Introduction to Electric Systems Course Code: EE 111 Course Code: EE - - PowerPoint PPT Presentation

Introduction to Electric Systems Course Code: EE 111 Course Code: EE 111 Department: Electrical Engineering Department: Electrical Engineering Instructor Name: B G Fernandes Instructor Name: B.G. Fernandes E‐mail id: bgf @ee iitb ac in E‐mail id: bgf @ee.iitb.ac.in

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

Lecture 9 1/10

Sub‐Topics:

• Concept of Reactive Power
• Power factor improvement

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

Lecture 9 2/10

Review

• Instantaneous power in 1 ‐ Ø circuit pulsates at 2F

Instantaneous power in 1 Ø circuit pulsates at 2F

• Single phase motors require special resilient mountings
• Complex power S = VI* = P + jQ
• Complex power, S = VI = P + jQ

P active power = VI cosθ W = I2R

I V

θ = ∠

Q VI sinθ VAr = I2X Q VI sinθ VAr I X S = VI* VA

• In DC if P & V are known I can be determined
• In DC, if P & V are known, I can be determined
• However in AC, P, V & cosѲ or V & S should be known

to determine I

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

to determine I

Lecture 9 3/10

For a given P

• I drawn by load as cos θ (P.F.)

⇒ Drop in the line ⇒ I2R , I2X in the line and therefore ‘S’ of source ⇒ I2 R loss in source also increases ⇒ I R loss in source also increases

• VL< Vs for lagging & unity P.F.
• VL ≤ Vs or VL>VS for leading P.F.

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

Lecture 9 4/10

s L

|V | |V | >

Source P.F.= cos

s L S

I I V =

∠

S

If the P.F. is unity If P.F. is leading

s L

|V | |V | >

• r

L L

|V | |V | |V | |V | ≥ ≤

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

s L

• r

s L s L

|V | |V | |V | |V | ≥ ≤

Lecture 9 5/10

Concept of Reactive Power k 1 kVA, 200V, 50 Hz Generator ⇒ Rated current = 5A ⇒ Assume load = 1 kVAr, 200V ⇒ Current drawn by the load = 5A ⇒ Current drawn by the load = 5A = rated current of generator P d b th l d 0 ⇒ Power consumed by the load =0 Assume generator is ideal (losses = 0) ∴Input power = o/p power + loss = 0 ⇒ No input is required.

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

p q

Lecture 9 6/10

⇒ If losses are taken into account, I/P power = losses ⇒ If additional load (P) is connected ⇒ Source has the capability to supply P I/P power = losses ⇒ If additional load (P) is connected

2 2

5 5

s a

I I ⇒ = + ≥

For any Ia

≠

⇒ Fuse will operate ⇒ Fuse will operate ⇒ Else I2R losses ,

l

⇒ Cooling requirement ⇒ Temperature rise

RMS value

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

⇒ Cooling requirement

Lecture 9 7/10

⇒ Though ‘L’ does not consume any P, source capacity can not be utilized to cater other loads not be utilized to cater other loads ⇒ Energy meter reading α power α VI cosθ α I cosθ Load is drawing IL ⇒ Energy Meter reading α IL cosθ ⇒ e gy e e ead g α L cosθ ∴Tariff α ILcosθ Who pays for ILsinθ ? Who pays for ILsinθ ? ⇒ Fuel (power input) to supply Q may not be required

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

Lecture 9 8/10

⇒ Utilities may not be able to cater other loads ⇒ Returns are low ⇒ Returns are low ⇒ Utilization and returns are maximum at unity p.f ⇒ Load requires reactive power ⇒ Load requires reactive power ⇒ Generate reactive power locally ⇒ Capacitor draws leading I ⇒ If I = I sinθ I = I cosθ ⇒ If IC = IL sinθ, Is= IL cosθ ⇒ Overhead line loss & drop ⇒ Voltage profile at load end also improves

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

Lecture 9 9/10

For a small consumer, power tariff depends only on ‘P’ ⇒ No direct benefit ⇒ Cross‐section of cable may reduce if ‘Q’is generated locally (one time investment) ⇒ For Bulk consumer : ⇒ For Bulk consumer : Power tariff depends on ‘P’ & ‘Q’ ⇒ Expected to maintain P.F. within permissible limit

Tue Aug 11 2009

EE 111: Introduction to Electric Systems B.G.Fernandes

Lecture 9 10/10