Method for simulating and measuring turn-to-turn short-circuit current of electric motor

Abstract

A method for simulating and measuring a turn-to-turn short-circuit current of an electric motor, in order to overcome technical defects of existing methods for detecting turn-to-turn short-circuit damage in a coil causing an irreversible damage to an electric motor, being incapable of measuring a turn-to-turn short-circuit current of the coil, having an uncontrollable test process, etc. The method comprises: simulating a back electromotive force of an electric motor on the basis of an electric motor model, calculating a reactance value and a resistance value of the electric motor, and on the basis of the back electromotive force and the reactance value, estimating a theoretical value of a turn-to-turn short-circuit current during the operation of the electric motor; then, designing an external test circuit on the basis of the theoretical value, and constructing a test apparatus; after the construction of the test apparatus is completed, installing the electric motor on a test bench, and measuring the back electromotive forces of a single coil turn under different rotating speeds of the electric motor; and measuring a resistance value of a resistor connected in parallel with the external circuit to calculate a turn-to-turn short-circuit current value of a coil after the external circuit is removed, determining the maximum safe rotating speed threshold value for a test of the electric motor on the basis of the turn-to-turn short-circuit current value of the coil, and finally measuring a back-driving turn-to-turn short-circuit current after the resistor is removed.

Description

A method for simulating and testing short-turn current of a motor

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number CN202311792312.6 and application date of December 25, 2023, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby incorporated into this disclosure by introduction. Technical Field

[0003] The present disclosure relates to the technical field of simulation and testing of motor short-turn faults, and in particular to a method for simulating and testing a motor short-turn current. Background Art

[0004] Permanent magnet synchronous motors (PMSMs) generate back electromotive force during operation. When a short-turn fault occurs in the coil, the short-turn current can instantly reach several thousand amperes due to the low resistance of the short-turn windings. This can damage the motor coils and even cause the motor to burn out. In rail transit, due to the limitations of vehicle routes, when a PMSM short-turn fault occurs, the vehicle must wait for assistance or operate at a low speed to prevent further damage from the short-turn current, disrupting traffic flow.

[0005] To assess the extent of motor damage caused by coil shorting during actual vehicle operation, the current traction motor design process involves mechanically short-circuiting the two coils to simulate actual conditions. However, this method causes irreversible damage to the motor coils and can only simulate the hazards of coil shorting, failing to theoretically assess the short-circuit current and damage mechanism. Furthermore, when a short circuit occurs between the two turns, the relatively low resistance between the two turns causes a short-term high current surge in the loop, leading to severe heating and coil damage. Existing methods also involve using a hairpin to damage the insulation between the two turns or wedging a nail or other sharp metal object between the two turns to physically create a short-circuit. The permanent magnet synchronous motor is then reverse-towed using a load machine, and the extent of coil damage is observed as the speed increases, thereby assessing the motor's short-circuit damage. However, this method of detecting short-turn damage in the coil is simple and limited, and will cause irreversible damage to the motor. It is also unable to detect the short-turn current of the coil, and there is no theoretical support for the damage caused by short-turn damage to the coil. At the same time, the test process may become uncontrollable, and it may easily cause motor smoke and fire, and test device burnout, etc., which is very dangerous.

[0006] Therefore, a method for simulating and testing the short-circuit current of the coil turns is urgently needed in the traction motor design process. Summary of the Invention

[0007] To overcome the technical shortcomings of existing methods for detecting coil short-turn damage, such as irreversible damage to the motor, inability to detect coil short-turn current, and uncontrollable testing processes, this disclosure provides a method for simulating and testing motor short-turn current. This method enables detection and analysis of coil short-turn current.

[0008] The present disclosure provides a method for simulating and testing a short-turn current of a motor, comprising the following steps:

[0009] Step 1: Based on the motor model, simulate the back EMF value of the traction motor at various speeds when no-load, calculate the reactance value Xr and resistance value Rr of the motor's single-turn coil, and finally deduce the theoretical value of the motor's short-circuit current at various speeds when no-load;

[0010] Step 2. Design an external test circuit according to the theoretical value of the short-circuit current of the motor turn at each no-load speed. The external test circuit includes a single-turn motor coil connected in series, a test line connected to the single-turn coil, and an external resistor. In addition, a parallel voltmeter in the external test circuit measures the back electromotive force of the single-turn motor coil, and a series ammeter in the external test circuit measures the current value in the circuit. Construct a test device according to the external test circuit. The test line selects an electromagnetic wire with the same material as the motor coil, and the number of test lines is two, which are respectively connected to the first turn of the coil and the second turn of the coil. The two test lines are respectively welded to the coil and then wrapped. Then, the two test lines are led out from the wire outlet hole of the machine base. The external resistor selects an adjustable resistance cabinet, and the adjustable resistance cabinet is connected to the two test lines to form a loop.

[0011] Step 3: Based on the test device constructed in Step 2, use a voltmeter to measure the inter-turn voltage of the motor at different speeds when the test device is not connected to an external resistor, and compare the inter-turn voltage with the back EMF value simulated in Step 1;

[0012] Step 4: Detect the resistance value of the test line, which is R 线 , then connect the adjustable resistor cabinet to the test device, the resistance of the adjustable resistor cabinet is R 外 , drag the motor to a certain speed, record the voltage and current values ​​corresponding to different speeds, and infer the reactance Xr and resistance Rr of the motor's single-turn coil through the voltage and current values;

[0013] Step 5: Calculate the maximum safe speed threshold corresponding to the motor based on the reactance value Xr, resistance value Rr and maximum safe current value of the motor's single-turn coil;

[0014] Step 6. Remove the adjustable resistance cabinet in the test device, and drag the motor to repeat the short-turn current test at different speeds. The motor speed starts at 100 r / min and increases by 100 r / min each time. The maximum speed does not exceed the maximum safe speed threshold calculated in step 5. Record the corresponding voltage and current values ​​at different speeds respectively, and make a voltage-current curve graph based on the voltage and current values. Calculate the current value at the highest back electromotive force based on the voltage-current curve graph.

[0015] In the method disclosed herein, an external resistor is introduced when designing the external test circuit. This effectively prevents a short circuit between two turns, which, due to the relatively small resistance between the two turns of the coil, can cause a large current surge in the loop, leading to severe heating and damage to the coil. Furthermore, the method disclosed herein introduces a test line, which, because the test line itself has resistance, can further prevent current surges caused by a coil short circuit. The method can detect the short-circuit current of the coil without causing irreversible damage to the motor's own coil.

[0016] The technical solution provided by the present disclosure has the following advantages over the existing technology: the present disclosure simulates the situation where the power supply is cut off after a short-turn fault occurs in the motor at different vehicle speeds through ground tests, and can detect the loop current value in the single-turn coil of the motor during the vehicle running at different speeds. Therefore, the loop current value can provide theoretical support for the analysis of the damage mechanism of the short-turn coil; the method described in the present disclosure can avoid direct damage to the motor coil and prevent irreversible damage to the motor; and the test process is controllable, which can effectively avoid the occurrence of faults such as motor smoking, fire and burning of test devices, thereby ensuring the safety of test personnel and improving the safety factor of the overall test. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0018] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] FIG1 is a flow chart of a method for simulating and testing a short-turn current of a motor according to an embodiment of the present disclosure;

[0020] FIG2 is a circuit diagram of a test external circuit in a motor short-turn current simulation and testing method according to an embodiment of the present disclosure;

[0021] FIG3 is a schematic diagram showing the connection between two test wires and a coil in an experimental device for simulating and testing a motor short-turn current according to an embodiment of the present disclosure.

[0022] FIG4 is a schematic diagram showing the arrangement of the first turn and the second turn of a coil connecting two test wires in an embodiment of the present disclosure:

[0023] FIG5 is a schematic diagram of connecting two test lines in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0024] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features therein can be combined with each other in the absence of conflict.

[0025] In the description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance. It should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, removable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms based on specific circumstances.

[0026] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0027] The specific embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

[0028] In an optional embodiment of the present disclosure, as shown in FIG1 , the present disclosure provides a method for simulating and testing a short-turn current of a motor, comprising the following steps:

[0029] Step 1: Based on the motor model, simulate the back EMF value of the traction motor at various speeds when no-load, calculate the reactance value Xr and resistance value Rr of the motor's single-turn coil, and finally deduce the theoretical value of the motor's short-circuit current at various speeds when no-load;

[0030] Step 2. Design an external test circuit according to the theoretical value of the short-circuit current of the motor turn at each no-load speed. The external test circuit includes a single-turn motor coil connected in series, a test line connected to the single-turn coil, and an external resistor. In addition, a parallel voltmeter in the external test circuit measures the back electromotive force of the single-turn motor coil, and a series ammeter in the external test circuit measures the current value in the circuit. Construct a test device according to the external test circuit. The test line selects an electromagnetic wire with the same material as the motor coil, and the number of test lines is two, which are respectively connected to the first turn of the coil and the second turn of the coil. The two test lines are respectively welded to the coil and then wrapped. Then, the two test lines are led out from the wire outlet hole of the machine base. The external resistor selects an adjustable resistance cabinet, and the adjustable resistance cabinet is connected to the two test lines to form a loop.

[0031] Step 3: Based on the test device constructed in Step 2, use a voltmeter to measure the inter-turn voltage of the motor at different speeds when the test device is not connected to an external resistor, and compare the inter-turn voltage with the back EMF value simulated in Step 1;

[0032] Step 4: Detect the resistance value of the test line, which is R 线 , then connect the adjustable resistor cabinet to the test device, the resistance of the adjustable resistor cabinet is R 外 , drag the motor to a certain speed. In a specific embodiment, the speed can be adjusted to 500r / min, 1000r / min, 1500r / min, etc., and record the voltage and current values ​​corresponding to different speeds. The reactance value Xr and resistance value Rr of the motor single-turn coil are inferred from the voltage and current values;

[0033] Step 5: Calculate the maximum safe speed threshold corresponding to the motor based on the reactance value Xr, resistance value Rr and maximum safe current value of the motor's single-turn coil;

[0034] Step 6. Remove the adjustable resistance cabinet in the test device, and drag the motor to repeat the short-turn current test at different speeds. The motor speed starts at 100 r / min and increases by 100 r / min each time. The maximum speed does not exceed the maximum safe speed threshold calculated in step 5. Record the corresponding voltage and current values ​​at different speeds respectively, and make a voltage-current curve graph based on the voltage and current values. Calculate the current value at the highest back electromotive force based on the voltage-current curve graph.

[0035] In the method disclosed in the present invention, an external resistor is introduced when designing the test external circuit, which can effectively avoid the situation where a short circuit occurs between two turns. Since the resistance value between the two turns of the coil is relatively small, it will cause a large current shock in the loop, resulting in severe heating and damage to the coil. In addition, the test line is introduced in the method disclosed in the present invention. Since the test line itself has resistance, it can further prevent the current shock caused by the coil short circuit. The method can detect the short-circuit current of the coil without causing irreversible damage to the motor's own coil. The maximum safe current value in step five is known. In this embodiment, based on the maximum electrical density of 40, the maximum safe current I = 650A.

[0036] The above description is merely a specific embodiment of the present disclosure, which enables those skilled in the art to understand or implement the present disclosure. Although detailed descriptions have been made with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents; and such modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments, and they should all be covered by the scope of protection of the claims.

Claims

1. A method for simulating and testing the short - circuit current of motor windings, wherein, It includes the following steps: Step 1: According to the model of the motor, simulate the back electromotive force values at various speeds of the traction motor under no-load conditions, calculate the reactance value Xr and resistance value Rr of a single-turn coil of the motor, and finally deduce the theoretical values of the turn-to-turn short-circuit current of the motor at various speeds under no-load conditions; Step 2: Design the test external circuit based on the theoretical values of the turn-to-turn short-circuit current of the motor at various no-load speeds. The test external circuit includes a single-turn coil of the motor connected in series, a test wire connecting the single-turn coil, and an external resistor. In addition, a voltmeter is connected in parallel in the test external circuit to measure the back electromotive force of the single-turn coil of the motor, and an ammeter is connected in series in the test external circuit to measure the current value in the circuit; construct a test device according to the test external circuit. The test wire selects electromagnetic wire with the same material as the motor coil, and the number of test wires is two, which are respectively connected to the first turn and the second turn of the coil. After the two test wires are welded to the coil respectively, they are bandaged, and then the two test wires are led out from the wire outlet hole of the machine base. The external resistor selects an adjustable resistor cabinet, and the adjustable resistor cabinet is connected to the two test wires to form a loop; Step 3: Based on the test device constructed in Step 2, use a voltmeter to measure the turn-to-turn voltage of the test device at different speeds of the motor when the external resistor is not connected, and compare the turn-to-turn voltage with the back electromotive force value simulated in Step 1; Step 4. Detect that the resistance value of the test line is R 线 , then connect an adjustable resistor cabinet to the test device, and the resistance value of the adjustable resistor cabinet is R 外 , drive the motor to a certain speed, record the corresponding voltage and current values at different speeds respectively, and calculate the reactance value Xr and resistance value Rr of a single-turn coil of the motor by inversely deducing from the voltage and current values; Step 5: Calculate the highest safe speed threshold of the motor according to the reactance value Xr, resistance value Rr of the single-turn coil of the motor, and the maximum safe current value; Step 6: Remove the adjustable resistor cabinet from the test device, drag the motor to repeat the turn-to-turn short-circuit current test at different speeds. The motor speed starts from 100 r / min and increases by 100 r / min each time, and the maximum speed does not exceed the highest safe speed threshold calculated in Step 5. Record the corresponding voltage values and current values at different speeds respectively, make a voltage-current curve graph according to the voltage values and current values, and deduce the current value at the highest back electromotive force according to the voltage-current curve graph.

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