Tech Take Smart Grid Technology Review: PQube Power Quality Monitor Oct 20, 2009    var addthis_config = { data_track_clickback: true } var addthis_pub="smartgrid"; var addthis_brand = "Smart Grid News";var addthis_header_color = "#ffffff";var addthis_header_background = "#6b7ba4";

In SGN's Tech Take articles, power engineer and architect Erich Gunther evaluates actual products and services against the SGN Smart Grid Scorecard. Unless disclosed explicitly at the beginning of the article, neither SGN nor Erich Gunther has received any compensation from the vendor nor do they own stock in the company.

One of the promises of the Smart Grid is improved power quality.  The reliability or continuity of service is one of the results that will come from the implementation of the self-healing aspects of the Smart Grid.  Power electronics are getting smarter, as well.  Sensitivity to minor perturbations of the electricity supply is becoming less of a concern.  That may be due to the design of equipment for the global marketplace and standards around the world that address voltage quality.

Matching equipment specifications to the delivered electric power is a matter of faith.  The wiring from the utility to the point of use has been done by experienced technicians and inspected by safety experts.  The protection has been carefully planned, installed, and inspected.  The interactions of different electric equipments have been considered, so normal operation of elevators don’t interfere with the normal operation of copiers.  Equipment disruptions are often blamed on the incoming electric power.

The PSL PQube is a power quality monitor that can help determine the cause of electric disruptions.  Installed at the service entrance, it monitors the commercial electricity, noting the time and duration of any abnormal voltage or current.  It will draw a picture of the event, and send you an email if you like.  It records events and trends and preserves the history of the electric service.  Installed at the point of use, the PQube sees what the equipment sees, so if a disruption occurs, a record is made for investigation.

It’s impressive.  We now use it on Smart Grid Lab projects and have another monitoring the power to our offices.  If you need a low-cost, high-performance instrument that does full-blown power quality monitoring, lab-grade energy monitoring, DC bus monitoring, and carbon footprint monitoring, take a look at the PQube.   When you add all the options discussed below, it costs roughly $2k.

There is no software cost (actually, there is no software), there is no on-going service cost, and the firmware upgrades are free.

The SGN Scorecard

The SGN Scorecard was developed for a very important reason: Most of today's products do not adhere to Smart Grid principles. They do not support the requirements envisioned by Smart Grid researchers such as EPRI, the California Energy Commission's Public Interest Energy Research program, the Modern Grid Initiative and DOE's GridWise program. Nor do they adhere to the mandates in the Energy Independence and Security Act of 2007.

 In particular, several elements of the EPRI IntelliGrid Architecture are critical to implementing a Smart Grid:

• Proven, Internet-derived communication technologies
• Service-based architecture at the enterprise level
• Self-healing technology
• Well-defined interfaces and points of interoperability
• Application of industry and international standards
• Built-in security and network management

The SGN Scorecard is a checklist that measures whether products meet minimum Smart Grid standards. We use it as the benchmark for all Smart Grid technology reviews. You are invited to use it free of charge for your own evaluations. For a further explanation and a blank version you can copy freely, download the PDF version of the Scorecard. (See link below.)

Background

The PQube puts all of its outputs on a removable SD card (digital camera memory card) using Windows FAT32 file structure.  The folders are well structured and labeled.  The standard 2GB card included with the PQube holds roughly 2 years of data.  When nearly full, the PQube will delete the oldest month’s data, making a circular saving pattern.

There is no software from PSL.  Instead, the PQube stores all of its data in widely-supported file formats.

The PQube stores data on the SD card in three native file formats:

·         CSV (Excel) files for raw data

·         GIF (picture) files for quick review

·         PQDIF files. 

The user can choose to have data stored in any or all of these formats. Summaries are also available, stored as text, HTML, and XML files.

The PQube itself is a DIN-rail mounted instrument roughly the size of a large digital camera.  It has four AC voltage screw terminals (L1, L2, L3, and N) that are UL-recognized for connection to up to 690-volts nominal (useful in wind turbine applications).  It also has two +/- 60V DC screw terminals, with available attenuators for +/-600Vdc and +/-1500Vdc, typically used for DC bus monitoring.  There is a digital input that is wetted for direct connection to relay or switch contacts, and a dry relay contact output. 

Optional modules snap onto the PQube like Legos.  They include various 4-channel current modules (20-amp, 100-amp, 1-amp, 5-amp, 1-volt, 5-volt, and 10-volt), and an Ethernet module with firmware that includes an email client, a web server, an FTP server, and an SNTP client.  We snapped together a PQube, an optional Ethernet module, and a 1-amp current module for testing in the server room.

The PQube allows the user to set PT ratios up to 10,000:1 and CT ratios up to 10,000:1.  It supports calculated current waveforms when N-1 CTs are installed.

The $2k single-quantity price mentioned above includes the base 3-phase PQube, an optional 4-channel current module, an optional Ethernet module, and a power supply.   Through their web site PSL offers “kits” for the most common configurations.

The PQube has three classes of outputs:

·         On-screen live meters.  On its organic LED color screen, the PQube provides meters for L-L and L-N voltages, currents, frequency, time, date, RMS flicker, watts, watt-hours, CO₂ grams per hour, CO₂ grams generated or avoided, VA, VAR, power factor, lists of recent events, temperature, humidity, DC voltages, THD, TDD, unbalance, phase rotation vectors.

·         Triggered events. These include sags, swells, interruptions, frequency variations, DC undervoltage and overvoltage, 1-microsecond impulse detection.  A triggered event causes 256-samples-per-cycle waveform recording, plus cycle-by-cycle RMS recording.  Cross-triggering is supported.  The raw data for all of these recordings is available in CSV (Excel) files, GIF (picture) files, and PQDIF files.

·         Trends and statistics.  These include 24-hour, weekly, and monthly graphs of min/avg/max values for all parameters: voltage, current, frequency, DC, RMS flicker (Pinst, Pst, PLT), two channels of temperature and humidity, power, power factor, unbalance, THD, TDD, etc.  The 24-hour files contain minute-by-minute min/avg/max values of each parameter.  The weekly and monthly files contain 5-minute min/avg/max values of each parameter.  The PQube calculates and graphs cumulative probabilities, histograms, and load duration curves for each parameter.  All of this raw data is available CSV (Excel) files, GIF pictures, and PQDIF files.

A typical graph recorded at EnerNex by the PQube as a GIF picture – the raw data is also available as CSV spreadsheet files, or PQDIF files.

Voltage, current, and frequency trends recorded by the PQube (not at EnerNex).  Again, the raw data is also available as CSV spreadsheet files, or PQDIF files.  This picture downloaded through http directly from a PQube (no software, no server).

Communications

The PQube works with or without an Ethernet connection.   We used it in the server room both ways.

Without an Ethernet connection, the user just pops the SD card out and looks at the contents (just like a digital camera) on his PC.

With an Ethernet connection, the PQube can:

·         Send email to up to 10 recipients each time it records an event, or a daily, weekly, or monthly trend/statistics report.  The Excel, picture, and PQDIF files are sent as attachments to the email. The built-in PQube email client supports SMTP, POP, plain-text, MD5.  The PQube can also receive emails, which provides a convenient way to change the setup, upgrade the PQube’s firmware, etc.  Email is generally the least challenging way to deal with IT department issues.

·         Provide a real-time web site.  For example, during our testing we looked at a PQube in California.  The web site includes roughly 35 real-time meters, plus all events (including dual-language graphs) and all trend-statistics reports.

·         Provide FTP-protocol service.  This can be a simple way to transfer files from the PQube’s SD card to a local computer.

·         Provide Modbus-over-TCP service.  Simple access to meters via many low-cost programs.

NOTE:  The PQube does not provide any security for its communications, other than simple text-based passwords.  PSL  points out that it is a component in a system, and relies on the external system to which it’s connected to provide both communication security and physical security.

Setup

The user sets up the PQube by editing a SETUP.INI text file on the PQube’s SD card.  This makes it easy to set up hundreds of PQubes the same way – just copy the file.  The setup file contains things like thresholds, types of files to be written, email addresses to send to, and ways of turning channels and reports on and off.

The SETUP.INI file is long, but well documented with comments.  For many of the parameters, the user can choose “AUTO”.  For example, nominal line-to-line voltage can be set to any value between 100 volts and 690 volts, or the user can set it to AUTO and the PQube will figure it out.  The PQube knows more than 100 commonly used worldwide power configurations.

Accuracy

The basic accuracy specified for the PQube is 0.05% for voltage channels, and 0.2% for current channels.

Interestingly, you can download an individual NIST-trace Calibration Report for every individual PQube, just by entering its serial number on this page. A brief review of one of these reports showed that the PQube we were testing was, in fact, more than twice as accurate as the published specification.

With this level of accuracy, essentially all of the errors will be dominated by the external current transformer accuracy.

Agency Approvals

The PQube is UL-recognized, TUV-certified, CE-marked, and RoHS compliant.  PSL certifies 61000-4-30 Class A for voltage dips, swells, and interruptions.

Pre-packaged Portable Version

The PQube is clearly designed as a fixed-installation component.  But PSL does offer it pre-packaged in a portable, IP65 (waterproof) enclosure for about $5k.  The price includes water-resistant connectors and cables, voltage clip leads, four premium-grade clamp-on current transformers, Ethernet connectivity, 480-volt-rated UL-recognized circuit breaker, etc.  We’re told these are used in locations like offshore oil platforms, but that most users quickly realize that it’s cheaper and more effective to permanently install a PQube – the cost of returning to remove the portable package exceeds the cost of a PQube.

Comparing the PQube to Other Instruments

Probably the closest comparison is with the SoftSwitching iGrid monitor.

The PQube and the iGrid monitor are roughly the same price.  The iGrid is packaged for temporary installation, and comes with a web-based service that conveniently summarizes the data captured by the iGrid monitor (the PQube does not come with or require any service). 

The PQube samples roughly four times faster than the iGrid, and records many PQ parameters that the iGrid does not (impulses, flicker, THD and TDD, unbalance, frequency disturbances).  Unlike the iGrid, the PQube also records current and power (watts, peak demand, watt-hours, VARs, var-hours, power factor, carbon footprint).  The PQube provides detailed statistics and distributions for each parameter.  The PQube is roughly 10 times as accurate as the iGrid.

The PQube simultaneously monitors DC bus voltage and temperature/humidity; the iGrid does not.

The data from the iGrid belongs to SoftSwitching, and is licensed for a significant annual fee to the user.  The data from the PQube belongs to the user.  Unlike the iGrid, the PQube is standards-based: it supports PQDIF, 61000-4-30, and has better standards-based communication abilities (email, FTP, web server, etc.).  The PQube comes standard with 100 times as much memory as the iGrid.  The PQube can work either with or without a communication connection; the iGrid requires a communication connection to function.

Smart Grid Scorecard for PSL PQube Power Quality Monitor 

Score 90 of 100

Smart Grid Scorecard for PSL PQube Power Quality Monitor 

Score 90 of 100

Metric	Score (10 is best)	Comment
Impact	9	The PQube provides diagnostic information, but also up-to-date energy usage information.  Consumers see 1-second, 1-minute, 15-minute peak demand, carbon footprint rate, accumulated carbon from the source, etc.
Openness	10	The lack of proprietary software is a distinct advantage.  The system data can be accessed in a number of standard ways.  TCP/IP, FTP, email via POP and SMTP. File formats are CSV (Excel, OpenOffice), GIF (Microsoft Word, Photoshop) and PQDIF.
Standardization	10	The system is thoroughly based on recognized international standards. Certification by UL and accuracy to NIST standards.
Security	8	Only normal password protection.  Installed in an Ethernet network environment, additional layers of security might be applied.
Manageability

2010.7.22 낙뢰, 번개시 서울 서초동에서 잡은 이벤트 파형 그림들

PQube의 특정 이벤트를 PLC 경보 또는 MMI 경보로 이용하는 방법