Study of Starting Processes of Ship s Electrical Thruster

Transcription

1 arine Engineering Frontiers (EF) Volume Issue 4, November 23 Stuy of Starting Processes of Ship s Electrical Thruster Nikolay Djagarov *, ilen Bonev 2, Zhivko rozev 3 * Nikola Vaptsarov Naval Acaemy, Varna, Varna, 73, Vasil Drumev Str., Bulgaria 2.3 Electrotechnical Faculty, Technical University of Varna, Varna, Str. Stuentska, Bulgaria * jagarov@ieee.bg; 2 bonevi@abv.bg; 3 grozew@yahoo.com Abstract In the present article, mathematical moel of ship s power supply system is suggeste incluing electrical thruster with autotransformer starting. With the help of the create moel the process of starting is stuie, an the results are compare with those in irect starting. The results of the simulations show the effectiveness of the autotransformer starting that improves all parameters of starting process. Keywors Bow/Aft Thruster; Auto Transformer Starting; athematical oeling; Voltage Sag; Transient Process Introuction To ensure better maneuverability in moern ships, bow trusters are wily use. The power of the asynchoronous electric motors use for riving these evices is comparable to the power of generators. The starting process for these motors is very important for the electric rive as well as for the ship s power supply system. The electric motors are starte in the presence of significant loa on the shaft when the starting current an torque reach maximum values an excee times their nominal values. This causes overloa of synchronous generators, a failure of the main voltage in the net an istortion of normal operation of the ship's electrical loas. The voltage ip coul reach 4% or more. The rotating torque of inuction motors is proportional to the square of supply voltage, so the starting perio an voltage ip continue unacceptably long. To overcome these negative effects, ifferent methos are use to ensure lowere voltage at starting perio. The most commonly use metho is switching of stator wining from primary circuit Y into work circuit, where the supply phase voltage an phase current is reuce 3 an line currents 3 times. oreover, uring the launch into the stator circuit can be inclue aitional active or inuctive resistances. Switching of supply is also utilize through stepown autotransformer having multiple levels of switching. The metho of soft starter can be also useby means of static converter moifying the supply voltage/frequency at specific law, besies both phase an frequency regulation can be use. Common isavantages of these methos are the significant reuction of starting an maximum torque of the electric motor. Switching Y- is use in electrical rives with very little loa, besies by this switching peaks of current an torque arise. The magnitues of these peaks epen on the electrical motor magnitue an phase. By means of resistors in a stator wining big losses arise an great heat is exue from the starting current, so this metho is not use in high inertia loas. The autrotransformer start reuces the peaks of both current an torque, but the number of levels is limite an this metho fails to achieve high precision of control. In contrast to the switching Y-, the previous processes are close only insie in autotransformer thereby the peaks of current an torques are absent. By this metho, the time is reuce at all spees an at high time constant of the loa the time of transition processes may be greater. Soft start ensures smooth variation of voltage an current. The isavantage of the soft start is the relatively high cost of the converter an the creation of harmonic components into the motor supply voltage an in the current rawn from the network. In the present article, the starting processes of ship s thrusters are stuie with electrical rive in ship s power supply system at reuce voltage. This reuce voltage is obtaine by autotransformer. This is one of the cheapest an most effective methos use for this purposes. The main purpose of the present stuy is to create mathematical moel with which help the regime of starting of ship s truster by ifferent levels of the supply voltage variation an obtaining information for amenment of the basic parameters of the regime. 75

2 arine Engineering Frontiers (EF) Volume Issue 4, November 23 Diagram of Stuie Ship s Power Electrical Plant an Examinate Regimes On Fig., the iagram of stuie power elec-trical system is shown incluing iesel generator 3,33VA with it's automatic spee an voltage regulators (overnor), static active-inuctive loa, step-up transformer 2,6VA 44/66 V, autotransformer 2W an bow thruster with asynchronous inuction with motor 2W. Autotransformer (Fig. 2) using contactors K, K2 an K3 switches the supplie voltage to the inuction motor on three stages 65/85/% from nominal voltage. FI. 2 DIARA OF AUTOTRANSFORER athematical oel of Stuie Power System For creation of mathematical moel of stuie power system, non-iterative metho is use for calculation of transient electromechanical processes in electroenergetic FI. DIARA OF STUDIED POWER ELECTRICAL SYSTE systems, as suggeste in [2]. The moels of the system s components (generator, inuction motor, the static loa, step-up transformer an autotransformer) are written as ifferential equations in the Cauchy form with respect to their currents. oreover, the moels are written in a coorinate system, which rotates synchronously with the rotor of the generator. Bus voltages of the main switchboar (main switch-boars) are calculate using Kirchhoff's first law in ifferential form. oel of Synchronous enerator In matrix form, the moel of the synchronous generator will have the following shape: Is Ass Asr Is Bss Bsr U SB.. t = + = Ir Ars Arr Ir Brs Brr u f Hs Bss Bsr U SB = +. ; () Hr Brs Brr u f ω k = ( T m+ T) ; t τ m where subscript s refers to the stator parameters an variables, an subscript r - rotor; the elements of matrices an vectors A an В are in function of the stator an rotor resistance an inuctive impeance an the rotor angular spee q,, ω k ; T m - iesel engine torque; - the generator electromagnetic T torque; τ m - the turbine an generator mechanical time constant; u f - fiel voltage; U SB - vector of SB voltage. 76

3 arine Engineering Frontiers (EF) Volume Issue 4, November 23 i f I s i = ; I r = i g ; H s h = ; i i h h b u B ss = ; U SB =. b22 u q oel of Inuction otor In matrix form, the moel of the inuction motor will have the following shape: Is Ass Asr Is Bss..U SB t = + = Ir Ars Arr Ir Brs H B = +.U ; s ss Hr Brs SB r ( T Tb) t ω = ; τ m where subscript s refers to the stator parameters an variables, an subscript r - rotor; the elements of matrices an vectors A an В are in function of the stator an rotor resistance of motor an inuctive impeance an the rotor angular spee q,, ω k ; U SB - vector of SB voltage, τ m - the mechanical time constant of bow thruster, T b - mechanical breaking moment of bow thruster, T - electromagnetical torque of motor. I s i = ; H i oel of Static Loa s h = ; B h ss b =. b22 In matrix form the moel of the inuction motor will have the following shape: IL = A L.IL + B L.USB = HL + B L.USB ; (3) t where the elements of the matrixes A an B are function of inuctive an active resistance of loa an the angular spee of coorinate system q,, - ω k L i L h L b I L = L ; HL = L ; BL = L. i h b22 oel of Transformer an Autotransformer The step-up transformer an autotransformer are replace by their full active an inuctive resistances of ispersing inclue into moel of inuction motor. The control of switching of the autotranformer through contactors K, K2 an K3 is simulate by moifying the voltage on the output of the (2) autotransformer. oel of Distribution Network By the aopte moels of elements of stuie power system, it can be observe that the voltage vector of main switch boar is unknown. Its calculation is one using Kirchhoff's first law in ifferential form. m. Is + ml.i L + m. Is = ; (4) t t t where: m = S / S, ml = SL / S, m = S / S - scale factors, calculate as the ratio of the total power of the item to the full power of the generator. Substituting (4) erivatives of the currents through the right parts of the equations (), (2) an (3): m. + m..u + m.h + m.b.u + Hs Bss SB L L L L SB m. Hs m. Bss.USB + + = Then (5) can be transforme in terms of the unknown vector of SB voltage: m. Hs + ml.h L + m. Hs USB =. (6) m. B + m.b + m. B ss L L Algebric system of equations (6) allows calculating non-iterative SB voltage, reucing many times the necessary machine time for research. Stuy of Starting Process of Bow Thruster The starting processes of bow thruster by autotransformer is simulate an the results are compare with those of irect starting. The below figures show the results from performe simulation. The start of motor takes place in t = s an the switching of autotransformer - at t = 4,6,7s respectively. Inuction otor Voltage [p.u] Voltage I.2 I Voltage (Autotr. Starter) I Voltage (Direct Starter) FI. 3 INDUCTION OTOR VOLTAE ss (5) 77

4 arine Engineering Frontiers (EF) Volume Issue 4, November 23 Inuction otor Rotor Spee [p.u] Rotor Spee I Rotor Spee (Autotr. Starter) I Rotor Spee (Direct Starter) Rotor Spee [p.u] echanical Characteristic Electromagnetic Torque [p.u] Inuction otor Current [p.u] Inuction otor Electromagnetic Torque [p.u] FI. 4 ANULAR ROTOR SPEED OF INDUCTION OTOR Current I I Current (Autotr. Starter) I Current (Direct Starter) FI. 5 INDUCTION OTOR CURRENT Electromagnetic Torque -.6 I Electromag.Torque (Autotr. Starter) I Electromag. Torque (Direct Starter) FI. 6 ELECTROANETICAL TORQUE OF THE INDUCTION OTOR FI. 7 ECHANICAL CHARACTERISTICS OF THE INDUCTION OTOR BY AUTOTRANSFORER STARTIN Rotor Spee [p.u] echanical Characteristic Electromagnetic Torque [p.u] FI. 8 ECHANICAL CHARACTERISTICS OF THE INDUCTION OTOR BY DIRECT STARTIN Rotor Spee [p.u] Spee Characteristic Current [p.u] FI. 9 SPEED CHARACTERISTICS OF THE INDUCTION OTOR BY AUTOTRANSFORER STARTIN 78

5 arine Engineering Frontiers (EF) Volume Issue 4, November 23 Spee Characteristic.6 S echanical Power Rotor Spee [p.u] Current [p.u] FI. SPEED CHARACTERISTICS OF THE INDUCTION OTOR BY DIRECT STARTIN Voltage [p.u] S Voltage S echanical Power [p.u] Delta [eg] S echanical Power (Autotr. Starter) S echanical Power (Direct Starter) FI. 3 ECHANICAL POWER OF SYNCHRONOUS ENERATOR S Delta S Rotor Spee [p.u] S Voltage (Autotr. Starter) S Voltage (Direct Starter) FI. SB VOLTAE S Rotor Spee Uf [p.u] S Delta (Autotr. Starter) S Delta (Direct Starter) FI. 4 LOAD ANLE OF SYNCHRONOUS ENERATOR S Exciting Voltage.994 S Rotor Spee (Autotr. Starter).992 S Rotor Spee (Direct Starter) FI. 2 ANULAR SPEED OF SYNCHRONOUS ENERATOR S Uf (Autotr. Starter) S Uf (Direct Starter) FI. 5 EXCITIN VOLTAE OF SYNCHRONOUS ENERATOR On the presente iagrams, the amenment of basic 79

6 arine Engineering Frontiers (EF) Volume Issue 4, November 23 parameters of regime is shown: voltage, rotating spee, current an electromagnetic moment of inuction motor; voltage, rotating spee, mechanical power, loaing angle an inuction of synchronous generator. The mechanical an spee characteristics of the motor are shown. The experimental results obtaine as a result of stimulation show the effectiveness of autotransformer starting of electric thruster. The failure of voltage is significantly reuce, the time of acceleration of motor is reuce an the starting current of the motor is ecrease. Conclusions The starting process on the ship's electrical thruster causes failure of the mains voltage, which isturbs the work of other consumers, an of the evice itself. Non-iterative mathematical moel of ship s power electrical system is create incluing electric thruster performing autotransformer starting. The obtaine experimental results from the computer simulation of electric thruster starting show its efficiency. The create moel can be use for esigning of electric thrusters an their control. REFERENCES Djagarov Nikolay F., A etho of Transient Electromechanical Processes oeling in Power Systems, 29 IEEE Bucharest Power Tech Conference, June 28th - July 2n, Bucharest, Romania, 6 p. Djagarov Nikolay F., Ships Electrical Power Systems, Technical University of Varna, 997, 424 p. celveen Robbie F., an Toney ichael K., Starting High- Inertia Loas, IEEE Transactions on Inustry Applications, Vol.37, No., Jan/Feb, 2, pp Recommene Practice for Excitation System oels for Power System Stability Stuies IEEE Stanar , August, 992. Starting High Inertia Loas:. A Comparison of Starting Options, Trens in otor anagement, Rockwell Automation, Allen-Braley, Publication April /get/4793/ Yeager, K.E., an J.R.Willis, oeling of Emergency Diesel enerators in an 8 egawatt Nuclear Power Plant, IEEE Transactions on Energy Conversion, Vol. 8, No. 3, September, 993. Nikolay F. Djagarov was born in Bulgaria in 948. He receive the.eng, Ph.D an Dr.Sc egrees in electrical engineering from The Saint- Petersburg State Electrical University, Russia, in 972, 978 an 994, respectively. From 972 to 975, he worke at Varna Shipyar as ships electrical equipment esigner, Associate Professor an Full Professor in the Electrical Faculty of Technical University, Varna, Bulgaria since 979 to April 23 ( view&i=5&itemi=26). He is working in Nikola Vaptsarov Naval Acaemy Varna since April 23 as Full Professor ( orgstruktura/2fak/k- 22/NDjagarov.htm). His current research interests inclue transient process an control of power systems, FACTS - Flexible Altering Current Transmission Systems, Power quality investigation an control, Electrical rive control, oeling an Control of Renewable Power Sources. Hi is member of IEEE - Institute of Electric an Electronic Engineers member, WSEAS Worl Scientific an Engineering Acaemy an Society, ember of Eitorial Boar of WSEAS Transaction on Power Systems. ilen. B. Bonev was born in Troyan, Bulgaria on July 4, 97. He grauate from Elektrotechnical School, abrovo an stuie at the Technical University of Varna. His employment experience inclues the Varna Port as hea of Electrical Engineers an Technical University of Varna as assoc. professor. Bonev receive Ph.D egree Technical University of Varna of subject Aaptive Stabilizers for Autonomous Power Systems. His current research interests inclue transient process an control of power systems, FACTS - Flexible Altering Current Transmission Systems, Power quality investigation an control, Electrical rive control, oeling an Control of Renewable Power Sources. Hi is member of IEEE - Institute of Electric an Electronic Engineers memberan is working in Technical University of Varna as Assiatant Professor since 28. ( view&i=2&itemi=26). Zhivko. rozev was born in Varna, Bulgaria on January 24, 975. He grauate from Elektrotechnical School, Varna an stuie at the Technical University of Varna. His employment experience inclues the Zoiac aritime Shipping Agency as Ships Electrical Engineer an Technical University of Varna as assoc. professor. rozev receive Ph.D egree in Technical University of Varna on subject Aaptive Control of Shunt an Series System Devices for Damping of Oscillation in Autonomous Power System. His current research interests inclue transient process an control of 8

7 arine Engineering Frontiers (EF) Volume Issue 4, November 23 power systems, FACTS - Flexible Altering Current Transmission Systems, Power quality investigation an control, Electrical rive control, oeling an Control of Renewable Power Sources. Hi is member of IEEE - Institute of Electric an Electronic Engineers memberan is working in Technical University of Varna as Assiatant Professor since 28. ( n=com_content&task =view&i=9&itemi=26). 8