This document summarizes the upgrade of a major clutch and brake manufacturer's test stand from 1500HP to 3000HP capacity. The upgrade involved adding a second identical 1500HP VFD, motor, and control system and connecting them to a new combining gearbox. This allows either VFD to independently test 1500HP loads, or both to combine for a 3000HP test. Issues addressed in the upgrade included electrical harmonics, mechanical alignment challenges, expanded cooling requirements, and configuring the control systems for independent or combined ("master-follower") operation. The doubled capacity test stand now meets customer demands for testing larger and more demanding brakes and clutches.

1. 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
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,
Richard Mayberry
Altra Industrial Motion
Div. of Wichita Clutch
2800 Fisher Road
Wichita Falls, Texas
76302 USA
richard.mayberry@wichitaclutch.com
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.

2. 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

3. 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
nd
integrating a 2 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.

4. 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
rd
data points are linked to a 3 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 MasterFollower 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

5. 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).
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.
th
345 East 47 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
and Hoisting sectors. Located in Vancouver, BC Dave
is presently employed by Vacon Canada as a
Regional Manager for Western Canada.