28 renewable energy
the PXI connect to digital inputs on the relay. When the
protection relay is activated, the protection functions can
be removed from the control system, leaving computation
power for estimating the phase angle.
Labview was used to optimise the performance of
the system, with the program running on a computer
located at a safe distance from the trailer-mounted test
equipment, communicating with the PXI chassis using
the TCP protocol. The chassis transmits the states of the
circuit breakers and executes the user’s commands. If the
communication link is lost or the application crashes, the
system ensures that all the switches and circuit breakers
are in a safe state.
The design of the new user interface makes for easy
operation of the voltage dip generator. Each switch or
circuit-breaker can be operated by pushing the open
or close button; undesired operations are prevented
Fig. 2. The Fraunhofer Institute for Wind Energy and Energy System
automatically by means of programmed interlocking
Technology benefits from a specially constructed building for testing
functions. To generate voltage dips, the operator can
wind turbine rotor blades.
set different parameters such as the duration, the active
➠
that highlighted how AE events, even those emitted at power range, the reactive power range and the phase
relatively low load levels, clustered around the eventual angle. Once the sequence is started, the system waits
failure points. for the defined conditions to be met before closing and
Launched in 2009, the Fraunhofer Institute for Wind opening the circuit breaker. Active and reactive powers
Energy and Energy System Technology (IWES) serves and phase angle are computed in real time by a special
the wind energy industry, with areas of research and algorithm. Closing very accurately on a specific phase
development ranging from materials to integration within angle requires a relatively high sampling rate (several
the power grid. Although the IWES is a new organisation, kilohertz).
the researchers already have two years’ experience in
developing testing methods for wind energy systems: the
Fuel cells
CWMT, which has merged into the IWES, has specialised While wind turbines can be useful for relatively large-
in oversized material tests, making use of a specially scale generation of electricity, fuel cells offer potential
constructed building 85 m long and 25 m high for testing for portable devices, vehicles and equipment in remote
rotor blades (Fig. 2). locations. National Instruments’ computer-based
measurement products are helping scientists and engineers
Short circuit tests
in research, design, validation and production testing of
Meanwhile, National Instruments has been involved in a fuel cells.
project to develop a test system for use on wind turbines In research and development applications, fuel cell
operating in the field. Energy To Quality SL (E2Q) has testing is performed to characterise and optimise energy
trailer-mounted equipment that generates short circuits output as well as to extend the life and robustness of
in medium-voltage networks by using a voltage divider the fuel cell stacks. In validation, the main goal is to
to actuate a circuit-breaker. Due to the requirements of a optimise the design in preparation for mass production,
new customer and the need for an easy-to-use interface, and to reduce the overall cost of the stack without
E2Q developed a voltage dip generator that is controlled reducing the efficiency. For manufacturing applications,
by a National Instruments PXI-1052 chassis. the stacks are monitored to ensure that they meet the
The customer had requested additional controls design specifications. Scientists and engineers researching,
over and above what E2Q already offered, such as a developing or manufacturing fuel cells need a variety of
circuit breaker that generates the voltage dip and closes measurement, control, analysis and visualisation tools to
on a specific value of the voltage phase. The closing evaluate and validate fuel cell technologies.
angle determines the behaviour of the power electronics Fuel cell test systems need accurate monitoring and
converter installed in the wind turbine. E2Q therefore control of hundreds of measurements ranging from the
built a system based on the PXI-1052, a four-slot PXI flow, temperature, pressure and humidity of the hydrogen
chassis with eight slots for SCXI modules, so inputs could fuel to the output voltage and current of the fuel cell
be made at higher levels than with a standard PXI system. stack. Test systems must be able to monitor and control
To overcome the high power consumption of the tripping fuel cell operation under widely varying conditions and
coils, the digital outputs controlling the breakers interface accurately capture information relating to real-time
with a programmable digital protection relay designed to performance and operational characteristics. Test systems
control medium-voltage elements. Digital outputs from must also provide flexible data acquisition, monitoring
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