Frequently Asked Questions
What is the Vycon VDC?
The Voltage Direct Connect or VDC is a new DC energy storage solution being offered by Eaton through a
partnership with Vycon Corporation, a Southern California based company that is a leader in the design,
manufacturing and integration of flywheel based energy storage systems. These systems are used in power
quality (UPS) and energy cycling applications such as port cranes and electric rail systems. The VDC is
designed so that it can integrated easily with most leading brands of UPS systems and has been tested with the
9390 Series UPS. The VDC is a more reliable and “Green” alternative to the traditional use of lead-acid battery
based DC energy storage for a UPS.
What is flywheel energy storage?
A flywheel energy storage system is a “mechanical battery” that stores energy kinetically in the form of a rotating
mass. When required during a utility outage, the energy stored by the rotating mass is converted to electrical
energy through the flywheel’s integrated electric generator. The system provides the DC energy to the UPS
until a stand-by emergency diesel generator can be started. Once either the utility is restored or the genset
provides power to the input of the UPS, the flywheel system will be re-charged by taken current from the DC bus
of the UPS until it is back up to full charge speed. This is similar to a battery re-charging after a discharge
How is the energy stored in a flywheel?
It is stored by means of a rotating mass; hence the energy stored in a flywheel is derived by the following
formula:
E = kMω 2
k – Depends on the shape of the rotating mass
M – Mass of the flywheel
ω – Angular velocity
A first consideration can be made by observing that the energy is proportional to the square of the angular
velocity. This is the reason why the technology trend line is to have a flywheel where energy is stored by having
higher speeds (RPM) values. This allows for lower weight, smaller footprint and allows for using full magnetic
levitation of the flywheel mass.
What are the advantages of using the VDC instead of lead-acid batteries?
When compared to the traditional lead-acid battery in UPS application the VDC has the following advantages:
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Reliability - Up to a 20x higher reliability than a single string of VRLA (Valve Regulated Lead Acid)
batteries that are typically used in UPS applications. The calculated MTBF for a single string of VRLA
batteries is estimated at 2200 hours. Due to the low component count of the flywheel and minimized
interconnection points, the calculated MTBF of the VDC is over 50,000 hours.
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Predictable availability – The flywheel energy storage availability and status is always known with its
built in monitoring and reporting system, unlike a battery system which requires a very expensive addon monitoring system. Even then the state of availability is only really known once the battery is called
upon to be used.
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Longer Life – The VDC has over a 20 year expected life and run time performance never degrades
during that period. VRLA batteries are typically replaced every 4 years and run time performance
degrades with age and usage. The VDC can perform thousands of discharges and the run time on the
last discharge will be the same as the run time as on the first.
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Reduction of Required Maintenance – The VDC requires little maintenance as it utilizes a magnetic
levitation system rather than mechanical bearings of previous generations of flywheels. Batteries on the
other hand must be checked on a quarterly basis for leakage, cracks, capacity, and corrosion.
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Footprint Savings – The high power density of the VDC means it can free up 50 to 75% of space that
would be taken up by an equivalent power rated battery bank. This lowers construction costs or allows
space to be freed up to used more productively.
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Does Not Require a Temperature Controlled Environment - The VDC can operated in temperatures
from 0 to 40°C, so not only does it take up less space than batteries, it can be installed in less
expensive space such as electrical equipment rooms instead of a computer room. Batteries require a
regulated environment for optimum performance and life.
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Environmental Friendly – Unlike batteries which contain toxic lead and acid which requires installation of
safety spill containment, the VDC does not contain any toxic materials.
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Lower Life-Cycle Costs – The VDC provides all the benefits noted above and at the same time provides
a significantly lower cost vs. batteries over the life of the installation. The ROI is typically within 2-3
years and over a 15-20 year operation the VDC total life-cycle cost is a fraction in comparison to
batteries.
What are the different configurations that clients use the VDC with their UPS?
The VDC can be used as a battery replacement or as a supplement in parallel with a battery bank. Generally
there are three configurations that our clients are utilizing the VDC and they are described below:
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Ride-through “Bridge” to generator
Most of our clients for the VDC are using it as a direct replacement for batteries on the UPS. The VDC
provides the back-up energy required by the load when the utility fails and until the emergency stand-by
diesel generator is on-line. This “Bride” time required is typically 6-10 seconds. The VDC can provide the
bridge time more reliably and predictably than lead-acid batteries.
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Short-duration ride-through
Some of our clients, particularly in the industrial sector don’t have emergency stand-by generators and
utilize the VDC with a UPS to provide protection against short-duration “glitches” or outages using only the
available energy from the VDC. The Electric Power Research Institute–EPRI—reports that only 2% of all
outages are longer than 10 seconds in duration. So many industrial customers may only experience a
longer term outage every 3 years, but they may experience 12 or more short term outages or “glitches” per
year that have same effect as a long term outages causing computer controlled processes to shut down and
be re-booted. This can lead to thousands of dollars in lost productivity and scrap.
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Battery “Hardening” and life extension
Because the VDC provides a programmable DC voltage it can be paralleled very easily with a bank of
batteries. This provides the client with redundant energy storage on the UPS DC bus and the VDC can
programmed to be the first line of defense against outages so the batteries are never cycled unless the VDC
has exhausted its energy. This shields battery banks from virtually all cycling events, preserving battery
capacity for longer disturbances. Consequently, this “battery hardening” effect extends battery life
expectation and improves UPS reliability.
What type of clients use the VDC?
The VDC is used wherever mission critical power is required. All companies that depend on power to keep their
businesses operational are potential users of the technology. These could be companies in the financial,
banking, securities, and insurance sectors as well as companies that provide IT services such as internet data
centers, web-hosting and co-location providers. In addition companies that provide essential services like
hospitals, telecommunication, radio / TV broadcasting are also potential clients. The one thing that all these
clients are seeking is a higher level of reliability and performance of their critical power systems. The VDC can
provide this and also show how it can be financially beneficial while also being “friendlier” to the environment.
What Series of Eaton UPS has the VDC been tested and approved
The VDC flywheel has been tested and verified compatible with the 9390 Series. Testing with the 9395 will
commence shortly, but since the 9390 and 9395 are similar platforms we don’t foresee any issues.. Since the
9315 has been verified to work with similar flywheel systems, the VDC would also be compatible. The 9390,
9395 and 9315 can be used either with single VDC units, or with multiple, parallel VDC units or with the VDC
units paralleled with batteries.
Can the VDC retrofit into existing UPS systems?
Yes, the VDC integrates into most UPS systems, new or existing.
Since the VDC provide a short amount of ride through, what are some the precautions that need to be
considered to add reliability on the start up of the generator?
Most standard generators can start and accept load within 6 seconds of receiving the start signal. Only 12-15
seconds of run time from the VDC are required to transition the UPS from utility to genset operation. In various
industry studies such as the IEEE Gold Book, genset start reliability for critical and non-critical applications was
measured at 99.5%. For applications where the genset is tested regularly and maintained properly, the
reliability is increased even higher. 80% of the time that a genset fails to start is because of failure of the battery
being used to start the generator. Just monitoring or adding a redundant starting system can remove 80% of
the non-start issues.
Many clients are under a false sense of security from having 10 or 15 minutes of battery run time. They assume
that if the generator does not start they will be able to have a chance to correct the issue. As many mechanics
will testify, if the genset does not start on the first one or two cranks of the engine, it will take much longer than
10-15 minutes to diagnose and repair the genset. The main concept here is therefore to improve the start up
reliability of the system. This can be done in several different ways; some of these are briefly described in the
following lines
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Test regularly the generator (once per month, which is required in hospital applications).
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Monitoring and remote diagnosis of main parameters (battery voltage, lubricating system, fuel level and
so on).
Positive pressure fuel line.
Coolant heating.
Use of redundant generator system.
What makes the VDC superior to other commercially available flywheels?
There are basically two categories of flywheels commercially available in the market
High Speed (RPM) Flywheels (Pentadyne, Vycon)
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angular velocity 30 – 60 krpm (potential limit up to 100krpm)
much lighter flywheels for high power needs (energy stored through higher spinning velocity)
full magnetic levitation
the flywheel has lower periodic maintenance
smaller footprint and lighter weight
easy commissioning, start up and shutdown
Low Speed (RPM) (Active Power, Piller)
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angular velocity <10krpm
energy for high power needs heavy steel flywheels (Heavy and bulky)
periodic maintenance and replacement to the mechanical bearings
high amount of parasite energy losses
requires special concrete slab specifications for installation
Another comparison can be made from different high speed (RPM) flywheel solutions of Vycon and Pentadyne
(promoted in the US by Toshiba and Liebert). While both systems use high speed, the materials used for the
flywheel design are different as well as the design of the motor / generator. Vycon utilizes standard, aerospace
grade 4340 steel. The material properties are very well known, available from numerous suppliers and this
material is used in many high speed rotating applications. Most important is the integrity of the material can be
measured through core samples and ultrasound to assure it complies with the application specifications.
Pentadyne utilizes 4.5 miles of carbon-fiber that is wound on a spindle with an epoxy resin that is provided from
a single source. Imperfections in the process and gaps between the fibers could lead to an “unbalancing” of the
wheel over time due to the stresses applied as the wheel is spun from high RPM to low RPM and back again,
which occurs during every discharge event. Once the flywheel becomes unbalanced, the entire flywheel module
much be replaced… a very costly and time consuming processes. The Vycon flywheel has been used not only
in UPS applications, but also in high-cycling, regenerating applications like in electric drive for cranes and
electric rail. These applications call on the flywheel to be charged and discharged sometimes 20 times per hour.
These applications prove the robustness of utilizing aerospace grade steel as the preferred flywheel material.
The other difference is in the motor generator configuration. Vycon utilizes a permanent magnet type motor
generator. The benefit of this is twofold; one benefit is higher efficiency of the motor generator when charging
and discharging. This allows the high cycling capability of the Vycon flywheel. The second is that the flywheel
can generate its own power to maintain the flywheel levitation even if control power is lost or a failure occurs in
the power electronics. Pentadyne utilizes a synchronous reluctance motor than cannot self generate power if a
failure occurs in the power electronics. Thus the unit requires a back-up supply from a small UPS to provide
power to the magnetic bearings if this occurs. Using a battery UPS to protect your battery-less flywheel solution
does not seem to make sense. In addition, if a power is lost to the magnetic bearings or if a failure occurs to
the magnetic bearing controller, the Pentadyne flywheel will go on to the touch down bearings at full speed. The
Pentadyne flywheel will come to a stop, but it will no longer be suitable for use, it must be replaced completely.
By contrast with the Vycon flywheel, the back-up ceramic bearings can support several drops at full speed and
recover normally.
What is the design life of the VDC?
The VDC is designed to have a greater than 20 year life in a UPS application.
What are the maintenance requirements of the VDC
The VDC product requires minimal maintenance. Because the flywheel utilizes a full levitation system with no
mechanical bearing, there is nothing in the flywheel module that needs to be maintained. The VDC also utilizes
a “medical grade” vacuum pump to maintain a high vacuum level in the flywheel chamber. Because all
materials located in a vacuum environment “out-gas” vapor molecules over time, these vapor molecules must be
captured and removed in order to keep the vacuum to the appropriate level in the flywheel chamber. The VDC
gathers these vapor molecules in the mineral oil of the vacuum pump. Typically this mineral oil will need to be
replaced after about 1 year of operation as the mineral oil has absorbed these containments. Replacing the
mineral oil “regenerates” the vacuum. The VDC vacuum regeneration procedure takes about 10 minutes to
perform and the unit does not have to be taken off-line, thus is available to function if called upon. Because
“out-gassing” rate decreases over time, the frequency of needing to regenerate the vacuum by changing the oil
is less. The estimated life of the vacuum pump itself is approx 8-10 years.
Flywheel systems that use a molecular vacuum sleeve (Pentadyne / Liebert / Toshiba) instead of an external
vacuum pump, also face the issue of “out-gassing” of the flywheel components. This vacuum sleeve system
directs the vapor molecules and containments from the flywheel chamber into an upper chamber where these
are absorb and collected in getter or desiccant materials, much like the external vacuum pumps collects these in
the mineral oil. Typical within 12-18 months of operation, the vacuum of the Pentadyne unit must also be
regenerated as the getters have been saturated and thus the vacuum sleeve is less effective in maintaining the
vacuum. Unlike a 10 minute operation with the changing of the mineral oil on the VDC unit, the regeneration of
the Pentadyne unit requires the unit be taken off-line for 8-10 hours as an external vacuum pump must be
attached to the flywheel and the getters/desiccant materials are heated up using a probe. The heating allows
the getters / desiccants to release the vapor molecules which are then removed by the external pump. During
this time the unit is not available to protect against an outage. Because the Pentadyne system is liquid cooled
and the inner housing in immersed in liquid with power and control cable feed throughs, it is susceptible to leaks
over time. If this occurs, the vacuum cannot be regenerated in the field and the flywheel module will need to be
replaced….again expensive and time consuming.
Besides the 10 minute vacuum regeneration on the VDC, the only other required maintenance is the
replacement of standard DC caps at around 7-8 years of operation. This is standard maintenance on all
flywheel systems that utilizes a bi-directional converter.
How much power and energy can a single VDC unit provide?
The current VDC-140 can provide for max power 165kW for 10 seconds of run time. For max energy storage,
the VDC-140 can provide 140kW for 16.8 seconds. For higher power requirements and/or longer durations,
multiple VDC-140 units can be run in parallel.
The new VDC-235 (Available in July) will be able to provide 235kW for 10 seconds of run time. For max energy
storage it will be able to provide 200kW for 15 seconds. Again for higher power requirements and /or longer
durations, multiple VDC-235 units can be run in parallel
What is the operating voltage range of the VDC?
The VDC has a wide operating voltage range. It is UL listed for 400 to 600 VDC, as limited by UL standards, but
it can connect at voltages up to 850 VDC.
How long does the VDC take to recharge after a full discharge?
The recharge time after a complete discharge is factory adjustable per application requirement. For UPS
applications the recharge time default is approximately 12 minutes from full discharge to full recharge.. The
current is limited by the current available from the UPS rectifier. Since after an outage, the UPS is typically feed
by the stand-by emergency diesel generator, the recharge current is set for an approx 12 minute re-charge so
not to over stress the diesel engine as typically even if the utility returns, the diesel will typically power the UPS
for 10 to 15 minutes to assure a stable utility supply. If the UPS and diesel engine are properly sized, the
recharge time can be reduced to approx 2 minutes. While recharging, if another event where to occur, the VDC
will provide whatever energy is available instantaneously although it is not fully charged.
What is the noise level of VDC?
The sound level from the flywheel module itself is less than 45dBA. Unlike other high speed flywheel that must
be liquid cooled with a water pump, a radiator, fans and the associated pumping, the VDC is forced air cooled.
The audible noise level when the fans are in operation is approx 66dBA.
How do I know “State of Charge” of the VDC?
The State of Charge (SOC) is always displayed on the touch screen, GUI on the front of the VDC.
What is the operating temperature range the VDC?
Operating: -4°F to 104°F (-20°C to 40°C) without derating. This in line with the operating temperature of the
UPS systems in which the VDC will be connected.
If a customer wants to see an application is there any existing installation where we can show a UPS
with a flywheel?
A demonstration can either be shown at the Vycon facility in Southern California or at the Eaton (Powerware)
facility in Raleigh.
What are the key technologies used in the VDC?
The Vycon VDC includes several key technologies:
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High speed Aerospace grade 4340 steel hub
Five-axis active magnetic levitation
High speed permanent magnet motor-generator
Touch Screen display that has graphical event capture display capability
What type of power conversion technology is used in the VDC?
The VDC uses a bi-directional power converter to either extract or supply energy to the DC bus. The Power
Conversion Module uses high-power IGBTs (Insulated Gate Bipolar Transistors) and PWM (Pulse Width
Modulation) technology. These are designed and produced by Semikron Corporation in Germany.
Does the VDC require a back-up supply like other flywheels?
Unlike the VDC, other high speed flywheels that use a synchronous reluctance generator don’t have the
capability to self generate an emergency back-up supply in the event of a power conversion (IGBT) failure.
They will rely on the DC bus of the rectifier or need another uninterrupted source. This can be from the output
of the UPS if batteries are paralleled with the flywheel on the DC bus, but if the flywheel is the only energy
storage on the UPS, then the back-up must be feed from another battery based UPS. The scenario is as
follows: A flywheel is used on the DC bus of a UPS. The magnetic bearing controls obtain power from three
redundant sources, the DC bus from the rectifier of the UPS, the self-generated DC from the output of the IGBT
converter (when flywheel is discharging) and the back-up power from the output AC of the UPS that the flywheel
is being used. If the utility fails and then a failure occurs on the flywheel IGBT converter then the rectifier DC
bus is not available due to the utility outage, the output of the flywheel IGBT is not available as the IGBT has
failed and since the flywheel cannot provide DC power to the UPS, the output of the UPS inverter is not longer
available so even the back-up supply is missing. This will result in flywheel losing its magnetic levitation,
dropping on the touch down bearings at full-speed and then needing to be completely replaced.
This is why Vycon has chosen a permanent magnet motor-generator technology as it can self generate critical
power to the magnetic levitation controller even with an IGBT failure. The unit can even go down on its back-up
bearings at full speed several times and recover completely without damage to the flywheel system. While the
Vycon VDC does require an AC input from the output of the connected UPS, it is used to power aux equipment
and it is not required for the survivability of the system.
What is the nominal operating speed of the flywheel?
The rotating group spins at speeds at 24,000 (fully discharged) to 36,000 (fully charged) rpm.
What is the energy efficiency of the VDC?
At a power rating of 165kW, the efficiency of the VDC is 99% energy efficient.