TRANSIENT STABILITY ANALYSIS ON AHTS VESSEL ELECTRICAL SYSTEM USING DYNAMIC POSITIONING SYSTEM

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 02, February 2019, pp , Article ID: IJMET_10_02_048 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed TRANSIENT STABILITY ANALYSIS ON AHTS VESSEL ELECTRICAL SYSTEM USING DYNAMIC POSITIONING SYSTEM Sardono Sarwito Doctoral Program, Department of Marine Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, 60111, Indonesia Semin Professor of Marine Engineering, Department of Marine Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, 60111, Indonesia Muhammad Badrus Zaman Department of Marine Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, 60111, Indonesia Soedibyo Department of Electrical Engineering, Institut Teknologi Sepuluh Nopember, Surabaya, 60111, Indonesia ABSTRACT The addition of dynamic positioning system on offshore auxiliary vessels leads to the installation of a large powered bow thruster. Unpredictable fieldwork conditions lead to uncertain loading. Changes in electrical system configuration and load shedding scheme are just a few of the many ways to maintain electrical system stability. This method is done in order to balance the generator mechanical power generated with the load needs. The configuration changes has been made and the result was that the closed bus of 2 generator thruster and 2 diesel generator configurations have excellent stability that can reach stable conditions with 110% loading on each bow thruster. While Rhe closed bus configuration of 1 thruster generator and 2 diesel generator provides an opportunity to rest 1 generator thruster to save generator usage. However, the stability of this configuration can be improved by conducting a load shedding scheme Keywords: Dynamic positioning system, transient stability, system configurations, load shedding editor@iaeme.com

2 Transient Stability Analysis on AHTS Vessel Electrical System using Dynamic Positioning System Cite this Article: Sardono Sarwito, Semin, Muhammad Badrus Zaman and Soedibyo, Transient Stability Analysis on AHTS Vessel Electrical System using Dynamic Positioning System, International Journal of Mechanical Engineering and Technology, 10(2), 2019, pp INTRODUCTION Anchor Handling Tug Supply (AHTS) vessel is a ships that assigned specifically to support offshore work generally required to install a system that make them different from any other ships [1]. Reviewing the field conditions and the level of accuracy needed at work, the ships must be equipped with a dynamic positioning system, a system that serves to control the ship movement [2]. Uncertain field condition correspond to environmental factor can cause a system to run into failure, more over on a ship which used closed bus configuration [3]. This failure can be cause by some interference, whether it is short term (transient) or interruption which has longer disturbance time. An electrical system is prone to interference, therefore the system needs to have the ability to maintain its sync condition. This ability is called transient stability. This transient stability disturbance can occur on ships equipped with dynamic positioning system in case of overload on one generator, motor starting, and also short circuit on component. The addition of a large powered bow thruster can affect system stability if the system does not have resistance to transient disturbances that are temporary. In the event of a transient disturbance and the system cannot maintain its stability, there has been be a loose synchronization of the generator and more fatal has been cause failure of the electrical system [3]. Objective of this paper is to analyze the transient stability on AHTS vessel electrical system using dynamic positioning system. The study of transient stability has been provided an assessment of the stability of the ship's electrical system so that practitioners can find a way out of the problem. Some ways to prevent the occurrence of stability problems is to change the system configuration and also by conducted load shedding when the motor with a large power has been do the starting. 2. POWER SYSTEM STABILITY 2.1. Vessel with Dynamic Positioning System s Electrical Stability In general, a ship that equipped with a DP system possess much larger numbers of thruster than vessel that not equipped with DP systems. The addition of this thruster resulted in a significant increase in electrical load so it is necessary to add an extra electrical power source to the vessel. The classification of the DP system differentiates the system into 3 classes, one of which is in terms of system redundancy [2]. This difference results in different configurations of power systems on board equipped with a DP system to minimize the risk of system failure due to interference with the power system [2]. In general, the ship has an electrical system with a closed bus configuration, a configuration that can put all buses in connected state. The point is an electrical system that allows one and more power plants to supply all loads on the ship. To maximize fault tolerance in DP systems, electrical systems are designed generally separately (islanded) to reduce the possibility of system disruption due to a single error. Unlike systems designed to use closed editor@iaeme.com

3 Sardono Sarwito, Semin, Muhammad Badrus Zaman and Soedibyo buses, the design of a split bus configuration has been impact only on the affected bus, effectively isolating the problem in the affected area only. The goal is to avoid system failure due to a mistake in which the entire system can experience blackouts by isolating failures on only one redundancy system [3] Definition of Stability The stability of the electric power system can be defined as the ability of the electric power system to be in normal condition when interference occurs [4]. Based on the IEEE Transactions On Power Systems paper entitled Definition and Classification of Power System Stability, the stability of the electric power system is categorized into three (1) Voltage stability; (2) Frequency stability; (3) Rotor angle stability. Figure 1 Classification of Stability [4] Voltage Stability Voltage stability is the ability of the power system to maintain the voltage conditions on all buses in order to remain stable after an interruption. Voltage stability is related to the ability of the system to maintain the stability between the supply of the power plant and the load requirements on the vessel. Disturbance in the voltage usually occurs due to the release of a significant load resulting a voltage drop. The stability of this voltage is influenced by large and small disturbances in the short and long term.[5] Major disruptions for example are loss of generation or lost synchronization of the generator and short circuit on the system. While minor disturbances are like the addition of small-scale load so the system seeks to improve itself Frequency Stability Frequency stability is related to the ability of the power system to maintain steady-state frequencies with a nominal range following some system disturbances due to the imbalance between the plant and the load. This is dependent on restoring the balance between load and generating systems by minimizing the amount of discharges / losses. The frequency condition must be stable to keep the system from losing sync [5]. Frequency stability can occur in the short and long term. For the short term usually the imbalance occurs due to changes in loads that cannot be adjusted by the generator. While long-term disturbance is the loss of governor's control ability editor@iaeme.com

4 Transient Stability Analysis on AHTS Vessel Electrical System using Dynamic Positioning System Rotor Angle Stability Rotor angle stability is the stability associated with synchronous machine capability (in this case the generator) connected to the power system to remain in sync condition after interruption. The stability of the rotor angle depends on the ability to restore the equilibrium between the electromagnetic torque and the mechanical torque of each machine on the system. The instability can cause an increase in the angle of the swing on the generator resulting in losing synchronization with other generators. The stability of the rotor angle is divided into two, namely the stability of the small disturbance (steady state) and the stability of the transient state.[5-8]. According to the study of transient stability has a period of 3-5 seconds after interference. As for the stability of small disturbances havea period of seconds after the interference 2.3. Standards Related to Transient Stability Analysis of transient stability in AHTS ship electrical system with dynamic positioning system is done by using simulation software to find out system response when transient disturbance occurs. Regulations on system stability have been issued by international agencies and used as reference by related industries. International standards concerning the limits of operating voltage on electrical systems have been issued by IEEE standard 1195 as follows: Figure 2 Standard operating voltage limits of transient stability [4] While in the marine industry, the government authority of this standard is the classification body (classification society). Some countries have their own classification society and have standards that refer to international standards. The AHTS BNI Castor ship that became the object of this final project is an Indonesian-flagged vessel sailing in Indonesian waters, the vessel is regulated by Indonesia's classification society BKI (Badan Klasifikasi Indonesia). Given that the ship was built to the ABS issued standard (American Bureau of Shipping), that is to say, it has a double class of BKI and ABS. The standards governing the limits of voltage and frequency operations in both transient conditions and their stable conditions are listed in ABS Rules Part 4: Vessel Systems and Machinery Chapter 8 Section 3 in the table below [6] editor@iaeme.com

5 Sardono Sarwito, Semin, Muhammad Badrus Zaman and Soedibyo Table 1 Variations of Frequency and Voltage According to American Bureau of Shipping Standard Quantity in Operation Voltage and Frequency Variations for AC Distribution Systems Permanent Transient Variations (Recovery Variations Time) Frequency ±5% ±10% (5s) Voltage +6%, -10% ±20% (1.5s) 3. METHOD Before performing a transient stability simulation using the software, a single line diagram of the AHTS vessel must exist as a reference for performing redrawing in the software. Referring to the single line diagram, a system replication is drawed in the simulation software according to the equipment specifications contained in the wiring diagram. After the system is fully illustrated, the simulation of transient stability can be done by using Transient Stability module in the software. The results obtained from the simulation is the data in the form of voltage and frequency per time unit. This data has been then be processed and analyzed so that the assessment of the stability of the system can be done. The simulation was run by conducting 2 study cases, motor starting and load shedding action. The system later to be set into 6 different scenarios of configuration stated on the Table 2. and by performing load shedding in the last scenario due to its configuration that allows system to put 1 generator on standby. The load shedding scheme was done to improve the system stability into its maximum ability. Table 2 Simulations Scenarios Scenario Power Supply Load Load Variations 1 2 Generator Thruster (Split Plant) 2 Bow Thruster 60% - 75% 100% - 80% 100% - 100% 110% - 110% 2 2 Generator Thruster (Closed Bus) 2 Bow Thruster 60% - 75% 100% - 80% 100% - 100% 110% - 110% 3 1 Generator Thruster (Split Plant) 2 Bow Thruster 40% - 40% 50% - 50% 60% - 60% Generator Thruster, 1 Diesel Generator (Closed Bus) 2 Generator Thruster, 2 Diesel Generator (Closed Bus) 1 Generator Thruster, 2 Diesel Generator (Closed Bus) 1 Generator Thruster, 2 Diesel Generator (Closed Bus) with Load Shedding 2 Bow Thruster & Ship Equipment Load 2 Bow Thruster & Ship Equipment Load 2 Bow Thruster & Ship Equipment Load 2 Bow Thruster & Essential Load 60% - 75% 100% - 80% 100% - 100% 110% - 110% 60% - 75% 100% - 80% 100% - 100% 110% - 110% 75% - 75% 80% - 80% 85% - 85% 80% - 80% 85% - 85% 90% - 90% editor@iaeme.com

6 Transient Stability Analysis on AHTS Vessel Electrical System using Dynamic Positioning System 4. RESULT AND DISCUSSION To get an electrical system that has high stability, there are several ways that can be done. In this final project has been be simulated changes in electrical system configuration and also designing the load shedding scenario to improve the stability of electrical system. A case study designed to assess the stability of a system is a starting bow thruster that has high power in various configurations that may be applied in the system. Configuration scenarios and variations of bow thruster loading can be seen in Table 2. The results of the following simulations are summarized per scenario as shown in Table 3 and so on. Table 3 Voltage and Frequency Responses of Scenario 1 Bus C Summary No Variation f min f steady state Simulation 1 Bus v min v max v steady state Condition f v 1 60% - 75% 97,513 97,513 C 98, ,286 99,9106 Normal Normal 2 100% - 80% 95, ,8057 C 96, ,043 99,7611 Normal Normal 3 100% - 100% 95, ,8057 C 96, ,043 99,7611 Normal Normal 4 110% - 110% 95, ,3122 C 77, ,297 - Normal Drop Voltage and frequency response in the split plant configuration scenario 1 thruster generator for each bow thruster shows that all load variations up to 100% load on the bow thruster can be borne by the system stably. Over 100% loading on each bow thruster results in stability of the system being disrupted. This is because the thruster generator can only provide power reserves for the start of the generator up to 100% load, above that value the generator cannot provide enough starting from the bow thruster. Figure 3 Voltage Response of Scenario 1 Variation 4 On bus C, transient conditions occur due to starting bow thruster where the voltage experienced up and down from seconds to 2.01 then tend to be decreased dramatically to the value of 77.14% in seconds to 3.21 and then jumped dramatically to the point of 140.3% in seconds to This condition does not conform to the ABS standard which states that the tolerance of the voltage values under transient conditions is only allowed up to 20% above or under stable conditions as well as recovery time of 1.5 seconds cannot be satisfied by the system. In addition, the system also cannot reach a stable state because the voltage continues editor@iaeme.com

7 Sardono Sarwito, Semin, Muhammad Badrus Zaman and Soedibyo to oscillate between the values of % and 88.82% during the simulation. While on the bus D, there is a similar transient condition due to starting bow thruster where the voltage experienced up and down from seconds to 2.01 then tend to be decreased drastically to the value 77.14% in seconds to 3.21 and then jumped dramatically to the point % in seconds to This condition does not conform to the ABS standard which states that the tolerance of the voltage values under transient conditions is only allowed up to 20% above or under stable conditions as well as recovery time of 1.5 seconds cannot be satisfied by the system. In addition, the system also cannot reach a stable state because the voltage continues to oscillate between the values of % and 88.82% during the simulation. Figure 4 Frequency Response of Scenario 1 Variation 4 Frequency response on bus C indicates the existence of transient conditions due to the starting bow thruster where the frequency decreased up to the value of 95.31% and directly stable at that value. The value is still in accordance with the standards allowed so the system is still allowed to operate. While the frequency response on bus D indicates the existence of transient conditions due to starting bow thruster where the frequency decreased up to the value of 95.31% and directly stable at that value. The value is still in accordance with the standards allowed so the system is still allowed to operate. Table 5 Voltage and Frequency Responses of Scenario 2 Summary No Variation f min f steady state Simulation 2 Bus v min v max v steady state Condition f v 1 60% - 75% 97,196 97,196 C,D 98, ,508 99,8 Normal Normal 2 100% - 80% 96, ,2364 C,D 98, ,97 99,8 Normal Normal 3 100% - 100% 95, ,8057 C,D 96, ,043 99,7 Normal Normal 4 110% - 110% 95,294 95,3312 C,D 77, ,297 - Normal Drop Voltage and frequency response in the split plant configuration scenario 2 thruster generators for 2 bow thruster shows the same result with the first configuration that all load variations up to 100% load on the bow thruster can be borne by the system stably. Over 100% loading on each bow thruster results in stability of the system being disrupted. This is because the paralleled thruster generator can only provide power reserves for the start of the generator up to 100% load, above which the generator cannot provide enough starting from the bow editor@iaeme.com

8 Transient Stability Analysis on AHTS Vessel Electrical System using Dynamic Positioning System thruster. This happens because the ratio of the amount of power generators can generate with the data required by the load is still the same as in the previous configuration. Figure 5 Voltage Response of Scenario 2 Variation 4 In the connected bus there is a transient condition due to the starting bow thruster where the voltage rises up from seconds to 2.01 then ten to be decrease drastically to the value of 77.14% in seconds to 3.21 then jumped dramatically to the point of 140.3% in seconds to This condition does not conform to the ABS standard which states that the tolerance of the voltage values under transient conditions is only allowed up to 20% above or under stable conditions as well as recovery time of 1.5 seconds cannot be satisfied by the system. In addition, the system also cannot achieve a stable state because the voltage continues to oscillate between the values of % and 88.66% during the simulation. Figure 6 Frequency Response of Scenario 3 Variation 4 Frequency response on the bus that connected indicate the existence of transient conditions due to starting bow thruster where the frequency decreased up to the value of 95.33% and directly stable at that value. The value is still in accordance with the standards allowed so the system is still allowed to operate. Table 6 Voltage and Frequency Responses of Scenario 3 Summary No Variation f min f steady state Simulation 3 Bus v min v max v steady state Condition f v 1 40% - 40% 96, ,6644 C, D 98, ,811 99,8 Normal Normal 2 50% - 50% 95, ,8057 C, D 96, ,043 99,7 Normal Normal 3 60% - 60% 95, ,3721 C, D 7, ,03 99,7 Normal Drop editor@iaeme.com

9 Sardono Sarwito, Semin, Muhammad Badrus Zaman and Soedibyo Configuration of split plant 1 thruster generator to bear 2 bow thruster arranged to achieve the purpose of saving the use of generator. However, the two connected C and D buses are split with buses A and B supplied by diesel generators. In this scenario we get 1 thruster generator savings of 800 kw, but due to power cuts of 800 kw, the loading on the bow thruster cannot be maximized. The voltage and frequency response in this configuration indicates that the system can only maintain stable conditions up to 50% loading on each bow thruster. This is actually in line with the two previous configurations because the power supply comparison and load requirements show the same value. In the two previous configurations the total supply is 1600 kw with 1030 kw of power requirement, whereas in this configuration the total supply is 800 kw with a power requirement of 515 kw. Figure 7 Voltage Response of Scenario 3 Variation 3 In the connected C and D buses, there is a transient condition due to the starting bow thruster where the voltage undergoes a considerable ups and downs before reaching a high of % at 3.41 seconds and the lowest 7.09% at 4.01 seconds oscillations between values of % to 93.56%. Then the system can reach steady state condition at 99.7%. In this condition, the voltage deviation is not in accordance with the ABS standard which states that the tolerance of the voltage value under transient conditions is allowed up to 20% above or under stable conditions, the system cannot meet the recovery time of 1.5 seconds so that the system continues to experience voltage oscillations before reaching a stable condition at 30 seconds. Figure 8 Frequency Response of Scenario 3 Variation 3 Frequency response on bus C and connected bus D indicates a transient condition due to the starting bow thruster where the frequency decreases up to 95.37% and is directly stable at editor@iaeme.com

10 Transient Stability Analysis on AHTS Vessel Electrical System using Dynamic Positioning System that value. The value is still in accordance with the standards allowed so the system is still allowed to operate. Table 7 Voltage and Frequency Responses of Scenario 4 Summary Simulation 4 No Variation f min f steady state Bus v min v max v steady state Condition f v 1 60% - 75% 98, ,1305 A,B,C,D 98, ,402 99,8 Normal Normal 2 100% - 80% 97, ,4944 A,B,C,D 97, ,394 99,7 Normal Normal 3 100% - 100% 97, ,2089 A,B,C,D 96, ,285 99,7 Normal Normal 4 110% - 110% 96, ,9208 A,B,C,D 89, ,223 - Normal Drop Configuration of closed bus 2 thruster generator with 1 diesel generator is designed by connecting all buses on the system with the supply of 3 generators. This configuration saves the use of 1 diesel generator of 350 kw. Power supply cuts of 350 kw did not significantly affect the total load of bow thruster. Voltage and frequency response of all variations indicates that the system is still categorized as stable up to 100% loading on each bow thruster. However in the 110% load variation the system is classified as unstable from being unable to meet recovery time. The voltage and frequency response drift in this configuration is still relatively safe, but long time to bear the voltage oscillation can cause the accumulation of heat on the equipment so it can be categorized as unsafe for electrical equipment. Figure 9 Voltage Response of Scenario 4 Variation 4 On the connected bus there is a transient condition due to the starting bow thruster where the voltage rises down from seconds to 2.01 until it touches the lowest point at 89.77% in seconds to 3.01 then and the highest point at % at second to For voltage rise and fall values are still allowed according to the ABS standard which states that the tolerance of the voltage values under transient conditions is allowed up to 20% above or under stable conditions, but the system cannot meet the recovery time of 1.5 seconds so the system continues to experience the voltage oscillation throughout the simulation. In addition, the system also cannot achieve a stable state because the voltage continues to oscillate throughout the simulation with a value between 106.1% and 94.08% even though near the end of the simulation this deviation becomes smaller with a value between % and 99.26% editor@iaeme.com

11 Sardono Sarwito, Semin, Muhammad Badrus Zaman and Soedibyo Figure 10 Frequency Response of Scenario 4 Variation 4 The frequency response on the connected bus indicates a transient condition due to the starting of bow thruster where the frequency decreases to 96.92% and is directly stable at that value. The value is still in accordance with the standards allowed so the system is still allowed to operate. Table 8 Voltage and Frequency Responses of Scenario 5 Summary No Variation f min f steady state Simulation 5 Bus v min v max v steady state f Condition v 1 60% - 75% 98, ,6037 A,B,C,D 98, ,314 99,8 Normal Normal 2 100% - 80% 98, ,1312 A,B,C,D 98, ,524 99,8 Normal Normal 3 100% - 100% 97,92 97,92 A,B,C,D 97, ,548 99,8 Normal Normal 4 110% - 110% 97, ,7082 A,B,C,D 97, ,309 99,7 Normal Normal The configuration of the closed bus 2 thruster generator with 2 diesel generators is designed by connecting all buses on the system with the supply of 4 generators. The voltage and frequency response in this configuration is the best compared to the previous configuration scenario because this configuration can maintain its stability up to 110% loading on each bow thruster. This configuration can be used if you want to get maximum loading from the bow thruster. Figure 11 Voltage Response of Scenario 5 Variation editor@iaeme.com

12 Transient Stability Analysis on AHTS Vessel Electrical System using Dynamic Positioning System On the connected bus, a transient condition occurs due to the starting bow thruster where the voltage rises and then falls within 0.6 seconds with the highest value of % at 2.01 seconds and the low of 97.51% at 2.61 seconds later can reach steady state condition at 99,7%. In this condition the voltage deviation value and its stable condition have met the standard so that this condition can be classified as stable. Figure 12 Frequency Response of Scenario 5 Variation 4 The frequency response on the connected bus indicates a transient condition due to the starting bow thruster where the frequency decreases up to 97.71% and is directly stable at that value. The value is still in accordance with the standards allowed so the system is still allowed to operate. Table 9 Voltage and Frequency Responses of Scenario 6 Summary No Variation f min f steady state Simulation 6 Bus v min v max v steady state Condition f v 1 75% - 75% 97, ,9151 A,B,C,D 96, ,653 99,7 Normal Normal 2 80% - 80% 97, ,7734 A,B,C,D 95, ,648 - Normal Drop 3 85% - 85% 97, ,6 A,B,C,D 77, ,906 - Normal Drop Configuration of closed bus 1 thruster generator with 2 diesel generator is designed by connecting all buses on the system with the supply of 3 generators. This configuration saves the use of a thruster generator of 800 kw. In contrast to the third configuration, a power supply cut of 800 kw can be covered because it is aided by the backup power of 2 diesel generators. The voltage and frequency response of all load variations indicates that the system can maintain its stability up to 75% loading on each bow thruster. This value is 25% larger than the configuration scenario 3 because the backup power to accommodate the starting bow thruster is available from 2 diesel generators. Over 75% loading on each bow thruster causes the system to become unstable editor@iaeme.com

13 Sardono Sarwito, Semin, Muhammad Badrus Zaman and Soedibyo Figure 13 Voltage Response of Scenario 6 Variation 3 On the connected bus transient conditions occur due to starting the bow thruster where the voltage experienced up and down from seconds to 2.01 to touch the lowest value at the point 77.93% in seconds to 4.21 then the highest value at the point % in seconds to In this condition, the voltage deviation is not in accordance with the ABS standard which states that the tolerance of the voltage values under transient conditions is allowed up to 20% above or under stable conditions, the system cannot meet the recovery time of 1.5 seconds so the system continues to experience the voltage oscillation until the end of the simulation even though the deviation value decreases. Figure 14 Frequency Response of Scenario 6 Variation 3 Frequency response on the connected bus indicates a transient condition due to the starting bow thruster where the frequency decreases up to 97.62% and is directly stable at that value. The value is still in accordance with the standards allowed so the system is still allowed to operate. Table 10 Voltage and Frequency Responses of Scenario 7 Summary No Variation f min f steady state Simulation 7 Bus v min v max v steady state Condition f v 1 80% - 80% 98, ,5969 A,B,C,D 98, ,051 99,8 Normal Normal 2 85% - 85% 98, ,4567 A,B,C,D 98, ,051 99,8 Normal Normal 3 90% - 90% 98, ,3163 A,B,C,D 97, ,051 99,8 Normal Normal editor@iaeme.com

14 Transient Stability Analysis on AHTS Vessel Electrical System using Dynamic Positioning System The configuration in this scenario is the same as configuration 6 but continues with a non-essential load-loaded load. This load release is done to provide backup power to meet the starting bow thruster requirement. The voltage and frequency response of this scenario indicates that the system has grown by 15% from 70% to 90%. This condition is achieved because the power obtained from the load release can be sufficient for starting bow thruster up to 90% loading on each bow thruster. Any loading above 90% has been cause the system to become unstable. Figure 15 Voltage Response of Scenario 7 Variation 3 The load shedding is done simultaneously with the starting bow thruster at 2 seconds with simulation time of 60 seconds. Visible changes from the previous results of the system only experienced up and down the voltage for 0.6 seconds with the highest value of % in the second second and the lowest value of 97.98% in seconds to 2.61 and then reached a stable state on the value 99.8%. This value is categorized as stable by ABS standards and allowed to operate. Overall a system with a configuration of 1 thruster generator and 2 diesel generators can tolerate up to 90% loading on each bow thruster. Figure 16 Frequency Response of Scenario 7 Variation 4 Frequency response on the connected bus indicates a transient condition due to the starting bow thruster where the frequency decreases up to 98.32% and is directly stable at that value. The value is still in accordance with the standards allowed so the system is still allowed to operate editor@iaeme.com

15 Sardono Sarwito, Semin, Muhammad Badrus Zaman and Soedibyo 5. CONCLUSION Based on the research results that have been done, it can be taken some conclusions as follows: (1) Modeling of AHTS ship's electrical system yields 6 different configuration scenarios, ie split plant 2 thruster generator to supply 2 separate bow thruster, split plant 2 thruster generator to supply 2 bow thruster in parallel, split plant 1 thruster generator to supply 2 bow thruster, closed bus 2 thruster generator and 1 diesel generator to supply all the load on the ship, closed bus 2 thruster generator and 2 diesel generator to supply all the load on the ship, and closed bus 1 thruster generator and 2 diesel generator to supply all the load on the ship. (2) From 6 scenarios of AHTS vessel system configuration configuration with dynamic positioning system under DP manouvering condition, closed bus configuration scenario 2 thruster generator with 2 diesel generator can bear 2 bow thruster load up to 110%. This condition can be achieved because the availability of power for the starting motor bow thruster becomes larger due to the addition of 2 diesel generators. While the generator usage savings materialized in the configuration scenario of closed bus 2 thruster generator and 1 diesel generator and configuration of closed bus 1 thruster generator and 2 diesel generator. In the configuration scenario of closed bus 2 thruster generator and 1 diesel system generator stable until 100% loading on each bow thruster, while in scenario 1 thruster generator and 2 diesel system generator stabilized up to 75% loading on each bow thruster. (3) In the closed bus configuration scenario of 1 thruster generator and 2 diesel generator, the system stability can be improved by non-essential load shedding on the system. The results can be seen in scenario 7 release load, seen the progress of the system stability increased up to 90% loading on each bow thruster. REFERENCE [1] G. Ritchie, Offshore support vessels: a practical guide, 1st. ed. London: The Nautical Inst, [2] IMCA, Guidelines for the design and operation of dynamically positioned vessels, IMCA, [3] M. Roa, Demonstration of fault ride through capability for closed bus operation on dynamic positioning vessels, [4] IEEE, Definition and Classification of Power System Stability IEEE/CIGRE Joint Task Force on Stability Terms and Definitions, IEEE Transactions on Power Systems, vol. 19, no. 3, pp , Aug [5] P. Kundur, Power System Stability and Control. California, CA: McGraw Hill, Inc., [6] American Bureau of Shipping, Rules for Bulding and Classing Steel Vessels, Part 4 Vessel Systems and Machinery. New York, NY: American Bureau of Shipping, [7] S Sarwito, Semin, T Hidayaturrahman. Analysis of transient response first order and second order theory in pneumatic control system using feedback instrument type PCM140. ICAMIMIA, [8] S Sarwito, Semin, M Hanif. Analysis of unbalanced load effect of three phase transformer feedback performance on the various connection windings, ICAMIMIA, editor@iaeme.com