A Laboratory sized power Grid (LabGrid)
Electrical engineering programs typically have motors, generators, and power meters as part of their regular laboratory curriculum but an actual multi-generator power grid which can be used to study disturbances in a power grid is rare. Figure 1 shows LabGrid in an early stage of development with control computer and National Instruments data acquisition system. Figure 2 highlights some of the grid components such as the Hampden synchronous machines for generators and a lumped circuit transmission line models.
Figure 1 Graduate students Chayanon Sontidpanya during an early stage of LabGrid construction.
Figure 2 Various components of LabGrid
The Servo Motors are the prime movers of the system, much like a coal fired power plant, or a diesel generator, the electric power is generated from the synchronous generator and fed into the grid consisting of transmission lines, busses, and loads. Computer controlled relays disturbance to be introduced to the grid, or separating of the grid into multiple islands depending on the grid configuration under study.
Figure 3 Undergraduate student Steven Corum running LabGrid’s LabView control program
Areas of Study
Many areas of power grid research can benefit from a physical power grid that is independent of the local power utility. Here are a few areas currently under study:
- Measurements of frequency in the power grid don’t always correlate well with generator rotational speeds providing incentive for a new laboratory sized power grid to study this phenomenon.
- Islanding detection and implementation algorithms can be tested.
- Improving simulation models through studying areas where physical measurements and simulation models don’t agree.
Figure 4: A Matlab Simulink model of a two generator system.
Two Generator Speed Demonstration
In the real world power grid you could never tell the generators to operate at different frequencies from each other (for any extended period of time) but with the LabGrid there is no such limitation. Figure 5 shows what happens when two different generators are set to two different speeds. The systems are subject to control loops and they fight each other as the two systems get more and more out of phase with one another till they snap away from each other when they are too out of phase to transmit significant power. This behavior cycles over and over as the two systems cycle between being in synch and out of synch with each other.
Figure 5 Measured frequencies and generator speeds expressed as electrical frequencies.
Microgrid Test bed
The Smart Grid Group at TTU, recognizing the benefits a physical grid have banded together to create a larger Micro-Grid Test Bed which will incorporate the smaller LabGrid in the near future.