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

Introduction to Electrical 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

EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

Tue Oct 27, 2009

1/19 Lecture 33

Sub‐Topics:

• Operation when feeding a local load
• Operation when connected to grid

S h i ti

• Synchronization
• Grid failure

EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

Tue Oct 27, 2009

2/19 Lecture 33

Review

• Cylindrical rotor → generally 2 pole construction
• Cylindrical rotor → generally 2 pole construction

∵ air gap is uniform, ‘L’ is independent of rotor position

• Salient pole → Air gap is minimum along field axis

(d‐axis) and maximum along quadrature axis (q‐axis) ∴ Xd > Xq For Generator:

• Purely ‘L’ load demagnetizing in nature while purely

‘C’ l d i ti i i t For Generator: ‘C’ load is magnetizing in nature

• In phase component → distort the field

→ cross magneti ing

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

→ cross‐magnetizing

3/19 Lecture 33

Cylindrical rotor Salient pole rotor

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

4/19 Lecture 33

[ ]

cos( ) cos 3V P E V Z = δ − θ − θ i

s s

π θ & |Z | |X | 2 → ≅ ∵

S

Z 2

• 3EV

P sinδ X =

s

X

• Operation at δ1 is stable & δ2 is unstable

‘δ’ is the angle between

F r Fs

∠

• At steady state, both fields are rotating at ‘ωs’

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

5/19 Lecture 33

Generator feeding local load A h i I ld lt i h i E & V ∴ Any change in If would result in a change in

• t

E & V ∴ ⇒ as the load changes, speed of the prime mover and ∴‘f’ of ‘V’ in stator would change mover and ∴‘f’ of ‘V’ in stator would change ⇒ rating of synchronous machine in MVA in MVA ⇒ only small portable DG feed h l l l d the local load ⇒ high power generators are connected to the grid ⇒ Grid is a network to which a large no. of generators are connected

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

connected

6/19 Lecture 33

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

7/19 Lecture 33

In India, there are two grids Southern grid In India, there are two grids Rest of India ⇒ Total installed capacity is approx. 1,40,000 MW ⇒ Total installed capacity is approx. 1,40,000 MW ⇒ assume that at Khopoli, engineer changes the it ti f th t ⇒ Its Eo would change excitation of the generator ⇒ If Vt changes, it would affect all the other generators ⇒ not practical ⇒ grid ‘V’ and ‘f’ are kept almost constant(50.5 < f < 49)

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

8/19 Lecture 33

⇒ behavior of synchronous generator connected to the grid is different from that of generator feeding local grid is different from that of generator feeding local load ⇒ grid is a network whose ‘f’ & ‘V’ are held constant & g they do not change for small disturbance ⇒ change of excitation of generator connected to grid will g g g not change the terminal ‘V’ ∵ power input is held constant, output also will not ∵ p p , p change

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

9/19 Lecture 33

Operation at variable excitation and constant load E V at constant load,

s

E V P sinδ X = PX i δ → t t

s

PX E sinδ V ∴ = → constant also, VIcosφ = P = constant also, VIcosφ P constant ∴ Icosφ = constant If excitation is varied, then E0 and δ would change such that ‘E0sinδ’ will remain constant

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

10/19 Lecture 33

How to connect to the grid:

• Process is kno n as s nchroni ation
• Process is known as synchronization

Just prior to closing the switch, ⇒Phase sequence should be same ⇒‘f’ & |V| should be ≅ same as that of grid ⇒Phase sequence should be same

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

11/19 Lecture 33

What is meant by grid failure? Assume that due to some reason, one of the power Assume that due to some reason, one of the power station (2000 MW) is tripped ⇒ prior to tripping there was a steady state & P = P ⇒ prior to tripping there was a steady state & Pm= Pe ⇒ loss of generation = 2000 MW ⇒ load is not disconnected ⇒ load is not disconnected ⇒ this load is now being shared by other generators ⇒ generators start slowing down ∴ frequency falls

http://www.mahatransco.in/load‐dispatch.shtm Maharashtra state electricity Transco web

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

http://www.caiso.com/ California iso web

12/19 Lecture 33

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

13/19 Lecture 33

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

14/19 Lecture 33

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

15/19 Lecture 33

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

16/19 Lecture 33

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

17/19 Lecture 33

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

18/19 Lecture 33

C t T t P

Tue Oct 27, 2009 EE 111: Introduction to Electrical Systems

• Prof. B.G.Fernandes

Courtesy: Tata Power

19/19 Lecture 33