Data Acquisition System for Synchronous Generator Transient Performance

The goal of this project is to create a data acquisition system for a synchronous generator under transient conditions. When a fault clears in a power system, the load angle will increase and potentially cause the generator to slip a pole. This data acquisition system will be used to analyze systems as they near this condition.

=Project Scope= Our project is to create a fully automated system to acquire measurements from a 20KV synchronous generator under transient conditions. We will operate the generator under rated conditions with a typical load. At a given point in time, we decrease or eliminate the field current. The generator will response in a predictable manner with correlated variations over time in speed, torque, load phase angle, terminal voltage, terminal current, field current, field voltage and power. We want to measure the variations accurately and record them in a correlated fashion. This data will be used to create software and hardware that protects the synchronous generator from deleterious effects of variations in the things that we measure.

=Project Requirements= We need to find a single device with 14 analog input that accept V&I as input signals and at least 10kHZ sample rate to measure current. NI USB 6356 (But it is not synchronous with 8 analog input, 1.25 MS/s sample rate, we need 14 analog input and at least 1kHZ sample rate). Current/Voltage Lems (we need to test first or we need to build a suitable one to measure the field current). Measurements must be time synchronized. Monitoring and storing stream measurements.

=Design= This is the topology of the data acquisition system. There are 6 differential analogue signals being measured by each data acquisition device for a total of 12 differential analogue signals.



Shunt Resistors
We are using high accuracy shunt resistors to create a DC circuit to measure the field current and voltage. R1 is large enough and R2 and R3 are small enough that the leakage current is negligible.

Torque Transducer
The Himmelstein MCRT 48202(1-3) consists of three port connections: a 2-pin DC power input, a 3-pin RS232 serial connection, and a 4-pin analogue readout. We have used serial communication to a PC with the Himmelstein DT 482 software simultaneously with analogue capture into LabVIEW to map a relationship between the average digital torque measurement and the magnitude from the analogue measurement. The magnitude of analogue average torque is calculated by dividing the analogue peak by 1.18. The harmonics in the analogue are the same as the mechanical frequency. The figure below shows the correlation and regression of average analogue measured torque versus average digital measured torque.



Software
National Instruments LabVIEW

In order to ensure all measurements are properly time synchronized, both data acquisition boards must capture simultaneously. In LabVIEW, one DAQ is designated as a master device and the other DAQ is designated as a slave device. The figure below shows the same analogue signal being captured by both boards simultaneously with no time skew.



=Budget=



=Project Learning=

LabVIEW is the software platform allowing us to communicate, configure, and display data from National Instruments devices. It has the ability to communicate with a DAQ using instrument drivers VISA or interface driver.



The data acquisition boards share the maximum sampling rate across all channels. Adding more input channels will reduce the maximum available sampling rate.



The following block diagram shows the sampling logic of the SCXI. A multiplexer cycles through each input buffer, causing a slight timing skew between channels.



In order to determine the timing skew, we input the same signal into channels 0-3 and 13-15. The error was later determined to be negligible for our purposes.



If the error was of significance, we found a solution in a different type of SCXI. This device trigger holds each input for the multiplexer. This has the effect of perfectly simultaneous sampling at the cost of reduced sampling rate.



=Final Design= To be completed

=Validation= To be completed


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=Team Members=

=Additional Documentation=

Team Contract



Project Schedule



Meeting Minutes



Presentations