MÖRSCH, Michael (Spardorfer Str. 40, Erlangen, 91054, DE)
AHLF, Gerd (Langenlohe 8, Wiesenthau, 91369, DE)
MÖRSCH, Michael (Spardorfer Str. 40, Erlangen, 91054, DE)
| Patent Claims 1. A method for modernization of a direct-current propulsion drive (1) which comprises a propulsion system (2) having at least one direct-current generator (5) and at least one direct-current motor (6) for driving a propeller, which motors are connected to one another via direct-current circuit breakers (7), characterized by the following steps: - replacement of the at least one generator (5) by a generator (5' ) having a higher rating than the previous generator (5) , - splitting of the propulsion system (2) into two, preferably symmetrical, sub-systems (3, 4), - interconnection of the two sub-systems (3, 4) via a direct-current quick-action switch (10), via a fuse (20) or via a fuse combination (30) . 2. The method as claimed in claim 1, characterized in that the direct-current quick-action switch (10), the fuse (20) or the fuse combination (30) is designed such that it carries the rated current flowing therein during operation, as well as overcurrents (for example starting currents) that occur during operation, without tripping. 3. The method as claimed in claim 1 or 2, characterized in that the direct-current quick-action switch (10), the fuse (20) or the fuse combination (30) is designed such that it trips considerably more slowly in the region of the rated current and of the overcurrents that occur during operation, than in the short-circuit current range. 4. A method for modernization of a direct-current propulsion drive (1) which comprises a propulsion system (2) having at least one direct-current generator (5) and at least one direct-current motor (6) for driving a propeller, which motors are connected to one another via direct-current circuit breakers (7), characterized by the following steps: - replacement of the at least one generator (5) by a generator (5' ) having a higher rating than the previous generator (5) , - replacement of at least some, and preferably all, of the direct-current circuit breakers (7) by direct- current quick-action switches (10). |
Method for modernization of a direct-current propulsion drive The invention relates to a method for modernization of a direct-current propulsion drive as claimed in patent claim 1 and patent claim 4.
The direct-current propulsion drive comprises a propulsion system having at least one direct-current generator and at least one direct-current motor for driving a propeller, which motors are connected to one another via direct-current circuit breakers (see also Figure 1) . In order to increase the drive power, two generators can in each case be connected in series, or else parallel operation is possible (see also Figures 2 and 3) . The circuit breakers are normally standard circuit breakers with a typical opening delay in the event of a short circuit of about 25 - 40 ms . In the case of large systems, dangerously high short-circuit currents can occur in the event of a short circuit and can lead to the circuit breakers reaching their limits or even being overloaded. The latter can occur in particular when generators with a higher rating than the previous generators are intended to be installed during conversion or modernization, in order to make the drive more powerful or faster. The object of the present invention is therefore to specify a method which allows a direct-current propulsion drive as explained initially to be modernized with little effort.
This object is achieved on the one hand by a method as claimed in patent claim 1.
This method provides the following steps:
replacement of the at least one generator by a generator having a higher rating than the previous generator, splitting of the propulsion system into two, preferably symmetrical, sub-systems,
interconnection of the two sub-systems via a direct- current quick-action switch, via a fuse or via a fuse combination.
(completely or at least substantially)
The two sub-systems are therefore either interconnected via a suitable direct-current quick-action switch. This is
preferably designed for the maximum coupling current as the operating current (that is to say it can carry the maximum rated current which flows through the quick-action switch during operation as well as overcurrents that occur during operation, for example starting currents, without this leading to opening of the quick-action switch) .
During normal balanced operation, only an equalizing current will flow via the coupling. However, if one or more
generators in a sub-system have to supply the propeller motor of the other sub-system (for example in the event of damage) a correspondingly high operating current will flow via the coupling. The starting currents must likewise be taken into account during configuration. Overloading of the motor switches, for example if all the generators were to feed one propeller motor in parallel, could be prevented by an
appropriate interlock.
This allows modernization to be carried out very easily. All that is required is to provide space for the additional direct-current quick-action switch. One major advantage is that the previously used circuit breakers can still be used. This allows the modernization to be carried out with little effort. Splitting into two sub-systems in the event of a short circuit by rapid disconnection of the direct-current quick-action switch in the coupling between the sub-systems isolates the faulty sub-system from the sound sub-system. Halving the short-circuit current allows the (standard) circuit breakers in the faulty sub-system to disconnect the short circuit. The sound sub-system could even still be used for further, restricted operation (the marine vessel does not lack propulsion and does not need to be towed) . It is therefore important for the opening delay of the direct- current quick-action switch in the event of a short circuit to be shorter than the opening delay of the already provided (standard) circuit breakers. This allows selective
disconnection of the faulty sub-system. This means that the direct-current quick-action switch trips more quickly in the event of a short circuit in the propulsion system than the already provided direct-current circuit breakers.
Furthermore, the direct-current quick-action switch is preferably designed such that it trips particularly quickly in the short-circuit current range, and trips considerably more slowly in the region of the rated current and of the overcurrents that occur during operation, than in the short- circuit current range.
The two sub-systems can also be interconnected via a suitable (special) fuse or a fuse combination, which is preferably likewise designed for the maximum coupling current as the operating current (that is to say it can carry the maximum rated current which flows through the fuse or fuse
combination during operation, as well as overcurrents that occur during operation, for example starting currents, without this leading to blowing of the fuse or of the
individual fuses in the fuse combination) .
Furthermore, the fuse or fuse combination is preferably designed such that it trips particularly quickly in the short-circuit current range, and trips considerably more slowly in the region of the rated current and of the
overcurrents that occur during operation, than in the short- circuit current range. The fuse or fuse combination therefore preferably does not have a "linear" response but a "non ¬ linear" response. Short-term starting currents must not lead to blowing of the fuse or fuse combination. It is likewise important in this case that the time for the fuse or fuse combination to blow is shorter than the opening delay of the previously used (standard) circuit breakers (this allows selective
disconnection of the faulty sub-system) . This means that the fuse or fuse combination trips more quickly than the existing direct-current circuit breakers, in the event of a short circuit in the propulsion system.
In this case, a fuse combination means two or more
(individual) fuses connected in parallel.
The solution with the fuse or fuse combination could be particularly appropriate if it is not possible to use the quick-action switch for certain reasons (for example high shock resistance and/or vibration resistance), or this would be difficult to achieve. In addition, it is also possible to provide fuses in the generator branches or in the motor branches.
The object of the present invention as explained initially is achieved on the other hand by a method as claimed in patent claim 4.
This method envisages replacement of at least some,
preferably all, of the (standard) circuit breakers by direct- current quick-action switches. The latter have shorter switching times (the typical opening delay of the quick- action switches is about 3 - 5 ms, the typical opening delay of the standard circuit breakers is about 25 - 40 ms) , and they therefore limit the short-circuit current even while the current is rising, such that neither the propulsion system, including the cable system, nor the switchgear assembly has to carry the full short-circuit current. The quick-action switches are thus also able to cope with the high prospective short-circuit currents. The invention as well as further advantageous refinements of the invention according to features of the dependent claims will be explained in more detail in the following text, with reference to exemplary embodiments in the figures, in which:
Figure 1 shows a direct-current propulsion drive as known from the prior art,
Figure 2 shows the direct-current propulsion
as shown in Figure 1, with series- connected generators,
Figure 3 shows the direct-current propulsion
as shown in Figure 1, with parallel connected generators,
Figure 4 shows the direct-current propulsion drive as shown in Figure 1 after modernization according to the invention,
Figure 5 shows a first operating situation of the modernized direct-current propulsion drive as shown in Figure 4, Figure 6 shows a second operating situation of the modernized direct-current propulsion drive as shown in Figure 4,
Figure 7 shows the direct-current propulsion drive as shown in Figure 1, after alternative modernization according to the invention,
Figure 8 shows a first situation of operation of the alternatively modernized direct- current propulsion drive as shown in
Figure 7, Figure 9 shows a second situation of operation of the alternatively modernized direct- current propulsion drive as shown in
Figure 7,
Figures 10 and 11 show the alternatively modernized direct- current propulsion drive as shown in
Figure 7, in each case with additional fuses ,
Figure 12 shows a fuse combination, and Figure 13 shows the direct-current propulsion drive as shown in Figure 1, after further alternative modernization according to the invention .
A direct-current propulsion drive 1, part of which is shown in Figure 1, comprises a propulsion system 2 which consists of two parallel-connected sub-systems 3, 4, each having two generators 5 and one motor 6, which are connected to one another via direct-current circuit breakers 7.
However, this is only an example; for example, the propulsion system 2, to be precise the respective sub-systems 3, 4, may also consist of fewer or more generators 5 or motors 6. The motors 6 jointly drive a marine-vessel propeller, which is not shown in any more detail.
The circuit breakers 7 are standard circuit breakers with a typical opening delay in the event of a short circuit of about 25 - 40 ms .
For high-speed propulsion of the marine vessel - as is shown in Figure 2 - two generators 5 are in each case connected in series. The generators 5 can also be operated in parallel - as shown in Figure 3 - for high starting torques, with the generators 5 being connected in parallel with one another. The respective current-carrying circuit branches are in this case represented by a thicker line.
The direct-current propulsion drive 1 can be modernized as shown in Figure 4 by replacing the generators 5 by generators 5' with a higher rating than the previous generators 5.
However, this also increases the short-circuit currents in the propulsion system 2. During the modernization process, the propulsion system 2 is therefore subdivided into the two symmetrical sub-systems 3, 4, and the two sub-systems 3, 4 are interconnected via a direct-current quick-action switch 10, which trips more quickly than the direct-current circuit breakers 7 in the event of a short circuit in the propulsion system 2.
The direct-current quick-action switch 10 is designed such that it carries the rated current flowing through it during operation and overcurrents that occur during operation (for example starting currents of the motors 6) without tripping. By way of example, in this context, Figure 5 shows the situation in which the generators 5' which have been
connected in parallel with one another in the sub-system 4 also have to supply current to the motor 6 in the sub-system 3, and Figure 6 shows the situation in which the generators 5' , which have been connected in series with one another, in the sub-system 4 also have to supply current to the motor 6 in the sub-system 3. In the event of a short circuit, the opening delay of the direct-current quick-action switch 10 is shorter than the opening delay of the already existing circuit breakers 7 (this allows selective disconnection of the faulty sub ¬ system) . This means that the direct-current quick-action switch 10 trips more quickly than the already existing direct-current circuit breakers 7 in the event of a short circuit in the propulsion system 2. By way of example, the direct-current quick-action switch 10 has a typical opening delay in the event of a short circuit of about 3 - 5 ms . The direct-current quick-action switch 10 is designed such that it trips particularly quickly in the short-circuit current range, and trips considerably more slowly in the region of the rated current and of the overcurrents that occur during operation, than in the short-circuit current range.
As is illustrated in Figure 7, the two sub-systems 3, 4 can also be interconnected via a suitable special fuse 20, or via a fuse combination (see Figure 12) .
The fuse 20 or the fuse combination is designed for the maximum coupling current as the operating current (that is to say it can carry the maximum rated current which flows through the fuse or fuse combination during operation, as well as overcurrents that occur during operation, such as starting currents, without this leading to blowing of the fuse or of the individual fuses in the fuse combination) .
The fuse 20 or the fuse combination is designed such that it trips particularly quickly in the short-circuit current range, and trips considerably more slowly in the region of the rated current and of the overcurrents that occur during operation than in the short-circuit current range. Therefore, the fuse or fuse combination preferably has a "non-linear" response rather than a "linear" response.
The time for the fuse 20 or the fuse combination to blow is shorter than the opening delay of the previously used
standard circuit breakers 7 (this allows selective
disconnection of the faulty sub-system) . This means that the fuse 20 or the fuse combination trips more quickly in the event of a short circuit in the propulsion system 2 than the existing direct-current circuit breakers 7. In this context, Figure 8 once again shows the situation during operation in which the generators 5' which are
connected in parallel with one another in the sub-system 4 also have to supply current to the motor 6 in the sub-system 3, and Figure 9 shows the situation during operation in which the generators 5' , which are connected in series with one another, in the sub-system 4 also have to supply current to the motor 6 in the sub-system 3. As is shown in Figures 10 and 11, even more fuses 21 can also be introduced into the generator branches or into the motor branches during modernization, as well.
By way of example, Figure 12 shows a fuse combination 30 which consists of a plurality of (individual) fuses 31 connected in parallel.
Alternatively, the (standard) circuit breakers 7 can also be replaced by direct-current quick-action switches 10 for modernization of the direct-current drive 1 - as shown in Figure 13. Direct-current quick-action switches 10 have shorter switching times (the typical opening delay of quick- action switches 10 is about 3 - 5 ms, the typical opening delay of the standard circuit breakers 7 is about 25 - 40 ms) , and they therefore limit the short-circuit current even while the current is rising, such that neither the propulsion system 2, including the cable system, nor the switchgear assembly has to carry the full short-circuit current. The quick-action switches 10 are therefore also able to cope with the high prospective short-circuit currents.
The invention will in this case be explained, by way of example as illustrated in Figures 1 to 13, with reference to a propulsion system 2 which consists of two sub-systems 3, 4, each having two generators 5 or 5' and one motor 6. However, this is only by way of example; for example, the propulsion system 2 and the respective sub-systems 3, 4 may also consist of fewer or more motors 6 or generators 5 or 5' . The level of the short-circuit currents in the individual branches can also be reduced by appropriate interlocks between the switches, that is to say it is in this case possible to prevent simultaneous opening and closing, with corresponding opening/closing of current branches which are potentially subject to short-circuits.