ri How much do you know about Navratri? By www.bbc.com Published On :: Fri, 04 Oct 2024 15:36:30 GMT See how much you know with our Navratri quiz Full Article
ri Kids in a cost of living crisis: A Newsround Special By www.bbc.co.uk Published On :: Wed, 05 Apr 2023 10:31:18 GMT Newsround has been finding out how the cost of living crisis and rising prices have affected children living in the UK. Full Article
ri 'History is just a treasure chest of stories' By www.bbc.co.uk Published On :: Tue, 19 Sep 2023 07:12:00 GMT Author Nazneen Ahmed Pathak tells Press Packers, Khadija and Jackson, how real history inspires her stories. Full Article
ri Press Pack: The school solving the crime of stolen lunches By www.bbc.co.uk Published On :: Mon, 13 May 2024 06:37:32 GMT A crimewave has shaken one school to the core...and the culprit? Not exactly who, or WHAT you’d expect. Full Article
ri Injury to keep dancer Amy Dowden out of this year's Strictly By www.bbc.com Published On :: Tue, 05 Nov 2024 07:26:18 GMT It has been announced that Strictly Come Dancing Star Amy Dowden will not be returning to this year's series of Strictly. Full Article
ri Trump vs Harris: Everything you need to know about the US Election By www.bbc.com Published On :: Tue, 05 Nov 2024 07:22:35 GMT With less than a day to go until the 2024 US election - here's everything you need to know... Full Article
ri Quiz: Can you spot the fake news stories from the US election? By www.bbc.co.uk Published On :: Mon, 28 Oct 2024 12:23:08 GMT Find out which viral news stories from the US election are real or fake with this quiz. Full Article
ri Happy News: Stories to make you smile By www.bbc.com Published On :: Mon, 11 Nov 2024 06:49:51 GMT De-Graft has this week's Happy News to put a smile on your face. We have an enormous Spider-Man, some happy rodents and a feathered duo brightening up a school. Full Article
ri Strange News: The week's weirdest stories By www.bbc.com Published On :: Fri, 08 Nov 2024 06:19:46 GMT Nina has our weekly dose of Strange news. We've got some cake, some giant masks and some apples in a bath! Full Article
ri I'm A Celebrity 2024: Who's going into the jungle? By www.bbc.com Published On :: Tue, 12 Nov 2024 09:20:21 GMT The new series is nearly here and we now know which ten famous faces will be going into the jungle. Meet all the stars set to star in this year's show - and let us know who you're most looking forward to seeing in action. Full Article
ri Rich celebs accused of harming planet by 'using private jets like taxis' By www.bbc.com Published On :: Fri, 08 Nov 2024 12:18:46 GMT New research shows the amount of carbon dioxide released into the atmosphere from private jets between 2019 and 2023. Full Article
ri What do friends do? By www.usingenglish.com Published On :: Tue, 01 Oct 2024 18:06:33 +0000 Full Article Ask a Teacher
ri "The disease originated in Britain" not "The disease originated." By www.usingenglish.com Published On :: Wed, 02 Oct 2024 20:55:30 +0000 Full Article General Language Discussions
ri Placentia Library District By ischoolapps.sjsu.edu Published On :: Sunday, November 3, 2024 10:40 am Children's Librarian Intern (Placentia--onsite) Full Article
ri Palos Verdes Library District By ischoolapps.sjsu.edu Published On :: Friday, November 8, 2024 3:32 pm Archives Internship (Rolling Hills Estates--onsite/virtual) Full Article
ri Peralta Community College District By ischoolapps.sjsu.edu Published On :: Tuesday, November 12, 2024 2:11 pm Community College Librarian/Faculty Diversity Internship (Berkeley--onsite) Full Article
ri Teaching Christmas By www.usingenglish.com Published On :: Fri, 30 Nov 2007 09:34:59 +0000 We have added a number of lessons for different levels and articles about Christmas and how it can be taught and used in the classroom. There will be more to follow in the next few days, so please check the What's New page for updates. Full Article General Topics
ri Once Upon A School - TED Prize Winner By www.usingenglish.com Published On :: Mon, 21 Apr 2008 21:27:00 +0000 I recently watched an inspiring talk given as part of the TED 2008 conference by Dave Eggers, a philanthropist and teacher-at-large (as they describe him). The talk shows ways in which dedicated one-to-one teaching can be provided to pupils who would not normally have access to this sort of personal tuition. What's more, the students seem to lap it up. The successful and growing network of professionals volunteering their time to shine their light on local students of all ages is only part of the story. His novel approach to teaching and the way he makes learning fun should be an inspiration to all of us. As Time puts it: "Many writers, having written a first best-seller, might see it as a nice way to start a career. He started a movement instead." Full Article General Topics Speaking Out Teacher Articles teaching TED
ri Drilling - Judicious Use of Brute Force in the ESL Classroom By www.usingenglish.com Published On :: Tue, 27 May 2008 08:34:58 +0000 Another training article. Something my trainees weren't doing very well -drilling. Not very exciting, but someone might find it useful. Full Article Teacher Articles
ri Trials and tribulations By www.usingenglish.com Published On :: Mon, 13 Sep 2021 23:59:59 +0000 Trials and tribulations are events that cause suffering and pain. Full Article
ri The essentials of automation applied to distribution systems via PLCs, SCADA, IEDs, and RTUs By electrical-engineering-portal.com Published On :: Mon, 15 Mar 2021 06:37:31 +0000 Nowadays, it seems that everything we do tends to be somehow automated. The very same is happening in electrical distribution systems. The distribution system at the medium voltage (MV) or low voltage (LV) levels is designed using different structures such... Read more The post The essentials of automation applied to distribution systems via PLCs, SCADA, IEDs, and RTUs appeared first on EEP - Electrical Engineering Portal. Full Article Low Voltage Medium Voltage SCADA actuators communication networks data acquisition distribution systems ieds intelligent electronic devices master terminal unit modulation multiplexing plc remote terminal unit rtu scada telemetry
ri Three most common SCADA applications in MV/LV distribution systems you SHOULD know By electrical-engineering-portal.com Published On :: Mon, 08 May 2023 06:30:56 +0000 Electrical distribution systems comprise a large number of remote applications and locations, and it has traditionally been challenging to monitor and regulate these remote applications and sites. Utility companies have been installing remote terminal/telemetry units, often known as RTUs, at... Read more The post Three most common SCADA applications in MV/LV distribution systems you SHOULD know appeared first on EEP - Electrical Engineering Portal. Full Article Power Substation Premium Content SCADA Substation Automation commercial office current transformer distribution substation control distribution systems ethernet bus ieds loads plc power factor correction rtu scada scada applications shopping buildings shunt capacitors sub-switchboard substation unmanned substations voltage transformers
ri The art of determining the right cross-section of low voltage conductors By electrical-engineering-portal.com Published On :: Mon, 16 Mar 2020 06:18:58 +0000 To be clear at the beginning of this article, determining the cross-section of conductors and cables is, for sure, not the most exciting part of electrical design. There are much more challenging and more exciting parts than staring at endless... Read more The post The art of determining the right cross-section of low voltage conductors appeared first on EEP - Electrical Engineering Portal. Full Article Cables Energy and Power Protection cables conductors correction factors cross-section current carrying capacity ground iec 60364-5-52 installation methods loaded conductors multi core cables parallel conductors reduction factors single core cables wiring systems
ri Dos, don’ts and precautions in wiring cables and conductors inside low-voltage switchboard By electrical-engineering-portal.com Published On :: Mon, 26 Apr 2021 06:33:13 +0000 To be clear from the very beginning of this article, there is no standard model for wiring low voltage switchboards and panelboards. However, for the wide variety of installations and ranges of power ratings, there are local work practices, regulations... Read more The post Dos, don’ts and precautions in wiring cables and conductors inside low-voltage switchboard appeared first on EEP - Electrical Engineering Portal. Full Article Cables Energy and Power Low Voltage Protection aluminium core conductors cross sections electrodynamic effects electrolytic corrosion flexible copper core horizontal trunking low voltage switchboard magnetic effects minimum cross-sections protective conductors rigid copper core switchboard wiring conductors wiring precautions
ri Daily Warm-Up 34 for Gr. 3 & 4: American History By www.teachervision.com Published On :: 2016-12-31T08:00 Help students master important reading skills with a passage about the Pony Express and reading comprehension questions, in this printable warm-up. Full Article
ri ERCOT: What’s changed since Uri and what weaknesses remain By www.power-eng.com Published On :: Mon, 14 Feb 2022 19:09:40 +0000 Everyone agrees Winter Storm Uri was a wake-up call. While the ERCOT grid operated successfully through Winter Storm Landon, some work remains to ensure the grid doesn’t snooze during the next major winter weather event. Full Article Gas Issues News Policy & Regulation ERCOT
ri How to Search Google Images by Usage Rights By careertechtesting.blogspot.com Published On :: Fri, 07 Feb 2014 19:02:00 +0000 I found a great resource by Joyce Valenza on Never Ending Search that I wanted to share with you. In her post, Google search by usage rights, she demonstrates an easy way to find copyright-friendly images on Google Image Search. First, enter your search term into Google Images and then click on Search Tools and then Usage Rights. A drop-down menu appears offering the following options: not filtered by license, labeled for reuse, labeled for commercial reuse, labeled for reuse with modification, labeled for commercial reuse with modification. Please read the rest of Joyce Valenza's article by clicking HERE to find many other copyright-friendly image search options! Full Article Curriculum Education Instruction Online Learning Technology
ri AirPano - Amazing 360 Degree Aerial Panoramas By careertechtesting.blogspot.com Published On :: Thu, 13 Feb 2014 14:53:00 +0000 After a few weeks of cold weather, cloudy skies and snow on the ground my mind begins to wander and think of where I would rather be than here. Hawaii sounds good, doesn't it? Unfortunately, my bank account usually says no to those types of dreams so I found AirPano.com which, at least, took my mind off of how cold I am and provided me a poor man's virtual vacation. AirPano.com was actually better than I expected as it provided incredible 360 degree imagery of landmarks and cities from all over the world. Their website features "over 700 panoramas showing over 120 amazing locations of all continents including Antarctic and the North Pole" and panoramas from some 50 other locations are in the works. Source: AirPano.com Much of the AirPano imagery now includes interactive pinmarks that you can click on to learn more about the places that you are visiting (as you can see on the Venice, Italy panorama below). I think AirPano is a great way to learn about other parts of the world, not only from the amazing images, but also from the history and facts about each site that they provide. Last, but not least, it is a great way to get your mind off of the cold winter weather... Visit Venice, Italy on AirPano.com Full Article CareerTechEd Instruction Online Learning
ri National Agriculture Day - March 15th By careertechtesting.blogspot.com Published On :: Wed, 16 Mar 2016 13:12:00 +0000 CIMC Agricultural Education Catalog Did you know the Oklahoma Department of Career and Technology Education (ODCTE) offers Agricultural Education in 355 high schools? Did you know these programs prepare students for careers in production agriculture, agribusiness, and other emerging agricultural-related occupations? Did you know the CareerTech Student Organization affiliated with Agricultural Education is the Future Farmers of America (FFA)? Study Guide Did you also know the Curriculum, Assessment, and Digital Delivery (CADD) areas of ODCTE have been supporting this occupational area for decades? CIMC produces competency-based instructional products and services for a variety of career and technical areas, including agricultural education. The CareerTech Testing Center creates and offers online assessments as a measure of occupational readiness for students and industry workers. Free study guides include assessment information, standards and test content, sample questions, a list of abbreviations, symbols, and acronyms, strategies for test taking success. ctYOUniverse ctYOUniverse.com hosts online student-ready classroom sites for CareerTech-related subjects. Each fully customizable course site comes pre-populated with curriculum materials developed by CIMC. This one-stop shop for learning materials provides instructors with everything they need to teach in a blended, flipped, or traditional setting. Many thanks to the men and women that produce and protect America's food supply! Full Article assessment CareerTech Testing Center CareerTechEd CIMC CTE Curriculum Education Instruction ODCTE Online Learning Skills Standards Study Guides Training and Resources
ri Seven golden foundations of good electrical installation work By electrical-engineering-portal.com Published On :: Mon, 24 Jul 2023 04:25:11 +0000 This technical article deals with the practical aspects of commercial and industrial electrical installation work. It is of the utmost importance that the practical task be done in the appropriate manner. Electrical installations in commercial and industrial settings are often... Read more The post Seven golden foundations of good electrical installation work appeared first on EEP - Electrical Engineering Portal. Full Article Cables Energy and Power Low Voltage Power Substation ac circuits cable ladder cable route cable runs conduit electrical installation work electrical installations electrical tools electricians explosive atmospheres incoming cables mineral insulated cables pvc cables rigid steel conduit single core cables trunking vertical cable shafts wiring regulations
ri Auxiliary DC power system used for fault detection, trip coils and remote operation By electrical-engineering-portal.com Published On :: Mon, 20 Nov 2023 08:07:53 +0000 The auxiliary DC control power system is considered the most crucial element of a protection, control, and monitoring system. The failure of the direct current (DC) control power can result in the inability of fault detection devices to identify faults,... Read more The post Auxiliary DC power system used for fault detection, trip coils and remote operation appeared first on EEP - Electrical Engineering Portal. Full Article Energy and Power Low Voltage Power Substation Protection auxiliary dc power system auxiliary direct current battery battery charger battery fuse battery types battery-based system charging system control and protection systems dc distribution system dc power dual dc auxiliary supply system fault detection nickel-cadmium batteries switch transfer trip coils uninterruptible power supply ups vrla
ri Five actions to achieve excellent energy savings in old electrical installations By electrical-engineering-portal.com Published On :: Wed, 04 Mar 2020 06:31:09 +0000 Not all existing electrical installations lack energy efficiency, but most of them do. Especially if they were built 15-20 years ago and older. Although it is generally acknowledged that substantial energy savings are possible in most existing installations, the process... Read more The post Five actions to achieve excellent energy savings in old electrical installations appeared first on EEP - Electrical Engineering Portal. Full Article Energy and Power Energy Efficiency Power Quality air conditioning analysis report consumption electrical installations energy energy consumption energy efficiency energy savings heating lighting load measurements
ri Six less known phenomena that can cause disturbance in electrical installations By electrical-engineering-portal.com Published On :: Mon, 30 Mar 2020 04:41:03 +0000 In addition to the known phenomena of lightning and switching, numerous new sources, in particular power converters, can cause disturbance in installations. This disturbance, which is generated by the installation itself or carried by the system from external sources or... Read more The post Six less known phenomena that can cause disturbance in electrical installations appeared first on EEP - Electrical Engineering Portal. Full Article Energy and Power Power Quality Protection capacitors disturbances harmonics inrush current leakage currents overcurrents overvoltages residual current resonance resonance frequency rlc circuit static converters switching overvoltages voltage surge voltage surge protectors
ri 31 Common Household Circuit Wirings You Can Use For Your Home (3) By electrical-engineering-portal.com Published On :: Tue, 14 Jun 2016 21:33:55 +0000 1st part | 2nd part | 3rd part The list of the last eleven household circuit wirings: Three-way switches & light fixture (fixture at start of cable run) Three-way switches & light fixture (fixture at end of cable run) Three-way... Read more The post 31 Common Household Circuit Wirings You Can Use For Your Home (3) appeared first on EEP - Electrical Engineering Portal. Full Article Energy and Power Lighting Low Voltage cable run circuit wiring end of cable fourway switch light light fixture light fixtures switches threeway switches
ri 31 Common Household Circuit Wirings You Can Use For Your Home (2) By electrical-engineering-portal.com Published On :: Tue, 14 Jun 2016 21:34:01 +0000 1st part | 2nd part | 3rd part The list of the next ten household circuit wirings: Double receptacle circuit with shared neutral wire (receptacles alternate circuits) Double receptacle small-appliance circuit with GFCIs & shared neutral wire Double receptacle small... Read more The post 31 Common Household Circuit Wirings You Can Use For Your Home (2) appeared first on EEP - Electrical Engineering Portal. Full Article Energy and Power Lighting Low Voltage appliance circuit cable circuit wirings double receptacle gfci light fixture neutral wire shared neutral switches
ri 31 Common Household Circuit Wirings You Can Use For Your Home By electrical-engineering-portal.com Published On :: Tue, 14 Jun 2016 21:34:06 +0000 The circuit wirings in this article show the most common wiring variations for typical electrical devices. Most new wiring you install will match one or more of the wirings shown. Find the wirings that match your situation and use them to... Read more The post 31 Common Household Circuit Wirings You Can Use For Your Home appeared first on EEP - Electrical Engineering Portal. Full Article Energy and Power Lighting Low Voltage cable run circuit circuit wirings duplex receptacle light fixture receptacle receptacle switch single-pole switch switch
ri Writing in English problems and solutions By www.usingenglish.com Published On :: Sun, 02 Jun 2024 10:31:32 +0000 New Articles Entry: 'Writing in English problems and solutions' has just been added to the Articles area of UsingEnglish.com. Full Article
ri How to write informal IELTS letters By www.usingenglish.com Published On :: Tue, 02 Jul 2024 01:54:11 +0000 New Articles Entry: 'How to write informal IELTS letters' has just been added to the Articles area of UsingEnglish.com. Full Article
ri How to write formal IELTS General Writing Task 1 letters By www.usingenglish.com Published On :: Sun, 11 Aug 2024 07:19:44 +0000 New Articles Entry: 'How to write formal IELTS General Writing Task 1 letters' has just been added to the Articles area of UsingEnglish.com. Full Article
ri IELTS Writing Task Two tasks on feelings By www.usingenglish.com Published On :: Tue, 20 Aug 2024 01:20:04 +0000 New Lesson Plans Entry: 'IELTS Writing Task Two tasks on feelings' has just been added to the Lesson Plans area of UsingEnglish.com. Full Article
ri Things to avoid in IELTS Academic Writing Task 1 giving reasons practice By www.usingenglish.com Published On :: Sat, 21 Sep 2024 22:42:41 +0000 New Lesson Plans Entry: 'Things to avoid in IELTS Academic Writing Task 1 giving reasons practice' has just been added to the Lesson Plans area of UsingEnglish.com. Full Article
ri Tricks in designing and analyzing schematics and diagrams of high voltage substations By electrical-engineering-portal.com Published On :: Mon, 08 Aug 2022 05:51:54 +0000 High voltage power substations are complex networks of power and control connections, represented by design elements like- Single Line Diagrams, layout and block diagrams, schematics, logic diagrams, schedules, and so many more. Wiring diagrams and schematics, in a sense, are... Read more The post Tricks in designing and analyzing schematics and diagrams of high voltage substations appeared first on EEP - Electrical Engineering Portal. Full Article High Voltage Power Substation Premium Content Substation Automation 132kv line block diagrams busbar protection scheme ieds inputs instrument transformer logic diagrams master trip relay outgoing line power substation rtu scada schematics single line diagrams sld transformer differential protection wiring diagrams
ri Fundamental concepts of schematic drawings: Going deeper into analysis and design intricacies By electrical-engineering-portal.com Published On :: Mon, 25 Dec 2023 08:03:30 +0000 Welcome to this comprehensive technical article that delves into the intricacies of electrical schematics, shedding light on crucial elements such as loops, wire connections, auxiliary contacts, MCBs, contactors, circuit breakers, isolators, earth switches, and terminal blocks. In the world of... Read more The post Fundamental concepts of schematic drawings: Going deeper into analysis and design intricacies appeared first on EEP - Electrical Engineering Portal. Full Article High Voltage Power Substation Premium Content Protection auxiliary contacts auxiliary relays circuit breaker notation circuit breakers contactors earth switches electrical schematic design isolators loop supply supervision relay loop wiring mcbs normally closed contact normally open contact schematic drawing schematic drawings schematics terminal blocks wire connections
ri A roadmap for engineers seeking mastery in the language of electrical schematics By electrical-engineering-portal.com Published On :: Wed, 03 Jan 2024 11:16:11 +0000 In the intricate landscape of electrical engineering, the ability to decipher and interpret schematic drawings is a skill that separates the adept from the novice. This technical article delves into the art of understanding schematics, unraveling the complexities through a... Read more The post A roadmap for engineers seeking mastery in the language of electrical schematics appeared first on EEP - Electrical Engineering Portal. Full Article High Voltage Power Substation Premium Content Protection auxiliary contacts auxiliary relays circuit breaker coil saving contacts early break and late break contact early make contact electrical schematics interlock circuits late make auxiliary contact limit switches magnetic contactors multi position switch normally closed contact normally open contact power contacts tripping and closing coils voltage transformer circuit
ri 11 factors that significantly influence the transformer price (Be careful when specifying) By electrical-engineering-portal.com Published On :: Mon, 18 Sep 2023 06:41:12 +0000 The majority of utilities are normally extremely well aware of the economic aspects and savings that can be obtained at all stages of the transformer’s life cycle. This is because the purchase of a transformer involves a very high capital... Read more The post 11 factors that significantly influence the transformer price (Be careful when specifying) appeared first on EEP - Electrical Engineering Portal. Full Article Energy and Power Protection Transformers Transmission and Distribution auxiliary equipment bushings cts de-energized tap changer detc environmental conditions insulation coordination insulation level load losses mva size no-load losses oltc on-load tap-changers overloading capability special transformer tests star/star transformers tap changers tertiary stabilizing winding transformer handbook transformer life expectancy transformer losses transformer price winding configurations
ri Mastering stability test of power transformer: Differential and Restricted Earth Fault (REF) protection By electrical-engineering-portal.com Published On :: Mon, 25 Sep 2023 05:55:16 +0000 This technical article discusses the essentials of transformer differential protection and restricted earth fault protection schemes, contrasting the two and elaborating on why the latter is necessary. Furthermore, it reveals the outcomes of stability tests performed on a 502 MVA... Read more The post Mastering stability test of power transformer: Differential and Restricted Earth Fault (REF) protection appeared first on EEP - Electrical Engineering Portal. Full Article Premium Content Protection Testing and Commissioning Transformers differential protection differential protection scheme failure fault hv windings injecting fault lv side primary current lv side secondary current lv windings measured primary currents measured secondary currents ref ref protection restricted earth fault protection stability test stable condition transformer differential protection transformer restricted earth fault protection tv windings unit protection scheme unstable condition
ri The loop electrical distribution system used to supply bulk loads (industrial plants and buildings) By electrical-engineering-portal.com Published On :: Mon, 23 Oct 2023 06:36:54 +0000 First, let’s say a word or two about the essentials of power distribution systems for our young electrical engineers. An electric distribution system, or distribution plant as it is sometimes called, is all of that part of an electric power... Read more The post The loop electrical distribution system used to supply bulk loads (industrial plants and buildings) appeared first on EEP - Electrical Engineering Portal. Full Article Power Substation Protection Transformers Transmission and Distribution distribution substations distribution transformers electrical distribution system fuses loads loop distribution system loop electrical distribution system loop primary feeder pilot-wire relaying primary feeders secondary circuits secondary substation sectionalizing breaker sectionalizing switches sub-transmission circuits supply bulk loads
ri Transformers in plant power distribution: The bigger picture By electrical-engineering-portal.com Published On :: Mon, 04 Mar 2024 06:10:41 +0000 This technical article provides an overview of the various choices and assists electrical engineers in determining the criteria that should be included in the transformer specifications in order to meet the requirements of their particular application. A power plant often... Read more The post Transformers in plant power distribution: The bigger picture appeared first on EEP - Electrical Engineering Portal. Full Article Energy and Power Power Substation Transformers autotransformer auxiliary losses delta-delta delta-star insulation class load losses no-load losses off-load tap changer oil tank on-load tap changer phase shift power distribution power plant sta-delta star star tap changers temperature rise transformer cooling transformer dielectric test transformer impedance transformer losses transformer phase markings transformer winding configurations turns ratio zigzag
ri The essentials of electrical systems in cement plants By electrical-engineering-portal.com Published On :: Mon, 14 Sep 2020 07:34:34 +0000 Many young engineers consider cement plants pretty complicated because of their weird technology. The reason probably lies in the fact that you cannot understand all those technologies unless you worked in such a plant and saw all processes from scratch.... Read more The post The essentials of electrical systems in cement plants appeared first on EEP - Electrical Engineering Portal. Full Article Electric Motor Energy and Power Variable Speed Drives captive power cement plants clinker electrical systems load factor maximum demand medium voltage drives mv motors power distribution power distribution system power factor power supply synchronization variable speed drives
ri Guidelines for selecting the proper Variable Frequency Drive (VFD) for motor applications By electrical-engineering-portal.com Published On :: Mon, 28 Jun 2021 06:02:24 +0000 This article addresses the Variable Frequency Drive (VFD) concept in several aspects that matter the most in selecting the proper VFD for applications. One of the important factors is the control type required for a given application since it is... Read more The post Guidelines for selecting the proper Variable Frequency Drive (VFD) for motor applications appeared first on EEP - Electrical Engineering Portal. Full Article Electric Motor Premium Content Variable Speed Drives bearing current direct torque control dV/dt harmonics insulation inverter motor motor terminals phasor-controlled drive switching frequency v/f control variable frequency drive vfd vfd control vfd grounding