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Power Meters and Analyzers for Data Acquisition and Control

SATEC Ltd. develops, designs and manufactures digital powermeters and analyzers for data acquisition and control, as well as advanced software packages for power analysis. Their latest product, the SA300 (ezPAC™) series of Power Intelligent Units (PIU), provides a comprehensive solution for sub-station automation, offering fault recording, power quality, automation and control features as well as comprehensive measurement and data collection. Data can be read on LED, graphical and remote displays and through RS-485 communications. SATEC chose to implement a USB interface in the SA300 series and selected WinDriver for quick hardware access and driver development purposes.

SATEC's SA300 ezPAC targets low and medium voltage utility (electricity) substations, providing a means to automate management of the substation without the need to replace electro-mechanical relays with digital relays (*a relay disconnects and reconnects the power if there is a fault [short-circuit], and after 3 re-occurrences, locks out and needs to be manually reconnected.) If the protection relay is digital it can be reconnected by means of remote communication. However most of the protection relays are electro-mechanical requiring an attendant to physically reconnect the line, and replacement of electro-mechanical relays with digital relays is seldom feasible due to expense, labor and the need to shut down the substation for weeks at a time.

 
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ezPAC Power Intelligent Unit
(Note USB connection in upper right-hand corner)

SATEC SA 300 ezPAC
Above, the ezPAC unit connects directly to current transfers (CTs), measuring the current that leaves the substation through feeders which may reach several hundred Amps. Transformers then convert this high current to about 5 Amps. Most measuring devices are only able to measure currents of up to 10 Amps. With such devices, if a fault occurs, for a short duration, current may increase dramatically and most devices cannot measure these fault currents. ezPAC can measure up to 150 Amps on the secondary (CTs measure 600 Amps on primary and 5 Amps on the secondary.) On the occurrence of a fault, the primary can go up to several thousand and the secondary will increase proportionately, thereby measuring up to 150 Amps - 30 times higher than normal.

SA 300 Features
Remote Display
Inputs:
4 AC voltage inputs
One direct voltage input up to 300V DC
4 current inputs up to 150A
4 additional current inputs for connection to high accuracy current
transformers (Deluxe option only)
Three serial communication ports (COM1, COM2 and COM3) and optional Modem Optional Infra-red communication port, USB (Universal Serial Bus) communication port
Input/Output Plug-in modules:
Digital inputs DI - 16 optically isolated inputs
Relay outputs RO - 8 relays for alarms, automatic and remote control
Analog inputs/outputs AI/AO - 4 analog inputs and 4 analog outputs
Setup is menu driven, with optional password protection.
Real Time Clock
TOU (Time of Use)
Waveform Recorder
Event and data logging

 
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ezPAC Diagram Indicating Ports, Switches and Current Inputs

Why implement USB?
Speed considerations and operational simplicity were key factors in SATEC's opting to develop a USB interface-based powermeter (as compared with traditional RS232 interface.) The SA300 is able to collect up to 128 MBytes of fault data in its internal storage and works in a substation or factory environment. Hence, the option of a simple connection to a user notebook or portable PC with fast transfer of a large amount of data to the PC is often critical. In comparison to other communication interfaces, USB can provide the best performance one can achieve and has simple standard cabling.

The SA300 makes use of USB data packets for transferring data between the device and SATEC's "PAS host application software" using the widely known Modicon Modbus RTU protocol as the application layer. Since it is the native application protocol for all the SA300 communication ports, integrating USB port into the device software required only implementing two device drivers: a USB node driver on the device side, and a client device driver on the PC.

USB Implementation
For USB communications, the SA300 uses a National Semiconductor USBN9603 node controller. The USBN9603 is a full-speed USB device that is compliant with the USB 1.1 specification. It simply interfaces with the SA300's AT91M63200 ARM-7 CPU through the 8-bit parallel bus. The USBN9603 provides 6 function endpoints, each one with a 64-byte dedicated FIFO that helps significantly reduce the CPU overload. The SA300 uses two of the endpoints for implementing transmit and receive pipes with bulk transfers. The sample USB WinDriver-based device driver code provided by National Semiconductor with the USBN9603 gives the user a good starting point for building a user-specific device driver for his own platform.

 
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SA300 USB GUI - enabling the user to view data in a graphical format

Why WinDriver?
The supporting software (PAS) that runs on the host PC has to access the Windows USB driver stack to communicate with the SA300 USB node controller. Developing and debugging a custom USB device driver that would run on different Windows platforms is a complicated and time-consuming task under the Windows DDK. "For the SATEC software development team whose primary specialization is embedded software, the Jungo WinDriver device driver development kit provided us with a simple and efficient solution for these three main reasons. Firstly, it enabled developers to connect their application software to the USB, without any prior knowledge of Windows USB internals. Secondly, the ready-for-use USB kernel driver and simple user-mode API function calls allow fast implementation and testing of the USB communications. As SATEC's host communication software was ready, it took only a couple of hours to implement API calls to the WinDriver library and get the USB communications working. Also beneficial is the fact that the user does not have to be concerned with future needs. If you find that the performance of your USB communication is not acceptable, you can customize the kernel driver using the Jungo Kernel Driver frameworks. Thirdly, the Debug Monitor helps visualize USB data traffic between the host and the device and allows fast debugging and testing of both the USB node hardware and the software driver in your device," said Michael Fishbein, engineer at SATEC Ltd.

About SATEC Ltd.
SATEC Ltd. is a world leader in development and manufacturing of digital electrical powermeters and control and data acquisition systems. Founded in 1987, SATEC has gained an international reputation for high quality and high reliability instruments for the measurement, control and analysis of electric power. SATEC offers an extensive line of power monitoring equipment and software packages, and specializes in providing complete solutions to specific customer needs.
For additional information, visit the company's website: http://www.oksatec.com or contact:
SATEC Ltd. (Jerusalem) Elan Roy, Tel. +972-2-541-1005, email: Elan.Roy@satec.co.il
SATEC Inc. (North America), Ed Hoinowski, Tel. +1-908-608-0500, email: ehoinowski@oksatec.com