Scott R. Smith
ENEE473
Lab 9: ThreePhase Synchronous Machine
(Equivalent Circuit Parameters)
April 13, 2007
Purpose:
As with the threephase induction machine, the threephase synchronous machine (SM)
has an equivalent circuit that gives us the tools to predict the way the device will react. The
threephase SM equivalent circuit is shown below in figure 1.
s
I
ˆ
f
I
s
R
s
X
s
V
ˆ
+
_
L
Z
f
V
s
ε
ˆ
Figure 1
It can be seen from the KVL that
(1)
s
s
s
s
s
s
V
I
jX
I
R
ˆ
ˆ
ˆ
ˆ
+
+
=
where
(2)
l
s
m
s
s
X
X
X
+
=
Rearranging equation (1) and substituting in equation (2),
( )
s
s
m
s
s
l
s
s
s
V
I
jX
I
jX
R
ˆ
ˆ
ˆ
ˆ
+
+
+
=
(3)
Since the leakages are very small the following approximation can be made.
m
s
l
s
X
X
<<
(4)
Therefore,
(5)
s
s
m
s
s
s
s
V
I
jX
I
R
ˆ
ˆ
ˆ
ˆ
+
+
≅
From the rules of phasors,
()
( )
()
2
2
2
s
s
m
s
s
s
s
V
I
X
I
R
+
+
≅
(6)
Rearranging equation (6),
() ( ) ( )
2
2
2
s
m
s
s
s
s
s
I
X
I
R
V
−
−
≅
(7)
By using the data from the open circuit and short circuit tests,
X
s
can be determined.
m
s
s
sc
oc
X
X
I
V
Z
≅
=
=
(8)
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View Full DocumentDevices and Instrumentation:
Resistor Banks
– Each bank of resistors is made up of ten individual resistors that can be
connected together using single pole double throw switches. By systematically setting the
switches it is possible to create many resistance values by combining series and parallel branches
in one bank. Each resistor has a power dissipation rating of 100
W
and a resistance value of
250
Ω
. The power dissipation capacity can be increased by using parallel branches of resistors to
achieve the same value as a series connection would.
Wattmeter
– The wattmeter is a threeterminal device where two terminals are connected
inline with the circuit to measure current and the third terminal measures voltage of the inline
voltage relative to the connected node. There are two wattmeters at the lab station. Using both of
them, threephase power can be measured.
ThreePhase Synchronous Machine
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 Spring '07
 Mayergoyz
 Electrical Engineering, Direct Current, Electrical resistance, DCD, SM field

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