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1.<br />

ABDESSALEM LAMARI .<br />

COMPUTER SIMULATION OF THE TRANSIENTS<br />

IN ASYNCHRONOUS MACHINES IN THE CASE<br />

OF SHORT-CIRCUIT AND CONNECTION TO NETWORKS<br />

Abstract:<br />

The ma<strong>the</strong>matical models <strong>of</strong> <strong>the</strong> Asynchronous Electrical mach<strong>in</strong>es developed on <strong>the</strong> basis <strong>of</strong> <strong>the</strong><br />

experimental frequency-response characteristics are proposed <strong>in</strong> this paper. The latter ones are<br />

recommended for <strong>in</strong>vestigat<strong>in</strong>g <strong>the</strong> transient processes occurr<strong>in</strong>g at short-circuits and connections <strong>of</strong><br />

<strong>the</strong> electrical mach<strong>in</strong>es to <strong>the</strong> bus bars <strong>of</strong> electrical system tak<strong>in</strong>g account <strong>of</strong> <strong>the</strong>ir rotor speed<br />

changes.<br />

Keywords:<br />

Asynchronous mach<strong>in</strong>es, frequency-response, networks connections, short-circuit<br />

INTRODUCTION<br />

It is a matter <strong>of</strong> familiar experience that <strong>the</strong><br />

methods <strong>of</strong> frequency-response characteristics<br />

[1, 2, 8, 9, 13 and 14] have received wide<br />

acceptance <strong>in</strong> <strong>the</strong> scientific-research and<br />

eng<strong>in</strong>eer<strong>in</strong>g practical activity for <strong>in</strong>vestigat<strong>in</strong>g<br />

and evaluat<strong>in</strong>g <strong>the</strong> transient conditions <strong>of</strong> <strong>the</strong><br />

AC mach<strong>in</strong>es <strong>in</strong> electrical systems. The above<br />

mentioned methods make possible to carry out<br />

<strong>the</strong> direct application <strong>of</strong> <strong>the</strong> experimental <strong>in</strong>itial<br />

data <strong>in</strong> <strong>the</strong> form <strong>of</strong> frequency-response<br />

characteristics <strong>of</strong> <strong>the</strong> separate electrical system<br />

elements or <strong>of</strong> <strong>the</strong> system as a whole. Such an<br />

approach, <strong>in</strong> <strong>the</strong> special cases that <strong>the</strong> system<br />

<strong>in</strong>ternal structure is <strong>in</strong>determ<strong>in</strong>ate, has much<br />

potential for yield<strong>in</strong>g <strong>the</strong> more precise<br />

calculations <strong>of</strong> <strong>the</strong> transient processes.<br />

The calculation technique for determ<strong>in</strong><strong>in</strong>g <strong>the</strong><br />

<strong>transients</strong> by <strong>the</strong> use <strong>of</strong> <strong>the</strong> frequency-response<br />

characteristics <strong>of</strong> synchronous mach<strong>in</strong>e stator<br />

admittance <strong>in</strong> <strong>the</strong> direct, Y d (js), and quadrature,<br />

Y q (js), axes or <strong>the</strong> circle diagram <strong>of</strong> an <strong>in</strong>duction<br />

motor was proposed <strong>in</strong> [1,2,3 and 4]. The<br />

graphic-analytical methods for determ<strong>in</strong><strong>in</strong>g <strong>the</strong><br />

armature current and electromagnetic torque <strong>of</strong><br />

<strong>the</strong> synchronous mach<strong>in</strong>e were developed <strong>in</strong> <strong>the</strong><br />

cited monograph too. The methods be<strong>in</strong>g<br />

considered allow carry<strong>in</strong>g out more accurate<br />

calculations <strong>of</strong> <strong>the</strong> transient processes tak<strong>in</strong>g<br />

<strong>in</strong>to account <strong>the</strong> follow<strong>in</strong>g characteristic<br />

features<br />

• electromagnetic asymmetry <strong>of</strong> <strong>the</strong> rotor;<br />

• representation <strong>of</strong> <strong>the</strong> turbogenerator solid<br />

rotor by means <strong>of</strong> <strong>the</strong> equivalent circuits<br />

correspond<strong>in</strong>g to <strong>the</strong> high order transfer<br />

function <strong>of</strong> <strong>the</strong> damper system;<br />

• current displacement <strong>in</strong> <strong>the</strong> w<strong>in</strong>d<strong>in</strong>gs <strong>of</strong><br />

electrical mach<strong>in</strong>es;<br />

• saturation phenomenon <strong>in</strong> <strong>the</strong> ma<strong>in</strong> and<br />

leakage paths <strong>of</strong> <strong>the</strong> magnetic fluxes <strong>of</strong> <strong>the</strong> AC<br />

mach<strong>in</strong>es;<br />

• external impedance <strong>in</strong>serted <strong>in</strong> <strong>the</strong> armature<br />

w<strong>in</strong>d<strong>in</strong>g <strong>of</strong> <strong>the</strong> AC mach<strong>in</strong>e.<br />

The above mentioned methods did not get wide<br />

dissem<strong>in</strong>ation <strong>in</strong> due course though.<br />

The great amount <strong>of</strong> <strong>in</strong>formation on <strong>the</strong><br />

frequency-response characteristics <strong>of</strong> <strong>the</strong><br />

© copyright FACULTY <strong>of</strong> ENGINEERING – HUNEDOARA, ROMANIA 67


ACTA TECHNICA CORVINIENSIS – BULLETIN <strong>of</strong> ENGINEERING<br />

synchronous mach<strong>in</strong>es and <strong>in</strong>duction motors<br />

compiled by now and availability <strong>of</strong> <strong>the</strong><br />

developed method designed for syn<strong>the</strong>sis<strong>in</strong>g <strong>the</strong><br />

equivalent circuits adequately reflect<strong>in</strong>g <strong>the</strong><br />

<strong>in</strong>itial frequency-response characteristics <strong>of</strong> <strong>the</strong><br />

AC electrical mach<strong>in</strong>es open up fresh<br />

opportunities for improv<strong>in</strong>g and fur<strong>the</strong>r<br />

development <strong>of</strong> <strong>the</strong> frequency-response<br />

methods for <strong>in</strong>vestigat<strong>in</strong>g <strong>the</strong> <strong>transients</strong> <strong>in</strong><br />

electrical mach<strong>in</strong>es.<br />

The objective <strong>of</strong> <strong>the</strong> paper is to develop <strong>the</strong><br />

ma<strong>the</strong>matical models <strong>of</strong> <strong>the</strong> AC mach<strong>in</strong>es based<br />

on <strong>the</strong> experimental frequency-response<br />

characteristics for <strong>in</strong>vestigat<strong>in</strong>g <strong>the</strong> <strong>transients</strong> at<br />

short-circuits and connections <strong>of</strong> <strong>the</strong> AC<br />

mach<strong>in</strong>es <strong>in</strong> electrical system tak<strong>in</strong>g <strong>in</strong>to<br />

consideration <strong>the</strong> occurr<strong>in</strong>g speed changes <strong>of</strong><br />

<strong>the</strong> AC mach<strong>in</strong>e rotor.<br />

BASIC RELATIONS<br />

The ma<strong>the</strong>matical relations realis<strong>in</strong>g <strong>the</strong><br />

graphic-analytical approach [1,2 and 3] to<br />

determ<strong>in</strong><strong>in</strong>g <strong>the</strong> components <strong>of</strong> <strong>the</strong> stator phase<br />

current and electromagnetic torque at shortcircuits<br />

or connections <strong>of</strong> <strong>the</strong> synchronous<br />

mach<strong>in</strong>es rotat<strong>in</strong>g at <strong>the</strong> synchronous speed to<br />

<strong>the</strong> electrical system are obta<strong>in</strong>ed <strong>in</strong> [5, 10, 11<br />

and 18]. When <strong>the</strong> mach<strong>in</strong>e with <strong>the</strong> rotor<br />

asymmetry operates at <strong>the</strong> short-circuit with <strong>the</strong><br />

speed changes relative to <strong>the</strong> synchronous<br />

speed or it is connected to <strong>the</strong> network at <strong>the</strong><br />

given slip, determ<strong>in</strong><strong>in</strong>g <strong>the</strong> components <strong>of</strong> <strong>the</strong><br />

generalised stator current vector is carried out<br />

<strong>in</strong> <strong>the</strong> follow<strong>in</strong>g way:<br />

We f<strong>in</strong>d <strong>the</strong> average value <strong>of</strong> <strong>the</strong> steady-state<br />

current I s<br />

for <strong>the</strong> s at <strong>the</strong> first <strong>in</strong>stant <strong>of</strong> <strong>the</strong><br />

0 av<br />

transient process<br />

I = Y (js<br />

(1)<br />

av<br />

where<br />

Y<br />

av<br />

s 0 av<br />

)<br />

s0<br />

Yd<br />

(js) + Yq<br />

(js)<br />

(js) =<br />

2<br />

We determ<strong>in</strong>e <strong>the</strong> pulsat<strong>in</strong>g component <strong>of</strong> <strong>the</strong><br />

steady-state current<br />

− j2δ0<br />

Δ I<br />

s0<br />

= (R<br />

e<br />

[ ΔY(js)<br />

s0<br />

] − j.Im[ ΔY(js)<br />

s0<br />

]).<br />

e (2)<br />

where<br />

Yd (js) + Yq<br />

(js)<br />

Δ Y (js) =<br />

, δ<br />

0<br />

=angle between<br />

2<br />

The q-axis <strong>of</strong> <strong>the</strong> rotor and <strong>the</strong> voltage vector at<br />

<strong>the</strong> <strong>in</strong>f<strong>in</strong>ite bus <strong>of</strong> an electrical system;<br />

We f<strong>in</strong>d <strong>the</strong> changes <strong>in</strong> <strong>the</strong> steady-state current<br />

with time, tak<strong>in</strong>g <strong>in</strong>to account <strong>the</strong> difference <strong>in</strong><br />

<strong>the</strong> rotor parameters on axes <strong>of</strong> its electrical and<br />

magnetic symmetry,<br />

I<br />

S 0<br />

(t)<br />

− j2 st j. ω.t<br />

= (I<br />

S 0<br />

+ ΔI<br />

S 0<br />

e ). e<br />

(3)<br />

av<br />

We determ<strong>in</strong>e <strong>the</strong> aperiodic current component<br />

I<br />

S 1 av<br />

Yav<br />

(js)<br />

−(1−s)<br />

= (4)<br />

And <strong>the</strong> periodic current <strong>of</strong> <strong>the</strong> frequency close<br />

to <strong>the</strong> doubled one<br />

− j.2. δ0<br />

Δ IS1<br />

= (Re[ ΔY(js)<br />

−(1−s)<br />

]j.Im[ ΔY(js)<br />

−(1−s)<br />

]). e (5)<br />

Aperiodic current and <strong>the</strong> current component<br />

caused by <strong>the</strong> rotor asymmetry are changed <strong>in</strong><br />

accordance with <strong>the</strong> follow<strong>in</strong>g expression<br />

I<br />

S1<br />

(t)<br />

j. ωn<br />

. ω.t<br />

−j2(1−S−ω<br />

n ) ω.t<br />

−t / τa<br />

= −[I<br />

S1<br />

.e −ΔI<br />

av<br />

S1.e<br />

]. e (6)<br />

The natural angular frequency <strong>of</strong> <strong>the</strong> aperiodec<br />

current vector, ω and <strong>the</strong> time constant <strong>of</strong> its<br />

n<br />

decay<strong>in</strong>g, τ<br />

a<br />

, are def<strong>in</strong>ed for <strong>the</strong> average<br />

complex admittance Y av<br />

(js) at <strong>the</strong> slip<br />

s = −(1<br />

− s) by equations<br />

ω = Im[ Y (js) ]. R<br />

(7)<br />

n<br />

av<br />

s=−(1−s)<br />

1<br />

τ<br />

a<br />

=<br />

(8)<br />

ω = Im[Y (js) ].R ω<br />

n<br />

av<br />

S0<br />

s= −(1−s)<br />

S0<br />

.<br />

The <strong>in</strong>itial value <strong>of</strong> <strong>the</strong> periodic component <strong>of</strong><br />

<strong>the</strong> transient current, is determ<strong>in</strong>ed by<br />

recogniz<strong>in</strong>g that<br />

I S 2<br />

I<br />

0(t)<br />

t=<br />

0<br />

+ I<br />

S1<br />

(t)<br />

t=<br />

0<br />

+ I<br />

S2<br />

(t)<br />

t=<br />

0<br />

S<br />

=<br />

Generally, <strong>the</strong> <strong>in</strong>itial value <strong>of</strong> <strong>the</strong> current vector<br />

I S<br />

t does not co<strong>in</strong>cide with <strong>the</strong> d-axis <strong>of</strong> a<br />

2<br />

( )<br />

t=<br />

0<br />

rotor (<strong>in</strong>clud<strong>in</strong>g <strong>the</strong> connections <strong>of</strong> <strong>the</strong><br />

synchronous mach<strong>in</strong>e occurr<strong>in</strong>g at <strong>the</strong><br />

angle ( δ 0<br />

= 0)<br />

result<strong>in</strong>g <strong>in</strong> aperiodic current<br />

components <strong>in</strong> both axes <strong>of</strong> <strong>the</strong> rotor symmetry.<br />

Implementation <strong>of</strong> <strong>the</strong> method proposed is<br />

associated with represent<strong>in</strong>g <strong>the</strong> <strong>in</strong>itial<br />

frequency-response characteristics <strong>in</strong> <strong>the</strong> form <strong>of</strong><br />

equivalent circuits <strong>in</strong> <strong>the</strong> d- and q-axis <strong>of</strong> a<br />

synchronous mach<strong>in</strong>e. The latter ones, e.g., <strong>the</strong><br />

equivalent circuit <strong>in</strong> d-axis shown <strong>in</strong> Figure1<br />

may be used for determ<strong>in</strong><strong>in</strong>g <strong>the</strong> changes <strong>in</strong> <strong>the</strong><br />

periodic current components with time [6].<br />

0<br />

68<br />

2010/Fascicule 2/April­June /Tome III


ACTA TECHNICA CORVINIENSIS – BULLETIN <strong>of</strong> ENGINEERING<br />

Figure 1. Equivalent circuit <strong>of</strong> <strong>the</strong> synchronous<br />

mach<strong>in</strong>e rotor <strong>in</strong> d-axis<br />

The mentioned equivalent circuits allow to<br />

obta<strong>in</strong> <strong>the</strong> <strong>in</strong>itial values I S<br />

, I ) and <strong>the</strong> time<br />

constants<br />

(<br />

dk<br />

τ ql )<br />

(<br />

2dk<br />

S 2ql<br />

τ , ) <strong>of</strong> <strong>the</strong> exponential<br />

components <strong>of</strong> <strong>the</strong> periodic armature<br />

current I ( t S 2<br />

) So <strong>in</strong> <strong>the</strong> d-and q-axis we have<br />

τ<br />

τ<br />

dk<br />

ql<br />

x<br />

=<br />

ω .r<br />

kD<br />

x<br />

lQ<br />

=<br />

ω .r<br />

kD<br />

lQ<br />

, I<br />

, I<br />

S 2 dk<br />

S 2 ql<br />

=<br />

=<br />

1<br />

x<br />

1<br />

x<br />

lQ<br />

kD<br />

, l<br />

, k<br />

= 1 ,2 ,...,<br />

= 1 ,2 ,...,<br />

M<br />

N ;<br />

(9)<br />

From <strong>the</strong> above, it might be assumed that <strong>the</strong><br />

time-dependence <strong>of</strong> <strong>the</strong> periodic current follows<br />

<strong>the</strong> law<br />

N<br />

t / dk 1 S ) . t j 0<br />

I<br />

j.(<br />

S 2<br />

( t ) =<br />

⎛ − τ<br />

I<br />

S 2<br />

.e<br />

⎞ − ω δ<br />

⎜ ∑<br />

⎟.e<br />

.e<br />

dk<br />

⎝ k = 1<br />

⎠<br />

(10)<br />

M<br />

− t / τ<br />

+<br />

⎛ ql j.( 1 − S ) ω . t jδ<br />

0<br />

I<br />

S 2<br />

.e<br />

⎞<br />

⎜ ∑<br />

⎟.e<br />

.e<br />

ql<br />

l = 1<br />

⎝<br />

⎠<br />

Where N, M =quantity <strong>of</strong> <strong>the</strong> elementary<br />

equivalent circuits <strong>of</strong> <strong>the</strong> rotor <strong>in</strong> d- and q-axis,<br />

respectively.<br />

In <strong>the</strong> general case <strong>the</strong> <strong>in</strong>itial current<br />

components <strong>in</strong> <strong>the</strong> d- and q-axis should be<br />

converted <strong>in</strong> proportion to <strong>the</strong> projection <strong>of</strong> <strong>the</strong><br />

I current vector on <strong>the</strong> direct, , and<br />

S 2<br />

quadrature I<br />

S 2 q<br />

rotor axes, e.g.,<br />

I<br />

S2d<br />

= mod[IS2<br />

(t)<br />

t=<br />

0<br />

].cos( ϕ − δ0<br />

),<br />

I = mod[I (t) ].s<strong>in</strong>( ϕ − δ )<br />

S2q<br />

S2<br />

t=<br />

0<br />

Whereϕ = argument <strong>of</strong> <strong>the</strong> I S<br />

t<br />

0<br />

I S 2<br />

I S 2d<br />

2<br />

( )<br />

t=<br />

0<br />

(11)<br />

current<br />

vector (<strong>the</strong> angle between <strong>the</strong> current vector<br />

and <strong>the</strong> real axis <strong>of</strong> <strong>the</strong> complex pla<strong>in</strong>).<br />

Then<br />

1 I<br />

S2d<br />

I<br />

S2<br />

= . ,<br />

dk<br />

x 1<br />

kD<br />

∑<br />

x<br />

kD<br />

(12)<br />

1 I<br />

S2q<br />

I<br />

S2<br />

= .<br />

ql<br />

x 1<br />

lQ<br />

∑<br />

x<br />

The total generalized vector <strong>of</strong> <strong>the</strong> transient<br />

armature current comprises <strong>the</strong> vector sum <strong>of</strong><br />

separate components:<br />

lQ<br />

I<br />

( t)<br />

= U.[<br />

I<br />

S 0(<br />

t)<br />

+ I<br />

S1(<br />

t)<br />

I<br />

S 2(<br />

t)]<br />

S<br />

+<br />

(13)<br />

Where V= voltage across <strong>the</strong> term<strong>in</strong>als <strong>of</strong> an<br />

armature w<strong>in</strong>d<strong>in</strong>g at <strong>the</strong> short-circuit condition<br />

or connection <strong>of</strong> a synchronous mach<strong>in</strong>e to <strong>the</strong><br />

network.<br />

The <strong>in</strong>stantaneous values <strong>of</strong> <strong>the</strong> phase currents<br />

are determ<strong>in</strong>ed as a projection <strong>of</strong> <strong>the</strong><br />

generalized current vector on <strong>the</strong> motionless<br />

time axes <strong>of</strong> <strong>the</strong> appropriate phases:<br />

i<br />

i (t) = mod[I (t)].cos( α(t)<br />

+ γ<br />

i<br />

A<br />

B<br />

C<br />

(t) = mod[I (t)].cos( α(t)<br />

+ γ<br />

S<br />

S<br />

(t) = mod[I (t)].cos( α(t)<br />

+ γ<br />

S<br />

0<br />

0<br />

0<br />

),<br />

2<br />

− π),<br />

3<br />

2<br />

+ π)<br />

3<br />

(14)<br />

Where α (t)<br />

=time-dependent argument <strong>of</strong> <strong>the</strong><br />

total generalized vector <strong>of</strong> <strong>the</strong> armature current.<br />

It is evident that <strong>the</strong> dynamic properties <strong>of</strong> an<br />

<strong>in</strong>duction mach<strong>in</strong>e can be described <strong>in</strong> full<br />

measure by means <strong>of</strong> a s<strong>in</strong>gle frequencyresponse<br />

characteristic Y(js) . In this case, <strong>the</strong><br />

expressions obta<strong>in</strong>ed above will not conta<strong>in</strong> <strong>the</strong><br />

additional current components and Δ <strong>the</strong><br />

are no needs <strong>in</strong> decomposition <strong>of</strong> <strong>the</strong><br />

ΔI S0<br />

I S 1<br />

I S 2<br />

current<br />

on <strong>the</strong> d- and q-axis components ei<strong>the</strong>r [20, 21].<br />

In accordance with <strong>the</strong> general approach <strong>the</strong><br />

electromagnetic torque is determ<strong>in</strong>ed us<strong>in</strong>g <strong>the</strong><br />

current and flux l<strong>in</strong>kage complexes, regardless <strong>of</strong><br />

<strong>the</strong> rotor symmetry <strong>of</strong> <strong>the</strong> AC mach<strong>in</strong>e, by <strong>the</strong><br />

expression:<br />

*<br />

* * *<br />

T<br />

s e S0 S1<br />

+ 2<br />

= Re[jψ<br />

.Is]<br />

= R [j( ψ + ψ )(IS0<br />

+ IS1<br />

IS<br />

) (15)<br />

The magnetic l<strong>in</strong>kages <strong>in</strong> (15) can be presented<br />

more detail as follows:<br />

j t jωn t −t<br />

/ τa<br />

ψ<br />

S<br />

= ψ<br />

S0<br />

− ψ<br />

S1<br />

= e<br />

ω − e e<br />

(16)<br />

As may be seen from <strong>the</strong> equations (15) and (16),<br />

<strong>the</strong> electromagnetic torque can be presented as<br />

<strong>the</strong> sum <strong>of</strong> <strong>the</strong> vector products <strong>of</strong> <strong>the</strong> currents by<br />

flux l<strong>in</strong>kage components. For example, <strong>the</strong><br />

product <strong>of</strong> <strong>the</strong> vector I<br />

S0<br />

by <strong>the</strong> vector ψ<br />

S0<br />

produces <strong>the</strong> steady-state torque be<strong>in</strong>g<br />

numerically equal to <strong>the</strong> vertical projection <strong>of</strong><br />

<strong>the</strong> current vector at <strong>the</strong> rated voltage across <strong>the</strong><br />

term<strong>in</strong>als <strong>of</strong> <strong>the</strong> stator w<strong>in</strong>d<strong>in</strong>g.<br />

The <strong>in</strong>fluence <strong>of</strong> <strong>the</strong> separate current and torque<br />

components on <strong>the</strong> features <strong>of</strong> <strong>the</strong> transient<br />

process hav<strong>in</strong>g been analyzed, it is possible to<br />

simplify <strong>the</strong> ma<strong>the</strong>matical model <strong>of</strong> an electrical<br />

mach<strong>in</strong>e with <strong>the</strong> given accuracy.<br />

2010/Fascicule 2/April­June /Tome III 69


ACTA TECHNICA CORVINIENSIS – BULLETIN <strong>of</strong> ENGINEERING<br />

At research<strong>in</strong>g <strong>the</strong> electromechanical <strong>transients</strong><br />

connected with <strong>the</strong> speed variations <strong>of</strong> AC<br />

mach<strong>in</strong>e rotor one should consider <strong>the</strong><br />

simultaneous solution <strong>of</strong> <strong>the</strong> equations deduced<br />

above and <strong>the</strong> supplementary equation <strong>of</strong> <strong>the</strong><br />

rotor relative motion. The latter one can be<br />

written <strong>in</strong> <strong>the</strong> follow<strong>in</strong>g form:<br />

ds<br />

M = T − T mech<br />

(17)<br />

dt<br />

Where T mech<br />

=shaft torque developed by <strong>the</strong><br />

prime mover; M =<strong>in</strong>ertia constant.<br />

THE PARAMETERS OF THE ALGORITHM<br />

If <strong>the</strong> <strong>in</strong>fluence <strong>of</strong> <strong>the</strong> rotor acceleration is not<br />

taken <strong>in</strong>to account <strong>the</strong> follow<strong>in</strong>g problem<br />

algorithm consider<strong>in</strong>g <strong>the</strong> rotor speed changes<br />

can be suggested:<br />

• The transient process is divided <strong>in</strong>to small<br />

uniform <strong>in</strong>tervals <strong>of</strong> time ;<br />

• The speed <strong>in</strong>crement over <strong>the</strong> given <strong>in</strong>terval<br />

is determ<strong>in</strong>ed by solv<strong>in</strong>g <strong>the</strong> equation (17) as<br />

follows :<br />

T − T<br />

Δ s =<br />

mech Δt<br />

;<br />

M<br />

• The susta<strong>in</strong>ed component <strong>of</strong> <strong>the</strong> I<br />

S0<br />

current<br />

is calculated at <strong>the</strong> constant speed obta<strong>in</strong>ed<br />

for <strong>the</strong> given time <strong>in</strong>terval ;<br />

• The amplitude <strong>of</strong> <strong>the</strong> I<br />

S1<br />

current component<br />

decay<strong>in</strong>g with <strong>the</strong> time constant τa<br />

is<br />

calculated at <strong>the</strong> <strong>in</strong>itial value <strong>of</strong> <strong>the</strong> rotor<br />

speed (at <strong>the</strong> beg<strong>in</strong>n<strong>in</strong>g <strong>of</strong> <strong>the</strong> first <strong>in</strong>terval) ;<br />

• The natural angular frequency, ω<br />

n<br />

, and <strong>the</strong><br />

time constant, τ a<br />

, <strong>of</strong> <strong>the</strong> aperiodic currant<br />

component are re-counted us<strong>in</strong>g equation<br />

(7),(8) <strong>in</strong> relation to <strong>the</strong> slip changes <strong>of</strong> a<br />

rotor ;<br />

• The amplitude <strong>of</strong> <strong>the</strong> I<br />

S2<br />

current component<br />

caused by <strong>the</strong> transient currents <strong>in</strong> <strong>the</strong> rotor<br />

circuits is determ<strong>in</strong>ed at <strong>the</strong> rotor slip<br />

correspond<strong>in</strong>g to <strong>the</strong> first <strong>in</strong>stant <strong>of</strong> <strong>the</strong><br />

process.<br />

• It should be po<strong>in</strong>ted out that <strong>the</strong> angular<br />

speed <strong>of</strong> <strong>the</strong> I S2<br />

current be<strong>in</strong>g taken <strong>in</strong>to<br />

account <strong>in</strong> (10) varies with <strong>the</strong> slip changes.<br />

The rotor slip dependence <strong>of</strong> <strong>the</strong> natural<br />

angular frequency and <strong>the</strong> time constant <strong>of</strong><br />

decay<strong>in</strong>g <strong>the</strong> magnetic flux ψ<br />

S1<br />

are taken<br />

<strong>in</strong>to account by equation (16).<br />

ESTIMATION OF MODEL VALIDITY<br />

The efficiency <strong>of</strong> application <strong>of</strong> <strong>the</strong> frequencyresponse<br />

characteristics for calculat<strong>in</strong>g <strong>the</strong><br />

transient process can be demonstrated with <strong>the</strong><br />

follow<strong>in</strong>g examples:<br />

1. Short-circuit at <strong>the</strong> term<strong>in</strong>als <strong>of</strong> <strong>the</strong> stator<br />

w<strong>in</strong>d<strong>in</strong>g and connection to <strong>the</strong> network without<br />

excitation <strong>of</strong> <strong>the</strong> model turbo generator <strong>of</strong> <strong>the</strong><br />

MT-3type:<br />

(S<br />

x<br />

d<br />

n<br />

=<br />

30KVA , V<br />

= 1.453; x<br />

q<br />

n<br />

= 414 V, I<br />

= 1.394;R<br />

S0<br />

n<br />

= 41.8A,<br />

= 0.00624 p.u.)<br />

In <strong>the</strong> case be<strong>in</strong>g considered <strong>the</strong> <strong>in</strong>fluence <strong>of</strong> <strong>the</strong><br />

sign and <strong>in</strong>itial slip value at connect<strong>in</strong>g <strong>the</strong><br />

generator to <strong>the</strong> network as well as <strong>the</strong> <strong>in</strong>fluence<br />

<strong>of</strong> <strong>the</strong> rotor speed changes at <strong>the</strong> transient<br />

conditions were analyzed.<br />

2. Connection to <strong>the</strong> network <strong>of</strong> <strong>the</strong> unexcited<br />

turbo generator <strong>of</strong> <strong>the</strong> ТГВ-200 type:<br />

S<br />

x<br />

n<br />

d<br />

= 235MVA , V<br />

= 1.9; x<br />

q<br />

n<br />

= 1.89;R<br />

= 15.75KV, I<br />

S0<br />

n<br />

= 0.0012p.u.<br />

= 8635 A,<br />

When calculat<strong>in</strong>g <strong>the</strong> electromechanical<br />

<strong>transients</strong> <strong>the</strong> errors be<strong>in</strong>g brought about by<br />

simplify<strong>in</strong>g <strong>the</strong> complicated equivalent circuits,<br />

reflect<strong>in</strong>g <strong>the</strong> electromagnetic <strong>of</strong> <strong>the</strong> solid rotor,<br />

were considered.<br />

3. Start<strong>in</strong>g <strong>of</strong> <strong>the</strong> <strong>in</strong>duction motor <strong>of</strong> <strong>the</strong> ДАЗО-<br />

1914-10/12А type:<br />

Pn = 1500Kw;I<br />

n<br />

= 204A; Vn<br />

= 6000V from <strong>the</strong> noload<br />

condition, and three-phase short-circuit at<br />

its term<strong>in</strong>als.<br />

Estimation <strong>of</strong> <strong>the</strong> results obta<strong>in</strong>ed, when us<strong>in</strong>g<br />

<strong>the</strong> techniques proposed above, was carried out<br />

by comparison with <strong>the</strong> appropriate calculations<br />

made by <strong>the</strong> use <strong>of</strong> algorithms based on<br />

numerical <strong>in</strong>tegrat<strong>in</strong>g <strong>the</strong> system <strong>of</strong> <strong>the</strong><br />

differential Parc-Gorev equations. The<br />

frequency-response characteristics reflect<strong>in</strong>g <strong>the</strong><br />

dynamic properties <strong>of</strong> <strong>the</strong> AC mach<strong>in</strong>es be<strong>in</strong>g<br />

studied were obta<strong>in</strong>ed experimentally from <strong>the</strong><br />

DC decay <strong>in</strong> <strong>the</strong> armature w<strong>in</strong>d<strong>in</strong>g at standstill<br />

test [8, 7, 17].<br />

Computer programs realiz<strong>in</strong>g <strong>the</strong> above<br />

mentioned algorithms for calculat<strong>in</strong>g <strong>the</strong><br />

electromechanical <strong>transients</strong> <strong>in</strong> AC mach<strong>in</strong>es<br />

were elaborated with<strong>in</strong> <strong>the</strong> framework <strong>of</strong> <strong>the</strong><br />

MathCAD 7.0.<br />

The time-dependence <strong>of</strong> chang<strong>in</strong>g <strong>the</strong><br />

generalized stator current vector and <strong>the</strong><br />

electromagnetic runn<strong>in</strong>g torque at connection<br />

70<br />

2010/Fascicule 2/April­June /Tome III


ACTA TECHNICA CORVINIENSIS – BULLETIN <strong>of</strong> ENGINEERING<br />

<strong>the</strong> unexcited model generator to <strong>the</strong> network<br />

under <strong>the</strong> various <strong>in</strong>itial rotor slips were carried<br />

out without <strong>the</strong> account and <strong>in</strong> view <strong>of</strong><br />

chang<strong>in</strong>g <strong>the</strong> rotor speed at transient .The<br />

<strong>in</strong>variable rotor speed was simulated by way <strong>of</strong><br />

sett<strong>in</strong>g <strong>the</strong> great value <strong>of</strong> <strong>the</strong> <strong>in</strong>ertia constant [9].<br />

As follows from comparison <strong>of</strong> <strong>the</strong> results<br />

obta<strong>in</strong>ed for <strong>the</strong> given slip values, equal to 0 ;<br />

0.01 ; 0.03 ; 0.05 and 0.1 put., <strong>the</strong> changes <strong>in</strong> <strong>the</strong><br />

time-dependence <strong>of</strong> <strong>the</strong> generalized stator<br />

current vector and electromagnetic torque<br />

practically does not differ from <strong>the</strong> analogous<br />

calculations made on <strong>the</strong> basis <strong>of</strong> <strong>the</strong> Parc-<br />

Gorev equations. In <strong>the</strong>se cases <strong>the</strong> difference <strong>in</strong><br />

<strong>the</strong> maximum values <strong>of</strong> <strong>the</strong> similar operat<strong>in</strong>g<br />

variables be<strong>in</strong>g compared did not exceed 10.4%.<br />

The typical changes <strong>in</strong> <strong>the</strong> <strong>transients</strong> differ not at<br />

all. So, when mak<strong>in</strong>g use <strong>of</strong> <strong>the</strong> static frequencyresponse<br />

characteristics, one can <strong>in</strong>fer that <strong>the</strong><br />

electromagnetic processes may be identified<br />

with a sufficiently high degree <strong>of</strong> accuracy.<br />

The analysis <strong>of</strong> <strong>the</strong> <strong>transients</strong> calculated with<br />

tak<strong>in</strong>g <strong>in</strong>to consideration <strong>the</strong> rotor speed<br />

changes, follow<strong>in</strong>g <strong>the</strong> connection <strong>of</strong> <strong>the</strong> model<br />

generator, po<strong>in</strong>ts to some differences <strong>in</strong> <strong>the</strong><br />

time-dependent variables. By way <strong>of</strong> example, <strong>in</strong><br />

<strong>the</strong> Figure 2 are shown <strong>the</strong> results <strong>of</strong> calculat<strong>in</strong>g<br />

<strong>the</strong> <strong>transients</strong> at connection <strong>the</strong> unexcited<br />

model mach<strong>in</strong>e to <strong>the</strong> network with <strong>the</strong> field<br />

w<strong>in</strong>d<strong>in</strong>g short-circuited.<br />

The calculations carried out <strong>in</strong> compliance with<br />

<strong>the</strong> system <strong>of</strong> Parc-Gorev equations (see dotted<br />

l<strong>in</strong>e) reflect <strong>the</strong> features connected with changes<br />

<strong>in</strong> <strong>the</strong> current, I s ,and electromagnetic torque,<br />

T , with <strong>the</strong> rotor speed changes. The time<br />

dependence <strong>of</strong> <strong>the</strong> slip <strong>in</strong> <strong>the</strong> case under<br />

consideration has <strong>the</strong> oscillatory character.<br />

Ma<strong>the</strong>matical <strong>simulation</strong> based on <strong>the</strong> static<br />

characteristics (see solid l<strong>in</strong>e) br<strong>in</strong>gs about <strong>the</strong><br />

monotonous changes <strong>in</strong> <strong>the</strong> rotor slip under <strong>the</strong><br />

transient process. Meanwhile, <strong>the</strong> resultant time<br />

<strong>of</strong> approach<strong>in</strong>g <strong>the</strong> rotor speed to <strong>the</strong><br />

synchronous one, be<strong>in</strong>g estimated at <strong>the</strong> <strong>in</strong>stant<br />

a rotor slip for <strong>the</strong> second time passes through<br />

zero, practically agrees with <strong>the</strong> time be<strong>in</strong>g<br />

determ<strong>in</strong>ed from <strong>the</strong> solid l<strong>in</strong>e obta<strong>in</strong>ed at<br />

simulat<strong>in</strong>g <strong>the</strong> <strong>transients</strong> by means <strong>of</strong> <strong>the</strong><br />

method proposed. As may be seen from <strong>the</strong><br />

Figure 2.<br />

Dist<strong>in</strong>guish<strong>in</strong>g features <strong>of</strong> <strong>the</strong> variables be<strong>in</strong>g<br />

considered are <strong>in</strong> close agreement; <strong>the</strong>ir<br />

maximum values appear<strong>in</strong>g at <strong>the</strong> <strong>in</strong>itial stage <strong>of</strong><br />

<strong>the</strong> transient process correlate well with <strong>the</strong> data<br />

got without regard for speed changes <strong>of</strong> <strong>the</strong><br />

rotor. In <strong>the</strong> Figure 3 are given <strong>the</strong> curves<br />

reflect<strong>in</strong>g <strong>the</strong> changes <strong>in</strong> <strong>the</strong> variables at <strong>the</strong><br />

short-circuit on <strong>the</strong> term<strong>in</strong>als <strong>of</strong> <strong>the</strong> <strong>in</strong>duction<br />

motor ДАЗО-1914-10/12А type.<br />

Figure 2 Connection to <strong>the</strong> network <strong>of</strong> <strong>the</strong> unexcited<br />

model turbo generator<br />

The quantities <strong>of</strong> <strong>the</strong> motor equivalent circuits<br />

syn<strong>the</strong>sized <strong>in</strong> accordance with [4,10] hav<strong>in</strong>g<br />

three parallel branches and <strong>the</strong> magnetiz<strong>in</strong>g one,<br />

separated <strong>in</strong> <strong>the</strong> manner as is shown <strong>in</strong> <strong>the</strong><br />

Figure 1, are as follows (<strong>in</strong> per unit on mach<strong>in</strong>e<br />

base) :<br />

R<br />

X<br />

δ<br />

+ X<br />

γ<br />

= 2.19 ; X = 0.271 ; X<br />

2<br />

X<br />

3<br />

= 0 .717 ;R<br />

0 .624<br />

1<br />

=<br />

= 0 .0055<br />

;R<br />

3 1<br />

2<br />

=<br />

1.179<br />

0 .1139<br />

The comparative analysis <strong>of</strong> <strong>the</strong> results obta<strong>in</strong>ed<br />

by calculat<strong>in</strong>g <strong>the</strong> generalized stator current<br />

vector, I<br />

s<br />

and electromagnetic torque, T ,<br />

calculated by various methods po<strong>in</strong>ts to <strong>the</strong>ir<br />

close agreement because <strong>of</strong> <strong>the</strong> maximum<br />

values <strong>of</strong> <strong>the</strong> mentioned variables differ less than<br />

7,8%.<br />

The analysis <strong>of</strong> <strong>the</strong> electromechanical <strong>transients</strong><br />

at start<strong>in</strong>g <strong>the</strong> non-loaded motor also <strong>in</strong>dicates<br />

to <strong>the</strong> satisfactory co<strong>in</strong>cid<strong>in</strong>g <strong>of</strong> <strong>the</strong> results<br />

obta<strong>in</strong>ed by us<strong>in</strong>g <strong>the</strong> mentioned calculation<br />

techniques. In particular, <strong>the</strong> start<strong>in</strong>g time<br />

determ<strong>in</strong>ed by <strong>the</strong> technique proposed differs<br />

from <strong>the</strong> same parameter obta<strong>in</strong>ed through <strong>the</strong><br />

use <strong>of</strong> <strong>the</strong> Parc Gorev equations less than 9, 2%.<br />

2010/Fascicule 2/April­June /Tome III 71


ACTA TECHNICA CORVINIENSIS – BULLETIN <strong>of</strong> ENGINEERING<br />

As is seen from <strong>the</strong> Figure 4, <strong>the</strong> electromagnetic<br />

<strong>transients</strong> with<strong>in</strong> <strong>the</strong> time <strong>in</strong>terval from 0 up to<br />

0,1 s<br />

correspond closely with <strong>the</strong> results obta<strong>in</strong>ed by<br />

<strong>the</strong> Parc Gorev equation (see dotted l<strong>in</strong>e).<br />

The mentioned acceptable results are<br />

attributable to <strong>the</strong> fact that <strong>the</strong> change <strong>in</strong> <strong>the</strong><br />

motor speed takes place at <strong>the</strong> small rotor<br />

acceleration. In this case, <strong>the</strong> application <strong>of</strong> <strong>the</strong><br />

frequency-response characteristics <strong>of</strong> a mach<strong>in</strong>e<br />

does not <strong>in</strong>troduce large errors <strong>in</strong>to calculation<br />

<strong>of</strong> <strong>the</strong> transient processes. When <strong>the</strong> rotor speed<br />

is close to <strong>the</strong> rated value <strong>the</strong>re are considerable<br />

deviations <strong>in</strong> <strong>the</strong> changes <strong>of</strong> <strong>the</strong> current and<br />

electromagnetic torque with time.<br />

As may be <strong>in</strong>ferred from <strong>the</strong> research, <strong>the</strong><br />

mentioned deviations decrease with <strong>in</strong>creas<strong>in</strong>g<br />

<strong>the</strong> <strong>in</strong>ertia constant, M, and <strong>the</strong> load<strong>in</strong>g factor <strong>of</strong><br />

<strong>the</strong> <strong>in</strong>duction motor. The <strong>transients</strong> <strong>in</strong> this case<br />

are accompanied by <strong>the</strong> less acceleration <strong>of</strong> a<br />

rotor.<br />

The <strong>in</strong>vestigation <strong>of</strong> <strong>the</strong> <strong>transients</strong> called forth by<br />

connection <strong>of</strong> <strong>the</strong> unexcited turbo generator<br />

ТГВ-200 type to <strong>the</strong> network was carried out<br />

with <strong>the</strong> use <strong>of</strong> <strong>the</strong> equivalent circuits conta<strong>in</strong><strong>in</strong>g<br />

five parallel branches <strong>in</strong> d- and q-axis [6]. It was<br />

ascerta<strong>in</strong>ed that <strong>the</strong> errors be<strong>in</strong>g <strong>in</strong>troduced <strong>in</strong><br />

<strong>the</strong> transient processes by reduc<strong>in</strong>g <strong>the</strong> quantity<br />

<strong>of</strong> <strong>the</strong> circuit branches, describ<strong>in</strong>g <strong>the</strong> physical<br />

properties <strong>of</strong> <strong>the</strong> solid rotor, to three do not<br />

exceed <strong>the</strong> errors <strong>in</strong> a frequency doma<strong>in</strong> equal<br />

to 11%.<br />

CONCLUSIONS<br />

The proposed ma<strong>the</strong>matical models <strong>of</strong> <strong>the</strong><br />

<strong>asynchronous</strong> mach<strong>in</strong>es based on <strong>the</strong><br />

experimental frequency-response characteristics<br />

allow to <strong>in</strong>vestigate <strong>the</strong> <strong>transients</strong> processes at<br />

short-circuits and connection <strong>of</strong> <strong>the</strong><br />

mach<strong>in</strong>es to <strong>the</strong> network without solution <strong>of</strong> <strong>the</strong><br />

conventional differential equations.<br />

REFERENCES<br />

Figure 3 Short-circuit on <strong>the</strong> term<strong>in</strong>als <strong>of</strong> <strong>the</strong><br />

<strong>in</strong>duction motor.<br />

Figure 4 The time –dependence <strong>of</strong> <strong>the</strong> generalized<br />

vector <strong>of</strong> <strong>the</strong> stator current at connect<strong>in</strong>g <strong>the</strong><br />

<strong>in</strong>duction motor<br />

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[2] SHIQIN DU; YUEJIN ZHANG; Jianzhong Jiang;<br />

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[3] LIUCHEN CHANG; An improved FE <strong>in</strong>ductance<br />

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[4] GUHA, S.; KAR, N.C.; A New Method <strong>of</strong> Model<strong>in</strong>g<br />

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[10] LAM, D.M.; YEE, H.; A study <strong>of</strong> frequency responses<br />

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[11] ARJONA L., M.A.; MACDONALD, D.C.; Characteris<strong>in</strong>g<br />

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[12] SLEMON, G.R.; AWAD, M.L.; On equivalent circuit<br />

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AUTHORS & AFFILIATION<br />

1.<br />

ABDESSALEM LAMARI<br />

1.<br />

Department <strong>of</strong> Electronics, ISSAT Mateur, Route de<br />

Tabarka 7030, Tunisia<br />

2010/Fascicule 2/April­June /Tome III 73


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