used to ground the shaft. The measured voltage is displayed on the Probe’s LCD screen.
Why is shaft earthed?
Earthing the propeller shaft to the ship’s hull prevents corrosion and spark erosion in the shaft bearings and gearboxes. The earthing is provided by spring loaded silver graphite brushes, and monitored by a compact mV meter.
What will happen if transformer in parallel connection has opposite polarity?
Same polarity The transformers should be properly connected with regard to their polarity. If they are connected with incorrect polarities then the two EMFs, induced in the secondary windings which are in parallel, will act together in the local secondary circuit and produce a short circuit.