JP4744956B2 - Surge low reflection device - Google Patents

Description

  The present invention relates to a surge low reflection device such as an electric motor that reduces reflection of surge generated when, for example, driving power is supplied from a PWM frequency converter via a power feeding cable.

  As is well known, a PWM (pulse width modulation) frequency converter and an electric device such as an AC motor or an AC generator are connected by a power supply cable, and driving of the connected AC motor or frequency conversion of power from the AC generator is performed. Is going. In such a case, for example, in an AC motor driven by a PWM frequency converter that switches at high speed, if there is a mismatch between the characteristic impedance of the feeding cable and the impedance of the AC motor, the PWM frequency converter is caused by this mismatch. And a reflection of a surge occurs at the connecting portion of the AC motor, thereby generating a high voltage (see, for example, Non-Patent Document 1).

  If a high voltage is generated due to such impedance mismatch, the coil insulation may be damaged in the AC motor connected to the power supply cable. Therefore, in a conventional AC motor, the coil may be subjected to an enhanced insulation treatment that can withstand a high voltage caused by a surge, or an electric circuit that does not generate a high voltage due to a surge. It was done.

  In addition, with regard to the electric circuit that prevents the generation of the high voltage, a reactor or a filter is inserted between the PWM frequency converter and the power supply cable to smooth the high-speed switching waveform of the PWM frequency converter. Another is an MTU (Motor) configured such that a series circuit of a capacitor and a resistor as an impedance matching unit is connected to each power supply line between the power supply cable and the AC motor. Termination Unit) is connected, and the impedance at the terminal portion of the AC motor is matched with the characteristic impedance of the power supply cable so that the surge reflected by the AC motor is reduced (for example, see Non-Patent Document 2). .

  For this reason, even in a low-voltage AC motor driven at a relatively low voltage, for example, coil insulation must be reinforced so as to withstand a high voltage of a surge, resulting in an expensive motor. In addition, when inserting a reactor or a filter between the PWM frequency converter and the power supply cable, it is possible to prepare reactors or filters of various sizes corresponding to the rated current values of the motors having various rated outputs. There are problems such as being necessary and expensive.

On the other hand, when connecting an MTU between a power supply cable and an AC motor, a capacitor and a resistor connected in series may be prepared in accordance with the assumed characteristic impedance of the power supply cable, depending on the rated output of the AC motor. It is possible to simplify the classification without any trouble, and the main parts to be prepared are capacitors and resistors so that they can be constructed at low cost. However, when the MTU cannot be installed near the terminal of the AC motor, the wiring for connecting the AC motor and the MTU becomes longer, the wiring stray inductance between them becomes larger, and the effect of suppressing the reflection of surge is reduced due to the influence. In addition, there is a risk that the value of the characteristic impedance of the power supply cable is not accurately known, and a reliable surge reduction effect cannot be obtained.
IEEJ Technical Committee on Induction and Insulation Materials “Technical Report of the Institute of Electrical Engineers” No. 739 August 1999 “Inverter Surge Insulation Investigation Special Committee” “Influence of Inverter Surge on Insulation System”, p. 12-20 IEC TS 60034-25 “TECHNICICAL SPECIFICATION” “Rotating electrical machines” Part 25 2004-04, p. 44-45

The present invention has been made in view of the above situation, and the object of the present invention is to prevent the surge voltage suppression effect from becoming high-cost, with the impedance matching portion being a line between the feeding cable and the rotating machine. It is an object of the present invention to provide a surge low reflection device which is connected so that it can be sufficiently obtained and its effect can be confirmed.

The surge low reflection device of the present invention is
One end of the feeding cable for power is connected to the external connection terminal, a rotating machine to which electric power supply from the PWM frequency converter is performed, the windings of the external connection terminal or external connecting terminals and the rotating machine of the rotating machine It is connected between the impedance matching between the rotating machine and the power supply cable, and the impedance matching unit for performing provided an impedance matching circuit, provided in the impedance matching section, the predetermined voltage or more surge to the rotating machine A surge low reflection device comprising a display circuit for displaying when a voltage is applied ,
The impedance matching circuit is constituted by a series circuit having a time constant of 2 μs to 3 μs based on a capacitor and a resistor having a value matching or close to the characteristic impedance of the power feeding cable.
The impedance matching unit is configured to be housed in a case, and the case is mounted on the outer surface of a terminal box that houses the external connection terminal fixed to the main body case of the rotating machine, and is mounted on the rotating machine. The matching portion is connected to the external connection terminal so as to be conductive .

As is apparent from the above description, according to the present invention, an impedance matching unit is provided on the line between the power supply cable and the rotating machine, and the effect of the wiring stray inductance is reduced. The connection can be made so that the suppression effect can be sufficiently obtained, and the effect of suppressing the surge voltage can be displayed and easily confirmed.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram illustrating a power supply state to a surge low reflection rotating machine using a power supply cable, FIG. 2 is a circuit diagram of an impedance matching unit, and FIG. 3 is a side view of the surge low reflection rotating machine.

  In FIG. 1 to FIG. 3, reference numeral 1 denotes a surge low reflection rotating machine which is one of surge low reflection devices. This surge low reflection rotating machine 1 includes a three-phase AC motor 2 and an MTU (Motor Termination Unit). An impedance matching unit 3 to be configured is provided. Reference numeral 4 denotes a power supply cable, and one end of each of the three power supply lines 5u, 5v, 5w is connected to the external connection terminals 6u, 6v, 6w of the AC motor 2. The other ends of the feeder lines 5 u, 5 v, and 5 w of the feeder cable 4 are connected to corresponding terminals of a PWM (pulse width modulation) frequency converter 7 that supplies power for driving the AC motor 2. In addition, 8 is a power receiving cable for the PWM frequency converter 7 to receive power from a transformer or the like (not shown).

  The impedance matching unit 3 includes an impedance matching circuit 9 and a display circuit 10. The impedance matching circuit 9 connects capacitors 11u, 11v, 11w and resistors 12u, 12v, 12w in series for each phase, and connects the ends of the series circuits 13u, 13v, 13w on the side of the resistors 12u, 12v, 12w. They are connected and Y-connected so as to be neutral. Further, the ends of the series circuits 13u, 13v, 13w on the side of the capacitors 11u, 11v, 11w are connected to the external connection terminals 6u, 6v, 6w of the AC motor 2.

  Further, the impedance of the AC motor 2 alone is larger than the characteristic impedance of the feeding cable 4. For this reason, the impedance is mismatched between the two as it is, and the surge voltage applied to the AC motor 2 from the feeding cable 4 is reflected at the mismatched portion, and a high voltage is generated. Therefore, the series circuits 13u, 13v, and 13w connected to the external connection terminals 6u, 6v, and 6w of the AC motor 2 are set so that the impedance on the AC motor 2 side becomes a value equivalent to the characteristic impedance of the feeding cable 4. The values of the resistors 12u, 12v, and 12w are values that match or are close to the characteristic impedance of the feeder cable 4. For example, since the characteristic impedance of the feeding cable 4 is usually about 40Ω to 120Ω, the resistance value is in this range (40Ω to 120Ω).

  On the other hand, the capacitors 11u, 11v, and 11w limit the current flowing through the resistors 12u, 12v, and 12w to reduce the loss. The value is desirably as small as possible from the viewpoint of reducing the loss, but is too small. Then, the surge voltage applied to the resistors 12u, 12v, and 12w is blocked, and the functions of the resistors 12u, 12v, and 12w are impaired. Therefore, the values of the capacitors 11u, 11v, 11w and the resistors 12u, 12v, 12w are set to appropriate values.

  That is, for example, each value is selected so that the time constant calculated by the product of the capacitance of each capacitor 11u, 11v, 11w and the corresponding resistance value of each resistor 12u, 12v, 12w is 2 μsec to 3 μsec. Then, when the resistance values of the resistors 12u, 12v, and 12w are 50Ω, the capacitances of the capacitors 11u, 11v, and 11w are about 50 nF. When the resistance values of the resistors 12u, 12v, and 12w are 100Ω, the capacitances of the capacitors 11u, 11v, and 11w are about 25 nF.

  Further, the display circuit 10 is provided with a Zener diode 14 and a light emitting diode (LED) 15 so that when the line voltage Vp of each phase becomes a high voltage such as a surge voltage and becomes a predetermined value or more, the LED 15 is turned on. For example, a resistor Ru and a rectifier (diode) Du are connected in series to the end of the capacitors 11u, 11v and 11w on the external connection terminals 6u, 6v and 6w side, and a resistor Rv and a rectifier Dv are connected in series. And connecting one end of the resistor Rw in correspondence with each other and connecting the other ends together to divide the line voltage Vp between the u-phase, v-phase and w-phase at a predetermined ratio, A divided voltage Vd is obtained.

  Further, the obtained divided voltage Vd is compared with the constant terminal voltage Vzd of the Zener diode 14, and when the line voltage Vp is a predetermined value, for example, a voltage that may damage the coil insulation, the LED 15 is turned on. A zener diode 14, a parallel circuit of a diode D and a resistor R1, and a capacitor C connected in series are connected to both ends of the resistor Rw and one end of the zener diode 14 is connected to the other end of the resistor Rw so as to be lit. Then, the LED 15 and the resistor R2 connected in series are connected in parallel to both ends of the capacitor C.

  And the impedance matching part 3 comprised as mentioned above is accommodated in the box-shaped case 16, and also accommodates the case 16 and the external connection terminals 6u, 6v, 6w fixed to the main body cover 17 of the AC motor 2. It is provided so as to be integrated with the AC motor 2 by being attached to the outer surface of the terminal box 18. Reference numeral 19 denotes a rotating shaft of the AC motor 2.

  Since the power supply cable 4 is configured as described above, the power supply lines 5u, 5v, and 5w of the power supply cable 4 are connected to the corresponding external connection terminals 6u, 6v, and 6w of the AC motor 2, and the power supply cable from the PWM frequency converter 7 is connected. When the driving power is supplied to the AC motor 2 via 4 and the operation is started, at the same time, the steep rising voltage constituting the PWM waveform from the PWM frequency converter 7 passes the feeding cable 4 toward the AC motor 2. Propagate.

  However, since the impedance matching unit 3 having the resistors 12u, 12v, and 12w having values substantially matching the characteristic impedance of the power supply cable 4 is connected to the external connection terminals 6u, 6v, and 6w of the AC motor 2, the power supply cable No impedance mismatch or reflection occurs at the external connection terminals 6u, 6v, 6w of the AC motor 2 to which 4 is connected. As a result, the surge voltage does not increase and the coil insulation is not damaged by impedance mismatch. Further, for example, when the propagated surge voltage is high and there is a possibility of damaging the coil insulation of the AC motor 2, the display circuit 10 is activated and the LED 15 is turned on, enabling the confirmation of the surge voltage suppression effect to be high. It can be clearly shown that the voltage is present.

  In the above embodiment, the impedance matching unit 3 is connected to the external connection terminals 6u, 6v, 6w of the AC motor 2. However, the connection between the external connection terminals 6u, 6v, 6w and the coil, etc. It is only necessary to make the wire as short as possible, and the surge low reflection rotating machine 1 is not limited to the AC electric motor 2 but is also applicable to the generator. Further, not only the surge low reflection rotating machine 1 but also the feeding cable 4 The same applies to electrical devices other than the rotating machine to be connected.

It is a circuit diagram which shows the electric power feeding state to the surge low reflection rotary machine by the electric power feeding cable which concerns on one Embodiment of this invention. It is a circuit diagram of the impedance matching part in one Embodiment of this invention. It is a side view of a surge low reflection rotating machine concerning one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surge low reflection rotating machine 2 ... AC motor 3 ... Impedance matching part 4 ... Feeding cable 6u, 6v, 6w ... External connection terminal 7 ... PWM frequency converter 9 ... Impedance matching circuit 10 ... Display circuit 14 ... Zener diode 15 ... Light-emitting diode 16 ... Case 18 ... Terminal box

Claims (1)

One end of the feeding cable for power is connected to the external connection terminal, a rotating machine to which electric power supply from the PWM frequency converter is performed, the windings of the external connection terminal or external connecting terminals and the rotating machine of the rotating machine It is connected between the impedance matching between the rotating machine and the power supply cable, and the impedance matching unit for performing provided an impedance matching circuit, provided in the impedance matching section, the predetermined voltage or more surge to the rotating machine A surge low reflection device comprising a display circuit for displaying when a voltage is applied ,
The impedance matching circuit is constituted by a series circuit having a time constant of 2 μs to 3 μs based on a capacitor and a resistor having a value matching or close to the characteristic impedance of the power feeding cable.
The impedance matching unit is configured to be housed in a case, and the case is mounted on the outer surface of a terminal box that houses the external connection terminal fixed to the main body case of the rotating machine, and is mounted on the rotating machine. A surge low reflection device characterized in that a matching portion is connected to the external connection terminal to conduct .

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