RU127538U1 - DEVICE FOR PEN CONDUCTOR INTEGRITY CONTROL IN THREE PHASE ELECTRIC NETWORKS WITH DIP EARTHED NEUTRAL - Google Patents

Abstract

The device for monitoring the integrity of the PEN conductor in three-phase electrical networks with a grounded neutral containing a transformer substation, a supply line, an input distribution device (ASU), a circuit breaker, a re-earthing switch, characterized in that it is equipped with a current transformer connected to the earthing conductor of the re-earthing switch ASU, to the secondary winding of which a unit for comparing the current value with a threshold value is connected, the signal from which is fed to the main mechanism of the circuit breaker ASU.

Description

The utility model relates to electrical engineering, namely to electrical safety and can be used to protect consumers of electrical energy from overvoltages caused by the deterioration of the PEN conductor or its breakage, and to ensure electrical, fire and explosion safety.

The utility model is intended for the organization of monitoring the continuity of a PEN conductor and its parameters relative to the earth of cable lines with a voltage of 0.38 kV of electric networks with a grounded neutral.

The supply lines of three-phase electric networks with voltage up to 1000 V AC, having a TN-C grounding system, are made of four-wire with a combined zero PEN conductor. It is entrusted with the functions of ensuring the normal operation of power consumers on the one hand, and the implementation of protective electrical safety measures on the other.

A very important role is played by the issue of the integrity of the circuit of zero connections from the neutral of the power source (power transformer) to the input-distribution device (ASU) of the facility.

Both three-phase and single- and two-phase power receivers can be powered from the distribution network of the facility, therefore, the symmetry of the total and average load can almost never be achieved and the PEN conductor is constantly under load. Given the fact that according to clause 7.1.45 [Rules for the installation of electrical installations. 7th ed. - M .: Publishing House NTs ENAS, 2003] the cross-section of the neutral conductor is allowed to be less than the phase cross-section (up to 50% for values from 35 mm ² and more), in the mode of significant asymmetry of loads, the PEN conductor may be exposed to a current exceeding its maximum allowable value for the corresponding section. The effects of thermal effects on the contact connections of the zero circuit are exacerbated by the practice of connecting copper and aluminum cores of power cables to the steel busbars and cases of the ASU cabinets.

A device is known (see RF patent No. 2348094, Н02Н 5/10, G01R 31/08, publ. February 27, 2009, bull. No. 6) for monitoring the continuity of zero conductors in 0.38 kV lines, containing a three-phase power transformer, a single-phase two-winding transformer , resistor and button.

The disadvantage of this device is the scope only for five-wire lines (TN-S grounding system), while most low-voltage power cables are four-wire (TN-C grounding systems).

A device is known (see certificate for utility model No. 26693, Н02Н 5/10, publ. 10.12.2002) for protecting a multiphase overhead power line from the effects of a zero wire break, containing a zero wire break detector, a short circuit with power contacts, a latch mechanism and a coil, connected to the output of the voltage monitoring relay block.

The disadvantages of this device are: lack of selectivity of the signal of the monitoring relay during voltage fluctuations in the network and an increased risk of electric shock to personnel while breaking the neutral wire and shorting to the electrical installation case.

The closest in technical essence to the claimed is a device for automatic monitoring of the parameters of the neutral wire (see RF patent No. 2295186, IPC Н02Н 5/00, publ. 10.03.2007, bull. No. 7), containing high-frequency pulse transmission units installed at the end of the protected lines and a receiving unit with decoders installed on the supply transformer substation.

The disadvantage of this device is the significant complication of the control circuit in radial networks with a large number of power consumers.

The technical result of the utility model is to improve the quality of monitoring the continuity of the PEN conductor and its parameters relative to the earth of cable lines with a voltage of 0.38 kV of electrical networks with a grounded neutral.

The essence of the utility model is that the integrity control device of the PEN conductor in three-phase electrical networks with a grounded neutral containing a transformer substation, a supply line, an input-distribution device (ASU), a circuit breaker, a re-earthing switch, is characterized in that it is equipped with a current transformer connected to the grounding conductor of the secondary ground switch of the switchgear, to the secondary winding of which is connected a unit for comparing the current value with a threshold value, the signal from which comes and the actuator main circuit breaker ASU.

The device is characterized in that for monitoring the continuity of the PEN conductor and its parameters relative to the ground, a current transformer is used in the grounding conductor of the electrical installation re-grounding device.

A distinctive feature of the utility model is the direct measurement of the current through the grounding conductor of the secondary switchgear ground electrode for subsequent adjustment of the threshold value from the maximum value of the asymmetry of the phase currents of the loads to the minimum value of the current of a single-phase circuit to the grounded electrical equipment case.

The essence of the proposed device is illustrated in the drawing.

In FIG. a generalized radial diagram of the power supply of an industrial facility from a step-down transformer substation is presented. As the power source of the facility, an ASU of 0.38 kV is adopted.

The device contains: 1 - transformer substation; 2 - repeated grounding; 3 - loads of consumers; 4 - power cable line; 5 - input-distribution device of the object; 6 - current transformer; 7 - block comparison; 8 - circuit breaker.

The device operates as follows. In the normal mode of operation of the distribution network, powered by transformer substation 1, and with continuity of the PEN conductor, the current in the ground conductor of the re-ground electrode 2 is practically absent for two reasons: 1) most power receivers 3 are symmetrical loads for a three-phase AC system; 2) the existing single and two-phase consumers cause the appearance of zero sequence currents in the circuit with the lowest resistance of the PEN conductor. A similar situation is observed in the emergency mode of phase closure on the electrical installation case 3, causing reliable operation of the corresponding protective device in the damaged line.

With a significant increase in the transition resistance of the contact connection (or break) of the PEN conductor of the supply cable 4 with the ASU 5 case at point A, the power of the three-phase symmetrical consumers will not be disturbed. However, in case of insulation damage of any phase relative to the electrical installation enclosure at any point of the distribution network, the single-phase fault current will pass through the circuit: transformer secondary 1 - supply cable 4 - damaged phase conductor - fault location - PEN conductor to the ASU 5 enclosure - ground conductor 2 repeated grounding switchgear - ground between the object and the grounding circuit of the transformer substation 1 - dead-grounded neutral of the secondary winding of the transformer. The magnitude of this current, which mainly depends on the resistance of the soil in section 1-2, may turn out to be less than the setpoint for the operation of protective devices both on the switchgear and in the power cabinets of the distribution network of the facility.

By means of a measuring current transformer 6 included in the cut of the grounding conductor of the re-ground electrode 2, a signal is received at the input of unit 7, the value of which, when a predetermined threshold value is exceeded, will cause the switching device 8 to trip on the switchgear.

Claims (1)

The device for monitoring the integrity of the PEN conductor in three-phase electrical networks with a grounded neutral containing a transformer substation, a supply line, an input distribution device (ASU), a circuit breaker, a re-earthing switch, characterized in that it is equipped with a current transformer connected to the earthing conductor of the re-earthing switch ASU, to the secondary winding of which is connected a unit for comparing the current value with a threshold value, the signal from which is fed to the main mechanism of the circuit breaker ASU.

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