RU214913U1 - SAFETY DEVICE FOR SHIP ELECTRIC NETWORK - Google Patents

Abstract

This utility model relates to the field of electrical engineering, namely to electrical safety engineering, and can be used on ships, ships and other moving objects.

The technical result is to ensure electrical safety in electrical networks with isolated neutral through the use of additional capacitors, the capacity of which is determined by the operation setting, voltage, frequency and number of phases of the supply network, taking into account capacitance on the load side. What is a feature of the use of RCDs in conjunction with an isolating transformer in networks with an isolated neutral. 1 ill.

Description

This utility model relates to the field of electrical engineering, namely to electrical safety engineering, and can be used on ships, ships and other moving objects.

It is known that short circuits in electrical networks with an isolated neutral of one of the phases on the case can lead not only to the occurrence of overvoltages and impulse noise, but also to a deterioration in the state of electrical safety.

Ensuring electrical safety on ships is a problem, as special electrical equipment is widely used on ships. The use of electrified mobile mechanization equipment and electric portable equipment and power tools for various purposes is also typical, which requires special attention when solving the problem of electrical safety on ships and vessels. Shipboard electrical AC networks, as a rule, are made with a neutral isolated from the ship's hull. In the normal state of the insulation between the phases and the absence of capacitive leakage currents on the case, damage to the insulation of one phase does not cause an emergency operation of the protection against inadmissible currents, ensuring the continuity of the power supply, which is an advantage of such networks. At the same time, in the presence of a single-phase short circuit to the hull, there is a danger of electric shock to a person while simultaneously touching the ship's hull and any other undamaged phase.

In real ship networks, in addition to insulation resistance, it is necessary to take into account the presence of network phase capacitances relative to the ship's hull. It is formed both by its own distributed capacitance of the electrical equipment used, including electrical cables, and by the capacitance of filters to protect electronic equipment from interference.

On ships and vessels, the level of phase capacitances significantly exceeds the level of electrical safety, and in some cases, the level of fire safety.

The use of portable and mobile electrical equipment with a voltage of 220 V and 380 V, a frequency of 50 Hz leads to the need to use additional means of protection, namely, the use of trip protection devices.

Such a device must turn off the power if the leakage current to the case exceeds 30 mA (breaking current).

Sufficient experience has been accumulated in coastal power networks in the use of trip protection devices (RCDs), primarily in networks with a grounded neutral in electrical installations of residential and public buildings. Analogues: 1. odinelectric.ru>equipment/circuit-breaker…uzo…vidy. 2. GOST 12.1.038-82 “SSBT. Electrical safety. Maximum allowable values of contact voltages and currents”, M., Izd. Standards, 1984. A trip protection device is known. Prototype. Source: https://odinelectric.ru/equipment/circuit-breaker/chto-takoe-uzo-naznachenie-m. It consists of: differential current transformer, threshold element, actuator and test circuit.

The principle of operation of the RCD.

The operation of the device is based on fixing the leakage current to the "ground" and turning off the power grid in the event of such an emergency. The device detects the presence of leakage only by the difference between the currents: those that left the device and those that returned back. If everything is in order with the power grid, then the currents are identical in magnitude, but differ in direction. As soon as a leak appears - for example, you touched a 100% uninsulated wire - part of the current goes "to the ground" along another circuit (in this case, through the human body). As a result, the current returned to the RCD through the neutral will be less than the current that came out. The same thing happens if the insulation is damaged in one of the electrical appliances. Then the housing or other part is under tension. Touching them, a person creates another contour "to the ground". In this case, part of the current will move along it, that is, the balance will collapse.

The disadvantage of both analog and prototype is that the RCD requires a separate protective earth wire along with a working ground wire. In this case, the protective earth wire is connected to the power receiver in such a way that it allows creating a bypass circuit and ensures the presence of a differential current that generates a signal to turn off the power when the leakage current exceeds a predetermined value.

In ship AC networks, made according to the isolated neutral circuit, the creation of a leakage current bypass circuit causes certain difficulties.

The purpose of the utility model is to ensure electrical safety in electrical networks with an isolated neutral.

This goal is achieved by the fact that a residual current device is introduced into the body of the safety device of the ship's electrical network, while the protective device is connected to the input and output of an isolation transformer, which changes the condition for the flow of various leakage currents through the resistance R _from or the human resistance R _h from the load side in power supply network, while only part of the leakage current, namely through the capacitance C _o , generates a trip signal, and the other part returns to the power source through the load capacitance C _n without affecting the operation of the residual current device, and the leakage current through the capacitance C _o is higher operation settings, as soon as the resistance falls below the permissible level, while the appliance is connected to the output of the transformer.

The proposed device consists of

1 - housing;

2 - trip protection device (RCD);

3 - electrical appliances;

4 - supply voltage (U _c );

5 - phase capacities relative to the housing on the side of the supply network (U _about );

6 - phase capacities relative to the housing on the side of the connecting load (U _n );

7 - resistance of the human body (R _h );

8 - insulation resistance in the power circuit (R _{out of 1;} R _{out of} 2);

9 - protective earth.

The resistance R _of is the insulation resistance in the RCD supply circuit. When the RCD is in a humid chamber with a relative humidity of 91-95% for 48 hours, the insulation resistance of its main circuit must be at least 2 MΩ, the insulation resistance between the metal parts of the mechanism and the case must be at least 5 MΩ. The measurement of insulation resistance is carried out at a voltage of 500 V DC. The RCD insulation must also withstand surge tests. The test involves the application of ten current pulses (1.2/50 µs) with a peak voltage of 6 kV between the phase poles connected together and the neutral pole. The second series of tests is carried out at a peak pulse voltage of 8 kV.

Capacitance C _o - the total capacitance of the phases relative to the ship's hull. On the side of the supply network, the capacitance can reach up to 20 μF per phase with asymmetry of not more than: 30% for a 380 V network; 40% for a 220 V network.

The current flowing in the neutral wire is equal to the sum of the currents that flow in the phases for a three-phase four-wire circuit. When in such a circuit, due to a person accidentally touching the non-insulated parts of the conductive elements of the circuit or upon contact of the bare part of the wiring (due to damage) with other conductive objects forming a new electrical circuit, the so-called current leakage occurs - the equality of the incoming and outgoing currents is violated . This violation is registered and used as a command to turn off the entire electrical circuit. In this process, an RCD is constructed. The "leakage" current is called differential current. When the RCD is turned on, the solenoid turns on and holds the rod of the contact group in the same way as an electromagnet. Since at the same moment the terminals of the winding of the solenoid itself and the terminals of the supply wires come into contact. But in the power circuit of the solenoid, transit opening contacts are installed, which are controlled by a magnetoelectric relay and the relay is given the function of self-shutdown of the RCD.

The outgoing and incoming current of the network, flowing in the corresponding windings of the transformer, due to the produced electromotive force (EMF), creates two equal but oppositely directed magnetic fluxes in the magnetic circuit (core). The resulting magnetic flux is zero, the current in the secondary winding of the differential transformer is also zero. Due to the complete compensation of magnetic fluxes, no EMF occurs in the secondary winding wound on the core, which feeds the control relay, and the relay is in a passive state.

At the moment of touching the bare part of the phase wire or the case of any household appliance, on which a phase breakdown has occurred, an additional differential current will flow through the incoming winding of the transformer. Violation of the equality of the incoming and outgoing currents instantly creates an uncompensated magnetic flux in the core of the transformer. And as a result, the instantaneous appearance of EMF in the secondary winding connected to the relay as its power source. If this current exceeds the value of the threshold element of the trigger, the latter operates and acts on the actuator. The actuator, usually consisting of a spring drive, a release mechanism and a group of power contacts, opens the electrical circuit. The relay, having received power, immediately operates and turns off the power to the solenoid (the transit terminals open), which holds the main contacts in the closed position. The contacts open, the solenoid de-energizes and releases the spring-loaded rod of the contact group, and the power supply to the network is interrupted. As a result, the electrical installation protected by the RCD is de-energized.

The more sensitive the control magnetoelectric relay is to the values of the differential current reset signal, the more effective the protective function of the RCD, classified according to the functions performed:

AC - response to a suddenly appearing or gradually increasing alternating leakage current;

A - additionally triggered by a constant pulsating differential current, which may appear unexpectedly or increase gradually;

B - response to direct and alternating pulsating leakage currents;

S - selective RCD with additional time delay for shutdown;

G - similar to S, but with less delay.

The generated reset signal is characterized by the trip time - the interval from the appearance of the tripping leakage current until the arc is extinguished, and the limiting non-operation time for the S type device - the time interval between the onset of the leakage current and the opening of the contacts. The last parameter determines the selectivity of the RCD. Its limit value is 0.5 s. In this case, it should be taken into account that for the protection of people, opening should occur within 10-40 ms and to prevent ignition of the insulation - up to 40-500 ms. RCD selective type S is used to prevent false operation from the influence of interference or power surges.

Leakage currents always take place in electrical circuits. In sum, they should not exceed 1/3 of the rated leakage current of the device. It is believed that for 1 A of load there is 0.4 mA of consumer leakage current, and for 1 m of the length of the phase wire - 10 μA. The protective device is adjusted according to the total natural leakage current. If this is not done, frequent false positives may occur. In this case, it should be borne in mind that a device with a leakage current of more than 100 mA will no longer protect a person from electric shock.

The design of the differential current transformer takes into account the mechanisms to eliminate false positives from discharges during a thunderstorm and sensitivity to differential current up to 30 mA. At the same time, the overall dimensions of the RCD allow it to be placed in electrical cabinets on a DIN rail. A high-speed protective switch that reacts to differential current in the conductors supplying electricity to the protected electrical installation disconnects the consumer from the supply network if a current leakage occurs to the grounding conductor "ground". The differential transformer has three windings. The primary and secondary windings are included in the phase and neutral wires, respectively, and the third winding is connected to the starting element, which is performed on sensitive relays or electronic components. The starting body is connected to the executive control device, which includes a power contact group with a drive mechanism. The test button is used to check and monitor the health of the RCD. In normal mode, in the absence of leakage current, the operating current of the load flows in the circuit along the conductors passing through the window of the magnetic circuit of the current transformer. It is these conductors that form the back-to-back primary and secondary windings of the current transformer. These currents will be equal in magnitude and opposite in direction. They induce equal but oppositely directed magnetic fluxes in the magnetic core of the current transformer. It turns out that the resulting magnetic flux is zero, the current in the third (executive) winding of the differential transformer is also zero, and the starting element is at rest and the RCD is operating in normal mode.

When a person touches open conductive parts or the body of an electrical device, on which an insulation breakdown has occurred along the phase (primary) winding of the current transformer, in addition to the load current, an additional current flows, which is differential for the current transformer. It turns out that our currents are unequal, therefore, magnetic fluxes are also unequal, which no longer compensate each other. Because of this, a current appears in the third winding. If this current exceeds the set value of 30 mA, then the starting element is activated, which acts on the actuator.

The actuator, consisting of a spring drive, a trigger mechanism and a group of power contacts, opens the electrical circuit, as a result of which the installation is disconnected from the network. To carry out periodic monitoring of serviceability (operability), a test button is provided in the RCD. It is connected in series with a resistor. The value of the resistor is selected so that the differential current is equal to the passport tripping leakage current of the RCD. If, when you press this button, the RCD is triggered, then it is working properly.

In three-phase RCDs, four wires pass through the core window - three phase and zero. If the load is equal in the zero and in the three phase wires, their geometric sum is zero (the current in the phase wire of the RCD flows in one direction, and the current in the neutral wire of exactly the same value flows in the opposite direction). In the event of a current leakage to the grounded housing of the electrical receiver, as well as in the event of a person standing on the conductive floor accidentally touching the phase wire of the electrical network, the equality of currents in the primary winding of the current transformer will be violated, since the phase wire, in addition to the load current, will carry a leakage current, and in its the secondary winding, the current flowing in the secondary winding of the transformer will appear, the current acts on the control element, which, through the switch, disconnects the consumer from the mains.

All structural elements are tightly connected to the body. In the device, the processing and generation of signals is carried out using semiconductor and microelectronic technology. To generate a clock signal, a transformer current sensor is used. As an executive body, a small-sized contactor of the PM 12 type in a marine version was used. TU3426-077-05758109-2014. The specified contactor provides the required speed (off time), the necessary service life and acceptable weight and size parameters. In the body of the protection device 2, there are boards of electronic blocks, a transformer leakage current sensor, designed to determine the strength of alternating or direct current in electrical circuits. It consists of a magnetic circuit with a gap and a compensation winding, a Hall sensor and an electronic board for processing electrical signals. Contactor and clamps for connecting external electrical cables (supply and load circuits).

Shutdown protection device 2 is operational with a total capacitance relative to the ship's hull up to 20 μF per phase with asymmetry of not more than: 30% for a 380 V network; 40% for a 220 V network.

The response time in the event of a differential current does not exceed the following values: 1.. 2 _Inom - 200 ms; 250 - 100 ms; >500 - 90 ms.

The use of the device in solving the problem of electrical safety on ships will undoubtedly have a positive effect on the state of electrical safety of ships and vessels.

Claims (1)

The electrical safety device of the ship's electrical network, consisting of a housing that contains an electrical appliance connected to the output of the transformer; a protective shutdown device in which a differential transformer with three windings is placed, a starting element, an executive control device, the primary and secondary windings of the differential transformer are included in the phase and neutral wires, and the third winding is connected to the starting element, which is connected to the executive control device; at the same time, the residual current device is connected to the input and output of an isolation transformer, which changes the conditions for the flow of various leakage currents through the insulation resistance in the RCD power circuit (R _out ) or through the resistance of the human body (R _h ) from the load side, while one part of the leakage current through the phase capacitances relative to the ship's hull (С _o ) generates a trip signal of the residual current device, as soon as the resistance becomes below the permissible level, and the leakage current through the phase capacitances relative to the ship's hull (С _o ) will be higher than the trip setting, while the other part of the leakage current returns into the power source through the load capacitance C _n , without affecting the operation of the residual current device, and all structural elements are tightly connected to the housing.

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