WO1998048497A1

WO1998048497A1 - Power supply network, especially on ships

Info

Publication number: WO1998048497A1
Application number: PCT/EP1998/002352
Authority: WO
Inventors: Ulrich Horn
Original assignee: Stn Atlas Elektronik Gmbh
Priority date: 1997-04-22
Filing date: 1998-04-21
Publication date: 1998-10-29
Also published as: DE19716826A1

Abstract

The present invention pertains to a power supply network, especially an on-board power supply network, comprising main distribution lines (11, 12) and secondary distribution lines (13, 14) powered by generators (17), current services (18 to 20) that capable of being connected to such lines, current switches inserted between the distribution lines (11 to 14), on the one hand, and the distribution lines (11 to 14) and the generators (17) and the current services (18 to 20), on the other hand, as well as protective devices (22) combined with the current switches (15) and connected to a protective meter (26). In order to effect a very quick switching-off of the network areas affected by a short-circuit on the on-board power supply network with loopings and meshings, the current pick-up shoes contained in the protective devices (22) are designed so as to measure in amount and phase the current flowing through the current switches (15) for comparison with a virtual network voltage. The protective meter (26) continuously compiles for the groups of current switches (15) which delimit predetermined network areas the current vectors measured by the current pick-up shoes and, when the result significantly deviates from null, generates a switching signal to the current switches belonging to the group concerned (15).

Description

DESCRIPTION

Power supply network, in particular ship's electrical system

The invention relates to a power supply network, in particular a ship's electrical system, of the type defined in the preamble of claim 1.

For the permanent availability of

Power supply networks, in particular of ship's on-board networks, it is essential that short circuits are quickly switched off and the short-circuit locations are quickly recognized for troubleshooting.

Ship electrical systems are still protected according to the principles of electricity and time selectivity. For this purpose, each circuit breaker between the main and sub-distribution lines and between the sub-distribution lines and important electricity consumers is equipped with protective devices which trip the circuit breakers in the event of a short circuit with different delay times, the tripping times increasing from the current consumers to the main distribution lines and the generators feeding the main distribution lines . This means that each circuit breaker gives the subordinate switch time to switch off a short circuit before it in turn trips. The time-selective switching off of the circuit breakers is implemented in such a way that a time counter is activated in all protective devices when a short circuit occurs in the on-board electrical system, and the protective device that first reaches its individual time limit, the assigned circuit breaker opens.

In order for time selectivity to work smoothly, the circuit breakers must be arranged in every conceivable short-circuit path, that is the path between the fault location and the generators, in the order of the delay times set on the protective devices. Regrouping is therefore only possible to a limited extent and only with great technical effort, and there is no ring and mesh formation in the electrical system. With the principle of time selectivity, it is also disadvantageous that short circuits are switched off later, the closer they are to the generators. This means that the most serious and powerful faults are the longest in the vehicle electrical system.

It has already been proposed (DE 196 34 094.2-32) to obtain an integrated, digital network protection in ship's onboard networks in that all protective devices receive a current sensor in addition to their switching relays for triggering the assigned circuit breaker, which detects the current flowing through the circuit breaker according to height and Direction detected. All protective devices communicate with a protective computer that knows the address of the individual protective devices. The protective computer recognizes the occurrence of a short circuit and the location of the circuit breaker closest to the short circuit on the basis of the measured values supplied by the current sensors and issues a trip or release command for these circuit breakers, so that the short circuit area of the vehicle electrical system is disconnected. In order to achieve complete selectivity, each outlet from the vehicle electrical system must be equipped with a current sensor that must be connected to the network computer. The invention has for its object to provide a power supply network of the type mentioned with an integrated, digital network protection that can also be used in networks with difficult network configurations, such as ring and mesh formation, and an extremely fast shutdown of the network area of the vehicle electrical system, in which a short circuit occurs.

The object is achieved according to the invention in a power supply network of the type specified in the preamble of claim 1 by the features in the characterizing part of claim 1.

The power supply network according to the invention has the advantage that the continuous addition of the current vectors supplied by the current sensors immediately detects in the event of a short circuit whether the short-circuit current flows through a network area delimited by a group of circuit breakers or has a sink in the network area. In the latter case, the short circuit is caused by network faults within this network area, and the protective computer activates the circuit breakers delimiting this network area by controlling the switching devices assigned to the circuit breakers in the associated protective devices, so that this network area is very quickly separated from the rest of the network and the function of the remaining power supply is maintained. In contrast to the time-selective switch-off principle described at the beginning, the network area affected by the short circuit is switched off regardless of whether it is far away or very close to the generators. This eliminates even the most powerful short-circuit faults, thereby preventing consequential damage. Because all current vectors are on the virtual mains voltage are related, the transformers present in the network and the swivel angles generated by them with regard to their input and output voltages do not cause any problems.

Since data transmission between the protective devices at the circuit breakers and a central operator station is usually already installed for other reasons in today's power supply networks, in particular ship's on-board networks, the technical effort for integrating the digital network protection is relatively low.

In the case of the power supply network according to the invention, the usual differential protection of the transformers can additionally be easily shifted into the protective computer, thereby saving commissioning and engineering costs. With differential protection of the transformers, the amplitudes and phase positions of the primary and secondary currents of the transformers are compared in order to be able to identify special faults in the transformer. With conventional differential protection, in the event that the transformers have a non-zero swivel angle between primary and secondary voltages, the currents must also be swiveled before comparison by means of auxiliary transformers. However, since the current sensors according to the invention automatically correctly detect the phase position of the currents in the circuit breakers, an error, e.g. a short circuit, immediately recognized in the transformer and the corresponding transformer can be switched off.

Expedient embodiments of the power supply network according to the invention with advantageous developments and embodiments of the invention result from the further claims.

The invention is described below with reference to an embodiment shown in the drawing. Show it:

1 is a block diagram of a ship's electrical system,

2 shows a block diagram of a protective device for a circuit breaker in the on-board electrical system according to FIG. 1.

The three-phase ship electrical system shown in the block diagram in FIG. 1 as an example of a power supply network is divided into main distribution lines 11, 12 and sub-distribution lines 13, 14. The number of main and sub-distribution lines 11 to 14 is arbitrary, and the network can also be split into third and fourth levels of sub-distributions. The main distribution lines 11, 12 and

Sub-distribution lines 13, 14 are coupled to one another via circuit breakers 15. In the illustrated embodiment of the vehicle electrical system, the sub-distribution lines 13, 14 are operated with a lower mains voltage than the main distribution lines 11, 12, so that voltage transformers 16 are arranged between the main distribution lines 11, 12 and the sub-distribution lines 13, 14, both of which are connected to the Main distribution lines 11, 12 and sub-distribution lines 13, 14 are connected by means of circuit breakers 15. If the sub-distribution lines 13, 14 with the same mains voltage as the

Main distribution lines 11, 12 operated, so the main distribution lines 11, 12 and Sub-distribution lines 13, 14 directly coupled to one another by circuit breakers 15.

The main distribution lines 11, 12 are fed by vehicle electrical system generators 17, which in turn are connected to the main distribution lines 11, 12 via circuit breakers 15. On the main distribution lines 11, 12 are large electricity consumers, such as

Supply transformers 18 and asynchronous motors 19, connected via circuit breakers 15, and on the sub-distribution lines 13, 14 there are any other current consumers 20 which can be switched on and off via mains switch 20.

A protection device 22 is assigned to each circuit breaker 15, as is shown in detail in FIG. 2 in the block diagram. Each protection device 22 has a switching device 23 for actuating the circuit breaker 15 and a current sensor 24 which detects the current flowing through the circuit breaker 15. The protective devices 22 communicate via data lines 25 with a protective computer 26, the protective devices 22 of the same distribution level each being connected to one of a plurality of data concentrators 27 to 29, which in turn are connected to the protective computer 26. In the embodiment of FIG. 1, the protective devices 22, which are assigned to the power switches 15 for connecting the vehicle electrical system generators 17 to the main distribution lines 11, 12, to the data concentrator 27, the protective devices 22 which are the power switches 15 for connecting the transformers 16, 18 and Asynchronous motors 19 are assigned to the main distribution lines 11, 12, to the data concentrator 28 and to the protective devices 22 which connect the circuit breakers 15 between the Sub-distribution lines 13, 14 and the circuit breakers 15 for connecting the transformers 16 to the sub-distribution lines 13, 14 are assigned to the data concentrator 29. The corresponding data lines 25 are shown in broken lines, dash-dotted lines and dotted lines in FIG. 1.

The switching device 23 comprises a switching relay 30 for actuating the circuit breakers 15, an amplifier 31 and a decoder 32 which decodes a switching command coming from the protective computer 26 and controls the switching relay 30. The switching relay 30 works according to the open-circuit principle, i.e. when charging with excitation current, it opens the circuit breaker 15.

The current sensor 24 is designed to measure the amount and phase of the current flowing through the circuit breaker 15. The phase measurement is based on a virtual line voltage U _vir , the phase position of which corresponds to the phase position of the line voltage immediately before the short-circuit occurs. This virtual mains voltage U _vir is determined by means of a follow-up synchronization, by a so-called

PLL (Phase Locked Loop) circuit 33, obtained, which is connected to a line voltage of the three-phase distribution line in which the circuit breaker 15 is located. Such a PLL is known for an application of communications technology from Tietze / Schenk, semiconductor technology 9th edition, Springer Verlag Berlin 1989, page 954 ff. And is implemented there in analog technology. Here it is preferably implemented as a program that can be implemented in the protection computer 26. In the exemplary embodiment shown in FIG. 2, the circuit breaker 15 connects the sub-distribution lines 13 and 14 with each other so that the PLL circuit 33 is connected to a line voltage of either the sub-distribution line 14 or the sub-distribution line 13. The virtual mains voltage U _vir generated by the PLL circuit 33 is at the input of an evaluation unit 34 to which a current measuring device 35 for measuring the phase currents in the three-phase distribution line (in FIG. 2 in the sub-distribution line 14) is connected. The evaluation unit 34 determines the magnitude of the three phase currents i _{1 #} i ₂ , i ₃ and their phase position in relation to the virtual mains voltage U _vir , that is to say the variables describing the vector of the phase currents i _lt i ₂ and i ₃ , which are supplied to a coding unit 36. The output of the coding unit 36 is connected to the protective computer 26 via the data line 25 and the corresponding data concentrator 27 to 28. The coded data transmission to the protection computer 26 takes place once per mains voltage period.

In the protection computer 26, the incoming data are assigned to groups of circuit breakers 15, which limit predetermined network areas. For example, in FIG. 1, the circuit 37 denotes a network area which is delimited by four circuit breakers 15. In the same way, the other circuit breakers 15 in the network are grouped together to define predetermined network areas. During network operation, the protection computer 26 continuously adds for each group of circuit breakers 15 the current vectors of the phase currents i ₁ measured by the current sensors 24 and transmitted coded via the data lines 25 _; the phase currents i ₂ and the phase currents i ₃ . As long as the vectorial addition of all of the current sensors 24 of the group of circuit breakers 15 to the protective computer 26 supplied currents i-_ or i ₂ or i _{3 is} approximately zero, this network area is error-free. A short-circuit current occurring in the vehicle electrical system flows through this network area, but is not caused by an error in this network area. If, on the other hand, the result of the vectorial addition differs substantially from zero, this is an indication that the short-circuit current does not flow through the network area but has a sink within the network area, that is to say the short-circuit current is caused by an error in this network area. In this case, the protection computer 26 generates a switching command for all the circuit breakers 15 delimiting this network area, which switches to the switching devices 23 of the protection devices 22 of these circuit breakers 15 via the data lines 25. The corresponding switching relays 30 of the circuit breakers 15 are energized and the circuit breakers 15 are opened. The faulty network area is thus activated, while the undisturbed operation of the remaining network areas is ensured.

The invention is not restricted to the exemplary embodiment described above. So instead of the direct measurement of the phase currents i _1; i ₂ , i ₃ the amount and phase of a co-system, a counter system and a zero system are also determined according to the amount and phase, which are calculated from the phase currents i _{1 #} i ₂ , i ₃ . For a ship's electrical system, it is sufficient if only the co-system is taken into account. If the co-systems (or the counter systems and the zero systems) are then vectorially added for all circuit breakers 15 by a group of circuit breakers 15 delimiting a network area, the same statement about a fault location inside or outside this network area is obtained. Through this conversion into the co-systems simplifies the mathematical calculation. In addition, the usual differential protection for the transformer transformers 16 present in the power supply network can be implemented very easily by a computing routine in the protective computer 26, so that considerable savings are achieved compared to the conventional differential protection. In differential protection, the primary and secondary currents are compared with one another to identify faults in the transformer. Since, as a rule, the primary and secondary voltages of transformers are shifted by a multiple of 30 ° relative to each other, a direct comparison of the primary and secondary currents is not possible; rather, this shift or swivel must be reversed beforehand, which is usually the case with current transformers and output converters can be used. The comparison then no longer takes place between the primary and secondary currents, but between appropriately swiveled images of the currents. This is very difficult to interpret and offers plenty of opportunities for confusion. However, if a current monitoring system is calculated from the phase currents at the input and output of the transformer, the current monitoring system of the secondary windings has approximately the same angle to the secondary voltage as the current monitoring system of the primary windings to the primary voltage, regardless of the pivoting angle of the transformer. By simply comparing the co-systems on the primary and secondary sides of the transformer, the differential protection can then be taken over by the protection computer 26 without any additional effort.

The same applies if the phase currents i _{1 #} i ₂ , i _{3 are not converted} into the co-systems and the vector addition of the phase currents relating to the virtual voltage U _vir in their phase position is carried out. Since the phase angles of the currents in each case relate to the virtual mains voltage obtained on the distribution line, the swiveling angles caused by the transformer transformer 16 between the conductor voltages on the primary-side distribution line 11 and 12 and on the secondary-side distribution line 13 and 14 are automatically compensated for.

The determination of the vectorial current sum is relatively complex. An equivalent statement about the location of a short-circuit source can be made according to a simplified embodiment of the invention by only evaluating the short-circuiting switches, i.e. it is checked whether the phase angles of the short-circuit currents at all allow the vectorial current sum to become zero. E.g. all short-circuit currents in a restricted network area approximately the same phase angle, then the vectorial sum cannot become zero, and the error must lie in this network area.

Claims

PATENT CLAIMS

Power supply network, in particular ship's electrical system, with main distribution lines (11, 12) fed by generators (17) and with sub-distribution lines (13, 14) as well as with current consumers (18, 19, 20) that can be connected to them, on the one hand, between the distribution lines (11 to 14) and the distribution strands (13 to 14) and the generators (17) and the current consumers (18, 19, 20) on the other hand arranged circuit breakers (15) with the circuit breakers (15) assigned protective devices (22), each of which is assigned to the assigned circuit breaker ( 15) actuating switching device

(23) and a current sensor (24) which detects the current flowing through the assigned circuit breakers (15), and with a protective computer communicating with the protective devices (22)

(26), characterized in that the current sensors

(24) for measuring the current (i _x to i ₃ ) according to amount and phase, which is based on a virtual mains voltage (U _vir ), the phase position of which corresponds to that of the mains voltage before the short circuit occurs, and that the protective computer (26) for Groups of power switches (15), which delimit predetermined network areas (37), continuously add the current vectors measured by the current sensors (24) and, in the event of a substantial deviation of the addition result from zero, a switch-off command for the circuit breaker (15) belonging to the group is generated.

Network according to claim 1, characterized in that instead of a complete vector addition, only a check of the phase positions of the phase currents is carried out to determine whether these permit a vectorial current sum of zero or not.

Network according to claim 1 or 2, characterized in that the measured values of the current sensors (24) are transmitted coded to the protective computer (26).

Network according to claim 3, characterized in that the coding and transmission takes place once per network voltage period.

Network according to one of Claims 1 to 4, characterized in that, in order to obtain the virtual network voltage (U _vir ), each current sensor has a PLL circuit (33) which is connected to a line voltage of the three-phase distribution line (11 to 14) and which has a short-circuit occurrence which occurs immediately previously existing phase position of the mains voltage.

Network according to Claim 5, characterized in that each current sensor (24) has a current measuring device (35) for measuring the phase currents (i _x to i ₃ ) in the three-phase distribution lines (11 to 14), an evaluation unit (34) for calculating the amount and phase which has phase currents (i _x to i ₃ ) and a coding unit (36) for coding the absolute value and phase values, which are connected via a data line (25) is connected to the protection computer (26).

Network according to one of Claims 1 to 6, characterized in that, instead of vector addition of the phase currents within a group of circuit breakers (15) which delimit predetermined network areas, vector addition of at least the co-systems calculated from the phase currents (i _x to i ₃ ) takes place.