Patent Publication Number: US-2013241571-A1

Title: High Voltage Testing Device and High Voltage Testing Method Thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT application No. PCT/JP2011/075303, which was filed on Nov. 2, 2011 based on Japanese Patent Application (No. 2010-246474) filed on Nov. 2, 2010, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high voltage testing device which uses a coaxial cable as an object to be inspected and applies a high voltage between a center conductor (a core wire) and a shield conductor of the coaxial cable to carry out a test of an electric insulation state and a high voltage testing method of the high voltage testing device. 
     2. Description of the Related Art 
     For instance, when an input of a radio device such as a radio or a television is connected to an antenna, a coaxial cable is ordinarily used. Such kind of coaxial cable is formed with a center conductor having a prescribed thickness and a shield conductor arranged in a tubular form so as to surround the periphery of the center conductor with a prescribed insulating material sandwiched between the shield conductor and the center conductor. When an input of a broadcasting radio receiver mounted on a vehicle is connected to an antenna, such a coaxial cable is also used. 
     As disclosed in JP-A-2001-202836, a capacitor may be sometimes inserted into a part of a center conductor of a coaxial cable. 
     On the other hand, when a user employs an electric wire such as this kind of coaxial cable for various uses, the user needs to carry out an electric inspection to ensure a safety or a quality of the electric wire. Specifically, the user recognizes that insulation is ensured between the center conductor and the shield conductor of the coaxial cable. Then, the user applies a DC high voltage (for instance, 1000 V) to a part between them to measure an insulation resistance or applies an alternating voltage (for instance, an amplitude is 1000 V) of a frequency (for instance, 50 Hz) the same as that of a commercial AC power to recognize that a problem does not arise in withstand voltage. 
     Further, for instance, JPA-2005-265684 discloses an insulation monitor which monitors a deterioration of an electric insulator of an electric wire in a switchboard. Namely, a technique is disclosed that an electromagnetic wave radiated due to a partial discharge caused by the deterioration of the insulation is detected and monitored by using an antenna arranged in the switchboard. 
     For instance, when an insulation resistance of an ordinary coaxial cable is measured, two electrodes of an insulation resistance tester are connected to a center conductor and a shield conductor of the coaxial cable as an object to be inspected and a prescribed voltage is applied to the electrodes so that a test may be simply carried out. 
     However, as described above, when the coaxial cable having the capacitor inserted into a part of the center conductor is tested, various problems may possibly arise. Namely, since one end and the other end of the coaxial cable in the longitudinal direction thereof cable are separated from each other in a direct current by the capacitor, when the two electrodes of the insulation resistance tester are merely connected to the center conductor and the shield conductor in the one end of the coaxial cable, only a range from the one end of the coaxial cable to one end of the capacitor can be tested. Accordingly, after the test of the one end side of the coaxial cable is finished, the two electrodes of the insulation resistance tester are reconnected to the center conductor and the shield conductor in the other end of the same coaxial cable to carry out a test again. 
     Further, when an insulation resistance test or a withstand voltage test is carried out, a high voltage of about 1000 V is ordinarily applied. A withstand voltage of the capacitor itself built in the coaxial cable is ordinarily about 50 V at the most. Accordingly, when an operator makes an erroneous connecting operation during the test or when there is a problem in an insulation property of the coaxial cable itself, the capacitor of the coaxial cable may be possibly broken by applying an excessively high voltage. 
     SUMMARY 
     The present invention is devised by considering the above-described circumstances, and it is an object of the present invention to provide a high voltage testing device which can carry out a test of an entire part of a cable by a simple operation without breaking a capacitor even when a coaxial cable having a capacitor built therein is tested. 
     In order to achieve the above-described object, a high voltage testing device and a high voltage testing method according to the present invention is characterized by below-described (1) to (8). 
     (1) In a high voltage testing device which uses as an object to be inspected a coaxial cable including a central conductor and a shield conductor arranged so as to surround a periphery of the central conductor with a prescribed insulating material sandwiched between the central conductor and the shield conductor and applies a high voltage between the central conductor and the shield conductor of the coaxial cable to carry out a test of an electric insulation state, the high voltage testing device includes: a cable connecting part that respectively connects two electrodes of an output of a tester which outputs a high voltage to the central conductor and the shield conductor of the coaxial cable as the object to be inspected, and the cable connecting part includes a core wire short-circuiting part which electrically short-circuits between one end and the other end the longitudinal direction of the central conductor of the coaxial cable and a shield wire short-circuiting part which electrically short-circuits between one end and the other end in the longitudinal direction of the shield conductor of the coaxial cable.
 
(2) A high voltage testing device according to the above-described (1) further includes a time constant circuit that is connected between the output of the tester and an input of the cable connecting part and that has at least one resistor and at least one capacitor.
 
(3) In a high voltage testing device according to the above-described (2), the time constant circuit has a surge removing circuit which absorbs an abnormal high voltage.
 
(4) In a high voltage testing device according to the above-described (1), the cable connecting part includes two or more coaxial connectors which are respectively connected to two connectors provided in one end side and the other end side in the longitudinal direction of the coaxial cable as the object to be inspected.
 
(5) A high voltage testing method of a high voltage testing device, includes the steps of: providing, as an object to be inspected, a coaxial cable including a central conductor and a shield conductor arranged so as to surround a periphery of the central conductor with a prescribed insulating material sandwiched between the central conductor and the shield conductor; connecting two electrodes of an output of a tester which outputs a high voltage to the central conductor and the shield conductor of the coaxial cable respectively; electrically short-circuiting between one end and the other end in the longitudinal direction of the central conductor of the coaxial cable and electrically short-circuiting between one end and the other end in the longitudinal direction of the shield conductor of the coaxial cable: and applying a high voltage between the central conductor and the shield conductor of the coaxial cable to carry out a test of an electric insulation state.
 
(6) The high voltage testing method according to (5), further includes a step of moderating a leading edge and a trailing edge of a wave form of the output of the tester by a time constant circuit.
 
(7) The high voltage testing device according to (6), further includes a step of absorbing an abnormal high voltage by a surge removing circuit of the time constant circuit.
 
     According to the high voltage testing device having the structure of the above-described (1), even when a capacitor is provided in the coaxial cable as the object to be inspected, the high voltage can be prevented from being applied between terminals of the capacitor. Further, the voltage for a test is applied to both the ends of the coaxial cable at the same time through the core wire short-circuiting part. Accordingly, an entire part of the coaxial cable can be tested by the test of one time without carrying out the tests individually two times. Even when the length of the coaxial cable as the object to be inspected is relatively large, the voltage applied between the terminals of the capacitor can be restrained from increasing. 
     According to the high voltage testing device having the structure of the above-described (2), a change speed of the high voltage applied to the coaxial cable as the object to be inspected from the tester can be moderated. Thus, an influence of an inductor component in the coaxial cable is mitigated. Accordingly, even when the length of the coaxial cable as the object to be inspected is relatively large, the voltage applied between the terminals of the capacitor can be restrained from increasing. 
     According to the high voltage testing device having the structure of the above-described (3), when an abnormal high voltage is temporarily applied due to any cause, the surge removing circuit absorbs the abnormal high voltage. Accordingly, the voltage applied between the terminals of the capacitor can be restrained from increasing. 
     According to the high voltage testing device having the structure of the above-described (4), when both the ends of the coaxial cable as the object to be inspected are merely connected to the two coaxial connectors of the cable connecting part, the test can be safely carried out. Namely, an excessively high voltage can be prevented from being applied to the capacitor in the coaxial cable by a mal-operation. 
     The present invention is briefly explained as described above. Further, when mode for carrying out the invention described below is read by referring to the attached drawings, a detail of the present invention will be more clarified. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
         FIG. 1  is a connection diagram showing a connection state when a wire harness for an antenna is tested by using a high voltage testing device of an exemplary embodiment; 
         FIG. 2  is an electric circuit diagram showing an equivalent circuit of an electric circuit shown in  FIG. 1 ; 
         FIG. 3  is a front view of a structural example of the wire harness for the antenna as an object to be inspected; 
         FIG. 4  is a schematic view showing the connection states of circuit elements of parts which respectively give an influence when a voltage for a test is applied to the wire harness for the antenna as shown in  FIG. 1  and  FIG. 3 ; 
         FIG. 5  is an electric circuit diagram showing an equivalent circuit of the wire harness for the antenna immediately after a DC voltage for the test is applied; 
         FIG. 6  is an electric circuit diagram showing the equivalent circuit of the wire harness for the antenna after the DC voltage for the test is applied, and then, a sufficient time elapses; 
         FIG. 7  is a wave form diagram showing a wave form of a voltage when a jig for a high voltage test has no time constant circuit; 
         FIG. 8  is a wave form diagram showing a wave form of a voltage when the jig for the high voltage test has the time constant circuit; 
         FIG. 9  is a wave form diagram showing an example of a wave form of a voltage appearing between terminals of a capacitor in the wire harness for the antenna in an actual test state; and 
         FIG. 10  is a connection diagram showing a connection state when the wire harness for the antenna is tested by using a high voltage testing device of a modified example. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Now, a specific exemplary embodiment of a high voltage testing device of the present invention will be described below by referring to the drawings. 
       FIG. 1  shows a specific example of a connection state when a wire harness for an antenna is tested by using a high voltage testing device of an exemplary embodiment. Further, in the present exemplary embodiment, as a representative example, a wire harness  10  for an antenna as shown in  FIG. 3  is supposed to be used as an object to be inspected. 
     The wire harness  10  for an antenna is used, as shown in  FIG. 3 , to connect a prescribed radio unit (an input of a broadcasting radio receiver mounted on a vehicle) X to an antenna amplifier (an amplifier which amplifies a high frequency signal from an antenna mounted on a vehicle) Y. Further, as shown in  FIG. 3 , the wire harness  10  for the antenna includes a coaxial cable (1.5C2V)  11  having a length to some degree (for instance, 1.6 m) and harness side connectors  12  and  13  respectively connected to one end  11 A and the other end  11  of the coaxial cable. Further, inside the harness side connector  12 , a capacitor  14  is built. 
     Specifically, the harness side connector is a JASO plug adapted to a standard of Japanese Automotive Standards Organization (JASO). Further, the harness side connector  13  is a high frequency connector (HFC) for the coaxial cable. 
     The coaxial cable  11  has a core wire  11   a  which is an electrical conductor having a prescribed thickness in its central part. An outer periphery of the core wire  11   a  is covered with a prescribed electrically insulating material. Further, in an outer side of the electrically insulating material, a shield conductor  11   b  formed in a cylindrical configuration is arranged so as to surround the core wire  11   a.  Namely, the core wire  11   a  and the shield conductor  11   b  are coaxially arranged and the core wire and the shield conductor are insulated from each other by the electrically insulating material. Further, an outer side of the shield conductor  11   b  is covered with a suitable sheath (an insulator). 
     The capacitor  14  provided in the harness side connector  12  serves to match the coaxial cable with a signal source of an antenna system (for instance, in  FIG. 3 , the radio unit X or the antenna amplifier Y corresponds to the antenna system) to which the coaxial cable  11  is connected, and functions as a matching correction capacitor. Namely, as shown in  FIG. 3 , one end of the capacitor  14  is connected to the core wire  11   a  in the one end  11 A of the coaxial cable  11 , and the other end of the capacitor  14  is connected to a central electrode  12   a  of the harness side connector  12 . As in this structure, the wire harness  10  for the antenna has a function for matching the coaxial cable with the signal source of the antenna system. 
     Further, an electrode  12   b  of an outer periphery of the harness side connector  12  is connected to the shield conductor  11   b  in the one end  11 A of the coaxial cable  11 . A central electrode  13   a  of the harness side connector  13  is connected to the core wire  11   a  in the other end  11 B of the coaxial cable  11 . An electrode  13   b  of an outer periphery is connected to the shield conductor  11   b  in the other end  11 B of the coaxial cable  11 . 
     When the wire harness  10  for the antenna shown in  FIG. 3  is tested as an object to be inspected, the wire harness for the antenna is connected to a jig for a high voltage test (a high voltage testing device)  20  as shown in  FIG. 1 . Namely, since the coaxial cable  11  has a flexibility, the wire harness  10  for the antenna is bent in the form of U to mechanically and electrically connect the harness side connector (a plug)  12  of one end side thereof to a tester side connector (a jack) and, to mechanically and electrically connect the harness side connector (a female)  13  of the other end side to a tester side connector (a male)  22 . 
     The jig for the high voltage test  20  shown in  FIG. 1  includes the tester side connectors  21  and  22  and a jig circuit  23 . The tester side connector  21  and the tester side connector  22  are arranged at positions close to each other. Further, a central electrode  21   a  of the tester side connector  21  is connected to a central electrode  22   a  of the tester side connector  22  at a core wire short-circuiting part P 1 . An outer periphery side electrode  21   b  of the tester side connector  21  is connected to an outer periphery side electrode  22   b  of the tester side connector  22  at a shield wire short-circuiting part P 2 . 
     The core wire short-circuiting part P 1  is connected to a terminal  24  through the jig circuit  23 . The shield wire short-circuiting part P 2  is connected to a terminal  25  through the jig circuit  23 . The terminals  24  and  25  of the jig circuit  23  are respectively connected to output electrodes  31  and  32  of an insulation resistance/withstand voltage tester  30 . 
     The insulation resistance/withstand voltage tester  30  has a function for carrying out an insulation resistance test using a DC high voltage and a withstand voltage test using an AC high voltage. Namely, under a state that the DC high voltage (for instance, 1000 V) is applied between the output electrodes  31  and  32 , the insulation resistance of the object to be inspected can be measured. Further, under a state that a high voltage (for instance, 1000 V) of a low frequency alternating current (for instance, 50 Hz) is applied between the output electrodes  31  and  32 , whether or not an electric breakdown is generated in the object to be inspected can be identified. 
       FIG. 2  is an equivalent circuit of main parts of the electric circuit shown in  FIG. 1 . The jig circuit  23  of the jig for the high voltage test  20  includes, as shown in  FIG. 2 , a time constant circuit  23   a  and a surge removing circuit  23   b.    
     The time constant circuit  23   a  is provided to moderate a leading edge and a trailing edge of a wave form of the DC voltage when an on/off of the DC voltage outputted by the insulation resistance/withstand voltage tester  30  are switched. In a structural example shown in  FIG. 2 , two resistors and three capacitors are provided, however, the time constant circuit  23   a  may be formed only by one resistor and one capacitor. 
     The surge removing circuit  23   b  is provided to protect an entire part of a system. Namely, the surge removing circuit  23   b  removes a surge voltage so that parts of the circuit are not respectively destroyed when an abnormally high voltage (the surge voltage) is temporarily applied due to any cause. In this structural example, the surge removing circuit  23   b  is formed with two diodes connected in series with polarities in reversed direction to each other. Since the surge removing circuit  23   b  is prepared for protection for the worst, the surge removing circuit may be omitted. 
       FIG. 4  shows supposed connection states of main circuit elements of the parts which give an influence to the wire harness  10  for the antenna when a voltage for a test is applied to the wire harness  10  for the antenna shown in  FIG. 1  and  FIG. 3 . Substances of the circuit elements shown in  FIG. 4  are respectively described blow. 
     C 1 : an electrostatic capacity corresponding to the capacitor  14  in the harness side connector  12 
 
R: the insulation resistance between the core wire  11   a  and the shield conductor  11   b  
 
C 2 : a floating capacity between the core wire  11   a  and the shield conductor  11   b  
 
L: an inductor component existing in the core wire  11   a  
 
     Accordingly, the equivalent circuit of the wire harness  10  for the antenna includes the components C 1 , C 2  and L respectively as shown in  FIG. 2 . 
     As shown in  FIG. 1 , the central electrode  21   a  of the tester side connector  21  and the central electrode  22   a  of the tester side connector  22  are short-circuited at the core wire short-circuiting part P 1 , so that the one end and the other end of the capacitor  14  are electrically connected to each other. Accordingly, in a steady state, a voltage between both the ends of the capacitor  14  is 0 V. However, even when the DC voltage is applied from the output of the insulation resistance/withstand voltage tester  30  is applied at the time of the test, a rise and a fall of the high voltage are generated during a switch of on/off. Thus, there is a possibility that influences of the components C 1 , C 2  and L respectively shown in  FIG. 2  may appear in an AC component at that time and the high voltage may appear between both the ends of the capacitor  14 . Particularly, when a length of the coaxial cable  11  is large, there is a possibility that the influences of the components C 1 , C 2  and L may be respectively increased. 
     The equivalent circuit of the wire harness  10  for the antenna immediately after the DC voltage for the test is applied is represented as shown in  FIG. 5  Namely, immediately after the DC voltage is applied, a counter electromotive force is generated for a short period (for instance, 8 ns) by the inductor component L. Thus, a voltage Vc 1  expressed by a below-described equation appears at both the ends of the capacitor  14  due to this influence. 
       V c 1=(applied voltage)× C 2/( C 1+ C 2)  (1)
 
     Further, the equivalent circuit of the wire harness  10  for the antenna after the DC voltage for the test is applied, and then, a sufficient time elapses is represented as shown in  FIG. 6 . Namely, when the sufficient time elapses after the DC voltage is applied, since the influence of the counter electromotive force of the inductor component L is eliminated, both the ends of the capacitor (C 1 ) are short-circuited at the core wire short-circuiting part P 1 . Thus, both the ends of the capacitor  14  (C 1 ) have the same electric potential. 
     Namely, even when one end and the other end of the wire harness  10  for the antenna are short-circuited at the core wire short-circuiting part P 1  by using the jig for the high voltage test  20 , the voltage expressed by the above-described equation (1) is temporarily applied to the capacitor  14 . When a level of the voltage exceeds a withstand voltage (for instance, 50 V) of the capacitor  14 , the capacitor  14  may be possibly broken down. 
       FIG. 7  shows a wave form of the voltage when the time constant circuit  23   a  is not provided in the jig for the high voltage test  20 . Namely, when an input voltage Vin (a voltage between a point A and a point D) applied to the wire harness  10  for the antenna suddenly changes like the wave form shown in FIG.  7 , the voltage Vc 1  appears at both the ends of the capacitor  14  (C 1 ) during a period T 1  of a transient state. In an example shown in  FIG. 7 , when a change of 5 V is applied as the input voltage Vin, the voltage Vc 1  of an amplitude of 3.8 V at the maximum is observed. Accordingly, if 1000 V is applied as the input voltage Vin, the high voltage of 760 V is applied to both the ends of the capacitor  14  (C 1 ) to electrically break down the capacitor  14 . 
     On the other hand,  FIG. 8  shows a wave form of the voltage when the time constant circuit  23   a  is provided in the jig for the high voltage test  20 . Namely, the input voltage Vin (the voltage between the point A and the point D) applied to the wire harness  10  for the antenna has a wave form the rise and fall of which are gentle like the wave form shown in  FIG. 8  due to an influence of the time constant circuit  23   a.    
     As a result, even during a period of a transient state, the voltage Vc 1  appearing at both the ends of the capacitor  14  (C 1 ) is lowered to a level as low as noise. 
     In  FIG. 9 , an example of a waveform of a voltage is shown which appears between terminals of the capacitor  14  (C 1 ) in the wire harness  10  for the antenna in an actual test state. In the example shown in  FIG. 9 , the voltage Vc 1  is shown which appears at both the ends of the capacitor  14  (C 1 ) in a transient state when DC 500 V is applied as the input voltage Vin. In this example, a maximum value of amplitude of the voltage Vc 1  is 4.68 V. Thus, when the ordinary withstand voltage (for instance 50 V) of the capacitor  14  is considered, a problem does not arise. 
     Specifically, at the time of the insulation resistance test of the wire harness  10  for the antenna, even when the DC high voltage (for instance, 1000 V) outputted by the insulation resistance/withstand voltage tester  30  is abruptly switched on and off, if the time constant circuit  23   a  is mounted on the jig for the high voltage test  20 , the high voltage exceeding the withstand voltage can be prevented from being applied between the terminals of the capacitor  14  in the transient state. When a change of the voltage outputted from the insulation resistance/withstand voltage tester  30  is gentle, or when the influence of the inductor component L is low as in the case of the coaxial cable  11  having a relatively small length, there is a possibility that even when the time contact circuit  23   a  is not provided, a problem does not arise. 
     (Modified Example) 
       FIG. 10  shows a connection state when a wire harness  40  for an antenna is tested by using a high voltage testing device of a modified example. In an example shown in  FIG. 10 , the wire harness  40  for the antenna used as an object to be inspected includes two coaxial cables  41  and  43  and harness side connectors  42 ,  44  and  45 . Namely, one end of the coaxial cable  41  and one end of the coaxial cable  43  are connected to the common harness side connector  45 . The other end of the coaxial cable  41  is connected to the harness side connector  42  and the other end of the coaxial cable  43  is connected to the harness side connector  44 . 
     The harness side connector  42  is a JASO plug. The harness side connector  45  is a high frequency connector (HFC). The harness side connector  44  is a JASO mini-plug. In the harness side connector  42 , a capacitor  46  is built. 
     A jig for a high voltage test (a high voltage testing device)  20 B shown in  FIG. 10  is formed so that an entire part of the wire harness  40  for the antenna may be inspected only by a test of one time. Namely, the jig for the high voltage test  20 B has tester side connectors  51 ,  52  and  53 . Further, the tester side connector  51 , the tester side connector  52  and the tester side connector  53  are arranged at mutually close positions. As shown in  FIG. 10 , the tester side connector  51  is connected to the harness side connector  42 . The tester side connector  52  is connected to the harness side connector  44 . The tester side connector  53  is connected to the harness side connector  45 . 
     Further, at a core wire short-circuiting part P 3 , a central electrode of the tester side connector  51 , a central electrode of tester side connector  52  and a central electrode of the tester side connector  53  are electrically and commonly connected. Further, at a shield wire short-circuiting part P 4 , an outer periphery side electrode of the tester side connector  51 , an outer periphery side electrode of the tester side connector  52  and an outer periphery side electrode of the tester side connector  53  are electrically and commonly connected. 
     Accordingly, under a connected state as shown in  FIG. 10 , when a voltage is outputted from an output of an insulation resistance/withstand voltage tester  30 , the voltage can be applied to an entire part of the coaxial cable  41  and an entire part of the coaxial cable  43 . Thus, a test of the whole part of the wire harness  40  for the antenna can be completed only by an operation of a time. 
     As described above, the high voltage testing device of the present invention can be used when an insulation resistance test or a withstand voltage test of, for instance, an antenna cable mounted on a vehicle is carried out. Especially, even when the cable as an object to be inspected has the capacitor built therein, the entire part of the cable can be completely tested only by the operation of one time, which contributes to an improvement of a working property. Further, since the test can be started only by connecting the connectors, an excessively high voltage can be prevented from being applied to the capacitor by a wrong connecting operation. Further, since the time constant circuit is mounted, an excessively high voltage can be prevented from being applied to the capacitor in a temporary transient state. 
     The present invention is described in detail by referring to the specific exemplary embodiment, however, it is to be understood to person with ordinary skill in the art that various changes or modifications may be added without deviating from the spirit and scope of the present invention. 
     According to the present invention, even when the coaxial cable in which the capacitor is built is tested, the entire part of the cable can be tested by a simple operation without breaking down the capacitor.