Thursday, December 23, 2010

CrazyEngineers Forum - Electrical & Electronics Engineering

CrazyEngineers Forum - Electrical & Electronics Engineering

wye delta combination of forwrad revers connection

Posted: 22 Dec 2010 11:47 PM PST

Hi, me i know the installation and schematic diagram of wye delta and forward revers connection.

Pen stylus next chapter for table productivity?

Posted: 22 Dec 2010 08:42 PM PST

You thought that with capacitive touchscreens, the world would be rid of pesky stylus pens for good, didn't you? Well N-trig, a company whose tech has been used on a number of Windows computing products, is eyeing the Android tablet platform as the next venue for pen input, which would include utilizing a stylus for inking, drawing, and digital note taking.

N-trig is arguing that companies can differentiate itself from competitors with a stylus, extending tablet products beyond just content consumption devices will give companies an edge–a strategy that HP has used on its HP Slate 500 Windows tablet, which was released with an active digitizer pen and geared towards enterprise customers. N-trig is saying that adding a pen can cost the company around $50, but would offer improved accuracy and more versatility to the end user.
Another company that's looking at this space is Adobe. Though the company is taking a wait and see approach as to what types of software that it may release, and when, the prospect is there for more a professional software suite or app–like a scaled down version of Photoshop–that would allow for better photo manipulation thanks to the accuracy of pen input. Adobe Vice President Michael Gough says, "Adobe will follow that, I think, just as much as they lead it. It all depends when the devices are in people's hands."
A more productive tablet environment would offer the company more business as it could potentially port some of its best-selling titles from Creative Suite to consumer tablets. Consumer tablets, like the iPad, are more geared at content consumption, which doesn't offer Adobe much business with consumers.- Via UberGizmo

Generator Stator Earth Fault Relay (64G) - 27TN.

Posted: 22 Dec 2010 09:26 AM PST

Generator Stator Earth Fault Relay (64G) - 27TN.






Generator Stator Earth Fault Relay (64G) - 27TN.


-For high impedance grounded generators, a voltage relay across the secondary winding of the generator neutral grounding transformer is used to detect the ground fault on the generator stator winding.


-The neutral over voltage function (59N) responds to the fundamental frequency voltage at the generator neutral that appears when a ground fault occurs.


-Normally, it will protect up to 90≈ 95 % of the stator windings.


-The neutral under voltage functions responds to 3rd harmonic voltage measured at the generator neutral. When used in conjunction with the neutral over voltage function, it provides 100% ground fault protection of the stator winding.


-In healthy state, the machine 3rd harmonic voltage is distributed over the windings such that the maximum occur at the star point neutral and at the line terminal. For a ground fault close to the neutral, all the 3rd harmonic voltage is transferred to the line terminals. Consequently, the relay function will see a 3rd harmonic under voltage at the neutral end and will operate the protection element.



Generator Loss of Excitation Relay (40G).

Posted: 22 Dec 2010 07:43 AM PST

Generator Loss of Excitation Relay (40G).


Electrical Generator Protection Relays.


Electrical Generator is the main source of Electricity at Power Plant, we should make a many methods to protect the Generator from any faults can happen while Operation.
The next figure shows the main single line diagram and Protection Scheme for the Generator.
The Generator made by Mitsubishi Heavy Industries (MHI) and its specification as follows:


Power-------------- 440 MVA
Power Factor----- 0.85 lag
Line Voltage------ 19 KV
Frequency--------50HZ
Speed-------------- 3000 rpm
Hydrogen (H2) Gas Cooled @ 4.5 barg.







Generator Loss of Excitation Relay (40G).


If a Synchronous machine losses the Excitation, the following condition will occur:


-When partial or complete loss of Excitation occurs on a synchronous generator, Reactive power flows from the other generator into the generator.


-The KW is controlled by the Prime-Mover input, while KVAR output is controlled by the Field Excitation. If the system is large enough to supply the deficiency in Excitation through the armature, the synchronous generator will operate as an induction generator, supplying essentially the same KW to the system as before the loss of Excitation.


-Since Synchronous generator is not designed for asynchronous operation, the machine output will oscillate slightly as the rotor oscillates in an attempt to lock into synchronism.


-Loss of Synchronism does not require immediate tripping unless there is an accompanying decrease in the terminal voltage that threatens system stability; it generally takes at least 2 to 6 Sec. to lose synchronism.




Data for setting calculations.
Generator capacity-------440000KVA
Generator Voltage--------19KVA
CT turns ratio-------------18000/5=3600
VT turns ration-----------19000/100=190
Gen. Transient impedance--------Xd'=24.8%
Gen. Synchronous impedance----Xd=195%


Relay setting calculations.
Relay Side Impedance
Z=Z% * ((KV2 * 10)/KVA) * (CT ratio/VT ratio)




Setting of small circle.

1-Circle #1 Diameter
Z=100 *((192*10)/440000)*(3600/190) = 15.55 Ω


2-Circle #1 Offset
Z=24.8 *((192*10)/440000)*(3600/190) = 1.93 Ω


3-Circle #1 Diameter
Setting=15 Cycles (0.3 Sec.)






Setting of large circle.

1-Circle #2 Diameter
Z=195 *((192*10)/440000)*(3600/190) = 30.31 Ω


2-Circle #2 Offset
Z=24.8 *((192*10)/440000)*(3600/190) = 1.93 Ω


3-Circle #1 Diameter
Setting=75 Cycles (1.5 Sec.)
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