AC Voltage Measurement, Intelligent Devices

By tchenwa | Published: February 7, 2019 – 12:24 pm

The accurate measurement of AC Voltage is complicated by the necessity to minimize the burden the measuring instrument places on the primary circuit. The incorporation of a 1:1 current style voltage transformer in the AC voltage measuring circuit offers several advantages.

Features

  • A minimal burden on the primary voltage circuit, with essentially zero primary circuit load,
  • Isolation of the primary AC circuit and the secondary output signal, and
  • Exceptional accuracy with a minimal phase shift.
The AC current style voltage transformer is designed with either a 1mA to 1mA or 2mA to 2mA ratio. An example of the implementation using an operational amplifier I/V (current to voltage) circuit or a resistor sampling circuit; The input resistor R limits the current to the 1mA or 2mA input. An application note document provide additional information – Application Note 1:1 Voltage Transformer (pdf 510kb). The TV31 with UL Recognition Certification is an example of a current style AC Voltage Transformer. TC

AC Current Measurement, Intelligent Devices

By tchenwa | Published: January 14, 2019 – 8:15 pm

Toroidal, Solid-core Current Transformer - AC Current Measurement - Intelligent DevicesThe Supervisory Control and Data Acquisition (SCADA) systems used by electric utilities to manage the distribution of electric power are highly dependent upon the intelligent, micro-processor based devices installed throughout the electric power distribution grid. These intelligent devices acquire in real time the critical performance measurements (e.g. current, voltage), transmitting that information back to the central SCADA control center. The SCADA control center can issue operate commands (CONTROL actions) to the intelligent devices. These CONTROL actions can operate a switch, operate equipment that adjusts voltage or current, operate equipment that adjusts phase shift or any number of actions necessary to manage the electric power distribution grid.

Intelligent Devices Measurements

The intelligent devices typically measure AC current based upon the secondary output of a primary current transformer, typically 0 to 5 ampere AC. Transforming the 0 to 5 ampere AC signal to level appropriate to a micro-processor based circuit is handled by solid-core, toroidal current transformers. The 0 to 5 ampere conductor is looped through the center opening of the current transformer. A solid core current transformer offers superior transformation accuracy at a very competitive component price. Solid-core current transformer can be designed to perform beyond the rated primary before magnetic core saturation offering the ability to measure AC current surges. The advent of digital signal processors (DSP) offers high signal sampling rates, enabling the measurement of the AC base frequency and the harmonics of the base frequency. Surface Mount Technology (SMT) components offers compact designs capable of operating in harsh operating environments.

3 Phase SCADA Remote Terminal Unit

3 Phase SCADA Remote Terminal UnitA three(3) phase SCADA Remote Terminal Unit (RTU) incorporates analog input measurement of AC current and AC voltage, digital signal processing necessary for the calculation of power, power factor, harmonics amplitudes, etc. and data transmission to the SCADA control center. TC

AC Electric Power Monitoring and Measurement Sensors

By tchenwa | Published: December 3, 2018 – 2:45 pm

AC Current Transformer Sensors - Retrofitting Existing Distribution NetworksRetrofitting Existing Distribution Networks

The current generation of electric power AC current sensors that are suitable for retrofitting existing distribution networks have obtained a level of accuracy capable of near revenue grade metering. These split-core sensor designs permit the installation of the AC current sensor without taking the primary conductor off-line. The standard solid-core AC current sensor used by electric power meters requires that the primary conductor be disconnected and threaded through the solid core current sensor for installation. The split-core design is simply clamped around the primary conductor and physically secured to the primary conductor.  

AC Current Transformer Sensors Most Widely Used

Split-Core Rogowski Coil Current Sensor - Retrofitting Existing Distribution NetworksThe technologies most widely used are the split-core AC current transformer sensors which incorporate advanced materials magnetic cores (e,g, silicon steel cold rolled grain oriented, Mn-Zn ferrite, …) and the Rogowski Coil current sensor “rope style split-core design. AC current transformer sensors offer excellent price/ performance. However, the AC primary current range and frequency response for each sensor design is relatively limited. The rigid physical design is not conducive to irregular primary conductor profiles (something other than a circular or rectangular profile).  

Benefits of Rogowski Coil AC Current Sensors

Rope style Rogowski Coil AC current sensors offer a very wide AC primary current range and frequency response. The flexibility of the “rope” style split-core design can be used for irregularly shaped primary conductor profiles. The Rogowski Coil current sensor does require additional electronics to perform the integration of the dv/ dt secondary output of the sensor.  

See Specs on the Following:

AC Current Transformer Sensors Rogowski Coil Current Sensors TC

Micro-Grid, Option for Restoring Electric Power to Puerto Rico

By tchenwa | Published: September 17, 2018 – 3:54 pm

I have read several interesting stories of organizations proposing and installing Micro-Grids as a means of restoring electric power to areas in Puerto Rico. The Micro-Grid systems incorporate electric power generation, electric power storage and/ or smart-grid connection to the electric utility distribution network. The installations goals are;
  • Restoring electric power.
  • Providing backup to critical infrastructure (e.g. hospitals) should the electric utility supply be inconsistent.
  • Incorporating alternative electric energy generation sources.
  • Hurricane Maria severely damaged the electric utility distribution grid. That damage coupled with the failing electric utility infrastructure left many areas without service for extended periods of time. These organizations are proposing to use solar arrays as the electric power generation source with battery backup for electric power storage. Technically, this solution is very doable. I would also assume that for remote locations that may not regain electric service any time soon, this may be the only solution. However, these systems are relatively complex to maintain and have the same miss-match between when power generation is at its mid-day peak and when usage is desired during evening and at night. I do believe that solar power will be part of the future electric generation mix. Maybe what has to change is our thinking and go back to the Thomas Edison idea of DC power. I have been exposed to the mathematics which justifies AC for transmitting electric power over distance. By taking the output of the solar array, converting the power to AC to power some usage, converting the electric power back to DC to charge the battery there are enormous loses. Maybe Micro-Grids should be DC, only using inverters to power the huge power loads (e.g. oven, washer, dryer). Tim C

    California Zero Net Energy Program: Part 2

    By tchenwa | Published: September 23, 2016 – 4:38 pm

    The California Zero Net Energy program discussed in the previous post will have a significant impact on new construction. The average residential electric power usage in the State of California is 6,741 kWh per year (U.S. Energy Information Administration) or 18.5 kWh per day on average. Presumably a residential home will generate electric power using a PV (solar) system. The average PV system is rated at 5 kWh (approximately 400 SFT of solar panels). This would appear to be sufficient to offset any usage but depending upon PV module efficiency, which will vary with time of day and weather, the electric power produced will be significantly less than rated. The difference will have to be made up through energy efficiency and the shifting of usage from the time of day with peak loads (e.g. evening) to time of day with peak generation (e.g. mid-day). I would think that from an electric utility perspective, electricity available at 7pm to 10pm during peak usage will be worth a lot more than electricity available at 12:00 noon. Time of day rates may become the norm. TC

    California Zero Net Energy Program

    By tchenwa | Published: September 16, 2016 – 1:56 pm

    I recently read an article about the California Zero Net Energy program whose stated goal is that all new residential construction in California will be zero net energy by 2020. All new commercial construction will be zero net energy by 2030. Zero Net Energy (ZNE) is defined to be that the building will produce as much energy as the building uses over a one year period. This goal will be achieved through a high level of energy efficiency and through the addition of clean, on-site renewable power generation, presumably solar PV. Wow … The implications are dramatic for both the home owner and the electric utilities that service the building. As we discussed in previous posts, the electric utility distribution networks have been designed over the last 100 years or so to be a one-way street. The regulated electric utilities built huge electric power generating plants that transmitted the electric power through a network of power transmission lines at ever decreasing voltage levels until the power arrives at the home at typically 120VAC or 240VAC. Balancing the power requirements for the service territory is the support base provided by the large electric power generation capability augmented with “standby” generators for peak loads. A fairly predictable power distribution model. What happens when a significant share of the end electric power user base becomes at times a power generator? Is the sun shinning in Los Angeles but Santa Barbara is overcast? (FYI Santa Barbara is northwest of LA along the Pacific coast). The source of the electric power generation becomes highly volatile and variable. More information can be found on the ZNE web site www.CaliforniaZNEhomes.com . TC

    Free Electric Power

    By tchenwa | Published: November 13, 2015 – 1:39 pm

    The New York Times published an article recently on how TXU Energy (Dallas/ Fort Worth, Texas) is offering their customers free electricity during certain times of the day. A little background may be helpful. There are three electrical grids that cover the mainland United States, essentially East coast, West coast and Texas. Several years ago, the Texas electrical power market was split into generation, transmission and distribution. The intent was to encourage competition at the generation level and distribution level where the electric power is used. According to the article, the abundance of wind electric power generation has resulted in a surplus of power in the evening. The TXU strategy is to train their customers to shift their variable loads to the evening hours, hopefully reducing the peak energy loads during the day. The article interviews several residential customers who shift their washing machine and dish washer use to the evenings. All of this is made possible by the implementation of the industry term Smart Grid. Intelligent electric meters that can transmit and receive user level data make this time-of-day rate application possible. Is this the killer app that will help to justify the internet of everything? I wonder if this program is available to large industrial users? A night shift from 9:00pm to 5:00am might be very cost efficient. New York Times article: “A Texas Utility Offers a Nighttime Special: Free Electricity”, Clifford Krauss, Diana Cardwell. TC

    Electric Power Generation Business Model – Part 1

    By tchenwa | Published: June 3, 2015 – 8:21 am

    In the 1990’s the trend was to break-up the electric utility monopolies into separate Generation, Transmission and Distribution businesses. The intent was to open up the electric power generation side of the business to more market oriented competition with the hope of lowering prices for electricity at the wholesale and retail level Two trends have evolved in the intervening years to disrupt this neat solution. • The increase domestic (USA) production of oil and natural gas plus other global factors has resulted in the significant reduction over the last year in the price of oil and natural gas. • The significant increase in solar panel electric power generation by consumers has shifted more power generation to the Distribution level. So why is the decrease in global oil and natural gas prices not a completely good thing for everyone? Certainly, those customers that are highly dependent upon electricity generated by oil and natural gas fired generators should benefit. Customers in my family home of Hawaii where oil electric power generators predominate, should see significant savings. The issue is different in parts of the USA that are dependent upon nuclear power plants for the majority of their electric power generation base. The current merchant wholesale rates for electric power generated by nuclear power plants is at a level that makes some of these generators uneconomical. Representing a huge capital investment, requiring years to build, these plants cannot be easily or quickly be added to the power generation mix. Their importance as an electric power generator at stable and predictable rates cannot be over stated. In addition, this type of electric power generation is significantly cleaner if “greenhouse gas emissions” and global warming are a consideration. I recently read an article which discussed the application of a nuclear power plant operator to the utility regulatory agency for financial relief. Their argument is that electric power generation mix needs a source of stable generation at predictable rates to form the base. Coal fired plants have been historically provided the foundation of electric power generation, however, their undesirable environmental impact should see the reduction in usage over time. In general, oil and natural gas generators are very appropriate for time of day and peak load requirements. What is the appropriate mix? Each power generation option has favorable and unfavorable features. Just a few months ago when the price of oil was around US$100 per barrel, nuclear power plants look very good economically (ignoring radioactive fuel disposal). We read every day about coal as a fuel and the undesirable impact on the environment. Oil and natural gas have better environmental impact, but what if we include what it takes to get it out of the ground!? Thrown into the generation mix is the power generation at the Distribution level through solar cell installations. Disruptive environment for both the power generation businesses and their governmental regulators. TC

    Globalization and Free Trade Agreements

    By tchenwa | Published: March 19, 2015 – 9:32 am

    I recently read an article in the Wall Street Journal that analyzed capital investments by multi-national car manufacturers in North America. These multi-billion dollar investments in car manufacturing facilities both completed and planned covered the period from 2005 through 2020. The time line of investments completed and planned during this period shows four (4) in the American Southeast and seven (7) in Mexico. The author’s thesis is that a significant reason that these companies have decided to make these huge investments in Mexico rather than the American Southeast is because of the greater number of Free Trade Agreements that Mexico has negotiated with other countries representing large current and future markets. Certainly, the USA and Canada currently represent a significant market for manufacturing facilities in Mexico. The NAFTA trade agreement has been a significant factor in this trade relationship. Even so, I would assume that the differences in labor costs / component material costs are not sufficient to justify the significant investments in local infrastructure, local suppliers and local work force training over many years. I think that we are seeing a shift in strategic planning by these companies (Audi, Nissan, Mercedes-Benz, and BMW). The Mexican Free Trade Agreements with the European countries, South American countries and those in the Far East will offer in the future a competitive pricing edge that cannot be matched by products manufactured in America’s Southeastern facilities. The current reluctance by some in the US Congress to accept Free Trade Agreements seems like an exercise in futility. As the saying goes – “That horse has already left the gate!”. From a moral perspective, we should congratulate Mexico for its far sighted thinking since Free Trade Agreements work both ways. They have opened themselves to trade coming in the other direction. I have read that the NAFTA Agreement has caused significant harm to Mexican small farmers since the American farmers are enormously productive. So what do I take away from this discussion? Globalization is no longer defined by how we address a market confined to a specific country, but how to efficiently serve many markets (which happen to be divided by political country boundaries). The WSJ article is “Trade Pacts Give Mexico An Edge” by Dudley Althaus and William Boston (March 18, 2015). TC

    Solar Arrays as Distributed Power Generators

    By tchenwa | Published: February 19, 2015 – 2:56 pm

    I have noticed several trends in the electric power market which I find very intriguing. The first is the development of distributed power generation. I am not referring to the growth of the large merchant power generators, but the growth of the individual residential power generators. My sister and brother-in-law live in Hawaii. They installed a solar cell array on their home. The solar cell array generates surplus electric power during the day, resulting in negative metering during the day. During the evening and at night the house draws power from the Hawaii Electric power distribution grid. The arrangement with Hawaii Electric is that the electric power that is distributed into the Hawaii Electric grid is applied as a credit up to the amount drawn from the grid during the periods that the solar cell array is not generating electric power. Assuming that the solar cell array has been sized to generate excess electric power over and above the peak daytime power requirements, Hawaii Electric is receiving essentially “free” electric power during the solar power generating period. I would guess that the kilowatt hour rate for electric power from Hawaii Electric is among the highest in the nation. The return on investment for the residential installation is probably very attractive. This arrangement leads to some interesting questions regarding the future of electric power distribution by electric utilities. Since Hawaii has minimal heavy industry (the exception being the various military bases), the peak requirements for electric power would be typically in the early morning and evening/ night when residential usage peaks. Does this match the distributed power generators anticipated contribution to the grid? Should electric power storage be added to residential distributed generation sites minimizing the electric power draw from the grid, does it make sense to charge the electric power billing method to a basic “connection to the grid” fee plus usage per kilo watt hour rate? How does Hawaii Electric manage the large numbers of distributed electric power generator sites adding power to their distribution grid (low voltage) versus the transmission grid (high voltage) designed for this purpose? TC