Until
recently, large-scale industrial energy users in Germany have benefited
from reduced tax rates on the electricity and gas they consume. Now the
German government has decided that companies will only be eligible for
such tax breaks if they take steps to reduce their energy consumption.
From 2013 onward, tax rebates will only be granted to companies equipped
with an energy management system that provides details of their power
consumption. This won’t be an easy task for the companies concerned,
because it means they will have to install individual auxiliary meters
to monitor the power consumption of individual loads such as presses and
welding machines, or bakers’ ovens, or electric motors. And in many
cases the metering instruments currently available on the market are too
large to fit into existing power distribution cabinets.
To
remedy this situation, researchers at the Fraunhofer Institute for
Integrated Circuits IIS in Erlangen have developed a novel, space-saving
metering unit that can be simply clipped onto a power cable like a
laundry peg, without even having to disconnect the load. The new “energy
analyzer” was developed in collaboration with Rauschert GmbH—a
manufacturer of advanced ceramic products that require energy-intensive
production processes. The research project was funded by the Bavarian
Ministry of Economic Affairs, Infrastructure, Transport and Technology
as part of its microsystems technology program.
Using magnetic field sensors to measure power consumption
The
device is based on the HallinOne 3-D magnetic field sensor originally
developed by IIS for use in Bosch and Siemens branded washing machines,
where it monitors the position and orientation of the rotating drum.
“This
new device is the first application in which we have used our 3-D
magnetic-field sensor technology to measure the magnetic field generated
by an electric current as a means of determining the energy consumed by
the connected load. As such, it is an entirely novel approach,” says
IIS research scientist Michael Hackner.
To
build the device, he and his team of qualified engineers mounted eight
sensors, in the form of application-specific integrated circuits
(ASICs), on a flexible, flat circuit board. What sets these sensors
apart from more conventional designs is that they measure the magnetic
field not only perpendicular to the surface of the chip but also in
tangential directions, which improves measurement accuracy. The recorded
data are transmitted to a microcontroller, which forwards them to a
central processor via a gateway switch.
“Our
power sensor is quick to install and can be integrated online,” says
Hackner, citing one of the advantages of the new product. He goes on to
emphasize another unique design feature, namely the fact that it
functions in the same way as a Rogowski coil, a component incorporated
in many standard instruments used to measure electrical currents. “But
the Rogowski coil only measures alternating current, whereas the IIS
sensor can also measure direct current—an important consideration when
measuring the power consumption of photovoltaic systems that include
solar inverters for converting DC output into AC power.”
Highly accurate measurements
The
metering device is cheap to build. And because the IIS researchers have
not used any magetizable materials in its design, there are no accuracy
errors from this source—a recurring problem with other clamp-on amp
meters that cease to function correctly after a short-circuit. Another
advantage is that, unlike clamp ammeters, the new device can also
measure voltages. In short, users now have an all-in-one instrument
capable of measuring all the parameters they need to monitor the quality
of the grid supply in addition to the power consumption.
Michael
Müller, head of energy management systems at Rauschert GmbH, provides
an example: “The new device helps us to rapidly identify production
problems. We can immediately detect irregularities in the firing process
and avoid having to scrap a whole batch of ceramics.”
He
intends to set up an energy-management consulting service for other
plants in the group and equip them with the new measurement system.
Power sensor suitable for use in power utility networks
The
sensor devices can even be installed in the power utility’s
medium-voltage network (20 kV). As a result of the German Renewable
Energy Sources Act (EEG), there are now a large number of small and
medium-sized electricity producers feeding energy into the grid, without
being obliged (or able) to inform the energy provider exactly how much
power is flowing on a specific line at any given time, and in what
direction.
“The
grid capacity could be utilized much more efficiently if detailed
measurement data were available,” affirm both Hacker and Müller. The two
experts reckon there is huge market potential for this application: In
Bavaria alone, the 20-kV distribution network contains tens of thousands
of transformer stations, which could be equipped with the new, low-cost
device without having to temporarily disconnect the stations or the
transmission lines from the grid. A prototype measuring system for
low-voltage networks has already been developed.
IIS
researchers will present live demonstrations of the device at the
Sensor+Test 2012 trade fair in Nuremberg from May 22 to 24 (Hall 12,
Booth 202). The working prototype was built by Loewe Opta GmbH, who will
also be manufacturing the final system.
Source: Fraunhofer Institute
