Download presentation

Presentation is loading. Please wait.

Published byBranden Tyler Modified over 2 years ago

1
RLC CCTs To Simulate Damping Φ:I of branch or V across the CCT Ψ:V across a comp. or I in CCT

2
Typical Differential Eq. of RLC The Parallel RLC Eq(1): The Series RLC Eq(2):

3
Load Switching Switch on & off loads : most Freq. RL, Low P.F. when Inductive High P.F. when Resistive C_ loadbus :role in After sw. off. Transient V 0 : V s (at instant I ceases) C charged to V 0, disch., In RL, Damp Os. Dis. A damped cosine wave of Fig. 4.6 As P.F. improve, Transient decrease

4
The RL Load and Switching off

5
Arc Furnace Example Low voltage & High Curent Fed by step down furn. Transformer Low P.F. & freq. switching Cap.s connected to HV bus impr. P.F. Delta & Wye Connections Example:Wye connection,Transf.60Hz 13.8 KV,20 MVA Y/Y solid Gr P.F. at Full Load;0.6,C corr. P.F.to 1.0 Transient?, sw.off fully loaded Transf.

6
Eq. CCTs & Discussion Schematic & Eq. I load =20000/(13.8 √3)=836.7 A (rms) Z=13.8/(√3x836) =9.522 Ω φ=cos−0.6=53. R T +R L = 9.52cosφ=5.7 X T +X L = 9.52sin φ=7.6 L=20.2 mH

7
Discussion Furn. Ex. continued open:I s (0)=0, required:I c(0) =-I(0) I c =-I=836.7sinΦ=669.4A (rms) I c is at peak since V c =0, and I c (t=0)=669.4√2=946.67A (text result should be corrected) V c (0)=0 X c =13.8/(√3x669.4)=11.9 Ω (please correct text book results) C=222.6 μF

8
Discussion of Transient Resp. for I, the current: dI/dt+1/T s dI/dt+1/T=0 i(s)(s+s/T s +1/T)=(s+1/T s )I(0)+I’(0) Transient of series RLC CCT: L dI/dt+IR=V c LI’(0)+I(0)R=V c (0)=0 I’(0)=-I(0)R/L=-I(0)/T s i(s)=s/(s+s/T s +1/T). I(0)- Fig4.6

9
Discussion Continued Z 0 =√L/C=√20.2/0.2228=9.52 Ω λ=Z 0 /R=9.52/5.713=1.6664 I, starts with –946.67 A, swing to +ve peak of 0.105 half cycle later. & -.06X946.67 after another half cycle (these values should be corrected in the text book) For V c : dV c /dt+1/T s dV c /dt +V c /T=0 v c (s)(s+s/T s +1/T)=(s+1/T s )V c (0)+V’ c (0) Vc(0)=0, V’ c (0)=-I(0)/c v c (s)=1/(s+s/T s +1/T). I(0)/c

10
Transformer Terminal Voltage Fig 4.4 λ=1.66 peak reaches 65% undamped:[-I(0)/C]T=-I(0)Z 0 The first voltage peak: 0.65x946.67x9.52=5.85 KV (please correct the value in the text book) The time scale is T=√LC= 2.121 ms Reaches peak in 1.4T=2.97 ms Fast Transient and Corona Damping Always higher freq. Damped quicker

11
Abnoraml Switching Normal : 2 pu Abnormal : mag. Far beyond this 1-current suppression 2- Capacitor Bank switching off 3-Other Restriking Phenomena 4-Transformer Mangnetizing Inrush 5-Ferroresonance

12
Current Suppression N.,I ceases, arc current, periodic Zero Abn., arc suppression force current 0 Current Chopping trapped mag. Energy Abn. Voltage Ex: sw. off Transformer magnetizing current Energy stored:½L m I 0 L m very large

13
Cur. Chop. ½ CV=1/2 L m I 0 V=I 0 √L m /C I 0 : Instant. current chopped i.e. 1000KVA, 13.8 KV Transformer 1- magnetizing current=1.5 A (rms) 2-L m =V/ωI m = 13800/(√3x377x1.5)=14 H eff.Cap. type of wind.&ins (1000-7000PF) If C=5000 PF, Z 0 =√[14/5x10^-9]= 52915Ω If C.B. chops I_peak, can be 2.5 A, V(peak)≈132KV Abnormal for 13.8 KV

14
Cur. Chop. Discussion Not So High: 1- damping, 2- fraction of Energy release shaded area< 30% stored energy I 0 √(0.3L m /C)= 55% V (transient) Dis. Transf. most vulnerable

15
Continued… Air cored reactors (core of significant air-gap) 1-All energy recoverable 2-If as shunt compensator, protected by L.A. Formal Evaluation of RLC CCT 1- I C +I R +I L =0, sub. & Diff. 2- dV/dt+1/RCdV/dt+V/L m C=0 3-v(s)(s+s/RC+1/L m C)=(s+1/RC)V(0)+V’ 0 V’(0)=-I c (0)/c=-I 0 /C V(s)=sV(0)/(s+s/RC+1/L m c)+V(0)/Rc x 1/(s+s/RC+1/L m c) –I 0 /[c(s+s/ RC+1/L m C )] Transforms of Fig4.4 & Fig 4.6 first two normal Transient terms without chop

16
… continued Chopping of Magnetizing current of a 13.8 kV

17
The response with cur. Chop. 1st term Fig4.6, pu=V(0) 2nd term fig4.4,pu=TV c (0)/T p = Vc(0)/η ζ− I 0 /{c[s+s/T p +1/T]}=TI 0 /C 2η/(√4η- 1). exp(-t’/2η) sin[√(4η-1) t’/2η] □ TI 0 /C=Z 0 I 0 peak Amp. Chopping Term (exclude damp.)

18
The response with cur. Chop. Practical Ex: Shown in Figure 1-chop only 0.5-0.6 A (I – to zero) TRV 20KV 2- chop occur instantaneously 3- in practice I declines on a measurable time 4-TRV and time-to- chop/period H.F. Osc. : Figure 5-TRV max if t c =0, TRV reduce as t c >T/4

19
Discussion on CB performance small contact sep. dielectric fails Successive attempts raise Higher Voltages until isolation TRV of Cur.Chop. Limited by reignitions (Fig) G. Practice: a cable between C.B. and Transformer drastic reduction in TRV 100 ft of 15 KV cable ( 100PF/ft ) Transformer( 3000PF eff. Cap.) TRV halved Motors No risk: Noload inductance very small compare to transformer

20
Semiconductor Devices Current Suppression Gen. OVs to destroy them end half cycle of diode conduction 1-carriers remained at junction region allow current to flow & reverses 2- then sweeps the carriers & returns device to Block state:I collapses fast inductive CCT Eng. Transf. to C, large V

21
Current Suppresssion Silicon Diode CCT and Current H.F. Osc. L&C Protection : 1-snubber cap. In P. 2-additional series R

22
Capacitance Switching Off Disconnect: C /unload Transmission lines Concerns: reignite/restrike in opening Chance low, Cap. Sw. frequent Cap fully charged Half Cycle VCB=2 V p

23
Capacitance Switching off

24
Discussion Cap. Sw. Off In fact Vc>Vsys Ferranti Rise Vsource_side decrease to Vsys There is a ∆V change (however,exist in weak systems) Discon. a C.B. in lower side of step down Transformer supplying an unloaded cable Current in Cap. Sw. is freq. small and it is possible to disconnect it In first zero -- with small contact sep., 2 V appear across contacts --- increased possibility of restrike (small separation) Oscillating to new voltage with f0=1/2Π√LC I(restrike)=2Vp/√L/C sinω0t Transient peak of 3 Vp

25
Capacitance Switching with a Restrike at Peak of Voltage

26
Capacitor Switching …continued A 13.8 KV, 5000KVAR, 3ph bank,NGr Source Gr, inductance:1 mH Restrike at V p : 1- c=5/(377x13.8)=69.64μF 2- Z=√1000/69.64=3.789Ω 3-I p =2√2x13.8/(√3x3.789)=5.947 KA 4-f 0 =603 Hz

27
Multiple Restrikes During Capacitance Switching

Similar presentations

Presentation is loading. Please wait....

OK

AP Physics C Montwood High School R. Casao

AP Physics C Montwood High School R. Casao

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Salivary gland anatomy and physiology ppt on cells Ppt on spiritual leadership conference Ppt on surface water flow Ppt on effect of global warming on weather for 2nd Ppt on business communication skills Ppt on model view controller design Ppt on power sharing in democracy it is important Ppt on eid festival pictures Ppt on computer languages 2015 Ppt on heritage and culture of rajasthan