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ADDITIONAL DIMENSIONS Neither supersymmetry nor technicolor gives us perfect solution hierarchy problems. Supersymmetric theories do not offer us experimentally consistent mechanisms for breaking supersymmetry, but to create on the basis of technicolor force

To measure losses and no-load current of the transformer, an no-load experiment is carried out. Measuring cold losses allows you to check the condition of the magnetic circuit. If it is damaged (the insulation between the sheets is broken), the loss of chemical increase. A sharp increase in the cold current. and losses x.x. are an indicator of the presence of a short circuit between the turns of one of the windings, local heating and damage to the windings.

Experience x.x. carried out after testing the electrical insulation strength. This is done in order to detect possible defects after this test.

When experimenting x.x to the winding low voltage LV with the HV winding open, the rated voltage is supplied.

ATTENTION! On the transformer, it is necessary to remove the ends of the cable from the HV terminals. To remove the characteristics x.x. it is necessary to assemble the circuit shown in Figure 3.4.

Figure 3.4 - Scheme for reading the idle speed characteristics: 1- induction regulator; 2 - set of devices K-50 or K-505; 3 - transformer under test.

Applying voltage to the LV winding in the range from 0.5 to 1.1 U n, take measurements of voltage, current and losses for each phase. U a is measured with the K-505 kit. The K-505 measuring kit measures phase voltage, phase current and phase power, and U av, U sun, U ac with a PV voltmeter. Enter the measurement data into table 3.6.

Table 3.6 Idling experience

Based on the measurement data, the calculated values ​​of U xx, P xx, I xx are determined

, (3.3)

Where U aw, U sun, U sa- line voltages on the low side of the transformer.

, (3.4)

Where I a, I in, I s– phase currents.

, (3.5)

where is the rated current value of the winding to which voltage is supplied.

For three phase transformer

, (3.7)

Where R st. - steel losses;

R f- phase resistance of the winding to direct current.

Power R xx almost entirely is spent on covering losses in the steel of the transformer core R st, since at x.x. losses in the windings are negligible compared to losses in steel, then we can accept R st » R xx.

Based on the measurements, it is necessary to construct the characteristics of the x.x. transformer I xx, P xx =f(U xx). For newly commissioned transformers, the values R xx should not differ from the factory data by more than 10% ( P xx =340 W for transformer TM-63/10).

7 Short circuit experience.

To measure losses and short-circuit voltage, a short-circuit (short-circuit) experiment is performed. With the experience of short circuit check the correct connection of the transformer windings and the condition of the contact connections.

Experience k.z. is carried out for the transformer at the rated voltage regulation stage according to the scheme shown in Figure 3.5.

Smoothly raising the voltage, set in the LV winding a current lower than the rated current within 20% I n, i.e. Ik =20 A.

ATTENTION! Make measurements as quickly as possible to avoid heating the windings.

Table 3.7 - Short circuit experience

Based on the measurement data, the calculated values ​​are determined and the voltage and loss values ​​are reduced to the actual short-circuit voltage. according to the formulas:

, (3.9)

Where I A, I B, I C– phase currents during experiment.

, (3.10)

Where U AB, U BC, U AC- line voltages on the high side of the transformer, measured experimentally.

, (3.11)

Where R a, R v, R s- phase powers measured during short-circuit testing.

, (3.12)

Where U K %- short circuit voltage as a percentage of the rated voltage;

U N- the nominal value of the winding to which voltage is supplied.

I N- the rated current value of the winding to which voltage is supplied.

Power supplied to the transformer in short circuit mode at rated voltage:

, (3.13)

According to catalog data P KN = 1290 W for transformer TM-63/10. Short circuit losses of transformers consist of the sum of losses in the windings åI 2 R, (R is the active phase resistance of the transformer winding) and additional losses P ext. from the passage of magnetic leakage fluxes through the walls of the tank, the metal parts of the magnetic core fastening and the conductors of the windings themselves, as well as losses in the magnetic core from magnetization. Magnetization losses are neglected due to their small value (less than hundredths of a percent). Then R ext. = R k - åI 2 R .

The obtained calculation results should be reduced to a nominal winding temperature of 75 ° C (according to GOST II677-65) according to the formulas:

, (3.14)

Where tmeas.- temperature at which the experiment was carried out, 0 C;

R n- rated power of the transformer (at сosj=1, R n=сosj ×S=63 kW).

, W; (3.15)

Based on the measurements, it is necessary to construct the short circuit characteristics. I k , P k =f(U k).

8 When measuring the DC resistance of transformer windings, the following characteristic defects may be revealed:

a) poor-quality soldering and poor contacts in the winding and in the connection of the inputs;

b) break of one or more parallel conductors.

Measurement active resistance The windings in this case are made using the bridge method or the ammeter and voltmeter method. The measurement is carried out on all branches and on all phases. These measurements should be entered in Table 3.8.

Table 3.8- Resistance of transformer windings to direct current

After all measurements have been carried out, a summary table 3.9 of test results is compiled and a conclusion is given on the technical condition of the transformer and its suitability for operation.

Table 3.9 - Summary table of test results given to normal conditions(75°C)

Note:

Conclusion:

Contents of the report. In the report, state the purpose of the work, write down the passport data of the transformer, give brief description control tests of transformers, draw diagrams for testing and measurements, present tables with experimental and calculated data and give their analysis, draw the characteristics of the cold-circuit, short-circuit characteristics, make a conclusion about the suitability of the transformer for operation.

Test questions.

1 What is the purpose of grounding the transformer windings before starting to measure the insulation resistance?

2 Name the main characteristics of transformer insulation.

3 What are the consequences of reducing the insulation resistance of the transformer winding?

4 How does the absorption coefficient change depending on the degree of moisture insulation and how is this explained?

5 How to measure the insulation resistance of the windings of power two-winding transformers?

6 For what purpose is the transformation ratio of a transformer measured?

7 What methods of checking the connection group of transformer windings are used in practice? Why is the two-voltmeter method the most common?

8 When measuring the transformation ratio, the following data were obtained: K av = 25, K sun = 25, K ac = 30. Determine the malfunction in the transformer.

9 How and for what purpose is the electrical strength of the main insulation of transformer windings tested?

10 For what purpose is the DC resistance of transformer windings measured and by what methods?

11 What is the purpose of the no-load test and why is it carried out after the electrical insulation strength test?

12 For what purpose and how is the short circuit experiment carried out?

13 What parameters of the transformer are determined from no-load and short circuit experiments?

LABORATORY WORK No. 4

DEFECTIVENESS OF INDUCTION ELECTRIC MOTORS

WITH SHORT-CIRCUIT AND PHASE ROTOR

DURING REPAIR

Purpose of the work: to study the main malfunctions of asynchronous electric motors and the causes of their occurrence, to master the methodology for detecting malfunctions of asynchronous electric motors.

Work program.

1 Conduct an external inspection of the electric motor and write down the passport data.

2 Carry out fault detection of the electric motor before disassembling:

Measure the DC resistance of the windings;

Measure the insulation resistance of the stator windings relative to the housing and relative to each other;

Check the rotation of the rotor and the absence of visible damage that would prevent further testing and inspection.

3 Disassemble the electric motor.

4 Carry out fault detection of the electric motor in disassembled form:

Check the condition of the mechanical parts and components of the electric motor;

Measure the size of the air gap between the stator and the rotor;

Check the absence of short-circuited turns (turn short circuit), a break in the winding;

Determine the location of damage to the stator windings;

Determine, record winding data and draw a winding diagram;

Check the condition of the stator active steel;

Check the rotor squirrel cage for breaks in the rods and rings.

If there is an electric motor with a wound rotor, then fault detection of the rotor winding is carried out in the same way as fault detection of the stator winding. Additionally, the insulation strength of the slip rings is tested and the condition of the active steel of the rotor is checked;

All detected malfunctions of mechanical parts, rotor and stator windings, electric motor data should be entered into the defect list or technological map repair.

1 Asynchronous electric motors received for repair are carefully inspected, and, if necessary, tested and disassembled in order to fully identify the causes, nature and extent of damage. Inspection of the electric motor, familiarization with the scope and nature of previous repairs and operational logs, as well as testing allow us to assess the condition of all assembly units and parts of the electric motor and determine the scope and timing of repairs, and draw up technical documentation for repairs.

Electric motors are most often damaged due to unacceptably long operation without repair, poor maintenance or violation of the operating mode for which they are designed.

Damage can be mechanical or electrical.

To mechanical damage include: smelting of babbitt in plain bearings, destruction of the cage, ring, ball or roller in rolling bearings; deformation or breakage of the rotor shaft; loosening of the stator core to the frame, rupture or slipping of the rotor wire bands; weakening of the compaction of the rotor core and others.

Electrical damage are: breakage of conductors in the winding, short circuit between the turns of the winding, broken contacts and destruction of connections made by soldering or welding, breakdown of insulation on the housing, unacceptable decrease in insulation resistance due to its aging, destruction or moisture, etc.

A short list of the most common faults and possible causes of their occurrence in asynchronous machines is given in Table 4.1.

Malfunctions and damage to electric motors cannot always be detected by external inspection, since some of them (turn short circuits in the stator windings, breakdown of insulation on the housing, soldering failure in the windings, etc.) are hidden and can only be determined after appropriate tests and measurements.

Table 4.1 - Malfunctions of asynchronous machines and possible causes of their occurrence

2 Defects of the electric motor before disassembly.

The number of pre-repair operations to identify faults in electric motors includes: measuring the insulation resistance of the windings, checking the integrity of the windings, testing the electrical strength of the insulation, checking the bearings at idle speed, the value of the axial run of the rotor, determining the condition of fasteners, the absence of damage (cracks, chips) in individual electric motor parts:

a) measuring the direct current resistance of the windings is carried out in order to check the absence of breaks in the winding, for example, due to a violation of the integrity of the connections as a result of poor-quality soldering. Resistance is measured using a DC bridge UMV, P353 and others with an accuracy class of at least 0.5. The measured winding resistances should not differ from each other by more than 2%;

b) measurement of the insulation resistance of the electric motor windings is carried out according to the methodology set out in the general instructions (page 8-9) .

c) the rotor of the electric motor is turned to check its free rotation and the presence of overrun. For small machines this operation is carried out manually. Such a check is required before the first start-up of the machine or after parking it for a long time in conditions where foreign objects could get into the machine.

3 The electric motor is disassembled using metalworking tools.

4. Defects of the disassembled electric motor are carried out in the following order:

4.1 Determine the condition of mechanical parts and individual components by external inspection.

4.2 Check the size of the air gap with a set of feeler gauges at at least four points, turning the rotor clockwise through an angle of 90°. The arithmetic mean value of the measurement results is compared with acceptable values(Table 4.2). The deviation should not exceed ±10%.

Table 4.2 - Normal values ​​of air gaps

asynchronous motors

4.3 Determine insulation damage in the electric motor that leads to short circuits.

Depending on the type of insulation damage, the following short circuits are possible:

Between the turns of one coil in a groove or frontal parts (turn short circuit) in case of damage to the interturn insulation;

Between coils or coil groups of the same phase in case of damage to the intersection insulation;

Between coils of different phases in case of damage to the interphase insulation;

Short circuit to the housing when the slot insulation is damaged.

Passing alternating current undervoltage Through the individual phases of the winding, the location of the turn short circuit can be determined. Short-circuited turns when the phase is turned on are like the secondary winding of an autotransformer, short-circuited. Large currents flow through the short-circuited turns, which heat the front part of the winding. Based on local heating, the location of the turn circuit is determined.

A closed turn is easily determined using a horseshoe-shaped electromagnet.

Figure 4.1 - Finding a closed turn using an electromagnet and a steel plate, where it is indicated: a) there is no short circuit of the turns; b) there is a closure of the turns; 1 - winding conductor; 2 – electromagnet; 3 - steel plate; F - magnetic flux of the magnet; F pr - magnetic flux of a short-circuited conductor with current.

To find short-circuited turns in the winding sections, the electromagnet is installed parallel to the stator slots. After turning on the electromagnet winding in electrical network alternating current (220 V at a frequency of 50 Hz), a current will flow through the winding, which will create a magnetic flux F, closing through the electromagnet core and part of the magnetic circuit of the stator of the electric motor. This alternating magnetic flux will induce an emf in the conductors covered by the loop.

In the absence of turn short circuits (Figure 4.1-a) in the winding, the EMF does not cause the appearance of current (there is no closed circuit for it). If there are short-circuited turns, the EMF will cause a current to appear in them, and of a significant magnitude due to the low resistance of the circuit. The current will create a magnetic flux F pr around the short-circuited turns (Figure 4.1-b). The latter are easily detected by a steel plate, which is attracted to the stator teeth above this groove. In production, an EL-1 type device is also widely used to determine turn faults.

Short to body(if the megohmmeter shows zero) can be determined using a millivoltmeter. This method is associated with alternately wiring the winding into separate coils and checking each of them. Voltage is supplied to both ends of the damaged phase from one terminal of the battery with a voltage of up to 2.5 V, and the second terminal is connected to the housing. When measuring the voltage on each coil, a change in the polarity of the instrument reading indicates the passage of the point of phase closure to the housing. Due to the complexity of the work, this method is not always acceptable, especially when large number coils

It is better to use the magnetic method (2), which is based on the following. From a reduced voltage source (U to 36 V), single-phase alternating current is supplied to the end (or beginning) of the faulty phase and through a rheostat and ammeter to the motor housing. Since the current is alternating, an alternating electromagnetic field is formed around the conductors with this current. Therefore, the grooves with a conductor through which current flows are easily determined using a thin steel plate (probe), which rattles slightly. The latter makes it possible to identify sections through which current flows from the end of the phase winding to the point of short circuit to the housing. To check and clarify the location of the winding short circuit found, the current is now supplied to the beginning of the faulty phase. With a single winding short circuit, the found short circuit locations in the first and second cases should converge.

The faulty coil found by the magnetic method is disconnected from the rest of the winding and the correct location of the short circuit to the housing is checked with a megohmmeter.

The same method can be used to find the location of a fault between phases.

In this case, voltage is applied first to one end of the closed phases, and then to the other. This makes it possible to identify closed sections.

Internal break of one of the phases.

If the winding has six terminals, then the broken phase is determined using a tester or a megohmmeter.

If the winding has only three terminals, then the broken phase is determined by measuring currents or resistances.

When connecting the phases in a star, (Figure 4.2) the current of the broken phase equal to zero, and the resistance measured relative to the output of the broken phase is equal to “infinity”.

Figure 4.2 - Determination of internal phase loss when connecting phases in a star.

When connecting the phases in a triangle, the currents approaching the broken phase (Figure 4.3) will be equal to and less than the currents in the (unbroken) phase, and the resistance measured on the broken phase (C1-C3) will be twice as large as the other phases (C1-C2, S2-NW).

Figure 4.3 - Determination of internal phase loss when connecting phases in a triangle.

After determining the broken phase, the location of the break is determined with

Figure 4.4 - Determining the location of a break in a broken phase:

a) using a voltmeter; b) using a control lamp.

Measure the voltage at the ends of each coil or coil group. At the moment the voltmeter reads, a broken coil is detected (Figure 4.4a). By touching the probe from the lamp to the beginning and end of each coil, coming from the potential end of the network, the lamp reading will indicate a break (the lamp goes out, which means there is a break, if on the other side, then vice versa).

For one of the induction motors under consideration (with a faulty coil), determine and record the winding data and draw the winding diagram.

Inspect the stator active steel package. The steel package should not have displacement, dents, weakening of the pressing of iron sheets, fluffy teeth, or burnout.

The integrity of the squirrel-cage rotor rods is determined by the AC electromagnet method. During testing, the rotor is installed on an electromagnet connected to the alternating current network (Figure 4.5).

A steel plate that overlaps a groove with a whole rod will be attracted and rattle. If the rod is torn, the plate does not attract or attracts very weakly. The location of the rupture is detected using a sheet of paper with steel filings sprinkled on it.

Detected malfunctions of mechanical parts, stator and rotor windings, data of electric motors submitted for defect detection should be entered in the defect list or repair flow chart.

TECHNOLOGICAL CARD No.

Customer ______________________________

I Technical characteristics

II Winding data

Note_____________________________________________________

III Mechanical part

IV Winding monitoring

Notes__________________________________________________________

V Bench tests

Head of Quality Control _____________________________________________________

Contents of the report. The report must include: the purpose of the work, basic diagrams and data on identifying faults in electric motors submitted for fault detection, sketches of missing parts that require manufacturing, a completed repair flow sheet, a detailed diagram of the stator winding of the motor whose winding needs to be replaced, a conclusion on the results of fault detection of electric motors .

Test questions.

1 For what purpose is an electric motor defective before repair?

2 In what sequence and how is the electric motor fault detection carried out before disassembly?

3 What are the consequences of reducing the insulation resistance of the stator winding and what should it be for motors with U< 500 В?

4 How to detect a turn short circuit in the stator winding when the electric motor is running?

5 In what sequence and how is the electric motor defective after disassembly?

6 What are the main faults in the stator winding and how to identify them?

7 When an electric motor with a squirrel-cage rotor is connected to the network, increased heating of the active stator steel is observed in idle mode. What is the problem with the electric motor?

8 When the electric motor operates, the stator winding becomes very hot. The magnitude of the current is not the same across the phases. The electric motor makes a loud noise and develops reduced torque. What could be the problem with the engine?

9 The electric motor runs poorly and makes a loud noise. The current value in all phases is different and when the engine is idling it exceeds the rated value. What is the problem with the electric motor?

10 A squirrel-cage motor does not reach normal speed rotation, but “gets stuck” and begins to work stably at a low rotation speed, which is significantly less than the nominal one. What is the problem with the electric motor?

LABORATORY WORK No. 5

Testing an asynchronous electric motor

with wound rotor after repair

Purpose of the work: to master the testing methodology for an electric motor with a wound rotor after repair.

Work program:

1 Inspect the electric motor, check the tightness of the mounting bolts, the rotation of the rotor, write down the passport data.

2 Measure the insulation resistance of the stator windings relative to the housing and relative to each other and the insulation resistance of the rotor windings relative to the housing.

3 Mark the output ends for direct and alternating current.

4 Measure the resistance of the stator and rotor windings to direct current.

5 Check the transformation ratio of an asynchronous electric motor with a wound rotor.

6 Carry out an idle test.

7 Carry out a turn-to-turn insulation test.

8 Carry out a short circuit experiment.

9 Carry out an insulation strength test.

1 During an external inspection of the electric motor, check the tightening of the mounting bolts and the rotation of the rotor. When rotating the rotor manually, there should be no jamming or play in the bearings. The passport data of the electric motor is recorded.

2 Measuring the insulation resistance of the electric motor windings is carried out according to the methodology set out in the general instructions (page 8-9) . . Record the measurement data in table 5.1.

Table 5.1- Insulation resistance of electric motor windings

3 GOST 183-66 provides designations for winding terminals electric machines three-phase alternating current (table 5.2).

Table 5.2 - Designation of the winding terminals of three-phase alternating current electrical machines

Typically, the terminals of all phases of the stator winding are connected to the terminals, as shown in Figure 5.1 a. In some machines, the stator windings are tightly connected in a star and only four terminals are connected to the terminal board: phases C1, C2, C3 and zero point 0.

If there is no marking of the stator winding terminals, then paired phase terminals are first found using a test lamp; one of the phase terminals is taken as the beginning of the winding and connected to the plus of a DC source with a voltage of 4-6 V; one of the terminals of the test lamp is connected to the negative of the source, and the second terminal of the lamp is used to find the end of the phase winding. Or a megohmmeter is connected with the “Line” clamp of the megohmmeter to the expected beginning of the phase of the stator winding and the end of the phase is found with a wire connected to the “Earth” terminal of the megohmmeter. In this case, the megohmmeter will show zero. After this, a tag with markings (C1, C2 ...) is put on each phase terminal.

Marking of the output ends is carried out using direct or alternating current. With direct current, two options are most common (Figure 5.2)

The terminals are marked using a battery ( U = 4 - 6 V) and a millivoltmeter (M104).

In the first option a) we take C1, C2, SZ as the beginning of phases 1,2,3, and C4, C5, C6 as the ends of these phases. If the beginning of phase 1 is connected to the “plus” of the battery, and the end to the “minus” (Fig. 5.2, a) , then at the moment the current is turned on, an EMF with polarity “minus” at the beginning and “plus” at the ends of the phases will be induced in the windings of other phases (2 and 3). The millivoltmeter is connected to phase 2, and then to phase 3. If the arrow of the device in both cases deviates to the right, then all ends of the windings are marked correctly.

Figure 5.2 - Schemes for checking the marking of stator terminals using a direct current source: a) - first option; b) and c) - second option; N and K - respectively, the beginnings and ends of windings 1,2,3.

In the second option b) and c) two phases are connected in series (in pairs) with each other and the pulse is switched on to the battery. A millivoltmeter is connected to the third phase. If the first two phases are connected by terminals of the same name (Figure 5.2.b.), the millivoltmeter will not show anything. When the phases are connected with opposite terminals (Figure 5.2.c), at the moment the battery is turned on, the millivoltmeter needle will deflect to the right.

With alternating current and with six phase ends removed, the most common is the induction method of marking the terminals (Figure 5.3).

Figure 5.3 - Scheme of the induction method for marking stator leads using an alternating current source:

N and K - respectively the beginnings and ends of windings 1,2,3;

T V - adjustment transformer.