What is the reason for the three phase alternating current imbalance of electromagnetic crane?

Here's how to deal with it:

If the three-phase voltage is unbalanced, the three-phase load should be checked first. For the three-phase transformer with δ Y wiring, if the three-phase voltage is unbalanced, and the voltage exceeds 5V, it may be that the transformer has an inter-turn short circuit and must be treated as a power outage. For the transformer wired by y y, the voltage difference between the three opposite to the ground is allowed to be 10% at light load; In the case of heavy load, it is necessary to strive for three-phase voltage balance.

A transformer is a device that uses the principle of electromagnetic induction to change the alternating voltage, and the main components are the primary coil, the secondary coil and the iron core (magnetic core). The main functions are: voltage conversion, current conversion, impedance conversion, isolation, voltage regulation (magnetic saturation transformer), etc.

According to the use, it can be divided into: power transformer and special transformer (electric furnace transformer, rectifier transformer, power frequency test transformer, voltage regulator, mining transformer, audio transformer, intermediate frequency transformer, high frequency transformer, impact transformer, instrument transformer, electronic transformer, reactor, transformer, etc.). Circuit symbols often start with t.

Example: T01, T201, etc.

The reason for the large noise of electromagnetic attraction; The dust is stained in the inside, resulting in the core attraction is not in place, the voltage is insufficient will also produce vibration, the contact piece due to the fire stain charcoal or sticking together is not good separation, it will cause the motor to be energized unbalanced and heated, now the crane control is 36V, all contactor coils are with 36V voltage, so to check whether the 36 voltage is normal, otherwise the contactor should be replaced, in the high temperature and dusty place often occurs the contactor contact poor phenomenon, pay attention to dust. The motor used in the crane is more special, it has a spring inside, the rotor is conical, when it is not energized, the brake pad is pressed to the side due to the action of the spring and the brake disc is reached, when the power is energized, it pops out due to the electromagnetic effect, the brake pad is separated and runs, there are three screws outside the brake disc, it fixes the nut on the brake pad on the fixed spindle, adjusts the nut after disassembling the three screws, and the brake force is increased when tightened, and the brake is loosened on the contrary.

1. The motor is damp, overloaded and overheated for a long time, resulting in inter-turn short circuit due to winding insulation damage, which will make the DC resistance of the three-phase winding unbalanced.

2. The motor is seriously damp, seriously overloaded, and out of phase due to rain, resulting in damage to the winding insulation, short circuit, grounding or open circuit, which will make the resistance of the three-phase winding unbalanced.

3. Caused by the three-phase load imbalance and the asymmetry of the three-phase parameters of the system components. Three-phase imbalance.

This will result in additional heating of the rotating machine.

and vibration, increased magnetic flux leakage and local overheating of transformers, increased line loss of the power grid, and malfunction of various protection and automatic devices, etc.

The reason for the unbalanced three-phase resistance of the motor is the reduction of insulation and the short circuit between turns.

Electric machinery (commonly known as "motor") refers to an electromagnetic device that converts or transmits electrical energy according to the law of electromagnetic induction. In the circuit it is indicated by the letter M (D in the old standard).

Its main function is to generate driving torque, as a power source for electrical appliances or various machinery. Generators are denoted by the letter G in the circuit. Its main role is to use mechanical energy to convert into electrical energy, and the most commonly used at present is to use thermal energy, water energy, etc. to push the generator rotor to generate electricity.

The most basic reason is the reduction of insulation and the short circuit between turns.

If there is a short circuit in the winding, it is equivalent to a decrease in the number of coils, and the resistance is smaller.

Phase-to-phase short circuits, turn-to-turn short circuits, manufacturing defects.

Will the number of coil turns be deliberately reduced during maintenance?

The criteria are:

1.Not more than 10%.

2.The accuracy of current measurement meters is generally as follows, plus human reading errors;

3.Whether the resistance of the three phases of the stator winding of the motor is balanced and whether the insulation is normal.

Calculation formula: three-phase current unbalance = (three-phase current average current in any phase) 100 three-phase current average 10%.

As for the existence of that specification, I don't know, only that it is in the relevant motor standards.

Three-phase asynchronous motor is a kind of motor that is connected to 380V three-phase AC power supply (phase difference 120 degrees) at the same time, because the rotor and stator of the three-phase asynchronous motor rotate in the same direction and at different speeds, and there is a slip rate, so it is called a three-phase asynchronous motor.

When the three-phase stator winding of the motor is introduced with three symmetrical alternating current, a rotating magnetic field will be generated, which cuts the rotor winding, thereby generating an induced current in the rotor winding, and the sub-winding is a closed path), and the current-carrying rotor conductor will produce electromagnetic force under the action of the stator rotating magnetic field, thereby forming an electromagnetic torque on the motor shaft, driving the motor to rotate, and the motor rotation direction is the same as the direction of the rotating magnetic field

If the three-phase power factor compensation is above or the unbalanced current is less than 10% of the rated current of the transformer, it can be regarded as clicking on the three-phase current unbalance.

The standard of three-phase current unbalance of three-phase asynchronous motor is:

1. Not more than 10%;

2. The accuracy of the current measurement meter is generally as follows, plus the artificial reading error;

3. Whether the resistance of the three-phase of the stator winding of the motor is balanced and whether the insulation is normal;

4.Whether the supply voltage of the three phases is balanced.

Calculation formula: three-phase current unbalance = (three-phase current average current in any phase) 100 three-phase current average 10%.

When the three-phase power supply is balanced, the deviation z of the average value of any phase and the three-phase in the three-phase no-load current of the motor should not be greater than 10% of the average valueQuoted from "Technical Conditions for Y2 Series High-voltage Three-phase Asynchronous Motor" When the three-phase asynchronous motor is unbalanced during operation, the possible reasons are: (1) The three-phase current imbalance of the motor is caused by the unbalanced voltage of the three-phase power supply; (2) Short circuit between turns of motor winding; (3) Winding circuit opening (or one or more branches in the winding parallel branch circuit); (4) Part of the coil in the stator winding is reversed; (5) The number of turns of the three-phase winding of the motor is not equal.

The following methods can be used: (1) If the voltage of the three-phase power supply is measured by a voltmeter, if it is indeed unbalanced, the cause should be found out to eliminate; (2) For the inter-turn short circuit fault of the motor winding, first of all, you can observe whether the end of the winding has any scorched or discolored coil due to high temperature, or smells the smell of scorched insulation. When the location of the inter-turn short circuit cannot be found by visual observation, the short circuit reconnaissance can be used for inspection.

If there is an inter-turn short circuit in the coil, the ammeter reading connected in series to the loop of the short-circuit scout coil will increase significantly; (3) The break-circuit fault of the winding can be checked by measuring the three-phase resistance with a multimeter or bridge meter, and the maximum difference of the three-phase resistance of the motor winding shall not exceed 3% of the average value of the three-phase resistance; 4) Check the reverse connection fault of the coil of the stator winding, apply a low-voltage DC voltage to a certain phase winding, and check its polarity with a compass along the surface of the core groove groove one by one. If the direction of the compass on each polar phase group changes in turn by n, s, n, s, it means that the winding is connected correctly; Otherwise, it indicates that a polar phase group is reversed; If the compass is placed on several adjacent slots in the same polar phase group, and its orientation is uncertain, it means that there may be individual coils in the polar phase group that are reversed or misconnected. The polar phase group and coil with wrong docking or inversion should be corrected according to the connection method of winding ** or wiring schematic diagram; (5) For the fault that the number of turns of the three-phase winding is not equal, the first and last ends of each phase can be energized in series, and the voltage drop can be measured in sections with a voltmeter.

First measure whether the voltage of each phase is equal, then measure whether the voltage of each pole phase group of the abnormal phase is equal, and finally measure whether the voltage of each coil in the abnormal pole phase group is equal, so that the coil with the wrong number of turns can finally be found. View the original post

The standard formula for judging the unbalance of three-phase current for three-phase AC motors.

I have a three-phase asynchronous motor, and there is a two-phase current that is one phase, is it normal.

The standard is: no more than 10%.

The accuracy of current measurement meters is generally as follows, plus human reading errors;

Whether the resistance of the three phases of the stator winding of the motor is balanced and whether the insulation is normal.

Whether the supply voltage of the three phases is balanced.

1. Explanation of motor: motor refers to an electromagnetic device that realizes the conversion or transmission of electrical energy according to the law of electromagnetic induction, and its main role is to use mechanical energy to convert into electrical energy and generate driving torque, as a power source for electrical appliances or various machinery.

2. The role of the motor: the main role of the motor is to use mechanical energy to convert into electrical energy, the most commonly used at present is to use thermal energy, water energy and other energy to promote the generator rotor to generate electricity, with the increasing maturity of wind power generation technology, wind power has slowly entered our lives. Classification of working power supply types:

It can be divided into DC motor and AC motor, DC motor is a motor that relies on DC working voltage to run, and is widely used in tape recorders, video recorders, DVD players, electric shavers, hair dryers, electronic watches, toys, etc.

3. Three-phase current: through three wires, each wire acts as a loop for the other two, and the phase difference of the three components is one-third of a cycle or the current of 120° phase angle.

The no-load current deviation of the three-phase motor shall not exceed 10% of the average three-phase current.

Three-phase asynchronous motor, the current should be basically balanced, unbalanced, there must be a problem with a certain phase winding of the motor, generally a short circuit between the smashing, or there is a problem with the line, there is no standard for this, you must know that if the current of the three-phase asynchronous motor is unbalanced, it will make the three-phase winding uneven, accelerate the wear of multiple shafts, and it is likely to lead to eccentricity, resulting in further damage to the friction between the stator and the rotor. Anyway, I haven't heard of this being able to run within a standard range.

It depends on the value you set, the general motor is not more than 20%, more than there must be a problem, I mean the unbalanced ratio, according to the occasion set!

The current of a three-phase motor (1 kW) is:

The power calculation formula of the three-phase motor is: p=, so the calculation formula for the current is:

i=p (is the motor power, u is the three-phase electric voltage, cos is the motor power factor, generally taken.)

Knowledge expansion. Three-phase motor: refers to when the three-phase stator winding of the motor (each difference of 120 degrees of electric angle), after the three-phase alternating current is introduced, a rotating magnetic field will be generated, and the rotating magnetic field will cut the rotor winding, thereby generating an induced current in the rotor winding. The current-carrying rotor conductor will generate an electromagnetic force under the action of the stator rotating magnetic field, which will form an electromagnetic torque on the motor shaft, drive the motor to rotate, and the motor will rotate in the same direction as the rotating magnetic field.

1. (Maximum Current-Minimum Current) Maximum Current.

2. MAX (phase current - three-phase average current) Three-phase average current example description: For example, the three-phase current is ia=9a ib=8a ic=4a, then the three-phase average current is 7a.

The phase current - the average current of the three phases is 2A, 1A, and 3A, respectively, and the difference is the largest.

The three-phase conversion ratio and impedance of the transformer cannot be completely equal, so there will be circulation in the electromagnetic ring network, which may cause the three-phase current imbalance.

The biggest possibility is that the aluminum strip of the motor rotor has broken bars or severely thin bars. Because the motor is 90kw and the rated current value is about 160A, you may use it for half of the strong resistance, but it may not work if you use the rated current. Check the electromagnetic sound of the motor after loading, there will be serious electromagnetic noise after the no-load is normally loaded.

What happens when running with no load? What about load changes? How about the motor output? Remind you to pay attention to whether the motor rotor will be open.

You see if the measurement loop is normal. It is not a fluctuation caused by interference.

The other is to check the condition of the motor when it is unloaded.

In the case of the same three-phase voltage, the difference between the maximum (or minimum) value of the three-phase current and the average value shall not exceed 3% of the average value

Causes of three-phase current imbalance:

1. Three-phase voltage is unbalanced.

2. The internal wiring of the winding is wrong.

3. The number of winding turns is unequal (especially the winding with more turns).

1) Unbalanced gap causes unbalanced magnetic pull;

2) After the short circuit between the rotor coils of the generator, the unbalanced magnetic pull increases;

3) The three-phase load imbalance generates negative sequence current and negative sequence magnetic field, forming alternating stress.