DOUBLE A VFD DRIVEN TEST-STAND S THROUGHPUT AND CAPACITY Copyright Material IEEE Paper No. PCIC-(PCIC-2013-82) Lead Author Craig Sims Vacon Inc. 1500 Nitterhouse Drive, Houston Chambersburg, PA 17201, USA craig.sims@vacon.com David R. Schumaker Vacon Canada Inc. 221 Griffith Road Stratford, Ontario Canada, N5A 6T3 dave.schumaker@vacon.com Richard Mayberry Altra Industrial Motion Div. of Wichita Clutch 2800 Fisher Road Wichita Falls, Texas 76302 USA richard.mayberry@wichitaclutch.com ABSTRACT - The marine & offshore and drilling markets are requiring larger brakes, and more demanding cyclic loading of tension and brake control system. Because of a backlog of testing, customer requirements for extended life of friction materials, and demand for larger clutches and brakes, The Clutch manufacture decided that the throughput and capacity of their existing 1500HP test stand needed to be doubled.. The existing test stand utilized a 1500HP Variable frequency drive (VFD) and motor to: performance test and burnish brakes for customers, run static and dynamic load changes on clutches and brakes for research and development, and for customer specific applications. The existing VFD and motor were to remain and be re-used. A second identical VFD and motor would be added, and both would be connected to a combining gearbox. Each VFD and motor can test a single 1500HP brake, or both VFDs systems can be combined to run a single 3000HP brake. The upgrade of the test stand offers an opportunity to examine the application considerations (closed loop and torque control), installation considerations (harmonics and environmental), and operation considerations (dynamic load changes and master-follower control) of large VFD systems and clutch/brake performance. Index Terms - Variable Frequency Drive, Closed Loop Control, Torque Control, Master-Follower Control, Water Cooled Clutch, Water Cooled Brake, Combining Gearbox. I. INTRODUCTION A major clutch and brake manufacturer is an industry leader in applying their clutches and brakes into many industrial markets. In the marine industry you will find clutches and brakes used with propulsion systems, anchor handling, mooring, and wenches. In Oil & Gas industry, This leading manufacturer of clutches and brakes products are used with Drilling rigs, mud pumps, and drawworks. Because of a backlog of testing (5 man years), customer requirements for extended life of friction materials, and demand for larger clutches and brakes, this manufacture of clutch and brake products recognized the need and decided that the throughput and capacity of their existing 1500 HP test stand needed to be doubled. The existing test stand utilized a 1500HP Variable frequency drive (VFD) and an OEM motor connected to a 1:1 ratio belt and sheave gearbox. Up to 1500HP brakes were performance tested, burnished for customers, and run through static and dynamic load changes on the existing test stand. The offshore and drilling markets are requiring larger brakes and more demanding load cycling of tension control system. The existing VFD and OEM motor were to remain and be re-used. A second 1500HP VFD from the same manufacture and an OEM motor would be added. The two VFD/motor pairs would then be connected to a combining gearbox. This combining gearbox allow a configuration such that either each VFD and motor can run a single 1500HP load, or both VFDs and motors can be combined to run a single 3000HP load. Electrical issues to be considered during the installation and operation of the new capacity test stand include: Harmonic content back to the utility, closed loop control and torque performance of the VFDs and motors, Environmental concerns, and master follower control of the two VFDs.
Mechanical issues to be considered with the new integrated test stand included: Water cooling system of the clutches and brakes, alignment, balancing and set up of the new combining gearbox, cooling of gearbox oil, and coupling selection and alignment. Since the two 1500HP 18 pulse drives (working together) meet IEEE-519-1992 calculations, the Utility company approved the installation. The operational control, and performance criteria considered during this upgrade included: Individual test stand parameters and operation, combined test stand parameters and operation, Control locations, system feedback and performance, and the ability to use customer specific load profiles for performance testing. A. - Electrical Considerations - Harmonics Adding the second 1500HP Drive and motor to the test stand system meant there would have to be a harmonic analysis calculation completed before the local utility would sign off on the installation. The harmonic analysis needed to take into account the existing 18 pulse, 1500HP drive operating at 600VAC, and the addition of a second identical system. The local utility required that the two drives operating together meet the IEEE-519 (1992) specification for harmonic content (Reference; Electrical One-line of one 18 Pulse Drive System Figure 1). Figure 2. Harmonic Calculations - two 1500HP 18 Pulse Drives B. - Drive and Motor Sizes Figure 1. Electrical One-Line for one 18-Pulse Drive System. The utility Transformer: 1500KVA, 5.43% Z, Primary Voltage 12,470VAC, Secondary Voltage 600VAC. The Utility had set a dedicated (1500KVA) transformer for the first test stand, and stated that it would handle both drives when run together. Harmonics were calculated at the Point of Common Coupling (PCC) stipulated to be point at the primary side of the utility transformer. The %TDD (2.57%) total demand current distortion and % VTHD (0.016%) voltage harmonic distortion calculations are listed in figure 2. The air cooled drives were assembled by an industry recognized Systems Integrator (SI) with common DC bus components. Since the drives were an 18 pulse configuration, three input bridges were required. Each input bridge is rated for 650Amps continuous/ 715 Amps for one minute. The aggregate of the 3 bridges rated at 950Amp continuous /2145 amps for one minute. The four inverter modules are paralleled to achieve the desired current output required by the motor and the draw works application. Each inverter module is capable of 416 amps continuous and 458 amps for one minute. Collectively the four inverter modules are capable of 1664 amps x.95% (de-rate for parallel operation and inclusion of DV/DT filters) = 1581 amps continuous and 1740 amps for one minute with a maximum of 2223 amps for 2 seconds. Motor Nameplate Information: Motor HP: 1500HP Motor Voltage: 575V Base HZ: 40HZ FL Amps: 1350Amps NL Amps: 400Amps Max RPM: 2300RPM Power Factor:.89 Max Torque: 9844Ft-Lbs @ 788RPM, 40HZ
C. - Mechanical Selection and layout. One of the biggest design concerns for the engineering lab expansion was to utilize as much of the existing 1,500 HP VFD test stand system as possible, to keep expansion costs down while integrating a 2 nd VFD system. With this expansion it was necessary to be able to combine the twin 1,500 HP units into a single 3,000 HP test. For this reason the clutch and brake manufacturer coordinated it s efforts with a sister gearbox manufacturing company to assist in selection of gearbox hardware. The solution provided was a combining gearbox assembly that would facilitate an input from both 1,500 HP motors into a single 3,000 HP. Mechanical load sharing and balancing was provided by the VFD manufactures Master-Follower control function inherent as part of the drive systems capability. The gearbox also allows for two independent 1,500 HP tests simultaneously. To keep as much of the existing VFD system in place, 3D solid modeling CAD was used to engineer and layout the mechanics of the new test stand systems (see figure 3). The existing motor was moved over to accommodate the installation of the new identical motor. By ordering the new motor with the cooling fan (and junction box) assembly installed on the opposite side, both motors were mounted as close together as possible. This approach allowed matching of the motor pairs to the selected combining gearbox input shafting (48 inch center to center). The new VFD controlled the existing motor and the existing VFD controlled the new motor. The steel T-slotted floor currently used to mount test assemblies was reused and was used to install the combining gearbox and two new Test Stand Assemblies (which are used to mount clutch/brake units for testing). Figure 3. Mechanical Layout of Motors-Gearbox and Brakes Once the motors were set and the gearbox installed on the t-slotted floor, connecting drive shafts from the motors to the gear box input shafts were fabricated and assembled. These drive shafts were designed as floating end configuration. Initially dial indicator were used for alignment of the shafts and the motors and gearbox were shimmed to provide final alignment. During initial commissioning of the twin VFD test stand, this alignment process appeared successful. However, at speeds above 300 RPM and increased loads a significant vibration on the master motor shaft was revealed. The manual dial indicator alignment may not have been accurate enough for this style of drive shaft configuration so a third party laser alignment service was contracted to recheck the alignment. This resulted in a slightly tighter alignment, but the vibration was still too large to allow high speed and load testing. Due to project time constraints a bootstrap fix was quickly designed to alleviate the vibration. The drive shaft configuration might have been more vibration resistant if a flexible disc element style coupling was installed in lieu of the gear style coupling. Pillow block bearings where installed at the shaft mid-points (where they penetrated the building concrete wall). This supporting bearing design removed the vibration and allowed the commissioning of the twin test stand drive system to be completed. D. - Cooling System. As a result of the installation of the second VFD system and gearbox components, a significant increase in cooling was required. This water based cooling system cools the brake and/or clutch water during testing [when testing water cooled products]. In addition the implementation of the combining gearbox created the need to cool the gearbox oil during high HP testing. The combining gearbox has an integral liquid to liquid heat exchanger located atop the frame. The existing single 1,500 HP drive test stand system used a 125 ton evaporative cooling tower and a pair of 500 gallon tanks. On hot North Texas Summer days the ambient air temperatures can reach 105-110 Degrees Fahrenheit. This taxed the existing cooling system, and sometimes testing had to be suspended or scaled back to allow the cooling tower to expel the heat being generated by the test brake. As part of this dual test stand system, the water cooling system was also expanded to handle continuous 3,000 HP operation even on those hot North Texas Summer days. The existing 125 ton cooling tower remains but was re-plumbed to a new 2,500 gallon storage tank that supports both 1,500 HP test stands and the gearbox oil cooling water.
E.- Control System. The existing 1,500 HP VFD system was set up was to test both water cooled and air cooled clutch and brake products. The data items being extracted from the testing include: power, torque, temperature, and coefficient of friction (both static and dynamic). These data points are linked to a 3 rd party PC based software package configured to record data from a variety of sensors on the test stands where the brakes or clutches are located. Both manual and automatic control functions are used for controlling the drives, depending on the requirements of the testing. Each VFD uses an encoder mounted on its associated motor for closed loop control. The encoder signal is shared between the VFD and the PLC located in the control room. For the automated control, a programmable control module provides outputs for motor speed, torque and coordination of the inputs for air control system used to actuate the brake during testing. This control supplies the ability to input various brake and clutch test performance profiles. Testing to specific profiles allows for the duplication and simulation of customer operating conditions. In addition to any normal operation a variety of potential input conditions and associated reactions on the product can be tested. This also gives the manufacture of the brake and clutch products a precise tool in the development of friction material and mating surface combinations to provide customers unique solutions to difficult applications. Those applications that we can currently test against are Drilling Rig Draw Works Braking, Draw Works Main Braking, Traction Winch Braking, Caliper Braking just to name a few. The test stand was configured to run in two separate modes of operation. The first mode was a single VFD system and its corresponding motor to run independent. One or both systems can run independently at the same time. Each 1500hp motor would drive its connected input shaft on the gear box. In this first mode each VFD/Motor pair operate completely independent of the other VFD/Motor. No mechanical or electrical connection exists between the two independent systems in this configuration. Each VFD/Motor pair could be run closed loop in either Torque or Speed mode taking its required control signals from the control system. Each VFD system utilizes CANbus to communicate to the drive manufactures VFD configuration/commissioning software tools located in the control room. In the second mode of operation each VFD/motor pair would drive its connected shaft on the gear box. Through a mechanical connection in the gear box enabled by the control system the two input shafts driven via a motor/vfd pair would be summed to deliver the combined 3000HP total to a single common output shaft on the gearbox. In this Master- Follower mode the VFD s parameters were changed by a digital input signal to allow each to operate from a second set of parameters (combined operation). In this configuration one VFD is allocated as a Master the alternate VFD allocated as the follower. The follower is configured to run in Torque control, receiving it s torque reference from the Master drives torque actual. The slave drive receives its control signals via the Master drives analog/digital outputs. The Master VFD is capable of running in speed or torque control This combined operation of the two VFD Test Stand Systems provides very good load sharing (See figure 4). Figure 4. Master and Follower Drive load sharing II. CONCLUSION Re-using the existing 1500HP VFD test stand system and adding a second identical VFD and motor, into a combining gearbox proved to be a challenging project. There were vibration, alignment, and cooling issues to overcome. There were also control applications, issues and scenarios that needed to accounted for
and programmed. Since the system has been commissioned by the VFD manufacture and the local System Integrator it runs six days a week without any faults. The Brake and Clutch manufacturer now has the largest test stand for clutches and brakes in the industry. This capability alone now saves one marine customer a day of production to have a large brake burnished before it arrives offshore ($500K day rates). and Hoisting sectors. Located in Vancouver, BC Dave is presently employed by Vacon Canada as a Regional Manager for Western Canada. References IEEE Standard 519-1992, IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems. (June 18, 1992) The Institute of Electrical and Electronic Engineers, Inc. 345 East 47 th Street, New York, NY. Vacon NXI User s Manual, Document Code: ud01063b (October 18, 2006) Vacon Inc. NCDrive Software, 2.0.16, Vacon PLC, 2003. VITAE. Craig Sims Craig Sims is a 1986 graduate of Texas A&M University with a B.S. degree in Industrial Distributions. Craig is also a 2013 graduate of the Executive MBA program of the Mays Business School at Texas A&M University. He has worked in the electrical automation and drives industry his entire career, with Westinghouse, Rockwell/Allen-Bradley, Schneider, ABB, Converteam and most recently as a regional manager for Vacon. Areas of specialization include, oil & gas, marine and offshore, cranes, highspeed, and permanent magnet motor applications. Craig is an IEEE member. Richard Mayberry Richard W. Mayberry is a 1984 graduate of Wichita State University with a degree in Mechanical Engineering Technology. He has worked for several Original Equipment Manufacturers since then including Beechcraft Airplane Company, Tracor Electronics, and Boeing Military Airplanes and since 2004 has been the Engineering Manager for Wichita Clutch Company of Wichita Falls, Texas. He is a past member of the Society of Mechanical Engineers and The Old Crows Associations (Electromagnetic Warfare Technology). Dave Schumaker Dave Schumaker is a 1982 graduate of British Columbia Institute of Technology and an honors graduate in Electrical and Electronic Engineering in the Controls option. During his career Dave has worked in the field of industrial controls with extensive application experience with AC/DC variable speed drives and PLC based control systems. During his tenures while representing VFD manufactures and Systems Integrators has been exposed to various applications in the Oil and Gas, Marine, and Crane