What is generator shaft voltage and shaft current

During the rotation of the generator, as long as there is an unbalanced magnetic flux cross-chain on the rotating shaft, then the induced electric potential will be generated at both ends of the rotating shaft of the generator. This induced potential is called the shaft voltage.

When the shaft voltage reaches a certain value, a closed loop is formed through the bearing and its base to generate current, and this current is called the shaft current. In order to eliminate the current loop formed by the shaft voltage through the bearing, the base and the foundation, etc., and prevent the shaft current from burning out the tile surface, the bearing seat should be insulated from the ground. In order to prevent the shaft from forming a suspended potential, the shaft is also grounded by brushes.

This brush grounding can be applied with a point of ground protection required by the rotor"Grounding"Shared as one. The key to preventing shaft voltage is to prevent the formation of shaft currents, and as long as there is no shaft current loop between the bearings, it is not necessary to insulate all the bearings.

The electromagnetic shaft voltage can be mainly divided into two parts, one is the shaft voltage generated at both ends of the shaft due to the magnetic flux due to the unbalanced cutting of the shaft when the shaft rotates, and the other is the shaft voltage generated at both ends of the shaft due to the presence of axial leakage flux. The main reasons for the imbalance of the magnetic field of the generator are: The air gap between the stator and the rotor is uneven.

The magnetic circuit is unbalanced. For example, the stator split core, the magnetic flux change caused by the stator core trunking, the relationship between the number of pole pairs and the number of seams of the stator core fan-shaped piece, etc. Manufacturing, installation caused by the imbalance of the magnetic circuit.

In addition, the armature reaction of the fractional groove winding also creates a shaft voltage on the shaft.

When the bearing base insulation pad loses its insulation performance due to oil, damage or aging, the shaft voltage is enough to break through the oil film between the shaft and the bearing and discharge. The discharge will gradually deteriorate the oil quality of the lubricating oil, and the arc of the discharge will cause the shaft journal and bearing pad to burn out pitting, which will cause accidents in serious cases.

In a steam turbine generator, due to the imbalance of the stator magnetic field or the magnetism of the large shaft itself, when there is an alternating magnetic flux, a certain voltage is induced on the shaft, which is called the shaft voltage. The shaft voltage consists of the journal, the oil film, the bearing, the base and the bottom layer of the foundation, when the oil film is destroyed, a large current is generated in this circuit, which is called the shaft current.

The generator shaft current should not be exceeded. If the shaft current is exceeded, the sliding surface and bearing of the generator shaft journal calendar.

may be damaged.

A generator is a mechanical device that converts other forms of energy into electrical energy, which is driven by a hydro, steam turbine, diesel engine, or other power machinery to burn water, air, fuel, or atomic nuclei into fission.

The energy produced is converted into mechanical energy.

It is transferred to the generator, which converts it into electrical energy.

Introduction to generators.

Generators have a wide range of uses in industrial and agricultural production, national defense, science and technology, and daily life. There are many forms of limb macro generators, but their working principles are all based on the laws of electromagnetic induction.

and the laws of electromagnetic force. Therefore, the general principle of its construction is to use appropriate magnetic and conductive materials to form magnetic circuits and circuits that induce electromagnetic induction with each other, so as to generate electromagnetic power and achieve the purpose of energy conversion.

There are many types of generators. In principle, it is divided into synchronous generators, asynchronous generators, single-phase generators, and three-phase generators. In terms of generation mode, it is divided into steam turbine generators, hydro generators, diesel generators, gasoline generators, etc.

In terms of energy, it is divided into thermal power generators, hydroelectric power generators, etc.

Under normal circumstances, a three-phase symmetrical current flows through the three-phase AC motor's three-symmetrical windings, generating a circular rotating magnetic field. At this time, the magnetic field at both ends of the motor is symmetrical, there is no alternating magnetic field that is cross-linked with the motor shaft, there is no potential difference between the two ends of the shaft, and there is no current flowing through the bearing. In the following cases, the symmetry of the magnetic field may be broken, and there is an alternating magnetic field of the axis of the interlinked motor, which induces the shaft current.

When this situation occurs, it will cause the magnetic field at both ends to be asymmetrical, resulting in a shaft voltage

1) Three-phase current asymmetry;

2) The punching piece is a ring spliced together by a fan-shaped piece;

3) cold-rolled sheet, which is not absolutely isotropic;

4) The existence of core grooves, ventilation holes, etc., resulting in unbalanced magnetic resistance in the magnetic circuit;

5) There is an alternating flux cutting hinge around the hinge.

Generation of shaft current:

According to the structure and working principle of the synchronous generator, the spindle of the unit will inevitably rotate in an incompletely symmetrical magnetic field due to the combination seam of the stator core, the seam of the stator silicon steel sheet, the uneven air gap between the stator and the rotor, and the inconsistency between the shaft center and the magnetic field center. In this way, an alternating voltage is generated at both ends of the shaft. Under normal circumstances, the insulation resistance of the rotating part of the unit to the ground is required to be greater, and if the two ends of the large shaft are grounded at the same time, the shaft current may be generated.

The role of the large shaft grounding:

1. Prevent the shaft current from burning the bearing.

2. It is used for various protections of generator excitation circuits.

3. It is used for the measurement of rotor (ground insulation).

Shaft voltage cannot be avoided, if the large shaft is not well insulated and causes two points to be grounded, a shaft current will be generated.

Shaft currents can cause damage to the pads, which in turn can further damage the generator.

There are many reasons for the generation of shaft current.

1. The magnetic circuit is unbalanced and produces shaft current.

2. The use of inverter power supply such as inverter will produce shaft current, mainly because of the high harmonic content of this power supply.

3. The high-power equipment around the motor will also generate shaft current when a strong electric field is generated.

4. There are others, such as the motor with a temperature measuring element, electrostatic charge accumulation, etc., which may also generate shaft current.

Big brother, is there an electric current passing through the motor shaft? Can you please be specific.

In the motor, it is called the longitudinal axis (also called the straight axis, D axis), and the vertical axis with the magnetic pole axis is called the horizontal axis (also called the intersection axis, Q axis);

When there is a current in the armature winding, an armature reaction will be generated, and the armature reaction has a longitudinal axis armature reaction and a transverse axis armature reaction, and we call the current that produces the longitudinal axis armature reaction the longitudinal axis current, and the current that produces the transverse axis armature reaction is called the transverse axis current, that is, the q-axis current.

When drawing a motor vector diagram, you can decompose the current into two parts, the one that is in the same direction as the electric potential is called id, and the one that is perpendicular to the electric potential is called iq.

Yes, what is the axial current, what is the Q-axis current?

Reason: Due to the combination seam of stator core, the seam of stator silicon steel sheet, the uneven air gap between the stator and the rotor, and the inconsistency between the shaft center and the magnetic field center, the spindle of the unit will inevitably rotate in an incompletely symmetrical magnetic field. In this way, an alternating voltage is generated at both ends of the shaft.

Under normal circumstances, the insulation resistance of the rotating part of the unit to the ground is required to be greater than a certain resistance value (for example, if the two ends of the large shaft are grounded at the same time, the shaft current may be generated.

Prevention: By replacing the insulating pad at the connection of the oil pipe of the oil collector, it is necessary to ensure that the large shaft is not grounded at two points, so as to avoid the generation of shaft current. In addition, during the usual maintenance and inspection, pay attention to supervise the operation status of the motor.

The shaft voltage and shaft current of the motor are generated due to the asymmetry of the magnetic circuit around the motor shaft, the rotor operation is not concentric, and the pulsating magnetic flux is generated, which will make the shaft-bearing-base circuit have shaft current flow, and the shaft voltage is formed at both ends of the motor rotor shaft, between the shaft and the bearing, and between the shaft and the bearing to the ground.

The asymmetry of the magnetic circuit generates the shaft current.

Prevention: Insulate the housing.

The current of the motor shaft is generated because in the magnetic circuit composed of the shaft, bearing, bearing sleeve, end cover and base of the motor, there is a time-varying magnetic flux through, which induces the electric potential on the shaft and generates a current in the loop, and when it flows through the bearing, it forms an electric erosion phenomenon. There are two conditions for the generation of shaft current: there must be alternating magnetic flux passing through and an unbalanced potential being induced on the shaft; There should be a closed path through which the axial current flows.

The unbalanced potential can be induced on the motor shaft in the following cases: a) The motor stator is assembled with fan-shaped pieces and there are seams between the sheets. b) The positioning groove and tension bolt hole for fixing the machine base are opened on the fan-shaped piece.

c) Although the stator is a whole circle, the rotor is eccentric. That is, the air gap is asymmetrical or the stator winding is asymmetrical. d) Motors for frequency conversion or motors powered by frequency converters e) Asymmetrical, unshielded wiring.

f) The high-frequency grounding current is generated due to improper grounding method, mainly due to the impedance of the grounding return wire is too high or the grounding with the stator is poor.

The above situations are the main reasons for the shaft voltage, but sometimes the uneven thickness of the stator punch, the different stacking coefficients of the whole circumference, and the uneven core may induce an electric potential on the shaft and produce the shaft voltage. This voltage is generally small, but it is still possible to generate a higher shaft voltage in some motors, such as inverter motors or inverter-powered motors, and motors with fan-shaped plates for the stator. The bearing parts of these motors need to be insulated to block the circuit of the shaft current, so that it cannot be closed and cannot form a path, so as to achieve the purpose of protecting the bearing.

The motor shaft current is generated by three parts, the first part is caused by the induction shaft potential, the second part is the high-frequency loop current, which is generally only generated by more than 75kw, and the third part is the magnetic circuit unbalanced current, which can only be prevented by cutting off the connection point! Both the first and second parts are mainly found in inverter motors.

The shaft current is formed by the shaft voltage, which is formed by the incomplete symmetry of the motor's magnetic field. Blocking the shaft current mainly depends on the insulating pad under the bearing seat, and it should be noted that there should be no metal object short-circuit insulating pad.

The shaft current is formed by the shaft working under unequal magnetic fields, which should be fully considered in large motors, and the harm is great.

Why does a motor running at power frequency have shaft current?

It's leaking! Is the insulated housing broken? Or use ceramic bearings for insulation!