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POWER ANGLE CHARACTERISTIC OF AN ALTERNATOR

By:-ROHIT KUMAR

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Introduction of an ALTERNATOR

Classification of an ALTERNATOR

Power relation of a salient pole ALTERNATOR

Power angle characteristic of a salient pole ALTERNATOR

Power relation of a cylindrical pole ALTERNATOR

Power flow in an ALTERNATOR

Power angle characteristic of a cylindrical pole ALTERNATOR

conclusion

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An alternator is also called as SYNCHRONOUS GENERATOR.

In Synchronous Generator, a DC current is applied to rotor winding (produce rotor magnetic field).

The rotor is turned by primemover producing a rotating magnetic field.

The rotating magnetic field produce three phase sets of voltages within the stator.

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SALIENT POLE ROTOR Alternator

CYLINDRICAL POLE ROTOR Alternator

ON THE BASIS OF TYPE OF ROTOR

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Not all the mechanical power going into a synchronous generator becomes electrical power out of the machine. The difference between input power and output power represents the losses of the machine. The input mechanical poweris the shaft power in the generator.

Rotational losses (Pr)

Pconverted

(Pm)

Pout

Stray losses (Pst)

Core losses (Pc)

Copper losses (Pcu)

cos3 LT IV

AA RI2

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mindconvP

msinP

strc PPP

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POWER RELATION OF A SALIENT POLE ALTERNATOR…

P=3(EV Sin /Xd ) +{v^2(Xd – Xq) Sin2 /2 Xd Xq}

=power angle.

E=Generator internal emf.V=Terminal voltage.Xd= Direct axis synchronous reactance.Xq=Quadrature axis synchronous reactance.

The TOTAL power relation of a salient pole alternator is:-

The second term in the above equation is due to power due to variable reluctance Called as reluctance power OR power due to SALIENCY.

The first term in the above equation indicates EXCITATION POWER.

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OF A SALIENT POLE ALTERNATOR….

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CONTINUE…

The power angle characteristic of an alternator is the curve between total power developed and the load angle.

For a given excitation, bus bar voltage is constant the power developedIs significantly depending on load angle .

Operating region of synchronous machine is 30-40 degree{ ).

As the generator is loaded, it supplies power proportionally with upto 90 degree . If the load increases further, the machine goes out of synchronisation with the bus bar.

=90 is the steady state stability limit.

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The power converted from mechanical to electrical is given by;

cos3 AAIEmindconvP

Where is the angle between EA and IA:

If the armature resistance RA is ignored (XS >> RA), Therefore:

S

AA

X

EI

sincos

S

A

X

EVP

sin3

Substituting this equation into Pout, gives;.

Where is the angle between EA and VT.

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Power Angle Characteristics of cylindrical pole alternator.. The P(δ) curve shows that the increase of power increases the angle between the induced voltage and the terminal voltage.

The power is maximum when δ=90o

The further increase of input power forces the generator out of synchronism. This generates large current and mechanical forces.

The maximum power is the static stability limit of the system.

Safe operation requires a 15-20% power reverse.

S

A

X

EVP

3max

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As the generator is loaded, it supplies power proportionally with upto 90 degree . If the load increases further, the machine goes out of synchronisationwith the bus bar.

=90 is

thesteady state stability limit.

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