KR900007580B1 - Over current reley - Google Patents

Abstract

The overcurrent relay for operating regadless of the temperature variation comprises a current sensor (2) converting the sensed current to corresponding voltage, a charger/discharger (4) charging and discharging the voltage amplified at an amplifier (3), an overcurrent sensor (5) detecting the overcurrent, a comparator (8) comparing the load voltage and the reference voltage (Vref) of the reference voltage supplier (7), a driver (9) controlling the load current with outputs of the overcurrent sensor and the comparator, and a checking circuit (10) supervising the operating state of the driver.

Description

Overcurrent Protection Relay

1 is a circuit diagram of an overcurrent protection relay of the present invention.

2 is a detailed view of the reference voltage supply of FIG.

3 is a trip characteristic curve graph of the overcurrent protection relay of the present invention.

* Explanation of symbols for main parts of the drawings

1: load 2: current detector

3: amplification part 4: charging and discharging part

5: overcurrent detector 6: buffer

7: reference voltage supply unit 8: comparison unit

9: drive unit 10: operation check unit

OP ₁ -OP ₃ : Operational Amplifiers D ₁ -D ₅ : Diodes

VR ₁ , VR ₂ : Variable resistor R _1- R ₁₄ : Resistance

Vcc: Power Terminal

The present invention relates to an overcurrent protection relay that detects when an overcurrent exceeding the rated current flows to the load and trips, that is, cuts off power supply to the load.

Conventionally, a mechanical relay such as an induction disk type overcurrent relay or a thermal relay is used to block the flow of overcurrent to a load. However, such a mechanical relay is not accurate and is affected by a change in ambient temperature. But there is a defect that a lot of errors caused by aging change.

When the current flowing to the load is detected by a current transformer and converted into a voltage, and the converted voltage is equal to or greater than the operating voltage of the Schmitt trigger circuit, a constant current flows to the relay coil after a certain time, and the relay switch opens to supply power to the load. There is also an electronic overcurrent relay that blocks the supply of the electronic overcurrent relay. However, when the zener voltage of the constant voltage diode that supplies a constant voltage to the Schmitt trigger circuit is changed according to the change of the ambient temperature, the operating power of the Schmitt trigger circuit The variable power supply to the load cannot be accurately performed, the load on the current transformer to detect the flow of current is varied, and the trip point suitable for driving a load such as a motor is insufficient, that is, about When the current flows about 200%, it not only trips, but also the combination of narrow setting time there was.

In view of such a conventional defect, the present invention provides an electronic overcurrent protection relay that operates accurately regardless of the change in ambient temperature, maintains a constant burden on the current transformer, has a wide trip time setting, and has a long time short-time characteristic. The invention is described in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram of the overcurrent protection relay of the present invention, and as shown therein, includes a current transformer (CT), a resistor (R ₁ ), and a capacitor (C ₁ ) for detecting and converting a current flowing to the load 1 into a voltage. The current detector 2, the resistors R ₂ -R ₄ , the diodes D ₁ , D ₂ , the capacitors C ₂ , C ₃ , and the operational amplifier OP that amplify the output voltages of the current detector 2. ₁ ) an amplifier 3, a resistor (R ₅ , R ₆ ), a variable resistor (VR ₁ ), a diode (D ₃ ) and a capacitor (C) for charging and discharging the output voltage of the amplifier (3). ₄ ) an overcurrent detector composed of constant voltage diodes ZD ₁ and ZD ₂ and resistors R _{7 which} detect whether an overcurrent flows to the load 1 by the output voltages of the charge / discharge unit 4 and the amplifier 3. (5) and the resistor (R ₈ ), the capacitor (C ₅ , C) which is output from the charging and discharging unit (4) to compare the voltage through the buffer 6 and the reference voltage (V _ref ) of the reference voltage supply unit (7) ₆₎ and a comparison unit (8) with a comparator (COMP _1), , A capacitor (C _7), thyristors (SCR), the relay coil (RL), a diode (D ₄₎ for controlling the power supply to the load (1) to the output voltage of the over-current detector 5 and a comparison unit (8) The driver 9 includes a resistor R ₁₀ , a light emitting diode (LED) and a transistor TR ₁ , resistors R ₁₁ and R ₁₂ for checking an operating state of the driver 9, and a capacitor C _8. ) And an operation check unit 10 composed of switches SW ₁ and SW ₂ , wherein reference numeral RSW in the drawing of FIG. 1 is a relay switch that is opened when current flows through the relay coil RL. Vcc, L ₁ and L ₂ are power terminals.

FIG. 2 is a detailed circuit diagram of the reference voltage supply unit 7 of FIG. 1, in which a resistor R ₁₃ , a variable resistor VR ₂ , and a resistor R ₁₄ are connected to a power supply terminal Vcc as shown in FIG. connected by connecting the variable terminal of the variable resistor (VR ₂₎ to the non-inverting input terminal (+) of the operational amplifier (OP ₄₎ to, and an output terminal of the operational amplifier (OP ₄₎ a diode (D _5), the resistance (R via ₁₅ ) and the inverting input terminal (-) of the condenser C ₉ and the operational amplifier OP ₃ , and the connection point thereof were connected to the comparator 8.

According to the present invention configured as described above, when power is applied to the power supply terminals L ₁ and L ₂ , the power is applied to the load 1 through the relay switch RSW so that the load 1 is operated and the power supply terminal Vcc. When power is applied to the power supply, the power supply Vcc is divided by the resistor R13, the variable resistor VR ₂ and the resistor R ₁₄ of the reference voltage supply unit 7 to thereby input the non-inverting input of the comparator OP ₄ . As applied to the terminal (+), the operational amplifier OP ₄ outputs a constant voltage, and the output voltage of the operational amplifier OP ₄ is fed back to its inverting input terminal (-) through the diode D ₅ to supply the reference voltage. (7) always outputs a constant reference voltage (V _ref ) regardless of the change in the ambient temperature, that is, outputs a constant reference voltage (V _ref ) regardless of the temperature change by feeding back the temperature characteristic change of the diode (D ₅ ). The reference voltage V _ref is applied to the inverting input terminal (-) of the comparator COMP ₁ of the comparator 8.

The current transformer CT detects a current flowing from the power supply terminal L ₂ to the load 1 through the relay switch RSW, and is constant in proportion to the current flowing to the load 1 between both ends of the resistor R ₁ . A voltage is applied, the voltage is amplified by the amplifier 3 and input to the overcurrent detector 4, and the resistor R ₅ and the variable resistor VR ₁ are charged in the control capacitor C ₄ , The charging voltage of the capacitor (C ₄ ) discharges the diode (D ₃ ) and the resistor (R ₅ ) to the control ground, and the non-inverting input terminal (+) of the comparator (COMP ₁ ) through the buffer (6) and the resistor (R ₈ ). Is applied.

Here, if the zener voltage is set so that the constant voltage diode ZD ₁ (ZD ₂ ) is turned on when an overcurrent of 600% or more of the rated current flows to the load 1, the load 1 is 600% or less of the rated current. When the overcurrent flows, the constant voltage diodes ZD ₁ and ZD ₂ are turned off, so the overcurrent detector 5 outputs a low potential.

When the variable resistor VR ₁ is changed so that the charging time constant and the discharge time constant of the capacitor C ₄ are the same when the rated current flows to the load 1, the current 1 or less of the rated current is supplied to the load 1. When flowing, the charge / discharge unit 4 outputs a low potential, and the low potential is applied to the non-inverting input terminal (+) of the comparator COMP ₁ through the buffer 6 and the resistor R ₈ . (COMP) _{1 Since} the voltage applied to the inverting input terminal (-) is higher than the voltage applied to its non-inverting input terminal (+), the comparator COMP ₁ outputs a low potential, and thus the gate of the thyristor SCR. A low potential is applied to the relay coil RL so that no current flows in the relay coil RL, and the relay switch RSW keeps a short circuit, so that the power supply of the power terminals L1 and L2 is loaded (1). Supplied to.

In this state, when a current equal to or greater than the rated current flows to the load 1, the charging voltage of the capacitor C ₄ gradually increases to increase the voltage applied to the non-inverting input terminal (+) of the comparator COMP ₁ . , if the voltage applied to the non-inverting input terminal (+) of the comparator (COMP ₁₎ higher than the reference voltage (V _ref), the comparator (COMP ₁₎ is a thyristor via a resistor (R ₉₎ outputs a high potential ( Since the thyristor SCR is applied to the gate of the SCR, the power supply of the power supply terminal Vcc flows to the thyristor SCR through the transistor TR ₁ and the relay coil RL according to this. TR ₁ ), resistance (R ₁₀ ), light emitting diode (LED) flows to the thyristor (SCR), so the relay switch (RSW) is open to cut off the power supply to the load (1), the light emitting diode (LED) It turns on to indicate that power supply to the load 1 has been cut off.

Here, since the charging voltage of the capacitor C ₄ increases in proportion to the current flowing to the load 1, as the current flowing to the load 1 increases as shown in the characteristic curve graph of FIG. 3, the relay switch RSW becomes faster. Open.

In addition, when an overcurrent of 600% or more of the rated current flows to the load 1, when the constant voltage diodes ZD ₁ and ZD ₂ are turned on and a high potential is applied to the gate of the thyristors SCR, an overcurrent of 600% or more flows. The thyristors SCR are electrically connected to each other, the relay switch RSW is opened, and the light emitting diode LED is turned on.

If the switch SW ₁ is pressed and shorted to check the operation state of the relay, the power supply of the power supply terminal Vcc is connected to the gate of the thyristor SCR through the switch SW ₁ and the resistor R ₁₂ . When applied, the thyristor SCR is turned on, the relay switch RSW is opened, the light emitting diode LED is turned on, and when the switch SW ₂ is pressed and shorted, the transistor TR ₁ is turned off and the thyristor ( SCR) is cut off, and the relay returns to its original state. When the discharge time constant of the capacitor C ₉ of the reference voltage supply unit 7 is set to be larger than the discharge time constant of the capacitor C ₄ , the instantaneous power failure lamp In this case, since the charging voltage of the capacitor C ₄ discharges in a time faster than the charging voltage of the capacitor C ₉ , during a power failure, a low potential is output from the comparator COMP ₁ and the thyristor SCR is not conducting. Will not.

As described in detail above, the present invention has a definite time characteristic up to 100-600% of the rated current, and blocks the flow of overcurrent to the load, and prevents the relay from malfunctioning during a momentary power failure, as well as a constant temperature change. By supplying a reference voltage, the operation is not only very accurate but also it is easy to check whether the relay is operating normally.

Claims (2)

A current detector 2 which detects a current flowing to the load 1 and converts it into a voltage, a charge / discharge unit 4 which charges and discharges the voltage output from the current detector 2 and amplified by the amplifier 3, and the An overcurrent detector 5 for detecting whether an overcurrent flows to the load 1, and a voltage output from the charge / discharge unit 4 and the buffer 6 compared with a reference voltage V _ref of the reference voltage supply 7. And a driving unit 9 for controlling and displaying the power supply to the load 1 with the output voltages of the overcurrent detecting unit 5 and the comparing unit 8, and the operation of the driving unit 9. Relay for overcurrent protection, characterized in that consisting of an operation check unit for checking the state (10). The method of claim 1, wherein the reference variable of the voltage supply 7 is a power supply terminal resistor (R ₁₃₎ and a variable resistor (VR _2), by connecting a resistor (R ₁₄₎ in series with a variable resistor (VR ₂₎ to (Vcc) connecting the terminal to the non-inverting input terminal (+) of the operational amplifier (OP _4), and an output terminal of the operational amplifier (OP ₄₎ through the diode (D _5), its inverting input terminal (-) connected to a reference at the access point An over-current protection relay, characterized in that configured to output a voltage (V _ref ).

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