Monday, 23 March 2015

Types of Motor Starting Methods

Types of Motor starting Methods,motor speed control,frequency control,voltage control for motor,auto transformer speed control,winding control for motor


Motor starting methods 

MethodAdvantagesDisadvantages
Across - the - LineSimple, Cost-EffectiveHigh Current Inrush
High Starting Torque
Abrupt Start
Reduced-voltage autotransformerHigh output torque vs. starting current.
Some Flexibility in starting characteristics due adjustable taps on auto-transformers
Limited duty cycle
Large equipment size due to autotransformers
Reduced-Voltage Resistor or ReactorHigh output torque vs. starting currentLimited duty cycle
Limited flexibility in starting characteristics
Higher inrush current than with reduced-voltage autotransformer
Large equipment size due to resistors/reactors
Wye-DeltaRelatively low inrush current
Relatively simple starter construction
Good for long acceleration times
Relatively low output torque vs. starting current
Limited flexibility in starting characteristics
Requires special motor construction
Part-WindingRelatively Simple starter constructionRelatively low output torque vs. starting current
Not suitable for frequent starts
Requires special motor construction
Solid-state soft starterSmooth Acceleration
Low inrush current
High flexibility in starting characteristics
Typically offers deceleration control also
Typically integrates with industrial automation
infrastructure
Relatively Expensive
Sensitive to power quality
Heat dissipation and ambient temperature are a concern
Rotor ResistanceSmooth acceleration available
Good flexibility in starting characteristics
Can be used for speed control also
Complicated controller design
Requires expensive wound-rotor motor construction
Adjustable
Speed Drive
Smooth Acceleration
Low inrush current
High flexibility in starting characteristics
Offers deceleration and speed control also
Typically integrates with industrial automation
infrastructure
Cost-prohibitive unless speed control is required also
Sensitive to power quality
Heat dissipation and ambient temperature are a concern
Continuous harmonic currents can create power quality issues

Ref:  http://electrical-engineering-portal.com/comparison-of-motor-speed-control-methods?utm_source=Technical+Articles&utm_campaign=e9ea0b385f-RSS_EMAIL_CAMPAIGN_MAILCHIMP&utm_medium=email&utm_term=0_ae069f0d91-e9ea0b385f-320603685

Monday, 16 March 2015

Transparent solar cell-Turns Window & Screen a Power Source

Transparent solar cell-Turns Window & Screen a Power Source,window power,window solar,screen solar cell


Researchers at Michigan State University have created a fully transparent solar concentrator, which could turn any window or sheet of glass (like your smartphone’s screen) into a photovoltaic solar cell. Unlike other “transparent” solar cells that we’ve reported on in the past, this one really is transparent, as you can see in the photos throughout this story. According to Richard Lunt, who led the research, the team are confident that the transparent solar panels can be efficiently deployed in a wide range of settings, from “tall buildings with lots of windows or any kind of mobile device that demands high aesthetic quality like a phone or e-reader.”

Scientifically, a transparent solar panel is something of an oxymoron. Solar cells, specifically the photovoltaic kind, make energy by absorbing photons (sunlight) and converting them into electrons (electricity). If a material is transparent, however, by definition it means that all of the light passes through the medium to strike the back of your eye. This is why previous transparent solar cells have actually only been partially transparent — and, to add insult to injury, they usually they cast a colorful shadow too.

Transparent solar cell-Turns Window & Screen a Power Source,window power,window solar,screen solar cell
Transparent solar cell-Turns Window & Screen a Power Source,wavelength of transparent solar cell




The organic salts absorb UV and infrared, and emit infrared — processes that occur outside of the visible spectrum, so that it appears transparent.

To get around this limitation, the Michigan State researchers use a slightly different technique for gathering sunlight. Instead of trying to create a transparent photovoltaic cell (which is nigh impossible), they use a transparent luminescent solar concentrator (TLSC). The TLSC consists of organic salts that absorb specific non-visible wavelengths of ultraviolet and infrared light, which they then luminesce (glow) as another wavelength of infrared light (also non-visible). This emitted infrared light is guided to the edge of plastic, where thin strips of conventional photovoltaic solar cell convert it into electricity. [Research paper: DOI: 10.1002/adom.201400103- "Near-Infrared Harvesting Transparent Luminescent Solar Concentrators"]

If you look closely, you can see a couple of black strips along the edges of plastic block. Otherwise, though, the active organic material — and thus the bulk of the solar panel — is highly transparent. 

Michigan’s TLSC currently has an efficiency of around 1%, but they think 5% should be possible. Non-transparent luminescent concentrators (which bathe the room in colorful light) max out at around 7%. On their own these aren’t huge figures, but on a larger scale — every window in a house or office block — the numbers quickly add up. Likewise, while we’re probably not talking about a technology that can keep your smartphone or tablet running indefinitely, replacing your device’s display with a TLSC could net you a few more minutes or hours of usage on a single battery charge.

The researchers are confident that the technology can be scaled all the way from large industrial and commercial applications, down to consumer devices, while remaining “affordable.” So far, one of the larger barriers to large-scale adoption of solar power is the intrusive and ugly nature of solar panels — obviously, if we can produce large amounts of solar power from sheets of glass and plastic that look like normal sheets of glass and plastic, then that would be big.

Fundamentals of Resistance,Capacitance and Impedance


Resistance:
Resistance is essentially friction against the motion of electrons. It is present in all conductors to some extent (except superconductors!), most notably in resistors. When alternating current goes through a resistance, a voltage drop is produced that is in-phase with the current. Resistance is mathematically symbolized by the letter “R” and is measured in the unit of ohms (Ω).
Reactance:
Reactance is essentially inertia against the motion of electrons. It is present anywhere electric or magnetic fields are developed in proportion to applied voltage or current, respectively; but most notably in capacitors and inductors. When alternating current goes through a pure reactance, a voltage drop is produced that is 90o out of phase with the current. Reactance is mathematically symbolized by the letter “X” and is measured in the unit of ohms (Ω).
Impedance:
Impedance is a comprehensive expression of any and all forms of opposition to electron flow, including both resistance and reactance. It is present in all circuits, and in all components. When alternating current goes through an impedance, a voltage drop is produced that is somewhere between 0o and 90o out of phase with the current. Impedance is mathematically symbolized by the letter “Z” and is measured in the unit of ohms (Ω), in complex form.
Perfect resistors (Figure below) possess resistance, but not reactance. Perfect inductors and perfect capacitors (Figure below) possess reactance but no resistance. All components possess impedance, and because of this universal quality, it makes sense to translate all component values (resistance, inductance, capacitance) into common terms of impedance as the first step in analyzing an AC circuit.
Resistor,capacitor,inductor example explanation,resistance vs reactance,Fundamentals of resistance,capacitance and reactance
Perfect resistor, inductor, and capacitor.
The impedance phase angle for any component is the phase shift between voltage across that component and current through that component. For a perfect resistor, the voltage drop and current are always in phase with each other, and so the impedance angle of a resistor is said to be 0o. For an perfect inductor, voltage drop always leads current by 90o, and so an inductor's impedance phase angle is said to be +90o. For a perfect capacitor, voltage drop always lags current by 90o, and so a capacitor's impedance phase angle is said to be -90o.
Impedances in AC behave analogously to resistances in DC circuits: they add in series, and they diminish in parallel. A revised version of Ohm's Law, based on impedance rather than resistance, looks like this:
ohms law


Kirchhoff's Laws and all network analysis methods and theorems are true for AC circuits as well, so long as quantities are represented in complex rather than scalar form. While this qualified equivalence may be arithmetically challenging, it is conceptually simple and elegant. The only real difference between DC and AC circuit calculations is in regard to power. Because reactance doesn't dissipate power as resistance does, the concept of power in AC circuits is radically different from that of DC circuits.
Know This:
  • Impedances of any kind add in series: ZTotal = Z1 + Z2 + . . . Zn
  • Although impedances add in series, the total impedance for a circuit containing both inductance and capacitance may be less than one or more of the individual impedances, because series inductive and capacitive impedances tend to cancel each other out. This may lead to voltage drops across components exceeding the supply voltage!
  • All rules and laws of DC circuits apply to AC circuits, so long as values are expressed in complex form rather than scalar. The only exception to this principle is the calculation of power, which is very different for AC.