We needed to test marine power generators with high output power, so we developed a specialized load bank performance. With its programmable logic controller (PLC), our system offers controllable load increases and decreases, and it can monitor or reactive power output performance and analyze generator performance. The original design has room for improvement in terms of data collection and analysis. Customers requested the collection of voltage and current change data during sudden load increases and decreases, along with high-speed data collection and recording. They also want to collect data on generator vibrations under different power levels to evaluate generator performance within other parameters.
We used the NI 9225 C Series analog input module for voltage acquisition. The rated output phase voltage of the generator is 220 V, so a measuring range of ±300 V met our measurement needs. For current acquisition, we used the NI 9227 C Series current input module. The system output electrical current flowed through the current transformer and stabilized on an output current of 0 A to 5 A, and the NI 9227 met measurement needs. In addition, we wanted to test the generator vibration, so we used the NI 9234 measurement system for accelerated speed testing requirements.
Before a marine generator is used for electrical power generation, it undergoes testing with load. Test experiments are organized into two categories: stable-state experiments and transient-state experiments. A stable-state experiment tests the generator’s ability to finish continuous power output within a specific period of time. The transient-state experiment sets several power output points and evaluates the generator output power variation in response to the transient changes of external loading for these points.
The entire system can be divided into three major sections: generator under test, load bank (including PLC, resistance, reactance, and data collection module), and remote monitoring system. The rated power of the generator under test is 560 kW. We can test them separately or in parallel with up to three units for concurrent test. Using the PLC and contactor, the resistance and reaction of the load bank controls load increase and decrease to collect real-time system operation data. This gives users a timely understanding of the power output performance of the generator.
System Design and Software Implementation
The main interface of the system monitor is made up of two sections. On the left side is the display area, which shows the real-time output active and reactive power and target value of the generator to illustrate its power output condition. The right section is the system control and operation status display. Here, users can set the rated power of the generator. The system calculates the active and reactive power based on its rated power, power factor, and percentage setup. The system performs calculation using predefined algorithms to calculate which output points the PLC controls. Commands are generated to send to the PLC to control the addition and reduction of the load. Because the load is not linear and the reactance varies as load temperature changes, it is necessary to compare the actual value collected by the collection module against the target value and perform real-time load adjustments.
By collecting system voltage and current as well as calculating information on active and reactive power, power factor, and frequency using specialized algorithms, the system creates control commands and distributes them to the PLC, which controls load increases and decreases, achieving the target value required by the system. Due to load characteristics, the system cannot achieve the target value with only one command distribution. Real-time data collected by the collection module is required to continuously adjust the system load output. Therefore, the data collection module is a significant component of system control.
Control and Adjustment
We can perform generator tests in two different ways: stable-state test and transient-state test. The stable-state test ensures that the condition of the generator’s output power is stable, with a continuous load each time, and that the generator progressively increases or decreases power output. In many cases, an overload test checks the situation when the generator’s rated power is exceeded by usually no more than 10 percent. A transient-state test evaluates the generator power output performance with the sudden change of external load. In this case, the load does not continuously increase or decrease as in stable-state test but changes sharply with an uncertain changing direction. The system can effectively test the generator’s power output performance with a sudden change of external load.
During stable-state test, only the active power percentage and power factors on the right section are adjusted. Based on the preset rated power, the system calculates the actual power. When the system arrives at a stable state, this node is latched and saved to record the current system operation status: active power value, reactive power value, and power factor. Then the next stable-state test starts. When the system arrives at another stable state, the operation status of the new point is latched and saved again. The purpose of keeping a record of the series of operation statuses is to prepare for the next-step transient test with data. After the stable-state test is completed, the system records a few key test data points. During transient-state test, these saved points are not tested in order but instead are randomly based on test needs.
Historical Data and Report Processing
Historical data inquiry helps reproduce the testing procedure and analyze problems during the test. It is an important analysis and inquiry tool for system test. In Figure 7, the green curve is the target value, and the red one represents the actual value of generator output. A test report is generated for the result of each test and exported to Excel to print and document. The report tool is useful in meeting such a function requirement. It frees developers from spending resources on report functions development.
For convenience in transportation and ease of use for testing at the dock, we needed to meet tough integrated system design challenges. Therefore, we chose the container-style system integration design strategy, which is convenient for transportation because most shipyards and docks have container cranes to easily place the system onto a lorry. The container-style design is also waterproof to protect the internal electronic devices from erosion in damp and rainy environments, which extends the service life of the system.
Saving Time and Money
Using the LabVIEW development platform and modularized CompactRIO data collection modules helped our developers quickly build a system for data collection, processing, analysis, display, and storage, so that they could focus on function and algorithm analysis design. This saved precious time in system development. The modularized data collection tools, used with LabVIEW, can easily implement functions such as data collection, analysis, and display. And the system’s high-speed, high-resolution data-collecting function provides hardware assurance for accurate system control.
Shanghai Rui You Technology Development Co. Ltd.