Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… DESIGN AND CONSTRUCTION OF STAR-DELTA STARTER FOR 50HP EXTRUSION COOKER MOTOR 1 *KALUNTA,1 F. O. and ONU,2 L. I. Fabrication Technology Division, Federal Institute of Industrial Research, Oshodi, Lagos, Nigeria. 2 Works & Services Division, Federal Institute of Industrial Research, Oshodi, Lagos, Nigeria. *Corresponding author: felka3@yahoo.co.uk Abstract A major component of an extrusion cooker (also known as extruder) is the electric motor which produces the mechanical power needed to drive the main shaft of the extruder. When a highly rated motor is involved; careful design is required for maximum protection of the electric motor. This work is therefore all about the construction of a star delta starter panel required to power, protect and control the operation of a 50hp extruder motor at the Federal Institute of Industrial Research, Oshodi, Lagos, Nigeria (FIIRO). The circuit is in two parts namely – the power circuit and the control circuit. The circuit is housed in a metallic enclosure and connected to the terminals of the motor through a flexible power cable. Proper design of a motor starter for heavy duty application such as these entails guided selection of control components, assembly and wiring method. The materials used for the construction were purchased from the local market and assembled together to form a unit. The design was carried out in such a way as to minimize cost and increase the safety level. Keywords: Starter, Star-Delta, Control and Extruder Introduction A squirrel cage induction motor is the source of mechanical power which drives the extrusion cooker. It is a device that takes in electric power and converts it to rotational motion that is transmitted to the shaft via a belt or gear system. The mechanical output power and electrical input of the motor are related as follows (Moeller, 1982). P0 = 1.73VIcosфη -------------------- (1) P0 = Output power in Watts V = supply voltage in Volts I = supply current at full load in amperes Cos ф = power factor Journal of Industrial Research and Technology… η = efficiency A magnetic motor starter is a connection of button switches, contactors and protection devices in a way that is capable of opening and closing a set of contacts that energise and de-energise the supply circuit to a motor. Proper design of a motor starter requires careful selection of the control components, assembly, wiring and testing. Control components are the on-off devices that start and stop the flow of electricity to the equipment that consumes the electricity (Keith et al, 2002). The selection of these control devices is based on the motor data. Normal motor ratings are given on the motor name plate. JIRT Vol. 4 No 1, 2015 69 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… In a typical star delta starter one should note that the motor phase current which flows through the contactors is less than the supply current which flows through the circuit breaker by a factor of . Since all control components include exposed terminals; they must be enclosed in such a manner as to prevent accidental contact and the external cables must be made to enter the enclosure through cable glands to avoid injuring the cable covering. Most of the control components included in this design are electrical actuators such as manual switches, contactors, relays etc. Relays are electrically operated switches in which changing a current in one circuit switches a current on or off in another circuit (Moeller, 1982). Materials and methods Operating Principle of Star Delta Starter Star delta starting is when the motor is connected in STAR during starting sequence and allowed to accelerate to the normal running speed after which the motor is connected in DELTA. The most significant advantage of using star delta is the huge reduction in the starting current (by approximately 67%) resulting in cost savings for cables and switchgears. However, the disadvantage is in the huge reduction in starting torque of the motor (about a square of voltage reduction) resulting in increased run up time may lead to stall conditions which can damage the motor very easily (Swardt, 2007). A typical star delta starter comprises the following power components: 1. A back-up protective device, either a fuse or circuit breaker. Journal of Industrial Research and Technology… 2. 3. 4. 5. 6. Three contactors switch namely – the main, star and delta contactors. One thermal overload relay for motor protection. An on-delay timing relay meant to switch on the delta contactor after a pre-set time. Manual switches. Panel indicators. The induction motor is of high inertia and starts very slowly resulting in a high initial current. This can be reduced by starting the motor at a low voltage. The star delta starting is a reduced voltage starting. At the application of electrical supply, the main and star contactors are energised instantaneously to run the motor in star connection. This applies a voltage of 240V to the motor windings thereby lowering the starting current. Starting with reduced voltage decreases the Full Load Current (FLC) at the motor terminals in proportion to the voltage reduction while the Full Load Torque (FLT) is reduced by the square of the voltage reduction (Motorpact, 2004). After the motor has gained sufficient speed, the supply current reduces further thereby making it safe to run the motor at the normal voltage of 415V. At this time, the timing relay operates to change over from star to delta contactor, while the main contactor remains energised. In the event of any problems such as continuous overloading of the extruder, loss of phase in the supply, low level fault, the overload relay operates to cut off the supply to prevent damage to the extruder motor. One of the features of any system JIRT Vol. 4 No 1, 2015 70 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… design is to minimise damage to equipment and interruptions to the power system when electrical faults or failure occur (Robinson, 2007). Wiring Diagram The design of the motor starter and control panel begins with circuit diagrams which comprise the following: i. Power circuit diagram ii. Control circuit diagram The schematic diagrams of these two circuits are shown in fig. 1. The control devices are represented with standard symbols. There is a description legend to assist the reader in understanding of the symbols. Design Calculations The purpose of the design calculations is to determine the ratings or specifications of the various circuit components involved in the project in compliance with acceptable engineering standards. Choice of components to the exclusion quality, reliability and safety can also result in motor and machine damage and possibly catastrophic failure, human injury or death (Rocky Mountain, 2011). The engineering standards for the design of motor controls can be obtained from National Electrical Code (NEC or American standard) or, and International Electrotechnical Commission (IEC or European standard). The information Journal of Industrial Research and Technology… available on the motor nameplate forms the basis for the design of the starter circuit. Table 1 describes the exact information on the motor nameplate utilised in this project and what each item represents. With these information, one can take the following steps to carry out the design calculations. Step 1: To determine the motor full load supply amperage (FLA) For an electric motor of 50hp (or 37kW), V = 415V, Cos ф= 0.86, η = 0.9 (Moeller, 1982). Full load supply current (FLA) = 66A Full load motor winding current (FLW) = 66/1.73 = 38A Equation (1) or the nameplate values can also be applied to calculate the full load supply current. Step 2: To determine the size of branch circuit conductor required NEC 430-22 stipulates that, Conductor amperage = FLA x 125% 48A for motor winding current = 83A for motor supply current →25mm2 supply cable and 10mm2 motor cables were therefore selected. All cables used in this work are Nigerian made copper cables. JIRT Vol. 4 No 1, 2015 71 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… Figure 1: Schematic Diagram Journal of Industrial Research and Technology… JIRT Vol. 4 No 1, 2015 72 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… Table 1: Nameplate Data for the Low Cost Extrusion Cooker V I K I N G Exclusive Interpretation Nameplate Data Manufacturer VIKING exclusive Phase 3 phase JONCOD TYPE Y 160L – 4 380V 38 38 kW IP 44 Rated Voltage 380 V 50 HP CONT ∆ Rated full load 38 A 50 Hz B INS. CL amperage 1460 r/min No: 080511.30 Rated horsepower 50 hp Frequency 50Hz Rated full load speed 1460 rpm Capacitor rating - Motor terminal Delta- ∆ connection Time rating Continuous Insulation class B Ambient temperature 130oC rating Journal of Industrial Research and Technology… JIRT Vol. 4 No 1, 2015 73 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… →Also selected is contactor rating between 40A to 60A, 220V as operation coil voltage, AC3 as utilization category. The contactors were wired with 10mm2 cable. Note that the size of the contactors should carry the motor winding current. Step 3: To determine the size of branch circuit overcurrent device for back up protection Back up protection refers to protection against short circuits and ground faults. The most appropriate device is a time delay fuse or inverse time circuit breaker. These devices have both thermal and instantaneous trip features that allow the motor starting current flow for a short time without blowing the fuse. NEC 430-152 standard requires that the size of: →the inverse time circuit breaker should not exceed 250% of motor full load supply current. →the time delay fuse should not exceed 175% of motor full load supply current. This informed the choice of CB rating between 68A – 170A. Therefore, a 100A circuit breaker was selected for back-up protection. Step 4: To determine the size of motor overload protection device The choice of overload relay is based on the value of full load motor winding current which will flow through the contactors i.e. 38A. This value must fall between the chosen ranges. →Thermal overload relay of rating 30A – 40A was selected. NEC section 430-32 specifies the maximum value of the overload relay Journal of Industrial Research and Technology… rating as FLW x 115% for ambient temperature of 40 oC and service factor of 1.0. Our selection complies with this selection. Step 4: To determine the rating of timing relay According to NEC standard, short circuit or overcurrent protection devices should be oversized to handle high inrush current upon start up so as to prevent frequent nuisance tripping. This is the determining factor in the selection of a timing relay. The recommended size of inrush current is about 6 x full load = 6 x 66 = 396A This is about 400% of the size of back up fuse. Time delay fuses can hold 400% or their amp rating for about 10 to 15 seconds. The motor run up time is therefore 10 seconds, and a timing relay of range 0 – 30s is acceptable. Assembly and Wiring The assembly of the various control components in the metal enclosure to form a unit was done. The components were arranged according to the layout diagram shown in fig. 2. The interior layout shows how the contactors, relays, protective devices and the cable tray and connector block are arranged and fixed on the base plate of the enclosure. The exterior layout is the arrangement of meters, pilot devices, push button switches and rotary switches of the door of the enclosure. The cabling process involves the electrical connection of the components together with the extruder motor in accordance with the schematic diagram in fig. 1. The cable sizes are already indicated in the diagram. JIRT Vol. 4 No 1, 2015 74 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… (i) Interior (ii) Exterior Figure 2: Layout Diagram Figure 3: The Photographic Views of the Starter Panel Showing the Interior Cable Connections Journal of Industrial Research and Technology… JIRT Vol. 4 No 1, 2015 75 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… Figure 4: An Engineering Drawing of the Extruder Showing the Electric Motor Compartment Journal of Industrial Research and Technology… JIRT Vol. 4 No 1, 2015 76 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… The cable size for the control circuit is 1.5mm2 single core flex. Testing and Evaluation The following tests were carried out to ascertain the functionality of the starter panel that has been constructed. The results are shown in Table 3. Motor Tests A preliminary test was first carried out on the extruder motor before connecting the motor cables. 1. Continuity Test on Motor Terminals The continuity test was carried out with a digital multimeter set to the ohms range and connected to phase terminals of the motor to determine the continuity of each phase windings. 2. Insulation Test between Motor Phase Windings This test was carried out with a 0 – 1kV megger insulation tester set to the MΩrange and connected between one phase and another to determine the insulation resistance between the motor windings. 3. Earth Leakage Test Phase – to – earth insulation test was also carried out with the megger connected between the stator frame of the motor and each of the motor terminals. Interlocking Test The mechanical interlock MI placed between the star and delta contactors was also tested by pressing down the plunger of the two contactors one after the other and also attempting to press the two simultaneously. The former exercise was possible but not the latter. Journal of Industrial Research and Technology… Off – load Test With the breaker F1 left in OFF position and the panel switch SW in ON position, the time delay relay KT was set to 10s and the START button was operated. It was observed that the two contactors KM and KY switched instantly, but after a time lag of 10s the contactor KY switched off while KM and KD were on. The STOP button was then operated to switch off the contactors. This exercise was repeated with the time delay adjusted to 15s, 20s and 25s. On – load Test The breaker and panel switch left in ON position. The time delay relay was set to 10s and overload relay set to 32A. Operating the START button, the motor began to rotate at lower speed. After 10s, only the contactors KM and KD were on to operate the motor at full speed. At this time, the current at the supply terminal was measured with digital clamp-meter at the three phases. Some quantities of soya beans were introduced into the extruder barrel one after the other together with drops of water for normal operation of the extruder. Observations The test results as displayed in Table 3 were satisfactory. The winding insulations were within the acceptable range. According to the load current readings, the extruder motor must be operating at its maximum torque thereby reducing the possibility of blocked barrel. Table 4 describes the characteristic design features of this starter and their comparison with acceptable standards. JIRT Vol. 4 No 1, 2015 77 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… T able 2: Legend/Specifications Symbol Description L1, L2, L3 415V, 3 ph supply V Panel Voltmeter to indicate supply voltage, range is 0 – 500V F1 100A, ABB Power circuit breaker F2 Telemecanique LR2-D3355 overload relay to protect motor against overload, single phasing and low level faults. F3 5A Control Isolator fuse KM, KD Contactors, Telemecanique (Square D), LC1-D40 KY Contactors, Telemecanique LC1-D6511 MI Functional type mechanical interlock: designed to prevent inadvertent closing of parallel delta and star contactors which operate alternately. KT Timing Relay, range 0 – 30s, acts as changeover switch between contactors KM and KY. C1 – C6 25mm2 cable Connector block for incomer and motor supply cables S1 ON/OFF switch for control panel H1, H2, H3 220V, Pilot lamps S2 START button S3 STOP button M Extruder motor, Viking Exclusive, 380V, 50hp LK Door Lock CTR 40mm x 40mm Cable Trays FR Flat Rail BP Base Plate of 600mm x 400mm x 220mm indoor type sheet metal enclosure CG Cable Gland for 25mm2 x 4 armoured cable incomer CG1, CG2 Cable glands for 16mm2 x 4 flexible cable as supply to motor terminals Journal of Industrial Research and Technology… JIRT Vol. 4 No 1, 2015 78 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… Table 3: Results Obtained from the Testing of the Extruder Motor and its Starter Panel TESTS RESULTS 1.Continuity test Phase a-a Phase b-b Phase c-c 0Ω 0Ω 0Ω Phase a-b Phase b-c Phase c-a 7MΩ 6.5MΩ 6-8MΩ Phase a-earth Phase b-earth Phase c-earth 10MΩ 10MΩ 10MΩ Switching Timing Interlock Ok Ok Ok 5.On – Load Test Phase a Phase b Phase c (Line Currents) 25A 27A 26A 2.Insulation test 3.Earth leakage test 4.Off – Load Test Table 4: Characteristic Features of the Constructed Starter Panel Designed values Standard Rated Operational Voltage 415V 415V Starting Voltage 240 0.58 x rated operational voltage Contactor coil operating voltage 240V 120, 240, 415 Overload setting 32A 0.58 x rated current Time delay setting 10s 15s as max starting time Starting current 55A 6 x rated current as maximum. No of starting stages 1 1 only Back-up protection rating 100 Greater than the max. Starting current and less than main supply cable rating Journal of Industrial Research and Technology… JIRT Vol. 4 No 1, 2015 79 Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP… Conclusion Selecting the electric motor controls that orchestrates the function of the motor is a critical decision in creating efficient and reliable operation. The star delta panel designed and constructed in this work is characterised by good finishing, optimal cost, use of Telemecanique Square D contactors for the continuous operation of the motor, use of inverse time delay circuit breaker for back up protection and decent arrangement of internal cabling using cable rack. Use of good and quality conductors, standard electrical codes and the need for structural safety has also been observed in this work. The constructed starter has been put to use on many occasions without any problem. It is now possible to design a star delta starter with high level of professionalism and local content. The design principles used in this work can be extended to other applications where the use of star delta starter of this magnitude is involved. This design can further be improved upon by the inclusion of other forms of protection such as Low Voltage Release and Phase failure Relay. Acknowledgement We wish to express our sincere gratitude to the Director General of FIIRO Dr./Mrs. G. Elemo and FIIRO management for the opportunity to publish this article. We appreciate also, Engr. S. K. Adeyemi the Head of Design and Fabrication Division in FIIRO. This appraisal will be incomplete Journal of Industrial Research and Technology… without mentioning the very industrious electrician who assisted in carrying out the cabling process, Mr. A. Adewumi of Electrical Maintenance Unit. References Henk de Swardt (2007). Star Delta Starting and Dual Voltage Motors Explained. Article published in Vector: A journal of South African Institute of Electrical Technician Engineer, October & November 2007. Klockner Moeller (1982), Power of Electric Motors. Wiring Manual. pp. 11/63, 11/73. Mobley Keith R. and Higgins Lindley R. (2002). Maintenance Motor Control Components. Maintenance Engineering Handbook (sixth edition), McGraw-Hill, Section 6.49 & 6.53. Motorpact Application Guide. (November, 2004). Publication from Schneider Electric Industries SAS France. Robinson E. (2007). Simple Protective Relay Matrices. Proceedings of International Conference and Exhibition on Power and Telecommunications (ICEPT), Ikeja, Lagos, Nigeria, 16th – 18th October 2007, Pg 102. Rocky Mountain Supplier. (2011). Five Reasons to Select Square D Electric Motor Starter and Controls. NNT Featured Publications, May 30, 2011. JIRT Vol. 4 No 1, 2015 80