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Power-grid quality monitors are GPS-equipped, networked

Posted: 03 May 2006 ?? ?Print Version ?Bookmark and Share

Keywords:G4000 Series Power Quality Data Center? power grid? waveform? GPS? global positioning system?

Elspec's G4000 Series Power Quality Data Center

With summer weather on the way, and air conditioners about to be cranked up, power line quality will soon be an issue for generation companies. As such, this product is timely.

It's typically installed at generation outputs and at various connection points to the grid and at transformers throughout a distribution system.

By installing on each side of transformers, it's possible to determine sources of failure and losses, giving you a handle on preventative maintenance as you monitor performance trends. The box can be DIN-rail mounted, too.

Perhaps best of all, the system lends itself to a distributed architecture that's also scalable using an unlimited number of local and remote devices. It uses TCP/IP, and is supplied with TCP/IP communication software.

Changing the way analysis of power lines is performed, Elspec's G4000 Series Power Quality Data Center instrument stores the waveform of every cycle on an AC line, and does that continuously, in a gap-free manner, for periods in excess of one year. It stores data in as much as 8Gbytes of flash, and can display readings on a built-in back-lit 160 x 128-pixel display.

To do that, the company uses a unique time-synchronization algorithm that ensures data from multiple locations is synchronized and displayed on the same time scale. The result is that anomalies can be analyzed and their source pinpointed.

The patent-pending PQZip compression mentioned in the company's press release provides 1,000:l compression so that you can store the vast amount of data from continuous readings.

Raw waveform storage
The data is stored in its raw waveform format, permitting all possible parameters to be subsequently calculated. You can generate information about rms voltages, currents, powers and harmonics, and also grid or electrical network impedances.

The system's time-sync algorithm ensures that measurements from different locations are synchronized within ?1-sample. By analyzing multiple locations with time accuracy, the exact propagation of an anomaly can be monitored and analyzed.

To accurately analyze an event using earlier-generation event-based meters, all meters in a network must detect the event and record it, and all meters must have adequate memory.

What's more, all possible parameters must be recorded and event thresholds set correctly, and all meters must be time-synchronized to within one sample (within microseconds). Then your analysis software must be able to analyze all of these operations simultaneously.

Enter the real world
In actuality, usually at least one of the above items doesn't happen, making it impossible to correctly analyze events. Even in cases where an educated guess can point to an answer, it's usually not definite enough so that you can take correction action.

That's where Elspec's G4000 Series Power Quality Data Center comes in. Using GPS satellite reception, it lets you obtain 1ms accuracy. Elspec claims that's superior to most GPS-based synchronization schemes on the market.

In addition to the G4000 Series's Power Quality Data Centers, the system uses Elspec's PQSCADA central analysis software, and optional Elspec G4100 remote monitor/displays.

With these tools and adjuncts, G4400s can be installed at key measurement points along a power grid or electrical network, and data will be logged continuously during every cycle of the network, at up to 1,024-samples/cycle.

Unlimited remote displays
With the optional G4100, an unlimited number of remote displays can be connected to one G4400m, and an unlimited number of G4400s can be monitored by a single remote display. However it's configured, data is stored for more than a year in internal memory, where it can then be periodically analyzed in detail using PQSCADA.

Elspec's press statement also briefly mentions that the G4400 uses a Web server architecture. The built-in Web server really expands the way comprehensive monitoring and control can be accomplished. The system uses OPC open server technology for seamless connection with SCADA (supervisory control and data acquisition) systems.

The Web server provides a three-level user privilege interface, and provides for 128bit SSL (Netscape secure sockets layer) encryption to ensure security.

The server also gives you graphical and tabular display, control and configuration screens. Thanks to the Web, you can monitor and analyze a power grid from anywhere in the world.

On the hardware side, the G4400 provides 12 channels to measure four voltage levels (up to 800V each) and six of current, as well as two temperature indicators. The system operates with simultaneous 12-channel sampling at 250kHz rates. Cycle-by-cycle trends are derived for all rms values and harmonics, up to the 511th harmonic. You can even see inter-harmonics and sub-harmonics on a G4400.

A pair of 10/100-BaseT Ethernet ports is also provided, and you can run PoE. In addition, the G4400 Power Quality Data Center offers USB and RS-485/RS-422 ports that can transmit at speeds to 115.2Kbps. An Ethernet to RS-485/RS-422 bridge is included, as is a CompactFlash port.

Finally, the system can actually sustain itself through a brownout or power loss, operating for at least 25s on its own.

- Alex Mendelsohn

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