METHOD AND GENERATING PLANT FOR SHIPS HAVING A SHAFT GENERATOR

Abstract: A method for supplying current to ships having at least one synchronous machine (1) as a shaft generator comprises distributing the power from the shaft generator(s) to two supply mains, a first mains (7), wherein voltage and frequency equal the voltage and frequency of the shaft generator, and a second mains (6), wherein voltage and frequency are kept at a constant level. The first mains comprising 85-95% of the power consumption is used for supplying current to electric motors, pumps, compressors, ventilating and cooling systems etc., and the second mains is used for supplying current to navigation and communication systems, steering engine, lighting and similar installations requiring constant voltage and frequency. The generating plant for performing the method therefore comprises a three-phase rectifier circuit (3) and a DCAC converter circuit (5) inserted between the shaft generator and the second mains. The result is fuel savings as well as substantially reduced wear of the consumers connected to the first mains, and these consumers are made to adjust themselves automatically so that they perform only the necessary work. Furthermore, such a generating plant is cheaper to install than the known plants because frequency and voltage regulations on part of the mains are avoided.

Description: 1 METHOD AND GENERATING PLANT FOR SHIPS HAVING A SHAFT GENERATOR The invention relates to a method for ' supplying cur- 5 rent to ships having at least one synchronous machine, as a shaft generator and a generating plant for per¬ forming the method. .There are known various methods and plants for sup- 10 plying current to ships where one or- more synchronous generators are connected to the main engine by means of gears or like coupling devices. The main engine of the ship will thus through the shaft generator supply the necessary electric power when the ship is 15 sailing. When the ship is not sailing, for instance when it is in port or at anchor, socalled auxiliary units are normally ' used, said ' units consisting of a small diesel engine driving a generator and thereby supplying the necessary electric power for the oper- 20 ation of the ship. When using a synchronous machine as a shaft generator, special measures must be tak * en as soon as the main engine is not kept at a number of revolutions cor- 25 responding to the synchronous frequency. It is pos¬ sible for instance to let the ship be ' supplied with current from the auxiliary ' units, the electricity production being shifted from the shaft generator to the auxiliary units. It is also possible to introduce 30. a Ward-Leonard system between the main engine and the shaft generator thereby keeping the generator at the synchronous number of revolutions. There are also known generating plants with shaft 35 generators where the shaft generator in the form of a three-phase AC generator rotates at varying numbers of revolutions and is excited by a rotating field, the size and frequency of which is adjusted in such a way that in the three-phase AC mains supplied by the shaft generator, there is pro ' duced a constant voltage with constant frequency. Such generating plants are more costly especially when designed for small nom¬ inal numbers of revolutions. The shaft generator will then have several poles and a small air gap. It is moreover a disadvantage that for producing the rotat¬ ing field varying in relation to frequency and size for exciting the shaft generator a costly inverter is require . Moreover, there is known a shaft generator designed as a DC machine. By means of a DC motor driving a three-phase AC generator, the ship * 's mains is sup¬ plied wifeh three-phase alternating current. By con- trolling the excitation of the DC machine, the fre¬ quency is kept at a constant level, and by control¬ ling the excitation of the three-phase AC generator, the voltage in the ship's mains is kept at a constant level. Also such a shaft generator plant with com- mutator motors is rather costly and requires much space and constant attendance. Furthermore, a shaft generator plant is known where the shaft generator produces the three-phase alter- nating current which is rectified and. by means of a self-controlling inverter reconverted into three- phase AC voltage. Self-controlling inverters, however,, are costly and complicated since means for producing the reactive current and commutation current are OMPI required. To obtain a more or less sinusoidal output voltage, filter circuits are moreover required. Fi¬ nally, it is diffi-cult to take protective measures against short circuits since the self-controlling inverter cannot produce a short circuit current which can melt the ' fuses. The abovementioned generating plants require various .types of auxiliary equipment which are partly price- raising additional units in the generating plant and which moreover require maintenance and which also require energy for the operation. Several of these known systems require much energy and some of them operate at full power all the time and therefore also when there is no need for it. The result is that substantial power is lost. The object of the invention is to provide a method and a plant for supplying current to a ship having at least one shaft generator whereby in relation to known methods and plants substantial savings in electric power and consequently fuel are obtained, without any substantial adverse effects on the oper¬ ation of the ship. This is achieved by proceeding as indicated in claim 1, for example by using the generating plant mention¬ ed in claim 4. By distributing the current supply of a ship into two mains, a first mains with fixed fre- quency and voltage and a second mains where frequency and voltage are allowed to vary with the shaft rev¬ olutions, there. a^e obtained substantial savings in electric power and also reduced wear and consequently reduced maintenance costs because the plant is dimen- sioned to generate the ordinary mains frequency of e.g. 50Hz at the normal sea speed which is frequent¬ ly at approx. Qθ% of full engine power. However, when operating at lower numbers of. revolutions, a lower frequency and a lower,mains, voltage " are obtained so that the greater part of the " auxiliary equipment operates at a lower number of revolutions and takes up less power and consequently wears less. Further¬ more, the no-load losses of the ' units which are run- ning are reduced. A substantial part of the fuel saving is moreover obtained because it is not nec¬ essary to shift to auxiliary ' units but possible to remain on shaft generator operation. By proceeding as indicated- in claim 2, for example with a generating plant as mentioned in claim » it is possible in many ships to minimize the part of the fuel consumption used for generating the necessary electric power for the ship. There may be special cases where the relation between the two generating systems will have to be different, but in most types of ships costs will be minimized by the use of the mentioned distribution. By proceeding as indicated in. claim 3, for example as mentioned in claim 6, the individual consumers • are distributed on the two mains in a suitable manner. The invention will be further described in the fol- lowing with reference to the drawings , wherein Fig. 1 is a graph showing the relation between frequency and voltages for a shaft generator, and Fig. 2 is a preferred embodiment of a gen¬ erating plant according to the in¬ vention. Fig. 1 of the drawing shows a graph A - substantial¬ ly a straight line - showing for part of the working area of a synchronous generator the relation between frequency and voltage, e.g. ' when the synchronous machine works as a shaft generator. The graph A applies to a certain load. When for example the generator operates at a synchronous num¬ ber of revolutions, such as 50Hz, a mains voltage of 380 volt is obtained at point C. If this frequency is maintained by maintaining ' the number of revolu¬ tions of the main engine and thus the propeller shaft, the voltage will fall, if the load is increased, ie. the graph A will move towards the ' upper dashed graph B', and if the load is decreased, the voltage will increase, ie. the graph A will move towards the lower dashed, graph:B".. Similar considerations apply to point D, corresponding to a supply voltage of 440 volt at 60Hz mains frequency. This.,is always the case with synchronous generators and furthermore permits several generators to operate in parallel without any problems of distributing the reactive power in the system wihtout the generators showing any cyclic variations. The graph A in fig. 1 thus shows a possible course for example corresponding to 80% engine power, ie. when the ship is sailing long distances. It is rarely the case that more than 80$ engine power is ' utilised, as in the main this will just result in increased wear and a higher fuel consumption, which financially bear no proportion to the modest increase in speed obtained. If for example the engine power is in¬ creased to 100$, an increase in speed of more than 5% is rarely obtained. Fig. 2 shows a skeleton diagram of a generating plant according to the invention wherein 1 is a three-phase synchronous generator connected to the propeller shaft, for example by a mechanical gear. The three- phase output. oltage of the generator, is transmitted to two current supply mains 6 and 7 both supplying three-phase alternating current to consumers. The mains 7 is. connected directly to the generator out- put end 2, whereas the mains- 6 is connected to the generator output end 2 through a controlled rectifier circuit 3 converting the. three-phase voltage to an ordinary direct current 4 which in another converter circuit .5 is converted to three-phase alternating current 6 with constant frequency and voltage. -The converter circuit 5 can be an electronically con¬ trolled inverter or an AC generator driven, by a DC motor such as a rotary converter or another suitable DC/ C converter circuit. * The mains 7 not having constant, frequency or voltage but a frequency depending on the number of revolu¬ tions of the shaft and a voltage depending on the load is used for supplying all the users which can - accept such lower quality supply such as electric motors, pumps, compressors, ventilation and cooling systems etc. Such apparatus are often driven by an ■ asynchronous motor. The mains 6, however, is used for supplying the users which can only accept a current supply with fixed frequency and voltage, such as navigation and communication systems, steering en¬ gines, lighting etc. On the mains ' 7 there will be a frequency which cor¬ responds to the number of revolutions of the propel¬ ler shaft, ie.' a mechanically bound frequency. At a given load, the voltage will increase if the fre¬ quency is increased, and the voltage will fall if the frequency is lowered. The result is that all auxiliary ' units will work in time with the main en¬ gine and thereby automatically* merely take up ' the necessary power which gives substantial power savings compared .with existing plants where attempts are being made to keep total current supply at constant voltage and constant frequency so that ' the auxiliary units will take ' up the total power irrespective of the number of revolutions of the engine. The electric power requirements of a ship may s be di¬ vided in the following manner- a 105. of the electric power is ' used for radio, communication and navigation equipment, lighting, steering engine etc.. Such equipment requires constant voltage and constant fre¬ quency. b 5052 electric power is ' used for engine opera- • .tion by pumps, compressors, ventilation and cooling systems etc. Such apparatus may either operate for long periods or be ' used for purposes where full capacity is not nec¬ essary when the main engine is not used 10052, OMPI if only the variation of the " current con¬ sumption (working requirement) is directly proportional to the number of revolutions . of the main engine. c_ 40$ electric power is used for heating and less important electric motors where the cut-in time is of no importance, and there¬ fore voltage and frequency may vary without problems, if only the engine is not damaged since" the cut-in or the cut-out period may be varied without causing Inconvenience to the unctioning of the ship. Usually the control of these ' functions takes place by means of thermostats, pressostats or level control equipment. It is therefore a modest part of the power consump¬ tion only that has to be " supplied at a fixed and constant frequency and voltage, and so it is neces¬ sary only to stabilise a small part of the electric power. Consequently, the circuits 3 and 5 become much less costly than in known plants where the en¬ tire power supply is normally stabilised. An ordinary type of shaft generator system, more¬ over , , is not applicable. under certain circumstances, namely at very low speed or in a heavy sea where the number of revolutions of the main engine fluctu- ates more than the permissible frequency variation. Under " such circumstances the auxiliary " units are therefore * used for producing electricity thereby increasing the oil consumption. OMPI A plant according to the invention, however, can be used under all circumstances, if only voltage or frequency do not fluctuate so much from the nominal values as to damage the consumers. Generally, the ordinary electric equipment can stand variations of up to plus iO * . to minus 15$ from the nominal volt¬ age without damages being incurred. If these limits are exceeded, the auxiliary ' units on the ship may fail or. be damaged and therefore the plant must be adapted in such a way that the current supply auxil¬ iary units are connected in the normal way.

Claims: P A T E N T C L A I M S 1. Method for supplying current to ships having at least one synchronous machine as a shaft generator, c h a r a c t e r i s e d i . that the power from • one or more shaft generators is distributed to two supply mains, a first mains wherein voltage and fre¬ quency equal the voltage 'and frequency of the shaft generator, and a second mains, herein voltage and frequency are kept at a constant level. 2. Method according to claim 1, c h a r a c t e r ¬ i s e d i n that the first mains is supplied with approx. 85-95% of the power supplied, by the genera- tor(s), and that the second mains is supplied with approx. 5-15$ of the generator power. 3. Method according to claim l or 2, c h a r a c ¬ t e r i s e d i n that the first supply mains is used for supplying current to electric motors, pumps, compressors, ventilating and cooling systems etc., and that the second supply mains is used for supply¬ ing current to navigation and communication systems, - steering engine, lighting and similar installations requiring constant voltage ' and frequency. 4. Generating plant for ships having at least one synchronous machine as a shaft generator (1) for performing the method according to claim 1, c h a r ¬ a c t e r i s e d i n . , comprising two separate supply mains (6,7), a first mains (7) being directly sup- plied with power from the shaft generator(s) (1), and • a second mains (6) also being 'supplied with power from the shaft generator(s) (1) but through a circuit (3,4,5) ensuring constant mains voltage and fre- quency. 5. Generating plant according to clai 4, c a r ¬ a c t e r i s e d i n that the first mains (7) is dimensioned and adapted so as to be supplied with approx. 85-95% of the generator power, and that the second mains (6) is dimensioned and adapted so as to be supplied with approx. 5-15% of the generator power. 6. Generating plant according to claim.3 or 4, c h a r a c t e r i s e d i n that electric motors, pumps, compressors, ventilating . and cooling systems etc. are connected to the. first ' supply mains, and that navigation and communication systems, steering engine, lighting and similar installations requiring constant voltage and frequency are connected to the second mains. OMPI

Inventors: FOURNAIS PETER JAN, FOURNAIS, PETER, JAN
Applicants: FOURNAIS PETER JAN, FOURNAIS, PETER, JAN
Application year: 1982
Main classification: B63J3
IPC codes: B63J3, H02P9