JPH019238Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a timer circuit using a CR circuit.

In general, protective relays require various time-limiting characteristics, and an example of the configuration of a time-limiting circuit for a ground fault overcurrent relay with inverse time-limiting characteristics is shown in FIG. In the figure, 1 is four resistors R ₁
A zero-phase current transformer is connected to the input terminals t ₁ and t _2.
ZCT is connected. Reference numeral 2 denotes a detecting section which receives a divided voltage of a voltage dividing circuit including resistors R ₃ and R ₄ of the input section 1, and is composed of a transistor Q ₁ , resistors R ₅ to _{R 8} and a capacitor C ₁ . 3 is a Schmitt circuit, consisting of transistors Q ₂ , Q ₃ and resistors R ₉ ~
_R14 , and is connected to the output terminal of the detection section 2 (collector of the transistor _Q1 ) via a series circuit of a capacitor _C2 and a diode _D1 .
4 is a trapezoidal time circuit with a resistor _R15 and a capacitor.
It is composed of C ₃ and C ₄ and is connected to the output terminal of the Schmitt circuit 3 (collector of transistor Q ₃ ) via diode D ₂ . 5 is auxiliary relay
In the drive circuit, transistors Q ₄ , Q ₅ and resistor R ₁₆
~ _R18 , and receives the output of the timer circuit 4 to energize the auxiliary relay X.

FIG. 2 shows the circuit configuration of the control power supply, in which a rectifying bridge circuit RF is connected to the secondary side of the transformer T, and a smoothing capacitor _C5 is connected to the output terminal thereof. The voltage V ₂ across this smoothing capacitor C ₅ becomes the power supply voltage _{of the} auxiliary relay
The voltage V ₁ is made into a constant voltage and becomes the control power supply voltage for the detection unit 2, Schmitt circuit 3, etc.

In the above-mentioned relay, when a zero-sequence current is detected by the zero-sequence current transformer ZCT, the input voltage of the Schmitt circuit 3 becomes equal to or higher than the trigger level, and the charging of the time limit circuit 4 is started with the output voltage, and a predetermined period of time is reached. After the time limit, the auxiliary relay X is energized by the operation of the drive circuit 5. That is, a protection operation is performed.

The normal operation of the Schmitt circuit 3 will now be explained. Now, when a ground fault occurs and the current from ZCT increases, when the signal amplified by transistor Q ₁ is a positive wave, Q ₂ turns ON and Q ₃ turns OFF, so R ₁₄ , Via D ₂ and R ₁₅ respectively,
Charge C ₃ and C ₄ .

Also, when the above signal is a negative wave, Q ₂ turns OFF,
Q ₃ turns ON, but the charges charged in C ₃ and C ₄ are discharged via R ₁₅ , R ₁₆ , and R ₁₈ , but when these constants are large, they are hardly discharged and the next During the positive wave of the cycle, they are charged again, and by repeating this, the charges of C ₃ and C ₄ are integrated, and Q ₄ and Q ₅
is turned on.

On the other hand, when the ZCT input is zero, the base current of Q ₂ is blocked by C ₂ , so Q ₂ turns OFF, and the base current flowing through R ₁₁ , R ₁₂ , and R _{13 Q3} is ON.

Ignoring the collector-emitter saturation voltage of Q ₃ , the collector-OV voltage (V ₃ c) of Q ₃ is R ₁₄ and R ₁₃
However, V ₃ c at this time is designed to prevent transistors Q ₄ and Q ₅ from turning on due to the forward drop voltage of D ₂ and the voltage division of R ₁₅ and R ₁₆ . .

Next, the response when the control power supply is turned on and off will be explained.

Now, when the control power supply voltage is turned off with the ZCT input being zero, as shown in Figure 4, as V ₁ slowly decreases, Q ₂ is OFF, but the base current of Q ₃ increases. _Q3 may turn OFF due to the decrease. As mentioned above, when Q ₃ turns OFF,
Charge C ₃ and C ₄ .

On the contrary, when the control power supply voltage is turned on, the change in the rise of V ₁ becomes the apparent operating current, as shown in FIG. 5, and Q ₂ turns on. this is
Compared to the threshold value where V ₁ is divided by R ₁₁ and R ₁₃ ,
When the apparent operating current due to the change becomes small, it is normally turned off, so _Q3 is turned off during this time, charging _C3 and _C4 .

In this way, in the conventional circuit, when the control power supply voltage is repeatedly turned on and off, as explained above,
The charges of C ₃ and C ₄ are integrated, and Q ₄ and Q ₅ turn on.
There is a possibility that the output auxiliary relay X may malfunction.

By the way, a relay with such a circuit configuration has
This method has the drawback of causing malfunctions during momentary power outages of the control power supply. This is due to the fact that when the constant voltage falls to zero during a momentary power outage, and when the voltage rises from zero to the constant voltage, the fall and rise occur exponentially on the DC side where capacitors and resistors are used. This point will be discussed next.

(i) At the time of falling, due to the nature of the Schmitt circuit, the voltage V ₁₁ always varies from voltage V ₁ to zero V.
(0<V ₁₁ <V ₁ ), the Schmitt circuit is inactive,
In other words, transistor _Q3 is turned off. Since the voltage V ₁₁ at this time is larger than the forward voltage drop value V _D of the diode D ₂ , the resistance R ₁₄ → diode D ₂
→ capacitor C ₃ , resistor R ₁₄ → diode D ₂ → resistor R ₁₅ → capacitor C ₃ in the path of capacitor C ₄ ,
_C4 is charged until the voltage _V11 is less than the voltage _VD .

(ii) At startup, while capacitor C ₁ is charged in the path of resistor R ₇ → resistor R ₆ → capacitor C ₁ → resistor R ₅ → input part 1, transistor Q ₁ is not turned on and during this charging period A charging current flows through the capacitor C ₂ through the path of resistor R ₇ → capacitor C ₂ → diode D ₁ → resistor R ₁₀ , and this current turns on transistor Q ₂ . As a result, transistor Q ₃ is turned off, and capacitors C ₃ and C ₄ are charged in the same way as at the time of falling.

(iii) The discharge circuit of capacitor C ₃ is resistor R ₁₅ → resistor
Parallel circuit of R ₁₆ and low resistance R ₁₈ , also capacitor C ₄
The discharge circuit is a parallel circuit of resistor _R16 and resistor _R18 , but since resistor _R15 is for time-limited setting, it cannot be made smaller, and as a result, the discharge of capacitor _C3 is not completed instantaneously.

(iv) If the instantaneous interruption time (the time from falling to rising) is shorter than the discharge time of capacitors C ₃ and C ₄ , falling and rising appear to be a series of phenomena, and the discharge may become impossible to follow. Become.

(v) As a result of the above items (i) to (iv), the timer circuit malfunctions and the auxiliary relay X malfunctions.

The present invention was made to eliminate the above-mentioned drawbacks, and by inserting a Zener diode with a predetermined Zener voltage into the charging path of the CR circuit that is charged with the output voltage of the Schmidts circuit, the control power supply can be It is an object of the present invention to provide a time limit circuit that can prevent malfunctions during momentary power outages.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 3 shows an embodiment of the present invention, which is applied to a ground fault overcurrent relay. In Figure 3, 3 is a Schmitts circuit, 4A is a time limit circuit, and 5 is a Schmitt circuit.
is the drive circuit for auxiliary relay X (see Figure 1),
The configuration is the same as the conventional one (FIG. 1) except that a Zener diode _ZD2 for preventing malfunction is inserted in the charging path of the timer circuit 4A. The timer circuit 4A is formed in a trapezoidal (π-shape) by a resistor R ₁₅ and capacitors C ₃ and C ₄ , and connects the charging path between the connection point of the resistor R ₁₅ and the capacitor C ₃ and the output terminal of the Schmitt circuit 3 (transistor Q ₃ diode between the collector of
D ₂ and Zener diode ZD ₂ are sequentially inserted in series. The Zener diode ZD ₂ has a Zener voltage greater than the dead voltage V ₁₁ of the Schmitt circuit 3;
Use a DC control power supply voltage smaller than V ₁ .
In this case, it is desirable that the Zener voltage be as large as possible within the aforementioned predetermined range.

When the Zener diode ZD ₂ is inserted in the charging path of the CR circuit in this way, when the control power supply falls during a momentary interruption, the Schmitt circuit 3 is in the operating state up to the voltage V ₁₁ and the transistor
Q ₃ is on, and when the voltage becomes smaller than V ₁₁ , transistor Q ₃ turns off, but the relationship is Zener voltage Vz > non-operating voltage V ₁₁ , and capacitors C ₃ and C ₄ are not charged. .

On the other hand, at startup, the transistor
Even if Q ₃ is off, if the DC control power supply voltage does not exceed the Zener voltage Vz, the capacitor C ₃ ,
C ₄ is not charged, and even if the voltage rises and charging starts, the Zener voltage is much larger than the forward voltage drop V _D of diode D ₂ , so the presence of Zener diode ZD ₂ reduces the charging time. will be significantly shortened.

As a result, the amount of charge in capacitors C ₃ and C ₄ decreases, the time required for discharging becomes shorter, and even if the instantaneous interruption time becomes shorter, the discharge can sufficiently follow up and malfunctions are prevented. .

In the circuit of Fig. 3, by inserting a Zener diode ZD ₂ into the collector of Q ₃ , the circuit shown in Figs.
Even if the output shown in the figure occurs, by setting the zener voltage (VZ ₂ ) of the zener diode to a value greater than the maximum value of V ₃ c, as shown in Figure 6,
Charging of C ₃ and C ₄ can be prevented.

Although the above embodiment uses a trapezoidal timer circuit, it is also applicable to other general CR timer circuits.
Furthermore, as a measure to prevent malfunction, it may be possible to increase the resistance R ₁₈ so as to increase the reference voltage of the transistor Q ₄ , but this would increase the resistance of the discharge circuit and have the opposite effect.

As described above, according to the present invention, it is possible to reliably prevent malfunctions in the event of a momentary interruption of the control power supply with a simple circuit configuration in which a Zener diode is inserted in the charging path of the CR circuit. Moreover, there is no risk of affecting the time limit characteristics or the detection circuit at the previous stage, and on the contrary, there is an effect that malfunctions due to surges can be prevented.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the circuit configuration of a ground fault overcurrent relay to which the time limit circuit is applied, Figure 2 is a circuit diagram showing the configuration of the control power source of the relay, and Figure 3 is a circuit diagram of the time limit circuit according to the present invention. Circuit diagram showing one embodiment, No. 4
FIGS. 6 to 6 are waveform diagrams. 1... Input section, 2... Detection section, 3... Schmitt circuit, 4A... Time limit circuit, 5... Relay drive circuit, R ₁
~ _R18 ...Resistor, _C1 ~ _C5 ...Capacitor, _D1 and _D2 ...
Diodes, ZD ₁ and ZD ₂ ...Zena diodes,
X...Auxiliary relay, _Q1 to _Q5 ...Transistor.

Claims (1)

[Scope of utility model registration request] In a time limit circuit using a CR time constant circuit that is charged by the output voltage of the Schmitt circuit, a Zener diode with a Zener voltage greater than the non-operating voltage of the Schmitt circuit and smaller than the DC control power supply voltage is connected to the charging path of the CR time constant circuit. A time-limited circuit characterized by being inserted into.