JPH0244220Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a surge counter circuit that detects and counts lightning surges or switch surges that enter power distribution lines.

Conventionally, the first surge counter of this type was
Something like the one shown in the picture was used. In Fig. 1, 11 is a measurement point, C ₀ and C ₁ are voltage dividing capacitors connected between measurement point 11 and ground terminal E,
PT is a pulse transformer whose primary winding is connected to both ends of the voltage dividing capacitor _C1 . A diode D and a variable resistor VR are connected between the voltage output terminals of the secondary winding of this pulse transformer PT.
Note that the neutral point N of the secondary winding is connected to the earth terminal E. The variable terminal of the variable resistor VR is connected to the trigger terminal T of the thyristor SCR via a resistor _R1 . A series circuit of a capacitor C ₂ and a counter 12 is connected between the anode and cathode of this thyristor SCR, and this counter 12 has a resistor R ₂
are connected in parallel. In addition, the above thyristor
A resistor _R3 and a DC power source (battery) B are connected between the anode of the SCR and the earth terminal E.

In such a configuration, the measurement principle will be explained. The surge voltage that has entered the measurement point 11 is connected to the ground via the earth terminal E, and at this time, voltages that are inversely proportional to the capacitances of the voltage dividing capacitors C ₀ and C ₁ are generated at both ends of each capacitor. The voltage generated in the above voltage dividing capacitor _C1 is output to the secondary side via the pulse transformer PT, and if the incoming surge is a positive wave, the variable resistor is connected to the diode D, variable resistor VR, earth terminal E, and the earth. Positive voltage appears across VR. At this time, the variable resistor VR is adjusted in advance according to the input voltage level, and when the input voltage (intrusion surge) exceeds the set level, the thyristor
Ignite the SCR. As a result, the thyristor SCR becomes conductive, and the voltage of the pre-charged capacitor _C2 is discharged in a closed circuit of the thyristor SCR, the resistor _R2 , and the capacitor _C2 , and becomes ready for charging. After that, the thyristor SCR becomes non-conductive, and the resistor R ₃ , capacitor C ₂ , counter 12,
Capacitor _C2 is charged in the path of ground terminal E,
The counter 12 is driven by the charging current at this time.

Through the above steps, the original state is restored again, and the next intrusion surge can be detected.

However, in the above-mentioned conventional system, since the voltage divider leading to the pulse transformer PT is composed of a capacitor, the transfer characteristic for input surges does not correspond to the first-order system, which has the disadvantage of causing undershoot due to kick-off in the secondary waveform. be. Therefore, when it is desired to detect surges of positive polarity and negative polarity, a circuit that cuts out undershoot (vibration) generated in the pulse transformer is required. The reason for this is clear from FIG. Figure a shows the positive surge input waveform, Figure b shows the secondary output waveform of the pulse transformer PT in response to this positive surge input waveform.
The figure c shows the negative surge input waveform, and the figure d shows the pulse transformer PT 2 for this negative surge input waveform.
This shows the next-side output waveform, and in b and d of the same figure, the portion indicated by X shows that an undershoot occurs. In this way, when an undershoot occurs in response to a surge input, when a circuit that normally only detects positive surges detects an undershoot in the negative surge input waveform, it is mistakenly treated as if a positive surge had occurred. May cause detection. For this reason, a circuit to cut out the undershoot is required.

In the past, in order to prevent malfunctions due to the undershoot, a diode D was provided on the secondary side of the pulse transformer PT as shown in FIG. 1, and the diode D was used to apparently cut out the undershoot. However, the diode D has the disadvantage that its forward voltage drop and temperature characteristics affect the forward surge voltage. Therefore, the conventional surge counter shown in Figure 1 has difficulties in setting the surge detection level and its stability, and also has problems with the thyristor.
Since the SCR trigger voltage itself has a large temperature coefficient, it has been extremely difficult to improve the accuracy of the surge measurement voltage as a whole. Furthermore, in order to prevent the circuit itself from being affected by noise caused by incoming surges, this type of device is often operated using a battery as a power source. For this reason, using a thyristor requires a relatively large operating voltage, which poses problems in terms of battery life, etc.

This idea was made in view of the above points,
Surge detection levels can be set accurately and easily, and bipolar surge detection is possible. Standards for surge-resistant design and electrical resistance design of various electrical equipment loaded on distribution lines can be easily established, and electrical equipment The purpose of the present invention is to provide a surge counter circuit that is extremely useful for ensuring safety and noise resistance.

An embodiment of this invention will be described below with reference to the drawings. In FIG. 3, 21 is a measurement terminal to which a surge voltage is input, R _a and R _b are voltage dividing resistors that divide the surge voltage into arbitrary voltage levels, and PT is a pulse transformer. The primary winding _A1 of this pulse transformer PT is connected to both ends of the resistor _Rb , one of the secondary windings A2 has resistors R _{c and} R d connected in series, and the other winding _A2 has resistors R c and R _d connected in series. The line _A3 has resistors R _e and R _f connected in series. Note that the above-mentioned resistances R _c and R _e are the above-mentioned resistances R _a and
This is a resistor that works with R _b to set the level of the surge voltage. Moreover, IC ₁ and IC ₂ are voltage comparators made of differential amplifiers with high gain, and the positive input terminal of comparator IC ₁ is connected to the above-mentioned resistor R _c and resistor R _d.
The positive input terminal of comparator IC ₂ is connected to the connection point P ₂ between the resistors R _e and R _{f .}
It is connected to the. Zener diodes ZD _{1 and} ZD ₂ for protecting the input stages of the comparators IC ₁ and IC ₂ are connected between the connection points P 1 and P ₂ and the ground, respectively. The negative input terminals of each of the comparators IC ₁ and IC ₂ are commonly connected and connected to a power supply circuit B that generates a reference voltage V _ref . These comparators IC ₁ and IC ₂ compare the reference voltage V _ref and the secondary voltages V _p and V _o of the surge voltage, and output when V _ref < V _p or V _ref < V _o . It is something. Additionally, a positive surge counter CUT 1 is connected to the output side of the comparator IC ₁ , and a negative surge counter CUT ₁ is connected to the output side of the comparator IC ₂ .
CUT ₃ is connected. These surge counters CUT ₁ and CUT ₂ are operated by the comparator outputs when the inputs of the comparators IC ₁ and IC ₂ become V _ref <V _p and V _ref <V _o .

The operation of such a configuration will be explained next. Surge voltage (several kV or more) at measurement terminal 21
When V _s is applied, the voltage V ₁ applied to the primary side of the pulse transformer PT is expressed as V ₁ =V _s R _b /R _a +R _b where R _b ≪(R _c +R _e ). If the winding ratio of the pulse transformer PT is 1:1, a voltage of V ₁ =V ₂ =-V ₃ is transmitted to the secondary side. At this time, the ratio of resistors R _a and R _b that determines V ₁ is set so that V ₂ and V ₃ , which correspond to the lowest level of the surge voltage to be measured, exceed the reference voltage V _ref .

In this way, even if a pulse transformer with an inductance of several mH is used, by setting the resistance R _b to a low value on the order of several tens of Ω, the pulse transformer PT will not be affected by the impedance on the primary side. . In other words, when considering the inductance L on the primary side of the pulse transformer PT, the impedance is ωL.

Therefore, the original formula is V ₁ = V _s R _b ωL/R _a + R _b ωL ... However, signals such as impulses have a high impedance due to very high ω, and R _b
If is set to a low value on the order of several tens of ohms, ωL can be ignored and the voltage can be reduced using a formula without using a formula. In other words, the primary voltage of the pulse transformer PT can be converted using only the impedance of the dividing resistor + pulse transformer PT (driven with a constant low impedance). From this,
Since ωL is large when the impulse input rises (kick-off), it can be absorbed (ignored).

Therefore, as in the conventional example shown in Fig. 1, there are two
Next side diode (diode D in Figure 1)
is no longer necessary, and the accuracy and stability of surge voltage detection can be significantly improved.

By the way, the input voltages V _p and _Vo to the comparators IC ₁ and IC ₂ for determining the surge voltage level are expressed by the following equations.

V _p =V ₁ R _d /R _c +R _d =V _s R _b /R _a +R _b・R _d /R _c +R _d |V _o |=V ₁ R _f /R _e +R _f =V _s R _b / R _a +R _b・R _f / _{R e} +R _f Therefore, the resistors R _{c ,} R _{d ,}
If R _e and R _f are selected, V _p > V _ref or V _o >
When a surge voltage equal to V _ref comes in, the outputs of comparators IC ₁ and IC ₂ become high level, and the positive polarity surge counter CUT ₁ and negative polarity surge counter CUT ₂ connected to their respective output terminals count. make it work. The Zener diodes ZD ₁ and ZD ₂ connected to the input stage of each comparator IC ₁ and IC ₂ are
Reverse polarity surge voltage (for the Zener diode ZD ₁ , when a negative polarity surge voltage is applied, for the Zener diode ZD ₂ , when a positive polarity surge voltage is applied)
When a voltage negative from the power supply 0V is applied to the IC ₁ and IC ₂ inputs, it conducts as a forward diode and protects _{the comparators IC 1 and} IC ₂ . This is to prevent excessive surge voltage from being applied to the comparators IC ₁ and IC ₂ when a negative surge is applied in the case of the Zener diode ZD ₂ .

In this way, this device uses a resistor R _b with a relatively small resistance value and a resistor connected in series with this resistor R _b .
R _a and its primary winding are connected in parallel to the resistor R _b , and the positive and negative polarity proportional to the input surge voltage is connected from the first and second 22nd windings to the resistor R b. Pulse transformer PT that outputs pulse signals and resistor
Consisting of R _c , R _d and resistors R _e , R _f, respectively,
Each resistor divider circuit sets an arbitrary surge detection level for each positive and negative polarity of the secondary winding of the pulse transformer PT, and each comparator compares the output of each resistor divider circuit with a reference voltage.
A surge counter device is composed of IC ₁ , _{IC 2} , a positive polarity surge counter CUT ₁ , and a negative polarity surge counter CUT ₂ that count the outputs of these comparators IC ₁ , IC 2 . With this configuration, it has excellent setting accuracy and stability, and can be measured for each positive and negative polarity, making it possible to establish standards for surge-resistant design and electrical resistance design of various electrical equipment that loads on distribution lines. This can greatly contribute to ensuring equipment safety and noise resistance. In addition, each of the above-mentioned circuits can use ICs that operate on the order of several volts, and liquid crystal displays can also be used to display the contents of the surge counter that calculates the surge voltage, so they essentially operate with minute currents. This makes it possible to extend the life of the battery.

As explained above, according to this invention, the surge detection level can be set accurately and easily, bipolar surge detection is possible, and surge-resistant design and electrical resistance design of various electrical equipment loaded on distribution lines are possible. Standards can be established easily, and surge counter circuits can be provided which are extremely useful for ensuring the safety of electrical equipment and noise resistance.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional surge counter circuit.
Figures 2a to d are diagrams showing the secondary output waveform of the pulse transformer in response to the surge input waveform, Figure 3 is a configuration diagram of a surge counter circuit according to an embodiment of this invention, and Figures 4a to f are diagrams showing the same implementation. It is a figure which shows the secondary side output waveform of a pulse transformer with respect to the surge input waveform in an example. 21...Measurement terminal, R _a , R _b ...Voltage dividing resistor,
IC ₁ , IC ₂ ...Comparator, ZD ₁ , ZD ₂ ...Zena diode, CUT ₁ ...Positive surge counter, CUT ₂ ...Negative polarity surge counter.

Claims (1)

[Claims for Utility Model Registration] (1) The first terminal connected between the surge voltage input terminal and the ground
A voltage dividing resistor circuit and a primary winding are connected in parallel between the voltage dividing point of the first voltage dividing resistor circuit and ground,
A pulse transformer that generates a pulse voltage with an amplitude proportional to the input surge voltage from a secondary winding, a second voltage dividing resistor circuit connected to the secondary winding of this pulse transformer, and a second voltage dividing resistor circuit connected to the secondary winding of this pulse transformer. It includes a comparator that compares the divided voltage output of the piezoresistive circuit with a preset reference voltage, and a surge counter connected to the comparator, and the resistance value of the first voltage dividing resistor circuit is determined by the pulse The surge voltage transmission waveform in the transformer is set in advance to a value that does not cause undershoot, and the voltage of the secondary winding is divided by resistance and compared with the reference voltage by the comparator, and the result of this comparison drives the surge counter. A surge counter circuit characterized in that the surge counter circuit has the following characteristics: (2) The secondary winding of the pulse transformer is composed of two windings, a first and a second winding, and the second voltage dividing resistor circuit is connected to the first and second secondary windings, 2. A surge counter circuit according to claim 1, wherein a comparator and a surge counter are provided to measure the surge voltage for each positive and negative polarity. (3) The surge counter circuit according to claim 1 or 2, wherein a constant voltage diode is connected to the input terminal of the comparator to which the divided voltage output of the second voltage dividing resistor circuit is supplied.