JPH0316068Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Technical Field of the Invention] The present invention relates to a contact resistance measuring device for measuring contact resistance at an electrical contact portion such as a switch contact. [Technical background of the invention and its problems] It can be said that the majority of failures in electrical equipment are caused by poor contact at electrical contacts in the electrical circuit. In order to prevent troubles in electrical equipment due to poor contact, it is necessary to measure the contact resistance of the contact portion in the mounted state and check whether the contact resistance value shows an abnormal value. FIGS. 1a, b, and c are diagrams showing the most basic conventional contact resistance measuring means. That is, as shown in FIG. 1a, when the circuit 1 includes a contact 2 such as a switch, the contact resistance of the contact 2 is R.
[Ω], the equivalent circuit is as shown in FIG. Therefore, the current I in this circuit 1
When , a voltage drop called IR occurs across the resistor R. Therefore, as shown in Figure c, an ammeter 3 is connected in series to the circuit 1, and a voltmeter 4 is connected between both ends of the resistor R to measure the current I and the voltage drop IR, so that the contact resistance R can be calculated as R= It can be calculated using the formula IR/I. However, the value of contact resistance R is generally 1×10 ^-3 [Ω]
This is a very small value. Therefore, even if the current I is about 10 [A], the voltage drop IR will only be about 1×10 ^-2 .
Therefore, it is necessary to use a voltmeter 4 with extremely high sensitivity and accuracy, and there are restrictions on the meters that can be used. Furthermore, in order to connect instruments to the circuit, the circuit 1 must be temporarily disconnected. Furthermore, measurement errors due to variations in the load current I increase. Therefore, it is not a measurement method suitable for on-site use. Note that measurement by a voltage drop method using a DC power source may also be considered in order to keep the current I constant. However, in this measuring means, the circuit in which the contact portion to be measured is interposed must be electrically isolated from other circuits before the measurement is performed. Therefore, there is a problem that the measurement work is complicated and it is difficult to measure the contact resistance simply and quickly. [Purpose of the invention] The purpose of the invention is to be able to easily and accurately measure the contact resistance of a contact part to be measured in a mounted state while in use with a load current flowing through the contact part. It is an object of the present invention to provide a contact resistance measuring device capable of preventing troubles in electrical equipment due to defects. [Summary of the invention] In order to achieve the above object, the present invention is characterized by the following structure. That is, a first circuit is connected to the secondary side of a first current transformer that is detachably attached to the line on which the contact part to be measured is interposed, and a variable resistor is connected between both ends of the contact part to be measured. A second circuit is connected through the device. And the first above,
A second current transformer is provided in which each part of the second circuit has a common primary winding with opposite polarities, and an ammeter for measuring secondary current is provided on the primary side of the second current transformer. Connecting. During measurement, adjust the variable resistor so that the ammeter indicates the minimum value, and calculate the contact part to be measured from the resistance value of the variable resistor at that time and the current transformation ratio of the first current transformer. Find the contact resistance. In this way, the measurement circuit can be connected at any time to the energized contact portion to be measured through which the load current is flowing, and the measurement circuit is characterized in that it is configured so that the value of the load current does not affect the measured value at all. [Embodiment of the invention] Figs. 2 and 3 are diagrams showing an embodiment of the invention, in which Fig. 2 shows a state in which the measuring device is used, and Fig. 3 shows a circuit configuration. In FIG. 2, 10 is the main body of the measuring device, and this main body 10 includes an ammeter 11 and a coarse adjustment resistor group 12A whose resistance value is known.
and a fine adjustment resistor group 12B, a variable resistor 12, a current transformer 13, a switch 14, and a fuse 1.
5 class is installed. A clamp type current transformer 18 having a current transformation ratio of k is connected to the first terminals 16A, 16B of the main body 10 via lead wires 17A, 17B. In addition, alligator clips 21 are connected to the second terminals 19A and 19B of the main body 10 via lead wires 20A and 20B.
A and 21B are connected. A clamp-type current transformer, that is, a first current transformer 18 is a current detecting section 18B that can be opened and closed by operating an operating section 18A.
2, it can be easily fitted. The alligator clips 21A and 21B are connected to both terminals M, which include the contact portion to be measured, that is, in this embodiment, one blade 24 of the switch 23 and the contact portion of the blade receiver 25 corresponding to this blade.
It is designed to be able to interlock with N. In FIG. 3, reference numeral 30 indicates the contact portion having a contact resistance R [Ω]. As shown in FIG. 3, the secondary current i ₁ of the first current transformer 18 flows through the first
The circuit 31 and the second circuit 32 in which the current i ₂ taken out from both ends of the contact resistance R flows through the variable resistor 12 and the switch 14 become a common primary winding of the second current transformer 13. It is wired as follows. Note that each part of the first and second circuits serving as the common primary winding is connected so that the polarities with respect to the secondary winding of the second current transformer 13 are opposite to each other. Next, the operation of the apparatus configured as described above will be explained. Now, assuming that a load current I is flowing through the line 22, the first current transformer 1 is connected to the first circuit 31.
8 secondary current i ₁ flows, and its current value is measured by ammeter 11
be instructed. When the switch 14 is closed in this state, a current i ₂ limited by the variable resistor 12 flows through the second circuit 32, and the indicated state of the ammeter 11 changes accordingly. So ammeter 1
After confirming that the indication of 1 decreases, the variable resistor 12 is variably adjusted so that the indication of the ammeter 11 becomes zero. If the reading on the ammeter 11 increases when the switch 14 is closed, the coupling relationship between the first circuit 31 and the second circuit 32 with respect to the current transformer 13 is reversed, and then the same adjustment as above is performed. . If the resistance value of the variable resistor 12 at this time is r, then i ₁ =I/K, i ₂ =IR/R+r, and i ₁ and i ₂ are equal. Therefore, IR/R+r=I/k∴R=r/k-1 (1). Note that if the first current transformer 18 is one in which the current transformation ratio k is k≫1, R≒r/k (2). Therefore, the contact resistance R can be determined from the current transformation ratio k of the current transformer 18 and the resistance value r of the variable resistor 12. As is clear from the above equations (1) and (2), the load current I does not intervene in these equations. Therefore, according to the present device, contact resistance R can be measured regardless of variations in load current I, and measurement errors due to variations in load current I do not occur. In addition, in this device, there is no need to use special instruments such as the ammeter 11, and the measurement circuit is simplified.
It is small, lightweight, and inexpensive to manufacture, making it suitable for carrying to measurement sites. Moreover, the line 22 as a circuit under test is in use without any circuit breakage.
Attach a clamp-type first current transformer 18 to the
In addition, alligator clips 21A and 21B can be attached to both ends of the contact portion 30, which is the portion to be measured. Therefore, preparation for measurement is simple, and contact resistance can be measured at any time and in a planned manner, regardless of how the contact portion to be measured is used. As a result, changes in contact resistance R over time can be known, and accidents caused by poor contact can be prevented. <<Experiment example>> An I meter capable of measuring minute currents with a current transformation ratio k = 1364 was used as the current transformer 18, and the variable resistor 12
As 10 [Ω], 1.5 [W] and [Ω], 1.5 [W]
Build a circuit as shown in Figure 4 using a slide type resistor and a shunt (50A, 100mV) with a resistance value of 2 x 10 ^-3 [Ω] as a substitute resistor 40 for the contact resistance R. The value of contact resistance R was determined. That is, the power switch 41 was closed, the voltage was adjusted by the induced voltage regulator 42, a predetermined load current I was passed through the circuit 43, and the variable resistor 12 was adjusted so that the reading on the ammeter 11 became zero. Ammeter 4 at this time
While recording the indicated values of 4, 45 and 11,
The resistance value r of the variable resistor 12 was measured using a Wheatstone bridge, and r/k was determined by calculation. Table 1 shows the results.

[Table] <<Experiment example>> As a substitute resistor 40 for contact resistance R, the resistance value is
A 0.6×10 ^-3 [Ω] current shunt (100 A, 60 mV) was used, and the experiment was otherwise conducted under the same conditions as in the experimental example. The results were as shown in Table 2.

[Table] As is clear from Tables 1 and 2, the error is
It is 0.02×10 ^-3 [Ω] or less, which is sufficient for practical use. Note that the measurement accuracy can be further improved if the indicated value of the ammeter 11 can be made completely zero by increasing the accuracy of the ammeter 11, the variable resistor 12, etc. and improving the operating method. It has also been demonstrated that contact resistance R=r/k can be determined regardless of changes in load current I. Note that the present invention is not limited to the above embodiments and experimental examples. For example, in the experimental example described above, a current transformer 18 with a current transformation ratio k of 1364 was used, but a current transformer with a current transformation ratio k set at 1000 may be used. In this way, the contact resistance R can be directly determined from the resistance value r of the variable resistor 12. It goes without saying that various other modifications can be made without departing from the gist of the present invention. [Effects of the invention] As explained above, according to the invention, it is possible to timely connect the measurement circuit to the contact part to be measured in the energized state, and also to ensure that the value of the load current does not affect the measured value at all. With this configuration, the contact resistance of the contact part to be measured in the mounted state can be easily and accurately measured in the operating state where the load current is flowing through the contact part, and troubles with electrical equipment due to poor contact can be easily and accurately measured. It is possible to provide a contact resistance measuring device that can prevent such occurrences.

[Brief explanation of the drawing]

Figures 1a, b, and c are diagrams showing conventional contact resistance measuring means, Figures 2 and 3 are diagrams showing an embodiment of the present invention, and Figure 2 is an explanatory diagram of the usage state of the measuring device. FIG. 3 is a circuit diagram of the measuring device, and FIG. 4 is a diagram showing the measuring circuit used in experiments of the present invention. 10... Measuring device main body, 12... Variable resistor,
13... Current transformer (second current transformer), 14... Switch, 15... Fuse, 16A, 16B... First terminal, 19A, 19B... Second terminal, 18
... Clamp type current transformer (first current transformer), 21A,
21B... Clip, 22... Line, 23... Switch, 30... Contact part to be measured, 31... First circuit, 32... Second circuit, 40... Alternative resistor for contact resistance, 41... Power switch, 42... Induction voltage regulator, 44, 45... Ammeter.

Claims (1)

[Scope of utility model registration request] a first current transformer that is detachably attached to a line in which a contact part to be measured is interposed; a first circuit connected to the secondary side of the first current transformer; and the contact part to be measured. a second circuit connected between both ends of the part via a variable resistor, and a second current transformation in which each part of the first and second circuits is a common primary winding having opposite polarities. and an ammeter that measures the secondary current of the second current transformer, and the resistance of the variable resistor when the variable resistor is adjusted so that the indication of the ammeter becomes zero. A contact resistance measuring device characterized in that the contact resistance of the contact portion to be measured is determined from the current transformation ratio of the first current transformer.