A 100 kW, 200 V, long-shunt commutative compound generator has equivalent armature resistance of 0.03 Ω and a series field resistance of 0.004 Ω . There are 1200 shunt turns per pole and 5 series turn per pole. The data of its magnetization characteristic at 1000 rpm is given below: If (A) 0 1 2.2

Question

A 100 kW, 200 V, long-shunt commutative compound generator has equivalent armature resistance of 0.03[latex] \Omega [/latex] and a series field resistance of 0.004 [latex] \Omega [/latex]. There are 1200 shunt turns per pole and 5 series turn per pole. The data of its magnetization characteristic at 1000 rpm is given below:

[latex] I_{f}(A)[/latex]	0	1	2.2	3.3	4.2	5.3	7.1
[latex] E_{a}(V)[/latex]	11	33	105	150	175	200	225

(a) Calculate the terminal voltage and rated output current for shunt field current of 5 A and a speed of 950 rpm. Neglect armature reaction effect.

(b) Calculate the number of series turns per pole for the generator to level compound with same shunt field current, series field resistance and generation speed to be the same as in part (a). The demagnetization due to armature reaction in equivalent shunt field current is 0.001875 [latex] I_{a}[/latex] where [latex] I_{a}[/latex] is the armature current.

Accepted Answer

The schematic diagram of long-shunt compound generator is drawn in Fig. 7.56(a)

Line current, [latex] I_{L} = \frac{100 imes 10^{3}}{200} =500A[/latex]

Shunt field current, [latex] I_{f} = 5 A[/latex] (given)

From Fig. 7.56(a)

[latex] I_{a}=500+5=505A[/latex]

[latex] I_{f,eq}=I_{f}+\frac{N_{se}}{N_{f}} I_{se}[/latex]

[latex] = 5 + \frac{5}{1200} imes 505 = 7.1 A[/latex]

From the magnetization characteristic of Fig. 7.56(b) (as per data given)

(a) [latex] E_{a} = 225 V[/latex] at 1000 rpm

[latex] E_{a} (950 rpm) = 225 imes \frac{950}{1000} = 213.75 V[/latex]

From Fig. 7.56(a)

[latex] V_{t}=E_{a}-I_{a} (R_{a}+R_{se})= 213.75 – 505 (0.03 + 0.004)[/latex]

The generator is under – compounded (armature reaction ignored)

(b) [latex] I_{fd}=0.001875 imes 505 = 0.95 A (demag)[/latex]

For level compound

[latex] V_{t}=200V[/latex]

[latex] E_{a}= 200 + 505 (0.03 + 0.04) = 217.17 (950 rpm)[/latex]

From the magnetization characteristic

[latex] I_{f}(net) =7.5A[/latex]

Excitation balance equation

[latex] I_{f}+\frac{N_{se}}{N_{f}} I_{a}-I_{fd}=I_{f}(net)[/latex]

[latex] 5 + 505 \left(\frac{N_{se}}{1000} ight) – 0.95 = 7.5[/latex]

which gives [latex] N_{se}[/latex] = 6.87 or 7 turns

Question 7.16: A 100 kW, 200 V, long-shunt commutative compound generator h...

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