"We cut down the test time of our cabinets from five days to one day,
making it feasible to increase production capacity.
Now we can automatically test all of the functions of our products,
which gives us a clear competitive advantage in the market."
- Michael Bove, kk-electronic A/S
The Challenge: Automating the final manufacturing tests of wind turbine control systems to increase test coverage, decrease test time, and address the rapidly growing production volume.
The Solution: Using NI TestStand and LabVIEW with NI PXI instruments and SCXI signal conditioning to develop a standard automated test system for kk-electronics that can be adapted to global production sites.
Reliable Wind Turbine Control Systems for Rough Weather Conditions
For three decades, kk-electronic has been developing and producing complete wind turbine control systems for leading wind turbine manufacturers. We supplied the first control system that connected the wind turbine to the grid, and have maintained a leading role within control systems over time.
Most offshore wind farms are equipped with kk-electronic control panels. Our products meet the high reliability and up-time requirements, often in an environment characterized by rough weather conditions. We employ more than 700 people with locations in Denmark and Poland and a joint venture in China.
Little Automation Leads to Longer Test Times
An integrated control solution of a wind turbine is a comprehensive package of distributed components such as the main computer, I/O modules, and components for monitoring and controlling the turbine. It also includes operating panels, voltage distribution boards, power quality analyzers, and yaw motor protection systems.
Five years ago we spent five days conducting the final tests of our control system. Because of the complexity of our control systems, we had very little test automation. This lack of automation resulted in long test times, and the test coverage for our control systems was not enough to meet our quality targets. As a result of these objectives, we developed an automated test system to decrease test time and increase test quality. We contracted CIM Industrial Systems A/S in Denmark to design and develop the solution based on NI LabVIEW and the NI PXI platform because it provided the best flexibility to meet the complexity of the design.
Integrated and Easy-to-Use Test Software
Our previous test system was a collection of small tools we tried to integrate to work together. We wanted to develop a new system that could test the whole system in a single application. We also needed a system that was easy to duplicate at our international production sites.
To meet these requirements, we designed a system based on the NI TestStand test management environment. We store test limits and functions in a central test database where NI TestStand retrieves the needed resources using Web services. Our typical test sequence contains almost 1,000 steps, making it very important to have an easy-to-use environment to configure these steps.
To make it easy to add and configure these steps, CIM developed custom step types for our platform. A custom step type is a specific test that is easy to add and configure for a nonprogrammer in NI TestStand; for example, such a test would be a step that generates a stimulus signal, measures the response, and compares the response to the defined limits.
Modular Test Hardware Solution
Our typical test sequence can return up to 2,500 results. Because we acquire a large number of measurements, we needed the test platform to provide a high-channel-count solution. In addition to the channel density, we required the system to include good signal conditioning to measure the wide signal mixture of our system. Also, we needed the ability to easily make future changes to the test computer to implement the latest processing power available.
Based on these requirements and the recommendations from our test system integrator, we architected our solution based on the modular NI PXI and SCXI hardware. This platform provided instrumentation and signal conditioning slots as well as an industry-standard solution for future compatibility.
The kk-electronic test system is based on NI PXI and SCXI hardware.
We used the NI PXI-4070 digital multimeter (DMM) with NI SCXI-1127 and SCXI-1130 switches and NI Switch Executive software to measure voltage, current, frequency, and resistance signals from the system under test. The NI PXI-6143 simultaneous sampling data acquisition module tests thyristor connections and frequency converter outputs.
In addition to the measurements, we have to output many signals to the system under test. For example, we used NI PXI-6704 analog output modules to stimulate the analog inputs in the control cabinets and verify emergency circuit connections through potential-free contacts. For testing the digital inputs in the cabinets and activating the isolation relays of the system, we used an industrial NI PXI-6512 digital output module.
The Results of the Project
The solution successfully met our early objectives. Now we can automatically test all of the functions of our products, which gives us a clear competitive advantage in the market. Also, we significantly cut down cabinet testing time from five days to one day, making it feasible to increase production capacity.
We are also pleased with the architecture of the system because factories can easily implement it. After connecting the system to the network, it configures itself automatically over the network using the configuration information in our database.
Even though we drastically decreased test time by automating the process, there is still room for improvement. After optimization, we expect to reduce our test time even further to three or four hours per cabinet.
Photos courtesy of kk-electronic a/s