Device for preliminary monitoring of insulation resistance of electrical installation connection

Abstract

FIELD: electrical engineering.SUBSTANCE: invention relates to devices for preliminary monitoring of insulation resistance of an electrical installation connection. This problem is solved by connecting to the same no-load voltage of the measuring current source from the doubled rectified voltage of the AC voltage source two resistive voltage dividers, to one of which the electrical installation connection monitored by the device is connected. Signals from said two resistive voltage dividers are compared by a comparator. The use of a comparator in the device control circuit ensures reliability and stability of blocking the electrical installation from being switched on when the insulation resistance of the electrical installation connection decreases below the response resistance value of the unit and removing the blocking when the insulation resistance of the electrical installation connection increases above the permissible minimum insulation resistance value.EFFECT: increased reliability and accuracy of monitoring the insulation resistance of an electrical installation connection when the AC voltage source voltage changes and the ambient temperature changes.3 cl, 2 dwg

Description

[0001] The invention relates to electrical engineering, in particular to devices for preliminary control of insulation resistance of an electrical installation connection, and can be used at enterprises in the coal, oil, gas and other industries that have an explosive atmosphere.

[0002] Units and devices for monitoring insulation resistance are known.

[0003] The known device for preliminary control of network insulation [1] contains a measuring voltage source, a reference voltage source, a measuring and control circuit made of semiconductor elements and transistors, capacitors, resistors, an autonomous generator and an actuator that switches on and off a switching device with a connection connected to it, the insulation resistance of which is monitored by the device [1].

[0004] The well-known Insulation Monitoring Unit type BKI [2] and the Insulation Resistance Monitoring Blocking Device [3] comprise a measuring and control circuit, capacitors, resistors, and an actuator relay element. A transistor is used as a measuring element in the control circuits of the unit [2] and the device [3], and an actuator relay element is used at the output of the unit [2] and the device [3], which switches on and off the switching device with the connection connected to it, the insulation resistance of which is monitored by the unit [2] and the device [3].

[0005] The disadvantage of device [1], block [2], and device [3] is that the base-emitter voltage of the transistors of the measuring and control circuits changes with changes in the ambient temperature. This leads to a change in the resistance values ​​at which the control circuit is triggered to turn on and off the actuator of device [1], block [2], and device [3] when the ambient temperature changes.

[0006] In the known device [1], unit [2], and device [3], the voltage of the no-load source of the measuring current, to which the insulation resistance of the connection is connected, corresponds to the rectified voltage of one half-period of the AC voltage source. Detection of damage to the insulation of the connection by the low voltage of the no-load source of the measuring current from the rectified voltage of one half-period of the AC voltage source is not sufficiently reliable.

[0007] The objective of the claimed invention is to improve the reliability and accuracy of monitoring the insulation resistance of an electrical installation connection. The device's control circuit must switch to blocking the electrical installation's operation when the insulation resistance of the connection decreases below the device's response resistance value. The device must also release the blocking when the insulation resistance of the electrical installation connection increases above the permissible minimum insulation resistance value.

[0008] This problem is solved by connecting two resistive voltage dividers, one of which is connected to the electrical installation's terminal, to the same no-load source voltage of the measuring current from the doubled rectified AC voltage source. The signals from these two resistive voltage dividers are compared by a comparator.

[0009] The claimed device for preliminary monitoring of insulation resistance of an electrical installation connection comprises a first input and a second input of an alternating voltage source, a first input and a second input of an electrical installation connection, a first diode, the anode of which is connected to the first input of the alternating voltage source, a first capacitor, the first terminal of which is connected to the cathode of the first diode, and the second terminal to the second input of the alternating voltage source, a second diode, the cathode of which is connected to the first input of the alternating voltage source, a second capacitor, the first terminal of which is connected to the anode of the second diode, and the second terminal to the second input of the alternating voltage source, a first resistor, the first terminal of which is connected to the cathode circuit of the first diode, and the second terminal to the first input of the electrical installation connection, a second, third, fourth, fifth and sixth resistors connected in series, the second resistor is connected to the second input of the electrical installation connection,a third capacitor, the first terminal of which is connected to the first terminal of the first resistor, and the second terminal of the third capacitor is connected to the connection circuit of the second and third resistors, a comparator, the positive contact of which is connected to the circuit of the second input of the AC voltage source, and the negative contact of which is connected to the circuit of the anode of the second diode, a key element, an executive relay element with a normally closed contact, the first terminal of the key element is connected to the circuit of the anode of the second diode, the second terminal is connected to the first terminal of the executive relay element, and the third terminal is connected to the output of the comparator, the second terminal of the executive relay element is connected to the circuit of the second input of the AC voltage source, series-connected seventh and eighth resistors are INTRODUCED, the seventh resistor is connected to the circuit of the cathode of the first diode, the sixth and eighth resistors are connected to the circuit of the anode of the second diode, the non-inverting input of the comparator is connected to the circuit of the connection of the fourth and fifth resistors,the inverting input of the comparator is connected to the connection circuit of the seventh and eighth resistors, the ninth resistor and the third diode, the ninth resistor's first terminal is connected to the connection circuit of the fifth and sixth resistors, its second terminal is connected to the cathode of the third diode, the anode of the third diode is connected to the output of the comparator, and the fourth capacitor, the first terminal of which is connected to the connection circuit of the third and fourth resistors, and the second terminal is connected to the anode circuit of the second diode, and the resistance of the fifth, sixth and eighth resistors must be such a value that the voltage drops across the fifth, sixth and eighth resistors should not exceed the supply voltage of the comparator.,

[0010] A tenth resistor and a zener diode can be additionally introduced into the device, the first terminal of the tenth resistor is connected to the circuit of the second input of the AC voltage source, the second terminal of the tenth resistor is connected to the cathode of the zener diode, the anode of the zener diode is connected to the anode circuit of the second diode, and the positive contact of the comparator power supply is connected to the cathode of the zener diode.

[0011] The device may be additionally equipped with elements for checking the device's functionality, including a switch, an eleventh resistor, and an indicator; the common contact of the switch is connected to the second resistor, the normally closed contact of the switch is connected to the second input of the electrical installation connection, the normally open contact of the switch is connected to the first terminal of the eleventh resistor, the second terminal of the eleventh resistor is connected to the first input of the electrical installation connection, and the indicator is connected to the executive relay element, wherein the resistance of the eleventh resistor must be less than the permissible minimum value of the connection resistance.

[0012] The proposed features of the invention, different from the prototype, are necessary and sufficient in all cases to which the scope of legal protection of the invention extends.

[0013] The essence of the invention is explained by the diagrams shown in Fig. 1 and Fig. 2.

[0014] The diagram in Fig. 1 shows the basic diagram of the device that provides the function of monitoring the connection resistance of an electrical installation.

[0015] The device for preliminary control of insulation resistance of the connection of an electrical installation comprises a first input 1 and a second input 2 of an alternating voltage source ~Uc, a first input 3 and a second input 4 of the connection of the electrical installation, a first diode 5, the anode of which is connected to input 1, a first capacitor 6, the first terminal of which is connected to the cathode of the diode 5, and the second terminal to input 2, a second diode 7, the cathode of which is connected to input 1, a second capacitor 8, the first terminal connected to the anode of the diode 7, and the second terminal to input 2, a first resistor 9, the first terminal connected to the cathode circuit of the diode 5, and the second terminal to input 3, series-connected second 10, third 11, fourth 12, fifth 13 and sixth 14 resistors, resistor 10 is connected to input 4, a third capacitor 15, the first terminal of which is connected to the first terminal resistor 9, and the second terminal of capacitor 15 is connected to the circuit connecting resistors 10 and 11, comparator 16, the positive power contact of which is connected to the circuit of input 2,and the minus power supply contact is connected to the anode circuit of diode 7, the key element 17, the executive relay element 18 with a normally closed contact 19, the key element 17 is connected with its first output to the anode circuit of diode 7, with its second output to the first output of the executive relay element 18, and with its third output to the output 20 of the comparator 16, the second output of the executive relay element 18 is connected to the input circuit 2, the seventh 21 and eighth 22 resistors are connected in series, the resistor 21 is connected to the cathode circuit of diode 5, resistors 14 and 22 are connected to the anode circuit of diode 7, the non-inverting input 23 of comparator 16 is connected to the connection circuit of resistors 12 and 13, the inverting input 24 of comparator 16 is connected to the connection circuit of resistors 21 and 22, the ninth resistor 25 and the third diode 26, the resistor 25 is connected with the first output to the connection circuit of resistors 13 and 14, the second output is connected to the cathode of diode 26, the anode of diode 26 is connected to output 20, and the fourth capacitor 27,the first terminal of which is connected to the connection circuit of resistors 11 and 12, and the second terminal is connected to the anode circuit of diode 7.

[0016] The diagram in Fig. 2 shows an additionally introduced tenth resistor 28 and a zener diode 29, to the cathode of which the positive power supply contact of the comparator 16 is connected, and additionally introduced elements for checking the serviceability of the device, including a switch 30, an eleventh resistor 31 and an indicator 32.

[0017] The resistances of resistors 13, 14, 22 must be of such a value that the voltage drops across resistors 13, 14, 22 must not exceed the voltage across the second capacitor 8 according to the circuit in Fig. 1 and the stabilization voltage of the zener diode 29 according to the circuit in Fig. 2.

[0018] The resistances of resistors 9-14, 22 are selected taking into account the permissible voltage at inputs 23, 24 of comparator 16. The resistance of resistor 21 is selected to be much greater than the resistance of resistor 22, while the voltage drop across resistor 22 is much less than the voltage drop across resistor 21.

[0019] The resistance of resistor 22 is selected to be such a value that comparator 16 must switch from the mode of turning on key element 17 and executive relay element 18 to the mode of turning off and maintaining the off state of key element 17 and executive relay element 18 when the insulation resistance of the connection increases more than the value set for turning off key element 17 and executive relay element 18.

[0020] The resistance of resistors 13-14 is selected in such a way that in the connection insulation resistance monitoring mode, the voltage drop across resistors 13-14 is equal to the voltage drop across resistor 22 when comparator 16 is switched from the mode of turning off key element 17 and executive relay element 18 to the mode of turning on and maintaining the on state of key element 17 and executive relay element 18.

[0021] In the idle mode of the measuring current source, there is no current through resistors 9-14; voltage between the cathode of diode 5 and the anode of diode 7 is supplied to inputs 3 and 4 of the connection, corresponding to the doubled rectified voltage of the AC voltage source ~Uc.

[0022] Connection 33 of the electrical installation is connected to inputs 3 and 4.

[0023] The electrical installation that is connected to connection 33 is not shown in the diagrams of Fig. 1 and Fig. 2.

[0024] The insulation resistance test of connection 33 is carried out in the absence of voltage from the electrical installation power supply network at connection 33.

[0025] The electrical installation may be switched on if the insulation resistance of the connection 33 is greater than the response resistance value of the unit.

[0026] The circuit in Fig. 1 works as follows.

[0027] With a constant input voltage of the AC voltage source ~Uc, the voltage drop across resistor 22 and the voltage at input 24 relative to the anode circuit of diode 7 do not change when the insulation resistance of connection 33 changes.

[0028] When the insulation resistance of connection 33 changes, the current through resistor 9, connection 33, resistors 10-14 changes, the voltage drop across resistors 13-14 and at input 23 changes relative to the anode circuit of diode 7.

[0029] When the insulation resistance of connection 33 decreases, the current through resistor 9, connection 33, resistors 10-14 increases, the voltage drop across resistors 13-14 increases, and the voltage at input 23 increases relative to the anode circuit of diode 7.

[0030] When the insulation resistance of connection 33 increases, the current through resistor 9, connection 33, resistors 10-14 decreases, the voltage drop across resistors 13-14 decreases, and the voltage at input 23 decreases relative to the anode circuit of diode 7.

[0031] The voltage at input 23 is compared with the voltage at input 24.

[0032] When the insulation resistance of connection 33 is greater than the response resistance value of the device, the current through resistor 9, connection 33, resistors 10-14 is small, the voltage drop across resistors 13-14 is small, the voltage at input 23 is less than the voltage at input 24, a low-level voltage is set at output 20, the key element 17 and the actuator relay element 18 are turned off.

[0033] When the insulation resistance of connection 33 is less than the response resistance value of the device, the current through resistor 9, connection 33, resistors 10-14 increases, the voltage drop across resistors 13-14 increases, and the voltage at input 23 increases. The voltage at input 23 exceeds the voltage at input 24, a high-level voltage is established at output 20, key element 17 and actuator relay element 18 are turned on, contact 19 is turned off, the control circuit of the electrical installation is broken, and switching on of the electrical installation connected to connection 33 is blocked.

[0034] When output 20 is at a high level, additional current is supplied to resistor 14 through diode 26 and resistor 25, further increasing the total voltage drop across resistors 13-14. This results in a stable high voltage at output 20 and a stable on-state for switch element 17 and actuator relay element 18.

[0035] The device returns to the insulation resistance control mode of connection 33 when the voltage drop across resistors 13-14 and at input 23 decreases to a value less than the voltage drop across resistor 22 and the voltage at input 24. A decrease in the voltage drop across resistors 13-14 and input 24 less than the voltage at input 23 occurs when the insulation resistance of connection 33 increases above the set value, at which a low-level voltage is established at output 20, key element 17 and actuator relay element 18 are turned off, contact 19 is closed, and the blocking of turning on the electrical installation is removed. When a low voltage is established at output 20, the current through diode 26 and resistor 25 stops, the voltage drop across resistor 14 decreases, the voltage across resistors 13-14 and input 23 decreases further, comparator 16 goes into the mode of stable holding of the switch-off of key element 17 and actuator relay element 18.The resistance of resistor 25 must correspond to the value at which the return of comparator 16 to the insulation resistance control mode of connection 33 is ensured.

[0036] The addition of resistor 25 and diode 26 enables comparator 16 to operate in hysteresis mode. This hysteresis mode enables rapid switching of comparator 16 from the insulation resistance monitoring mode of connection 33 to the mode of turning on and maintaining the on state of key element 17 and actuator relay element 18, and back. The forced switching of comparator 16 from turning on and maintaining the on state of key element 17 and actuator relay element 18, and back, increases the operational reliability of the proposed device.

[0037] To ensure that comparator 16 operates in hysteresis mode and supplies additional current to resistor 14 through resistor 25 and diode 26, the high-level voltage at output 20 must be greater than the voltage drop across resistor 14.

[0038] By connecting resistors 9 and 21 to the cathode circuit of diode 5 and connecting resistors 14 and 22 to the anode of diode 7, the synchronous change in voltage drops across resistors 13-14 and 22 and voltages at inputs 23 and 24 is ensured.

[0039] When the voltage of the AC voltage source ~Uc changes, the voltage drops across resistors 13-14 and 22 always change synchronously and in the same direction, the voltage at input 23 changes synchronously with the voltage at input 24.

[0040] The ratio of the voltage drop across resistor 21 to the voltage drop across resistor 22 and the ratio of the voltage drop across resistor 9, connection 33, resistors 10-12 to the voltage drop across resistors 13-14 are maintained when the AC voltage source ~Uc changes. When the said voltage ratios are maintained, the insulation resistance value of connection 33 is maintained, at which comparator 16 switches from the insulation resistance monitoring mode of connection 33 to the mode of turning on and stably maintaining the on state of key element 17 and actuator relay element 18, and the reverse switching of comparator 16 from the mode of turning on and maintaining the on state of key element 17 and actuator relay element 18 to the insulation resistance monitoring mode of connection 33.This achieves the stability of the response thresholds of the comparator 16 for switching on and off the key element 17 and the executive relay element 18 when monitoring the insulation resistance of the connection 33.

[0041] If the permissible supply voltage of comparator 16 is less than the voltage on capacitor 8 according to the circuit in Fig. 1, resistor 28 and zener diode 29 are introduced into the device according to the circuit in Fig. 2, the positive supply contact of comparator 16 is connected to the cathode of zener diode 29.

[0042] The operation of the device circuit with the connection of the power supply of the comparator 16 to the cathode of the zener diode 29 according to the circuit in Fig. 2 corresponds to the operation of the device according to the circuit in Fig. 1.

[0043] The device’s serviceability is checked using the switch 30, resistor 31 and indicator 32 shown in the diagram in Fig. 2.

[0044] To check the serviceability of the device, resistor 10 is connected to resistor 31 using switch 30 "CHECK", the resistance of resistor 31 is less than the response resistance of the device, a high-level voltage is set at output 20 of comparator 16, key element 17, executive relay element 18 and indicator 32 are turned on. When resistor 10 is disconnected from resistor 31 using switch 30 "CHECK", and resistor 10 is connected to input 4 through the normally closed contact of switch 30 with a serviceable insulation resistance of connection 33, a low-level voltage is set at output 20, key element 17, executive relay element 18 and indicator 32 are turned off, the device goes into the insulation resistance monitoring mode of connection 33.

[0045] The switching on of indicator 32 when resistor 10 is connected to resistor 31 by switch 30, and the switching off of indicator 32 when resistor 10 is disconnected from resistor 31 by switch 30, resistor 10 is connected to input 4 by switch 30, and the insulation resistance of connection 33 is in good condition confirms the serviceability of the device.

[0046] When the contactor that powers the electrical installation is switched off and the contactor contacts open, a small capacitive charge may briefly remain on terminal 33, which is disconnected from the power grid. The capacitive charge of terminal 33 is discharged through a special device installed in the electrical installation to compensate for the capacitive component of the leakage current and / or through phase short-circuiters, through the insulation resistance of terminal 33, and through resistors 9 and 10 to capacitor 15.

[0047] An electric motor can be used as an electrical installation.

[0048] After the contactor is turned off, an alternating current (AC) EMF may be present on the motor's connection wires (33) when the motor is switched off but still rotating. Capacitors 15 and 27 are included to smooth out the pulsations coming from connection wires (33) to the device.

[0049] Capacitors 15 and 27 provide a delay in the response of comparator 16 until the capacitive charge of connection 33 is discharged and the short-term action of the EMF voltage of the disconnected electric motor ceases.

[0050] In device [1], block [2] and device [3], the base-emitter voltage of the transistor, which is the measuring element of the control circuit, changes when the ambient temperature changes, and the control circuit is triggered to turn on and off the actuator relay element of the device at different insulation resistances of the connection when the ambient temperature changes.

[0051] In the proposed device, the control circuit is implemented on the comparator 16. The difference in voltage at the input 23 and 24 of the comparator 16 relative to the anode circuit of the diode 7, at which the output 20 of the comparator 16 switches from a low-level voltage to a high-level voltage and back, practically does not change when the voltage of the AC voltage source ~Uc changes and when the ambient temperature changes.

[0052] The use of comparator 16 in the control circuit ensures better stability of the device response thresholds, at which comparator 16 switches from the mode of monitoring the insulation resistance of connection 33 to the mode of turning on and stably maintaining the on state of the key element 17 and the executive relay element 18, and back.

[0053] In device [1], block [2] and device [3], control signals to the transistors of the control circuits are supplied from two resistive voltage dividers, one of which is connected to the rectified voltage of the positive half-period of the AC voltage source ~Uc, and the other to the rectified voltage of the negative half-period of the AC voltage source ~Uc. In this case, the voltage of the no-load source of the measuring current, which is supplied to the connection for monitoring the insulation resistance of the connection of the electrical installation, practically corresponds to the rectified voltage of one positive half-period of the voltage of the AC voltage source ~Uc.

[0054] In the proposed device, signals are fed to inputs 23 and 24 of comparator 16 from two parallel-connected voltage dividers connected to the same voltage between the cathode circuit of diode 5 and the anode circuit of diode 7. The voltage between the cathode circuit of diode 5 and the anode circuit of diode 7 practically corresponds to twice the rectified voltage of the AC voltage source ~Uc. Accordingly, the voltage of the no-load source of the measuring current, supplied to connection 33, practically corresponds to twice the rectified voltage of the AC voltage source ~Uc.

[0055] By doubling the voltage of the no-load source of the measuring current supplied to connection 33 in the proposed device, the reliability of detecting damage to the insulation of the connection and blocking the switching on of the electrical installation increases when the insulation resistance of the connection is less than the permissible value.

[0056] Sources of information

[0057] 1. USSR Author's Certificate No. 1666987 class G01R 31 / 02, 1991.

[0058] 2. Catalog of electrical equipment of the Russian Federation. Insulation monitoring unit type BKI.

[0059] 3. Author's certificate No. 918897 class G01R 31 / 02, 1982 (prototype).

Claims

1. A device for preliminary monitoring of the insulation resistance of a connection of an electrical installation, comprising a first input and a second input of an alternating voltage source, a first input and a second input of a connection of an electrical installation, a first diode, the anode of which is connected to the first input of the alternating voltage source, a first capacitor, the first terminal of which is connected to the cathode of the first diode, and the second terminal to the second input of the alternating voltage source, a second diode, the cathode of which is connected to the first input of the alternating voltage source, a second capacitor, the first terminal of which is connected to the anode of the second diode, and the second terminal to the second input of the alternating voltage source, a first resistor, the first terminal of which is connected to the cathode circuit of the first diode, and the second terminal to the first input of the connection of the electrical installation, a second, third, fourth, fifth and sixth resistors connected in series, the second resistor is connected to the second input of the connection of the electrical installation, a third capacitor,the first terminal of which is connected to the first terminal of the first resistor, and the second terminal of the third capacitor is connected to the connection circuit of the second and third resistors, a comparator, the positive supply contact of which is connected to the circuit of the second input of the alternating voltage source, and the negative supply contact is connected to the anode circuit of the second diode, a key element, an executive relay element with a normally closed contact, the key element is connected with its first terminal to the anode circuit of the second diode, with its second terminal to the first terminal of the executive relay element, and with its third terminal to the output of the comparator, the second terminal of the executive relay element is connected to the circuit of the second input of the alternating voltage source, characterized in that seventh and eighth resistors are introduced and connected in series, the seventh resistor is connected to the cathode circuit of the first diode, the sixth and eighth resistors are connected to the anode circuit of the second diode, the non-inverting input of the comparator is connected to the connection circuit of the fourth and fifth resistors,the inverting input of the comparator is connected to the connection circuit of the seventh and eighth resistors, the ninth resistor and the third diode, the first terminal of the ninth resistor is connected to the connection circuit of the fifth and sixth resistors, the second terminal is connected to the cathode of the third diode, the anode of the third diode is connected to the output of the comparator, and the fourth capacitor, the first terminal of which is connected to the connection circuit of the third and fourth resistors, and the second terminal is connected to the anode circuit of the second diode, and the resistances of the fifth, sixth and eighth resistors have values ​​at which the voltage drops on the fifth, sixth and eighth resistors do not exceed the supply voltage of the comparator., 2. A device for preliminary monitoring of the insulation resistance of a connection of an electrical installation according to paragraph 1, characterized in that a tenth resistor and a zener diode are additionally introduced into the device, the first terminal of the tenth resistor is connected to the circuit of the second input of the alternating voltage source, the second terminal of the tenth resistor is connected to the cathode of the zener diode, the anode of the zener diode is connected to the circuit of the anode of the second diode, and the positive contact of the comparator power supply is connected to the cathode of the zener diode.

3. A device for preliminary monitoring of the insulation resistance of a connection of an electrical installation according to paragraphs 1 and 2, characterized in that the device additionally includes elements for checking the serviceability of the device, including a switch, an eleventh resistor, and an indicator, the common contact of the switch is connected to the second resistor, the normally closed contact of the switch is connected to the second input of the connection of the electrical installation, the normally open contact of the switch is connected to the first terminal of the eleventh resistor, the second terminal of the eleventh resistor is connected to the first input of the connection of the electrical installation, and the indicator is connected to the actuator relay element, wherein the resistance of the eleventh resistor is less than the permissible minimum value of the connection resistance.

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