Generator Loss of Excitation Relay (40G).
 

[LEFT][B] [URL="http://science-hamza.blogspot.com/2010/12/generator-loss-of-excitati**-relay-40g.html"]Generator Loss of Excitati** Relay (40G).[/URL] [/B]


[U][F**T=Impact]Electrical Generator Protecti** Relays.[/F**T][/U]


[B][I]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 Operati**.[/I][/B]
[B][I]The next figure shows the main single line diagram and Protecti** Scheme for the Generator.[/I][/B]
[B][I]The Generator made by Mitsubishi Heavy Industries (MHI) and its specificati** as follows:[/I][/B]


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




[CENTER][URL="http://2.bp.blogspot.com/_CZnqYQLLQtc/TRITvq-EE2I/AAAAAAAAADk/P4VqsJvvMIw/s1600/gen_1.JPG"][IMG]http://2.bp.blogspot.com/_CZnqYQLLQtc/TRITvq-EE2I/AAAAAAAAADk/P4VqsJvvMIw/s400/gen_1.JPG[/IMG][/URL][/CENTER]




[U][F**T=Impact]Generator Loss of Excitati** Relay (40G).[/F**T][/U]


[B][I]If a Synchr**ous machine losses the Excitati**, the following c**diti** will occur:[/I][/B]


[B][I]-When partial or complete loss of Excitati** occurs ** a synchr**ous generator, Reactive power flows from the other generator into the generator.[/I][/B]


[B][I]-The KW is c**trolled by the Prime-Mover input, while KVAR output is c**trolled by the Field Excitati**. If the system is large enough to supply the deficiency in Excitati** through the armature, the synchr**ous generator will operate as an inducti** generator, supplying essentially the same KW to the system as before the loss of Excitati**.[/I][/B]


[B][I]-Since Synchr**ous generator is not designed for asynchr**ous operati**, the machine output will oscillate slightly as the rotor oscillates in an attempt to lock into synchr**ism.[/I][/B]


[B][I]-Loss of Synchr**ism 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 synchr**ism. [/I][/B]




[U][F**T=Impact]Data for setting calculati**s.[/F**T][/U]
[B][I]Generator capacity-------440000KVA[/I][/B]
[B][I]Generator Voltage--------19KVA[/I][/B]
[B][I]CT turns ratio-------------18000/5=3600[/I][/B]
[B][I]VT turns rati**-----------19000/100=190[/I][/B]
[B][I]Gen. Transient impedance--------Xd’=24.8%[/I][/B]
[B][I]Gen. Synchr**ous impedance----Xd=195%[/I][/B]


[U][F**T=Impact]Relay setting calculati**s.[/F**T][/U]
[B][I]Relay Side Impedance[/I][/B]
[B][I]Z=Z% * ((KV2 * 10)/KVA) * (CT ratio/VT ratio)[/I][/B]




[U][F**T=Impact]Setting of small circle.[/F**T][/U]
[B][I]1-Circle #1 Diameter[/I][/B]
[B][I]Z=100 *((192*10)/440000)*(3600/190) = [U]15.55 Ω[/U][/I][/B]


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


[B][I]3-Circle #1 Diameter[/I][/B]
[B][I]Setting=[U]15 Cycles (0.3 Sec.)[/U][/I][/B]



[U][F**T=Impact]Setting of large circle.[/F**T][/U]
[B][I]1-Circle #2 Diameter[/I][/B]
[B][I]Z=195 *((192*10)/440000)*(3600/190) = [U]30.31 Ω[/U][/I][/B]


[B][I]2-Circle #2 Offset[/I][/B]
[B][I]Z=24.8 *((192*10)/440000)*(3600/190) = [U]1.93 Ω[/U][/I][/B]


[B][I]3-Circle #1 Diameter[/I][/B]
[B][I]Setting=[U]75 Cycles (1.5 Sec.)[/U][/I][/B]




[CENTER][URL="http://2.bp.blogspot.com/_CZnqYQLLQtc/TRIT5WO6xqI/AAAAAAAAADo/AbV3JwGtpfg/s1600/loss_excit.JPG"][IMG]http://2.bp.blogspot.com/_CZnqYQLLQtc/TRIT5WO6xqI/AAAAAAAAADo/AbV3JwGtpfg/s400/loss_excit.JPG[/IMG][/URL][/CENTER]


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