JP2014229692A - Cooling mechanism of signal generator and portable ground fault point location signal generator including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling mechanism for stabilizing the internal temperature of a signal generator.SOLUTION: In a signal generator 10 including a signal generation unit 11 for generating a periodic signal of a predetermined frequency and a power supply unit 12 for supplying an operation voltage thereto, the signal generation unit 11 and power supply unit 12 are housed side-by-side in one housing 17 having an open upper surface, and the upper surface of the housing 17 is covered with a lid 105. In the housing 17, a cooling fan 18 for generating an air flow from the inside of the housing 17 to the outside is provided on the first sidewall 17R close to the power supply unit 12, and an opening 173 for making the outside air flow into the housing 17 is provided in the second sidewall 17L close to the signal generation unit 11.

Description

  The present invention relates to a cooling mechanism for a signal generator, and more particularly to a cooling mechanism suitable for a portable ground fault search signal generator that generates an AC search signal for ground fault search of an electric circuit.

  In large-scale plants such as power plants and substations, DC circuits are used to control various equipment. Such a DC circuit is normally connected to a DC ground fault overvoltage relay 64D defined by JEM1090 (Japanese Industrial Standard 1090), so that it can be detected that a ground fault has occurred in the DC circuit. Furthermore, by connecting other protective relays and protective devices, it is possible to cut off the power supply to the circuit where the ground fault has occurred.

  For example, for ground fault search of a DC circuit, an AC survey signal for ground fault search is injected between the P-side bus and ground and between the N-side bus and ground of the DC circuit, and the resistance component at each location of the DC circuit There is a method that is performed by measuring the leakage current. Resistance component leakage current can be measured by measuring the leakage current using a current transformer at any point in the DC circuit, and performing synchronous rectification, vector calculation, etc. with reference to the AC exploration signal. . For this reason, it is necessary to accurately transmit the AC exploration signal injected into the DC circuit to the apparatus for measuring the DC component leakage current of the DC circuit without a phase shift.

  With regard to such a problem, a DC electric circuit ground fault point searching device conventionally comprising a portable device (master unit) for injecting an AC exploration signal into a DC electric circuit and a portable device (child unit) for measuring a resistance component leakage current of the DC electric circuit. Before starting the search for the ground fault point, synchronize the slave unit to the master unit so that the AC search signal generated in the master unit is accurately reproduced inside the slave unit, and then the master unit and the slave unit are separated, It is possible to measure the resistance component leakage current with high accuracy by the separated slave unit alone (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 5-273291

  A crystal oscillator using a crystal resonator is often used as an oscillation source of a signal generator that generates a periodic signal of a predetermined frequency, such as a master unit of the DC circuit ground fault point search device. The crystal resonator is obtained by sandwiching the surface of a crystal piece between thin film electrodes and sealing it in a cage having a support thin plate that also serves as a mechanical support member and an electrical lead.

  A crystal oscillator is relatively inexpensive, but its frequency-temperature characteristics are not so good. That is, the crystal oscillator is easily affected by the environmental temperature, and its oscillation frequency or phase characteristic tends to fluctuate greatly due to a change in the environmental temperature. In addition, electronic components such as a capacitive element constituting a filter circuit often used in a signal generator are also easily affected by environmental temperature. In particular, since the master unit of the DC electric circuit ground fault survey device operates by receiving a high DC voltage (for example, DC 110 V) from the DC electric circuit, there is a situation in which the amount of heat generated in the DC-DC conversion operation is large. For this reason, the internal temperature of the master unit rises for a while after the master unit is activated, and the AC exploration signal cannot be stably supplied during this period. If the AC exploration signal of the main unit fluctuates after the synchronization of the master unit and the slave unit is completed, the phase of the AC exploration signal injected into the DC circuit and the AC exploration signal reproduced inside the slave unit will be shifted. There is a risk that the resistance component leakage current cannot be accurately measured in the machine. For this reason, in the conventional DC circuit ground fault point survey device, the master unit is started and the internal temperature rises and waits for a sufficiently long time (for example, several tens of minutes) before the master unit and the slave unit are synchronized. Needed to be completed. However, this can be a factor that hinders the start of exploration of the ground fault point promptly when a ground fault occurs in the DC circuit.

  Therefore, it is necessary to quickly stabilize the internal temperature of all signal generators equipped with electronic components that are easily affected by the environmental temperature, such as crystal oscillators and filter circuits, as well as the main unit of the DC circuit ground fault survey device. There is. In view of such a problem, an object of the present invention is to provide a cooling mechanism for stabilizing the internal temperature of a signal generator.

  A signal generator cooling mechanism according to an aspect of the present invention includes a signal generation unit that generates a periodic signal having a predetermined frequency and a power supply unit that supplies an operating voltage to the signal generation unit. The signal generation unit and the power supply unit are accommodated next to each other in one casing having an upper surface opened, and the upper surface of the casing is covered with a lid, and the power source A cooling fan that generates an airflow that flows outward from the inside of the housing on the first side wall near the unit, and an opening for allowing outside air to flow into the housing on the second side wall near the signal generating unit, respectively. It is provided.

  According to this, the outside air is forcibly circulated in the direction from the signal generation unit to the power supply unit inside the housing, and the air heated mainly by the heat generated from the power supply unit is efficiently discharged outside the device. An internal temperature rise can be suppressed.

  In the cooling mechanism, the signal generation unit may be disposed in the immediate vicinity of the opening, and the size of the opening is used to directly apply the outside air flowing into the housing to the signal generation unit. The minimum size may be required.

  According to this, the signal generating unit sensitive to the temperature change can be cooled by effectively applying the outside air to the signal generating unit.

  In the cooling mechanism, the cooling fan and the opening may be arranged to face each other.

  According to this, the outside air is generally improved inside the housing, and the stagnation of the air inside the housing is reduced, and the temperature rise inside the apparatus can be suppressed more effectively.

  In the cooling mechanism, the housing is accommodated in an outer box having an upper surface opened, and the inside of the outer box is partitioned by the first and second side wall portions of the housing to reduce the size for intake and exhaust. Each space may be formed. Moreover, the upper surface of each said small space may be covered with the said cover body, and the slit for ventilation | gas_flowing may be formed in the part which covers each said small space in the said cover body.

  According to this, it is possible to prevent the external appearance of the cooling fan and to prevent foreign matters from flowing into the signal generator from the outside.

  In addition, a portable ground fault search signal generator according to another aspect of the present invention generates a periodic signal having a predetermined frequency for ground fault search of a DC circuit and injects the periodic signal into the DC circuit. A portable ground fault search signal generator comprising: a signal generating unit that performs a DC-DC conversion on a DC voltage of the DC circuit and supplies an operating voltage to the signal generating unit; A cooling mechanism is provided.

  According to this, the internal temperature rise of the portable ground fault search signal generator can be suppressed, and a periodic signal with a predetermined frequency for ground fault search of a DC circuit can be stabilized in a short time after startup. Can be output.

  According to the present invention, it is possible to generate a stable periodic signal by suppressing an increase in the internal temperature of a signal generating device including an electronic component that is easily affected by an environmental temperature such as a crystal oscillator or a filter circuit.

1 is an external view of a signal generator according to an embodiment of the present invention. The circuit block diagram of the principal part of the signal generator which concerns on one Embodiment of this invention 1 is an exploded perspective view of a signal generator according to an embodiment of the present invention. The exploded perspective view from another angle of the signal generator which concerns on one Embodiment of this invention Plan view sectional drawing of the signal generator which concerns on one Embodiment of this invention

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.

  A signal generator according to an embodiment of the present invention is used as, for example, a master unit of a DC electric circuit ground fault search device, and generates a AC ground search signal for searching for a ground fault of a DC electric circuit. This is a generator (hereinafter referred to as a master unit). The master unit is a portable device with a size and weight. When exploring the ground fault point of the DC circuit, bring the main unit into the equipment room and connect it to the DC circuit. The master unit operates by receiving a DC voltage (for example, DC 110 V) from the DC circuit, generates an AC exploration signal, and injects it into the DC circuit. The AC exploration signal is a periodic signal such as a sine wave, a pulse (such as a rectangular wave), or a triangular wave, and the period is, for example, 0.2 sec (frequency 5 Hz).

  On the other hand, a DC circuit ground fault point portable detector (hereinafter referred to as a slave unit) used as a slave unit of a DC circuit ground fault point search device is a device that is smaller and lighter than the master unit. The slave unit can be driven by a battery. When exploring the ground fault point of the DC circuit, take the handset to the site and measure the leakage current at each location of the DC circuit. The slave unit includes a split-type current transformer, and clamps a single line or a plurality of lines of the DC electric circuit with the split-type current transformer to measure a leakage current caused by an AC exploration signal. By synchronizing the slave unit and the master unit before measurement, the AC exploration signal generated by the master unit is accurately reproduced inside the slave unit. The slave unit performs synchronous rectification and vector calculation based on an AC exploration signal that internally reproduces the measured leakage current, thereby measuring the leakage current measured as resistance component leakage current, capacitance component leakage current, and resistance component leakage current. Phase difference (given as the cosine of the phase angle), vector sum of resistance component leakage current and capacitance component leakage current, ground fault resistance value, ground capacitance value, etc. are calculated and displayed on the display . In addition, the slave unit can record each measured value together with the measurement date and time inside the apparatus.

  FIG. 1 shows the appearance of a signal generator according to an embodiment of the present invention. The signal generator 10 according to the present embodiment is a master unit (portable ground fault search signal generator) of a DC electric circuit ground fault search apparatus. The signal generator 10 is accommodated in a case structure (outer box) formed of a veneer plate having a thickness of 5.5 mm and an embossed aluminum plate having a thickness of 0.3 mm. Each edge part and each corner part of the outer box are further reinforced by a protective member made of aluminum. The outer box is composed of an upper part (outer box cover) and a lower part (outer box body), which can be separated. FIG. 1 shows the signal generator 10 with the outer box lid part removed. The outer shape of the apparatus is a substantially rectangular parallelepiped shape having a length of about 25 cm, a width of about 35 cm, and a height of about 20 cm (including the outer box lid and the outer box main body), and the weight is about 9 kg.

  In the signal generator 10, a carrying handle 102 is attached to the front side surface of the outer box main body 101. On the back side surface of the outer box, two pulling hinges 103 are evenly arranged at a boundary portion between the outer box lid part and the outer box main body part 101 (not shown) with an interval of about 20 cm. As described above, the outer box lid portion is provided so as to be rotatable and detachable with respect to the outer box main body portion 101 so that the front side surface thereof can move upward. In addition, on the front side of the outer box, two snap locks 104 are equally arranged at a boundary portion between the outer box lid part and the outer box main body part 101 with an interval of about 20 cm. When carrying the signal generator 10, the outer box lid can be fixed to the outer box body 101 with the two snap locks 104 so that the outer box lid does not open.

  The opened upper surface of the outer box body 101 is covered with a front panel 105 made of a cold rolled steel plate (SPCC) having a thickness of 1.2 mm. On the front panel 105, cable connectors 106 and 107, fuses 108 and 109, a display 110, a power switch 111, a clamp coil 112, and an optical connector 113 are arranged. In addition, slits 114 </ b> L and 114 </ b> R are formed at the left and right ends of the front panel 105, respectively.

  Two lead wires (not shown) are connected to the cable connector 106. One of them is a lead connected to the P-side bus of the DC circuit, and the other one is a lead connected to the N-side bus. One lead wire (not shown) is connected to the cable connector 107. The lead wire is connected to ground.

  The fuse 108 is a fuse for protecting the signal generator 10 from an overcurrent flowing into the signal generator 10 from the P-side bus of the DC circuit. The fuse 109 is a fuse for protecting the signal generator 10 from an overcurrent flowing into the signal generator 10 from the N-side bus of the DC circuit. The rated value of the fuses 108 and 109 is, for example, DC1A.

  The display 110 can be a liquid crystal display device with a backlight. Various messages are displayed on the display 110 when the signal generator 10 is warmed up or synchronized with the slave unit. During the injection of the AC exploration signal into the DC circuit, the P-pole ground fault resistance value, the N-pole ground fault resistance value, A ground fault resistance value, a parallel ground fault resistance value, an electric circuit voltage, a ground fault voltage, and the like are displayed.

  The power switch 111 is a main switch that switches on / off the operation of the signal generator 10. When the power switch 111 is turned on in a state where two lead wires (not shown) connected to the cable connector 106 are connected to the P-side bus bar and the N-side bus bar of the DC circuit, the signal generator 10 is connected to the DC voltage ( For example, the operation starts upon receiving DC110V.

  As will be described later, the clamp coil 112 is, for example, a coil connected between the midpoint of two capacitors connected between the P-side bus and the N-side bus of the DC circuit and the ground. The clamp coil 112 is a part of the coil protected by a protective member and exposed on the surface of the front panel 105. The clamp coil 112 is used by being clamped by a split type current transformer of the slave unit when a slave unit (not shown) is synchronized with the signal generator 10. The slave unit detects a synchronization adjustment signal flowing in the clamp coil 112 by a split-type current transformer that clamps the clamp coil 112. In addition, in order to easily clamp the clamp coil 112 with the split type current transformer of the slave unit, a recess having an appropriate size is formed at a position where the clamp coil 112 is arranged on the front panel 105.

  An optical fiber cord (not shown) for connecting the signal generator 10 and the slave unit is connected to the optical connector 113. In the signal generator 10, for example, a pulse signal having a period of an AC exploration signal is generated. The pulse signal is converted into an optical signal and transmitted to the slave unit through an optical fiber cord.

  The slave and the signal generator 10 are synchronized in a state where the clamp coil 112 is clamped by the split current transformer of the slave and the slave and the signal generator 10 are connected by an optical fiber cord. The slave unit includes a reference pulse oscillation source that generates a reference pulse signal with a period (for example, 0.2 μsec) sufficiently shorter than the period of the AC exploration signal. The slave unit generates a frequency-divided signal of the pulse signal received via the optical fiber cord, counts the number of pulses of the reference pulse signal generated during the on-duty period of the frequency-divided signal, and outputs the count value to the on-duty The period of the AC exploration signal injected into the DC circuit is calculated by dividing by the wave number present in the AC exploration signal detected by the split type current transformer during the period. And the subunit | mobile_unit starts the production | generation of the pulse signal of the said calculated period at the timing of the zero crossing point of the alternating current search signal detected with the split type current transformer. By the above series of operations, the synchronization between the slave unit and the signal generator 10 is completed.

  When the synchronization is completed, the split current transformer can be removed from the clamp coil 112 and the optical fiber cord can be removed to completely separate the slave unit from the signal generator 10. The AC exploration signal generated by the signal generator 10 is accurately reproduced inside the slave unit that has been synchronized and separated from the signal generator 10.

  Next, the circuit configuration of the signal generator 10 will be described. FIG. 2 shows a circuit configuration of a main part of the signal generator 10. The signal generator 10 includes a power supply unit 11 and a signal generation unit 12. Two capacitors 13 and 14 are connected in series between the P-side bus and the N-side bus of the DC circuit drawn into the signal generator 10 via the cable connector 106. These capacitors 13 , 14 and a ground coil drawn into the signal generator 10 through the cable connector 107, a clamp coil 112 is connected. Further, the signal generator 10 includes a current transformer 15 that detects a current flowing through the clamp coil 112 and a current transformer 16 that detects a current flowing through the ground.

  The power supply unit 11 is an electric circuit that generates operating voltages (for example, DC5V for driving a semiconductor circuit) of various circuit elements in the signal generator 10 from a DC voltage (for example, DC110V) applied to the DC circuit. . The power supply unit 11 includes a step-down type DC-DC converter as a main member, and further includes peripheral members such as a diode and a capacitor.

  The signal generating unit 12 is an electric circuit that generates an AC exploration signal and injects the AC exploration signal into the DC electric circuit. In the signal generation unit 12, the injection circuit 121 is an electric circuit that injects an AC exploration signal between the P-side bus and the ground and between the N-side bus and the ground of the DC circuit. The injection circuit 121 is composed of a PWM modulator, and the phase and voltage of the AC exploration signal can be easily adjusted under the control of the microcomputer 122. The AC search signal is a PWM-modulated pseudo sine wave AC signal.

  The voltage measurement circuit 123 is connected to the P-side bus, the N-side bus, and the ground of the DC circuit, and the voltage and resistance value between the P-side bus and ground, and the voltage and resistance value between the N-side bus and ground are measured. An electric circuit to be measured. The injection phase / potential monitor circuit 124 is an electric circuit that monitors the phase and potential of the AC exploration signal injected into each of the P-side bus and the N-side bus in the DC circuit. The injection voltage monitor circuit 125 is an electric circuit that monitors the voltage level of the AC exploration signal injected into the linear circuit by the injection circuit 121 based on the detected current of the current transformer 15. The voltage level is, for example, the peak value or average amplitude of the AC exploration signal. The external capacitance measuring circuit 126 is an electric circuit that measures the external capacitance (ground capacitance) based on the detected current of the current transformer 16. The injection phase / potential monitoring circuit 124, the injection voltage monitoring circuit 125, and the external capacitance measuring circuit 126 are all provided with a filter circuit (not shown) such as a low-pass filter. Perform filtering processing.

  The analog-digital conversion circuit (ADC) 127 receives the signals output from the voltage measurement circuit 123, the injection phase / potential monitoring circuit 124, the injection voltage monitoring circuit 125, and the external capacitance measurement circuit 126, and receives these analog signals. Is converted into a digital signal and output to the microcomputer 122. The crystal oscillator 128 uses a crystal resonator as an oscillation source, and generates operation clock signals for the microcomputer 122 and the ADC 127 based on the oscillation of the crystal resonator.

  The microcomputer 122 performs PWM control on the injection circuit 121 based on the digital signal received from the ADC 127 so that an AC exploration signal having a predetermined voltage level is injected into the DC circuit. The microcomputer 122 displays various information on the display 110. For example, the microcomputer 122 displays on the display 110 a warm-up message when the signal generator 10 is activated, and a message notifying the completion of synchronization when the synchronization between the signal generator 10 and the slave unit is completed. Further, the microcomputer 122, when injecting the AC exploration signal, based on the digital signal received from the ADC 127, the P-pole ground fault resistance value, the N-pole ground fault resistance value, the total ground fault resistance value, the parallel ground fault resistance value, the voltage of the electric circuit, The voltage at the ground fault point and the like are calculated, and these values are displayed on the display 110.

  For example, the microcomputer 122 generates a periodic pulse signal of an AC exploration signal and outputs it to the optical signal conversion unit 129. The optical signal converter 129 converts the pulse signal received from the microcomputer 122 into an optical signal and outputs the optical signal to the optical connector 113. The optical signal is transmitted to the slave unit through an optical fiber cord (not shown) in the synchronization process between the signal generator 10 and the slave unit.

  Next, the cooling mechanism of the signal generator 10 will be described. FIG. 3 is an exploded perspective view of the signal generator 10. FIG. 4 is an exploded perspective view of the signal generator 10 from another angle.

  The signal generator 10 is accommodated in a case structure (outer box) including an outer box main body 101 and an outer box lid 101 '. Various electric circuit units of the signal generation device 10 such as the power supply unit 11 and the signal generation unit 12 are accommodated in a substantially rectangular parallelepiped casing 17 whose upper surface is open. The casing 17 is made of, for example, an electrogalvanized steel sheet / hot rolled material (SEHC) having a thickness of 0.8 mm corresponding to the RoHS directive. The casing 17 is accommodated in the outer box main body 101.

  The height of the housing 17 is substantially the same as the height of the inner dimension of the outer box main body 101, and the separation between the front side wall 17F and the back side wall 17B facing it is larger than the vertical inner dimension of the outer box main body 101. The distance between the right side wall portion 17R and the opposite left side wall portion 17L is about 32 cm shorter than the lateral inner dimension of the outer box main body 101. The lateral widths of the front side wall portion 17F and the back side wall portion 17B are substantially the same as the lateral inner dimensions of the outer box main body portion 101. An angle portion 171 having a width of about 2 cm is formed at the upper end of each of the front side wall portion 17F and the back side wall portion 17B. Further, an angle member 116 for panel attachment is provided at each upper end of the front side surface and the back side surface inside the outer box main body 101. The front panel 105, the angle portion 171 of the housing 17, and the angle member 116 of the outer box main body portion 101 are fixed with screws. Thereby, the opened upper surfaces of the housing 17 and the outer box main body 101 are covered with the front panel 105, and the housing 17 is substantially sealed by the front panel 105.

  In the housing 17, the power supply unit 11 is disposed on the right side, and the signal generation unit 12 is disposed on the left side. That is, the power supply unit 11 and the signal generation unit 12 are accommodated next to each other in the housing 17. Further, in the housing 17, a circular opening 172 of an appropriate size for attaching the electric cooling fan 18 is provided in the right side wall portion 17 </ b> R near the power supply unit 11. The cooling fan 18 is attached to the inside of the right side wall portion 17 </ b> R in accordance with the opening 172.

The cooling fan 18 has, for example, a DC brushless motor and propeller blades that are axially attached to the rotor of the motor, and is driven by a direct current by the power supply unit 11 to generate an airflow in the axial direction from the inside of the housing 17 to the outside. It is a DC axial flow fan. As the cooling fan 18, for example, a DC axial fan having a frame size of 60 mm, a rated input of 24 V, and a maximum air volume of 0.61 m ³ / min can be used.

  On the other hand, in the housing 17, a rectangular opening 173 is provided in the left side wall 17L. The opening 173 is for allowing the outside air to flow into the housing 17, and the size of the opening 173 is that the outside air flowing into the housing 17 has a certain degree of momentum (flow force) to the signal generation unit 12. It is only necessary to have a minimum size that can directly and intensively take away a certain amount of heat generated in the signal generation unit 12 and keep the internal temperature of the housing 17 at the same level as the outside air temperature. That is, if the size of the opening 173 is too large, the flow rate of the outside air flowing into the housing 17 is not preferable, and conversely, the amount of the outside air flowing into the housing 17 is too small. Since it falls, it is not preferable. The size of the opening 173 is, for example, about 25 mm long and 95 mm wide. Note that the amount of heat generated inside the housing 17 varies depending on the units housed in the housing 17, and therefore the size of the opening 173 takes into account the amount of heat generated by each unit actually housed in the housing 17. It is good to decide.

  The opening 173 may be covered with an appropriately sized punched steel plate 19 in order to prevent foreign matter from flowing into the housing 17 from the opening 173. However, as the punched steel plate 19, a punched steel plate having an appropriate size and amount capable of allowing a necessary and sufficient amount of outside air to flow into the housing 17 should be adopted.

  Although there are some holes in the front side wall portion 17 </ b> F, these are holes for accessing various signal terminals in the signal generation unit 12 for inspection and debugging of the signal generation device 10. Outside air also flows into the housing 17 from these holes.

  FIG. 5 is a plan view cross-sectional view of the signal generation device 10, and schematically shows the positional relationship between the power supply unit 11, the signal generation unit 12, the opening 173, and the cooling fan 18 and the airflow generated inside the device. As described above, since the separation between the left side wall portion 17L and the right side wall portion 17R of the casing 17 is shorter than the lateral inner size of the outer box main body portion 101, the inside of the outer box main body portion 101 is the left side wall portion of the casing 17. The small spaces 101L and 101R are formed by being partitioned by 17L and the right side wall portion 17R, respectively. The upper surfaces of the small spaces 101L and 101R are covered with a front panel 105, and ventilation slits 114L and 114R are formed in portions of the front panel 105 that cover the small spaces 101L and 101R, respectively. As a result, the appearance of the cooling fan 18 is not apparent and foreign substances are prevented from flowing into the signal generator 10 from the outside.

  When the cooling fan 18 is driven, the outside air 200 is sucked into the small space 101L from the slit 114L, the outside air 200 flows into the housing 17 through the opening 173, and the outside air 200 flows out to the small space 101R through the opening 172. The outside air 200 is exhausted from the slit 114R to the outside of the apparatus. In this way, the outside air 200 is forcibly circulated by the cooling fan 18 to create an outside air circulation path inside the signal generator 10, thereby suppressing an increase in the internal temperature of the signal generator 10 and stabilizing the internal temperature. be able to. In particular, in the housing 17, the signal generation unit 12 having electronic components such as a crystal oscillator and a filter circuit, whose characteristics tend to fluctuate due to changes in the environmental temperature, is arranged on the upstream side of the airflow, and the power supply unit 11 having a large heat generation amount By disposing on the downstream side, the air heated by the power supply unit 11 is efficiently discharged to the outside of the apparatus without being carried to the signal generation unit 12. In addition, since the signal generation unit 12 is disposed in the immediate vicinity of the opening 173 having the minimum necessary size, it is possible to continue to apply a certain amount of outside air 200 directly and effectively to the signal generation unit 12. Thereby, the signal generation unit 12 can be kept substantially the same as the outside air temperature without being affected by the heat generation of the power supply unit 11 and the like in the housing 17.

  As described above, according to the present embodiment, in the portable ground fault search signal generator (signal generator 10) that generates an AC search signal for ground fault search of a DC circuit, The internal temperature of the apparatus can be kept substantially the same as the outside air temperature by antagonizing the cooling capacity of the cooling mechanism including the cooling fan 18 and the opening 173. That is, the temperature rise of the signal generation unit 12 that is easily affected by the internal temperature of the portable ground fault search signal generator (signal generation device 10), particularly the environmental temperature, can be suppressed. As a result, the master unit can output a stable AC exploration signal in a short time (in about a few minutes) after starting, and can quickly start the ground fault search of the DC electric circuit. .

  In the present embodiment, the opening 173 and the cooling fan 18 are disposed to face each other, but the present invention is not limited to such an arrangement. The signal generation unit 12 may be disposed on the upstream side of the airflow with respect to the power supply unit 11, and the positional relationship between the opening 173 and the cooling fan 18 is arbitrary. For example, the cooling fan 18 may be attached to the upper surface of the housing 17, that is, the front panel 105 instead of the right side wall portion 17 </ b> R of the housing 17.

  In addition, the cooling mechanism of the signal generator according to the present invention can be variously modified in addition to the above configuration. For example, the cooling mechanism of the signal generator according to the present invention can be applied to an insulation resistance measuring device that measures insulation of an electric circuit by injecting a signal for measuring the insulation resistance into the electric circuit.

10 Signal generator (portable ground fault search signal generator)
11 Power supply unit 12 Signal generation unit 17 Housing 17L Left side wall (second side wall)
17R Right side wall (first side wall)
173 Opening 18 Cooling fan 101 Outer box body (outer box)
101L small space (small space for intake)
101R small space (small space for exhaust)
105 Front panel (lid)
114L slit 114R slit 200 outside air

Claims (5)

A signal generator cooling mechanism comprising a signal generation unit that generates a periodic signal of a predetermined frequency and a power supply unit that supplies an operating voltage to the signal generation unit,
The signal generation unit and the power supply unit are accommodated next to each other in a single housing whose upper surface is open, and the upper surface of the housing is covered with a lid.
In the housing, a cooling fan that generates an air flow from the inside to the outside on the first side wall near the power supply unit flows outside air into the housing on the second side wall near the signal generating unit. And a cooling mechanism for the signal generator, characterized in that each of the openings is provided. The signal generating unit is disposed in the immediate vicinity of the opening;
2. The cooling mechanism of the signal generation device according to claim 1, wherein the size of the opening is a minimum size required to directly apply outside air flowing into the housing to the signal generation unit.   The cooling mechanism of the signal generator according to claim 1, wherein the cooling fan and the opening are disposed to face each other. The casing is housed in an outer box whose upper surface is open, and the inside of the outer box is partitioned by the first and second side wall portions of the casing to form small spaces for intake and exhaust, respectively. And
The upper surface of each small space is covered with the lid,
The signal generator cooling mechanism according to any one of claims 1 to 3, wherein a ventilation slit is formed in a portion of the lid that covers each of the small spaces. A signal generating unit for generating a periodic signal having a predetermined frequency for searching for a ground fault in the DC circuit and injecting the periodic signal into the DC circuit; and generating the signal by DC-DC conversion of a DC voltage of the DC circuit A portable ground fault search signal generator comprising a power supply unit for supplying operating voltage to the unit,
A portable ground fault search signal generator comprising the cooling mechanism according to any one of claims 1 to 4.

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