WEG-curso-dt-5-caracteristicas-e-especificacoes-de-geradores-artigo-tecnico-portugues-br
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DT-5 - Características e Especificações <strong>de</strong> Geradores<<strong>br</strong> />
7.3.5. EXEMPLO DE CÁLCULO DE QUEDA DE<<strong>br</strong> />
TENSÃO EM GERADORES ENVOLVENDO<<strong>br</strong> />
VÁRIOS MOTORES (UTILIZANDO LINHA G i-<<strong>br</strong> />
PLUS)<<strong>br</strong> />
Dados necessários:<<strong>br</strong> />
a) Gerador AG10250SI20AI, 292 kVA, 440V<<strong>br</strong> />
Xd'=18.39% (Xd’=0.1839pu);<<strong>br</strong> />
b) Motores <strong>de</strong> indução:<<strong>br</strong> />
b.1) 100cv - 04 pólos - 440V - In=120A - Ip=1056A<<strong>br</strong> />
b.2) 75cv - 04 pólos - 440V - In=87.5A - Ip=647.5A<<strong>br</strong> />
b.3) 25cv - 04 pólos - 440V - In=31.5A - Ip=271A<<strong>br</strong> />
c) Condição <strong>de</strong> recebimento <strong>de</strong> carga do gerador:<<strong>br</strong> />
c.1) Primeiramente parte o motor <strong>de</strong> 100cv<<strong>br</strong> />
utilizando chave compensadora no TAP <strong>de</strong><<strong>br</strong> />
65%<<strong>br</strong> />
c.2) Outra condição seria a partida (no TAP <strong>de</strong><<strong>br</strong> />
65%) do motor <strong>de</strong> 75cv, consi<strong>de</strong>rando que os<<strong>br</strong> />
motores <strong>de</strong> 100 e 25cv já partiram e estejam<<strong>br</strong> />
em funcionamento.<<strong>br</strong> />
SOLUÇÃO:<<strong>br</strong> />
Cálculo da corrente nominal do gerador:<<strong>br</strong> />
292000<<strong>br</strong> />
Ig = = 383<<strong>br</strong> />
A<<strong>br</strong> />
3 .440<<strong>br</strong> />
I - Cálculo da queda <strong>de</strong> tensão provocada<<strong>br</strong> />
pela partida do motor <strong>de</strong> 100cv (através<<strong>br</strong> />
<strong>de</strong> chave compensadora no Tap 65%)<<strong>br</strong> />
consi<strong>de</strong>rando os motores <strong>de</strong> 25 e 75cv<<strong>br</strong> />
<strong>de</strong>sligados:<<strong>br</strong> />
Inominal motor = 120A<<strong>br</strong> />
Ipartida motor = 1056A<<strong>br</strong> />
Obs: Supor queda <strong>de</strong> tensão <strong>de</strong> 15% no gerador<<strong>br</strong> />
(estimativa inicial).<<strong>br</strong> />
Utilizando chave compensadora no TAP 65 % e<<strong>br</strong> />
consi<strong>de</strong>rando uma queda <strong>de</strong> tensão inicial <strong>de</strong> 15%<<strong>br</strong> />
no gerador, a redução total <strong>de</strong> tensão nos bornes<<strong>br</strong> />
do motor é:<<strong>br</strong> />
(1-0,15) x 0,65 = 0,85 x 0,65 = 0,55<<strong>br</strong> />
Do gráfico da fig. 5.3.5, com 0,55 <strong>de</strong> redução <strong>de</strong><<strong>br</strong> />
tensão, obtemos a constante <strong>de</strong> redução <strong>de</strong><<strong>br</strong> />
corrente (K1):<<strong>br</strong> />
K1 = 0,45<<strong>br</strong> />
Assim, a corrente <strong>de</strong> partida do motor em seus<<strong>br</strong> />
terminais fica:<<strong>br</strong> />
IPmotor 65% = IPmotor 100% x K1<<strong>br</strong> />
IPmotor 65% = 1056 x 0,45 = 475A<<strong>br</strong> />
Mas, em se tratando da chave compensadora,<<strong>br</strong> />
teremos que referir a corrente <strong>de</strong> partida do motor<<strong>br</strong> />
(secundário da chave compensadora) ao gerador<<strong>br</strong> />
(primário da chave compensadora), obtendo-se<<strong>br</strong> />
então IPmotor ref<<strong>br</strong> />
IP prim IPmotor<<strong>br</strong> />
ref.<<strong>br</strong> />
= = 0,65<<strong>br</strong> />
I sec IPmotor 65%<<strong>br</strong> />
IPmotor<<strong>br</strong> />
ref. = IPmotor<<strong>br</strong> />
65% .0,65<<strong>br</strong> />
IPmotor<<strong>br</strong> />
ref.= 475 .0,65= 309 A<<strong>br</strong> />
Então, nos bornes do gerador, fazendo a relação da<<strong>br</strong> />
corrente <strong>de</strong> partida do motor referida, pela corrente<<strong>br</strong> />
nominal do gerador (IP/IN):<<strong>br</strong> />
IP<<strong>br</strong> />
motor ref<<strong>br</strong> />
I<<strong>br</strong> />
g<<strong>br</strong> />
309<<strong>br</strong> />
= = 0,<<strong>br</strong> />
8068<<strong>br</strong> />
383<<strong>br</strong> />
Teremos uma queda <strong>de</strong> tensão <strong>de</strong>:<<strong>br</strong> />
[X d<<strong>br</strong> />
. IP/IN]<<strong>br</strong> />
V =<<strong>br</strong> />
.100<<strong>br</strong> />
1+ [X d<<strong>br</strong> />
. IP/IN]<<strong>br</strong> />
[ 01839 , . 0,<<strong>br</strong> />
8068]<<strong>br</strong> />
V =<<strong>br</strong> />
. 100=<<strong>br</strong> />
12,<<strong>br</strong> />
92%<<strong>br</strong> />
1+ [ 01839 , . 0,<<strong>br</strong> />
8068]<<strong>br</strong> />
Refazendo o cálculo (1º iteração) para queda <strong>de</strong><<strong>br</strong> />
tensão no gerador <strong>de</strong> 5,85%, temos:<<strong>br</strong> />
Redução total <strong>de</strong> tensão:<<strong>br</strong> />
0,65 x (1- 0,1291) = 0,56<<strong>br</strong> />
Constante <strong>de</strong> redução total <strong>de</strong> corrente (K1) <strong>de</strong>vido<<strong>br</strong> />
à redução da tensão (0,61):<<strong>br</strong> />
K1 = 0,46<<strong>br</strong> />
IP motor 65% = IP motor 100% x K1<<strong>br</strong> />
IP motor 65% = 1056 x 0,46 = 485,76A<<strong>br</strong> />
Corrente <strong>de</strong> partida referida ao primário da chave<<strong>br</strong> />
compensadora (bornes do gerador) e relação IP/IN<<strong>br</strong> />
ref. = IPmotor<<strong>br</strong> />
.0,65<<strong>br</strong> />
485 ,76 .0,65= 315,<<strong>br</strong> />
IPmotor<<strong>br</strong> />
65%<<strong>br</strong> />
IPmotor ref.=<<strong>br</strong> />
74<<strong>br</strong> />
IP<<strong>br</strong> />
Ig<<strong>br</strong> />
motor ref.<<strong>br</strong> />
315,74<<strong>br</strong> />
= = 0,<<strong>br</strong> />
8244<<strong>br</strong> />
383<<strong>br</strong> />
Assim, com o valor <strong>de</strong> queda da 1° iteração,<<strong>br</strong> />
teremos uma queda <strong>de</strong> tensão <strong>de</strong>:<<strong>br</strong> />
X d<<strong>br</strong> />
. IP/IN<<strong>br</strong> />
V =<<strong>br</strong> />
.100<<strong>br</strong> />
1+ [X d<<strong>br</strong> />
. IP/IN]<<strong>br</strong> />
0,1839<<strong>br</strong> />
0,8244<<strong>br</strong> />
V <<strong>br</strong> />
100<<strong>br</strong> />
13,16%<<strong>br</strong> />
1 0,1839 0,8244<<strong>br</strong> />
<<strong>br</strong> />
II - Cálculo da queda <strong>de</strong> tensão provocada<<strong>br</strong> />
pela partida do motor <strong>de</strong> 75cv (através <strong>de</strong><<strong>br</strong> />
chave compensadora no Tap 65%),<<strong>br</strong> />
consi<strong>de</strong>rando que os motores <strong>de</strong> 100 e<<strong>br</strong> />
25cv já estejam em funcionamento.<<strong>br</strong> />
<<strong>br</strong> />
A<<strong>br</strong> />
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