Surge testing method and system for a bar-wound stator

A method for surge testing a bar-wound stator includes electrically connecting a conductive lead of a test system to a corresponding welded hair pin in each of the layers mid-way through the stator windings. A calibrated voltage surge is applied via the conductive leads into the windings of the stator at the welded hair pins. The method includes measuring a voltage drop between turns of the windings after applying the calibrated voltage surge, recording the measured voltage drop in memory of the test system, and executing a control event with respect to the stator when the measured voltage drop is more than a calibrated threshold voltage drop. A system for surge testing the bar-wound stator includes a test device having a capacitor for storing the calibrated surge voltage and a pin set that is electrically connected to the test device. The pin set includes the conductive wires and leads.

TECHNICAL FIELD

The present disclosure relates to a method and a system for surge testing of a bar-wound stator of a poly-phase electric motor.

BACKGROUND

A stator of a poly-phase electric motor typically undergoes electrical testing during manufacturing. Surge testing is one such test. During conventional surge testing, a capacitor is rapidly discharged to inject a voltage surge into the phase leads of the stator. This rapid electrical discharge produces a sinusoidal wave for one or more phases of the electric motor. The voltage surge stresses the stator's insulation, and thus can be used to detect electrical shorts or other potential insulation issues.

In a bar-wound stator, conductive coils of wire are replaced with solid copper bars known as “hair pin” conductors. The hair pins are individually inserted into slots of a laminated stack of the stator. The hair pins are generally configured with a curved section terminating in a pair of wire ends and are formed into a shape suitable for insertion into the stator slots. An insulating material is used prior to insertion of the hair pins in the stator slots such that adjacent surfaces of the hair pins are electrically insulated with respect to each other and from the laminated stack. Portions of the wires protruding from the laminated stack after insertion of the hair pins are bent or twisted to form a complex weave pattern, thereby creating wire end pairs. Adjacent wire end pairs are typically welded together at one side of the laminated stack to form the required electrical connections/circuits between the various layers of the stator.

SUMMARY

A method is disclosed herein for surge testing of a bar-wound stator, e.g., of the type used in some high-voltage electric traction motors. As is well understood in the art, a bar-wound stator differs substantially from a conventional wire-wound stator in the use of individual conductive bars in the stator slots in lieu of pre-wound coils of wire. The slots of a bar-wound stator have a significantly higher copper fill than the slots of a typical wire-wound stator. A bar-wound design thus exhibits unique performance characteristics. However, it is recognized herein that conventional surge testing alone may be less than optimal when used with bar-wound stators due to how the inductive load of a given coil changes when the same phase changes layers within the stator. The present method may be used to help solve this potential problem.

A bar-wound stator may have multiple interconnected layers. Each stator pole may be welded into a welded joint and insulated at one or both ends or sides of the laminated stack. The phase leads extend from the opposite end or side of the stack. Conventional surge testing electrically grounds two of the phase leads and injects a surge voltage into the remaining phase lead. This process can be repeated until each of the phase leads has been surge tested. A substantial percentage of electrical failures in a given motor occur at the coil turns between phases or turns of the same phase, for instance due to insufficient or stressed insulation at these locations. The present approach may be used to augment conventional surge testing techniques by directly accessing and stressing the stator at the approximate middle point of the layers, e.g., using the presently disclosed test system.

In particular, a method is disclosed for surge testing a bar-wound stator. The stator tested according to the present method includes a plurality of welded hair pins arranged to form a plurality of stator layers. The method includes electrically connecting a conductive lead of a test system to a welded hair pin of each of the layers of the stator such that each conductive lead is electrically connected to the stator approximately mid-way through windings of the corresponding layer. The method further includes applying a calibrated voltage from a capacitor to the windings of the stator via the conductive leads, and then measuring a voltage drop between the layers at turns of the windings. The measured voltage drop is then recorded in memory of the test system. A control event may be executed with respect to the stator in response to the level of the measured voltage drop.

A test system is also disclosed for surge testing a bar-wound stator. As noted above, the stator has welded hair pins arranged in a plurality of layers. The test system includes a test device having a capacitor. The capacitor is in electrical communication with a power supply/line through a set of power conditioning components, and is configured for storing a calibrated voltage when charged via the components. The test device selectively discharges the calibrated voltage as a calibrated voltage surge or spike.

A pin set is electrically connected to the test device. The pin set includes wires and a plurality of conductive leads. Each of the conductive leads is connected at one end to a corresponding one of the wires, and at another end to the test device. The conductive leads are selectively connectable to a welded hair pin of the stator, prior to insulating the welds, at each of the layers approximately mid-way through windings of the corresponding layer.

The test device is configured to selectively discharge the capacitor to thereby apply the calibrated voltage surge into the windings of the stator via the conductive leads. The test device also calculates a voltage drop between the layers at turns of the stator windings after discharging the capacitor. The test device may record the measured voltage drop in memory, and then execute a control event with respect to the stator in response to the value of the measured voltage drop.

The above features and advantages are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

DETAILED DESCRIPTION

Referring to the drawings, wherein like reference numbers represent like components throughout the several figures, an example bar-wound stator10is shown schematically inFIG. 1. The stator10is connected to a test system70during surge testing of the stator10as described below. The stator10may be sized and configured for use in, for example, a high-voltage (e.g., approximately 300 VDV) electric traction motor of a hybrid electric vehicle, an electric vehicle, or other system requiring motor torque for population or other purposes. The stator10has at least two layers of windings12, but may include as many additional layers as are required for the particular application in which the stator10is to be employed.

The test system70includes a test device50and a pin set15. The test device50is configured to execute a set of process instructions embodying a surge testing method100. In executing such instructions, the test device50ultimately discharges a calibrated voltage (arrows21) as a surge into the windings12of the stator10via the pin set15, doing so at the approximate mid-point of the various layers of the stator10.

It is recognized herein that a bar-wound design such as that of the stator10shown inFIG. 1and similar designs may be isolated or broken out into individual electrical circuits. As a result, the windings12of the stator10may be directly and more fully stressed during surge testing via cooperative use of a conventional surge tester60and the present test system70.

The example test system70ofFIG. 1may include an optional test probe17. The test probe17is configured for measuring a voltage (arrow23), hereinafter referred to as the measured voltage. The measured voltage (arrow23) may be received from the test probe17and recorded in memory55of the test device50. The measured voltage (arrow23) may be used to calculate a voltage drop relative to the calibrated voltage (arrows21) at various locations of the stator10, e.g., between phases or between windings12. In other embodiments, the test probe17may be part of a separate voltmeter that is placed in communication with the test device50, such that the measured voltage is ultimately transmitted to and received by associated hardware and software portions of the test device50as described below.

The stator10ofFIG. 1includes an annular laminated stack16having a first side11and a second side13. The laminated stack16may be formed by stacking laminations in a specific pattern, as is understood in the art. The lamination stack16defines a plurality of generally rectangular stator slots18. The stator slots18are equally spaced and extend end-to-end between the first side11and the second side13within the laminated stack16.

In the stator10shown inFIG. 1, each winding12is formed from a plurality of conductive bars or hair pins24. The windings12may also include terminals or connections forming phase leads20,120, and220. The hair pins24may be formed from a relatively heavy gauge, high conductivity wire such as copper, and with a generally rectangular cross section. Each hair pin24may have a curved section22, and may terminate in wire ends28. The hair pins24are accurately formed into a predetermined shape for insertion into the stator slots18in a weave pattern.

The hair pins24ofFIG. 1may be coated with a suitable insulating material26prior to insertion into the stator slots18, such that the adjacent surfaces of the hair pins24within the stator slots18are electrically insulated with respect to each other. To facilitate joining of the wire ends28, the wire ends28may be typically stripped of the insulating material26prior to insertion into the stator slots18. Each stator slot18may be lined with a slot liner30to help insulate the hair pins24from the laminated stack16and from each other, and to prevent damage to the insulating material26during insertion of the hair pins24into the various stator slots18.

FIG. 1shows the curved ends22of the various hair pins24protruding from the first side11of the lamination stack16. The wire ends28of the hair pins24likewise protrude from the second side13of the same stack16. The wire ends28may be bent after insertion so as to form a complex weave from wire to wire so that each respective wire end28may be paired with and joined to a different wire end28. The bent wire ends28are collectively referred to herein as the wire end portion14of the stator10.

Adjacent paired wire ends28may be joined to form an electrical connection, for instance by soldering one wire end to its paired wire end to form a soldered joint. Each of the paired wire ends28may be individually welded or soldered to thereby form the required electrical connections between the layers. The resultant weave pattern and welded joints determines the path of the current flow through the windings12.

Still referring toFIG. 1, the present test system70is configured for surge testing of the stator10, either alone or in conjunction with the surge tester60. The surge tester60can be used to inject a main voltage (arrow121) as a surge or voltage spike into the stator10. This causes a nonlinear voltage drop to occur as the electrical surge propagates through the windings12. Turn-to-turn and phase-to-phase voltage stresses can drop significantly as the surge propagates, potentially causing some insulation flaws and/or other defects to go unnoticed. The present test system10is therefore intended to increase the error detection rate of a given stator10during surge testing by fully stressing the insulating material26of the windings12, particularly at the turns.

The test system70may be configured as a bed of nails or another system providing similar levels of automatic engagement with non-insulated welds in the windings12. As is well understood in the art, a bed of nails is an electronic test fixture having an array of spring-loaded pogo pins. Thus, a plurality of wires34and conductive leads36of the pin set15may be optionally configured as spring-loaded pogo pins, as indicated generally by double-headed arrow25inFIG. 1, with the wires34being alternatively straight, rigid lengths of wire as indicated by wire134in phantom. Wires134would then be aligned with the stator10such that each of the conductive leads36of the various pogo pins makes contact with a different test point on the stator10. A bed of nails design may facilitate reliable and repeatable contact with numerous test points within the circuitry of the stator10. Due to the manufacturing steps needed for hair pin-type hybrid traction motors, this test may only occur before insulation material is applied to the welded ends.

Alternatively, the wires34may be independently positioned with respect to the stator10such that the calibrated voltage (arrows21) from the test system70may be injected or applied to any of the welded joints of the wire ends28. Regardless of the embodiment, the conductive leads36each have a first end31which contacts the windings12during surge testing, and a second end33which is electrically connected to one of the wires34.

The test device50may be embodied as a power control unit or module configured for executing process instructions embodying the present method100. An example embodiment of the present method100is described below with reference toFIG. 2. The test device50may include one or more processors56in addition to the memory55noted above. Memory55may be embodied as non-volatile or volatile media, and may include any non-transitory/tangible medium which participates in providing data or computer-readable instructions as needed. Such instructions can be executed by the processor(s)56.

The test device50ofFIG. 1may include any other required hardware and software components needed for executing the present method100. For instance, the host machine may include a high-speed clock, analog-to-digital (A/D) circuitry, digital-to-analog (D/A) circuitry, and any required input/output (I/O) circuitry, I/O devices, and communication interfaces, as well as signal conditioning and buffer electronics.

The test device50may also include power conditioning components57, some of which may be similar to those used in the surge tester60. For instance, the power conditioning components57may include one or more capacitors58and a transformer/boost converter which produces a threshold voltage from a power supply/input line voltage (arrow40), e.g., grid power of 110 VAC, 220 VAC, or a separate power source such as a 300 VDC test battery. The output of the transformer/boost converter then charges the capacitor58to the threshold voltage, e.g., approximately 100 VDC or more depending on the embodiment. Other power conditioning components57may include power switches or relays which can be tripped by the test device50to discharge the capacitor, and thus apply the calibrated voltage (arrows21) to the stator10.

During surge testing, the calibrated voltage (arrows21) may be injected as a surge/spike directly to any of the targeted wire ends28at the approximate midpoint of the stator10, or near the beginning and/or end of each layer of the stator10. Conventional surge testing may take place at the first side11of the stack16, for example by connecting tester60to one phase lead220while grounding the other two phase leads20,120and injecting the main voltage (arrow121) as a surge/spike into the phase lead220. After surge testing via the phase lead220, the phase lead220is grounded and the phase lead20is connected to the primary surge tester60, and so on until all phase leads have received a surge in turn.

It is further recognized herein that conventional surge testing can cause some coils or portions of the windings to be insufficiently stressed, particularly at the approximate mid-layer point with respect to the phase leads20,120,220. A voltage drop occurs at each successive layer. As a result, conventional surge testing solely via the phase leads20,120, and220may insufficiently stress the insulating material26, particularly at the last half of each winding at the turns where insulating material26may be at its weakest. Therefore, exclusive use of conventional surge testers such as the surge tester60ofFIG. 1may insufficiently stress the turns of the windings12.

Referring toFIG. 2in conjunction withFIG. 1, an example method100can begin with optional step102. Step102is optional in the sense that the present method100may be limited in some embodiments to steps108-116. Step102includes electrically connecting the surge tester60to one of the phase leads20,120,220of the stator10shown inFIG. 1, and then injecting the main voltage (arrow121) as a surge/spike into the connected phase lead20,120, or220. In a non-limiting embodiment, the main voltage (arrow121) may be at least approximately 500 VAC. In another embodiment, the main voltage (arrow121) may be at least approximately (1000 VAC) (2VL), where VLrepresents the line voltage (arrow40), or greater than 100 VDC when measured at the fully-charged capacitor58before discharge. Various options exist for the surge tester60, including commercially available combination surge, resistance, and hi-pot test devices having variable input voltages. The method100then proceeds to optional step104.

Step104includes measuring the voltage at turns of the windings12within the stator10, recoding the measured voltage (arrow23) via the test probe17or by other means, and then calculating the voltage drop using the processor(s)56of the test device50. As understood in the art, the voltage drop may be calculated by subtracting the measured voltage (arrow23) from the main surge voltage (arrow121) or differential voltage between any two hair pins. The calculated voltage drop may be recorded in memory55of the test device50. The method100then proceeds to step106.

At optional step106, the test device50ofFIG. 1may determine whether the turns of the windings12have been adequately stressed by the main voltage (arrow121). Adequacy may be determined as a calibration value and recorded in memory55. For instance, if at least a threshold percentage of the main voltage (arrow121) injected as a surge is still present at the turns, the test device50may determine, for that particular test location, that surge from the main voltage (arrow121) adequately stressed the turns of the windings12. The method100proceeds to step112if such stressing is adequate. Otherwise, the method100may proceed to step108.

Step108, which is not optional, includes electrically connecting at least one conductive lead36of the test system70shown inFIG. 1to each of the layers of the stator10. Such connection may occur at the welded joints proximate to the wire ends28, i.e., approximately mid-way through the winding12of the corresponding layer with respect to a phase lead20,120,220of the stator10. Step108includes injecting the calibrated voltage (arrows21) into the targeted winding(s)12of the stator10via the conductive leads36. Step108may entail rapidly discharging one or more capacitors58of the power conditioning components57ofFIG. 1as a voltage surge into the windings12. Such a surge may be, in one non-limiting embodiment, at least 100 volts AC or DC (100 VAC/VDC). The method100proceeds to step110once the surge has been injected.

At step110, the test device50measures the voltage, e.g., using the test probe17, at a desired location such as at the turns of the windings12, and then uses the measured voltage (arrow23) to calculate the voltage drop between the layers as explained above with reference to step104. The method100then proceeds to step112.

At step112, the test device50determines whether the insulating material26at the turns of the windings12has been adequately stressed by the calibrated voltage (arrows21) that is injected into the windings12at step108. As with step106, the adequacy of any stressing may be determined as a calibration value and recorded in memory55. For instance, if at least a threshold percentage of the auxiliary surge voltage (arrow21) is present at the turns, the test device50may determine, for that particular test location, that the calibrated voltage (arrows21) adequately stressed the turns. The method100proceeds to step114if the stressing is determined to be adequate. Otherwise, the method100proceeds to step116.

At step114, having determined at step112that stressing via the test system70is adequate, the test device50ofFIG. 1may then execute a suitable control action with respect to the stator10under test. For instance, step114may include any or all of recording a passing diagnostic code in memory55, activating an audio/visual indicator signaling a passing test for that particular phase, etc. The method100is thereafter complete for the tested phase. If other phases have not yet been tested, the method100may be repeated for the next untested phase. Once all phases have been successfully tested, the windings may be insulated at welded ends of the welded hair pins. The stator10may then be installed, e.g., into an electric traction motor, after insulating the windings.

At step116, having determined at step112that stressing via the test system70ofFIG. 1is inadequate, the test device50executes a different control action than that executed in step114. For instance, step116may entail recording a failing diagnostic code in memory55, retesting the same phase starting with either of steps102or108, signaling for further inspection and scrapping or repair of the stator10, etc.