RU2541418C2 - Device for measurement and control of live resistance insulation in alternating-current mains with resistive neutral line - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electrical engineering. The device comprises a resistor connected to the neutral line by its one end, a resistive current sensor, a source of direct-current stabilized voltage, a shunt capacitor C1, RC-filter per 50 Hz, a galvanic decoupler unit, an electronic voltage divider, a differential amplifier, a power supply unit, display and signalling units. At that the second output of the resistor in the neutral line is coupled to the resistive current sensor and the source of direct-current stabilized voltage connected in series. The second output of the resistor in the neutral line is coupled to frame through the shunt capacitor C1, while positive output of the source of direct-current stabilized voltage is connected to the frame through the added resistive current sensor. In parallel to the resistive current sensor there is the RC-filter, which midpoint is coupled to input of the galvanic decoupler unit while output of the latter is coupled to input of the electronic voltage divider; to the divider output the differential amplifier is coupled by its input and to the divider output the display and signalling units are coupled. All units of the device are supplied from the power supply unit.

EFFECT: continuous control of insulation resistance in alternating-current mains with resistive neutral line.

1 dwg

Description

The proposal relates to instruments for measuring, monitoring and signaling about a decrease in insulation resistance in AC power networks with a resistive neutral, that is, when the neutral of the power network is grounded through a resistor and is used for continuous monitoring of insulation resistance on ships, ships, mines, metro, etc. etc., that is, where there is an alternating current network with a resistive neutral.

There is a method of increasing fire safety of power generation and conversion systems by evaluating leakage currents in AC or DC power circuits with a grounded neutral or a grounded pole. The method is based on highlighting the difference between the input and output currents of the load at the power board. The difference in these currents is used to judge the level of fire safety, evaluating the possibility of an electric arc between the current-carrying conductors of the cable and the ground (housing). The leakage currents also judge the electrical safety of the operating personnel and provide protection at low leakage currents. An example is a residual current device of the UZO20 type according to TU 16-92 IZHTPI.656111.085 TU, Stavropol, the Signal plant. The disadvantage of this method is the relatively low reliability of fire safety and a limited scope.

A known method and device for measuring the insulation resistance in DC networks according to the USSR author's certificate No. 370551, IPC G01R 27/18 characterized in that in order to measure the insulation resistance under operating voltage an additional circuit is introduced from a DC power source and a diode connected in parallel with wires network, and their common point is connected to another terminal of the current device. The disadvantage of this method and device is the large measurement error, since the insulation resistance of the network pole is a function of the magnitude of the supply voltage. With large voltage fluctuations of the controlled network, the error in measuring the insulation resistance accordingly changes (increases).

The prototype is a relatively new device for measuring the insulation resistance of the power network of electrical installations of vehicles under operating voltage (RF patent 2175138 G01 27/18, publ. 01/20/2001, bull. 29) in which for measuring the insulation resistance of the power network of electrical installations of vehicles under operating voltage impose a measuring DC voltage on the power network.

The disadvantage of this method and device is that in the process of measuring the insulation resistance there is a recharge of the capacities of the electric network from zero to the full voltage of the network. In such a network, without applying the method and device for controlling the insulation resistance, a person touching one pole of the network falls under a voltage that is significantly lower than the voltage of the network, and when applying this method and device in a similar situation, a person falls under zero voltage relative to the ground or under the full network voltage , where electrical safety conditions worsen significantly when monitoring the power network.

The proposed device in comparison with the prototype provides increased reliability and allows you to measure and control the insulation resistance in a wide range of values of insulation resistance.

A device is proposed for measuring and monitoring the insulation resistance under operating voltage in AC power networks with a resistive neutral, a block diagram of the device is shown in Fig. 1, containing a resistor connected to the neutral by one terminal, and the second terminal connected to the housing (ground), characterized the fact that a resistive current sensor, a stabilized DC voltage source, a shunt capacitor CI, an RC filter, a galvanic isolation unit, an electronic voltage divider, and a differential voltage divider are introduced into the device a power amplifier, a power supply unit and indication and signaling units, moreover, one terminal of the neutral resistor is disconnected from the case (ground), and a resistive current sensor and a stabilized DC voltage source connected in series are connected to the gap, and the positive output of the source is connected to the case (ground) ) through the introduced resistive current sensor, and the shunt capacitor C1 is connected in parallel with the resistive current sensor and the stabilized DC voltage source, and the RC filter is connected by a resistor to plus the source of the measured stabilized DC voltage, and the bottom output of the RC filter is connected to the housing (ground), and the midpoint of the RC filter is connected to the input of the galvanic isolation unit, and the output of the galvanic isolation unit is connected to the input of the electronic voltage divider, to the output of which the input is on differential amplifier, the output of which includes indication and alarm units, and all units of the device are powered by a power supply.

A device for measuring and monitoring the insulation resistance under operating voltage in AC power networks with resistive neutral, containing a resistor 1, as well as a resistive current sensor 2, a stabilized DC voltage source 3, a shunt capacitor C1 - 4, an RC filter 5, a galvanic unit decoupling 6, electronic voltage divider 7, differential amplifier 8, power supply 9, display units 10 and alarm 11, the device with the top output of the neutral resistor 1 is connected to the neutral of the controlled network 12, and the source of the stabilized DC voltage 3 by the lower terminal is connected to the ground (housing) 13 through a resistive current sensor 2.

The proposed device for measuring and monitoring under operating voltage insulation resistance in AC power networks with resistive neutral operates as follows.

The device with one top terminal of the neutral resistor is connected to the neutral of the controlled network 12, and the other terminal is connected to the ground (case) 13

The measuring circuit includes a resistive current sensor 2, a stabilized DC voltage source 3, a neutral resistor 1, and phase insulation resistance R from the monitored network 12.

The signal voltage is allocated on the resistor of the current sensor Rdt 2 using the RC 5 filter, we are freed from interference of a voltage of 50 Hz, this is facilitated by the presence of a shunt capacitor of 50 Hz C1 (4). The inclusion of a large-capacity capacitor C1 contributes to the preservation of the parameters of an alternating current network with a resistive neutral, in order for these conditions to be fulfilled, it is necessary that the capacitance of the capacitor C1 be much smaller than the value of the neutral resistor 1, therefore, after cleaning the signal voltage from 50 Hz interference, the purified voltage the signal is allocated to the capacitor C of the RC 5 filter and fed to the input of the galvanic isolation unit 6, after which the signal voltage is fed to the input of an electronic voltage divider (EDN), the output of which we obtain a signal voltage proportional to the insulation resistance, and using the differential amplifier DU (8), you can correct and clarify the linear dependence of the signal voltage on the insulation resistance, and using the display units 10 and alarm 11, the display will show the exact value of the insulation resistance in AC networks with resistive neutral, which makes it possible to increase the reliability of AC networks with resistive neutral, and all blocks of the proposed device are powered us from the power supply.

Claims (1)

A device for measuring and monitoring the insulation resistance under operating voltage in AC power networks with a resistive neutral, containing a resistor connected to the neutral by one output, characterized in that a resistive current sensor, a stabilized DC voltage source, a shunt capacitor C1, RC are introduced into the device 50 Hz filter, galvanic isolation unit, electronic voltage divider, differential amplifier, power supply and indication and signaling units, and the second terminal of the resistor Ali is connected to the inputted resistive current sensor and a stabilized DC voltage source connected in series, in addition, the second output of the neutral resistor is connected to the housing through a shunt capacitor C1, and the positive output of the stabilized voltage source is connected to the housing through the inserted resistive current sensor, and parallel to the resistive an RC filter is included in the current sensor, the midpoint of which is connected to the input of the galvanic isolation unit, and the output of the galvanic isolation unit is connected electronic input voltage divider, whose output is enabled input differential amplifier, whose output is input includes indicating and signaling blocks, and blocks all devices are powered from the power supply.