Post on 14-Dec-2015
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Name: AUNG MIN THANT S/N: 11314693
IV. 2 Determination of Synchronous Reactance (Covered Question 2 of V. Lab
Report)
A. Open Circuit Test
Set the field current of the DC motor to 2 A, and maintain the speed at 1500 rev/min by adjusting
the armature circuit voltage.
Increase the excitation current of synchronous machine rotor field winding in convenient 5 or 6
steps up to 2.5 A, and record the stator open circuit terminal voltage versus the rotor excitation
current in the table below. Preferably limit the synchronous machine field excitation current to
2.5 A, and assume that the corresponding stator terminal voltage is the nominal voltage.
Stator Voltage Voc (Vline to line) 0 63 97.2 121 139.3 152
Stator Voltage Voc (Vphase) 0 36.3731 56.11845 69.8594 80.4249 87.757
Rotor Current Ir (A) 0 0.52 0.99 1.6 2.03 2.5
Table 1 Open Circuit Test
Figure 1 Stator Voltage (V phase) Vs Rotor Current
B. Short Circuit Test
Switch off the DC motor. Reduce the synchronous machine excitation current to minimum and
switch off the supply from the AC/DC rectifier. Connect an ammeter in series with one of the
three phase stator windings of synchronous machine, and short circuit the three terminals (i.e.
two terminals of the stator phase winding and one terminal of the ammeter).
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3
Stat
or
Vo
ltag
e V
oc(
V)
Rotor Current(Ir)
Voc(phase) Vs Ir(A)
Voc(phase) Vs Ir(A)
Name: AUNG MIN THANT S/N: 11314693
Start the DC motor and maintain the rotor speed at 1500 rev/min. Increase the synchronous
machine rotor field excitation current to 2.5 A (the value corresponding to the nominal stator
voltage recorded in the previous open circuit test), and record the corresponding stator short
circuit current in the table below. (Note: Throughout the test, the rotor speed should be kept at
1500 rev/min by adjusting the DC motor armature voltage).
Short Circuit Current, Isc (A) 1.25A
Nominal Stator Voltage Voc (V phase) 87.76V
Table 2 Short Circuit Test
Calculation of synchronous machine
,
= 70.208Ω
Figure 2 Nominal Stator Voltage (V phase) Vs Short Circuit Current
IV.3 Voltage Regulation Test
Switch off the DC motor. Reduce the synchronous machine excitation current to minimum and
switch off the supply from the AC/DC rectifier. Disconnect the short circuit of the stator winding
terminals and successively connect balanced three phase loads of (i) resistors, and (ii) capacitors.
Start the DC motor and maintain the rotor speed at 1500 rev/min. Switch on the excitation
current to 2.5 A, the value corresponding to the nominal stator voltage recorded in the previous
open circuit test. In the tables below, record the stator terminal voltage versus load current for as
many load values as permitted by the terminal connections on the load equipment. Keep the
rotor speed at 1500 rev/min during the test!
0
20
40
60
80
100
0 0.5 1 1.5
No
min
al S
tato
r V
olt
age
(Vp
has
e)
Short Circuit Current, Isc (A)
Nominal Stator Voltage Verus Isc
Nominal Stator Voltage VsIsc
Name: AUNG MIN THANT S/N: 11314693
Voltage Regulation Tests with Resistive Loads:
Rotor Current, Ir(A) Terminal Voltage, Vs (Vphase)
Load Current, IL(A)
Load Resistance, RL(Ω)
2.54 36 1.16 30
2.5 57.2 0.96 60
2.49 70 0.78 90
2.5 75 0.64 120
2.52 89 0.55 150
Table 3 Voltage Regulation Test (RL)
Figure 3 Terminal Voltage (V phase) Vs Load Current
0
10
20
30
40
50
60
70
80
90
100
0 0.5 1 1.5
Term
inal
Vo
ltag
e V
s(V
ph
ase
)
Load Current IL(A)
Terminal Voltage Vs Load current (resistive load)
Terminal Voltage Vs Loadcurrent(resistance)
Name: AUNG MIN THANT S/N: 11314693
Name: AUNG MIN THANT S/N: 11314693
Name: AUNG MIN THANT S/N: 11314693
Load Current, IL(A) Load Resistance, RL(Ω) VR (Theoretical)% VR (Practical)%
1.16 30 154.52% 147.3%
0.96 60 53.91% 54.55%
0.78 90 26.82% 26.97%
0.64 120 15.85% 16.57%
0.55 150 10.39% 9.011%
Table 4 Voltage Regulation Theoretical Vs Practical (RL)
Figure 4 Voltage Regulation Theoretical Vs Practical (RL)
Voltage Regulation Tests with Capacitive Loads:
Rotor Current, Ir (A)
Terminal Voltage, Vs (Vphase)
Load Current, IL(A)
Load Capacitance C(µF)
2.53 107 0.38 10
2.5 123.2 0.75 20
2.52 150 1.7 40
Table 5 Voltage Regulation Test (CL)
0
20
40
60
80
100
120
140
160
180
0 0.5 1 1.5
Vo
ltge
Re
gula
tio
n %
Load Current (A)
Voltage Regulation Vs Load Current with a Resistive Load
Voltage Regulation(Theoretical)
Voltage Regulation(Practical)
Name: AUNG MIN THANT S/N: 11314693
Figure 5 Terminal Voltage (V phase) Vs Current Load
0
20
40
60
80
100
120
140
160
0 0.5 1 1.5 2
Term
inal
Vo
ltag
e (
Vp
has
e)
Current Load (A)
Terminal Voltage(Vphase) Vs load current(Capacitive load)
Terminal Voltage Vsload current
Name: AUNG MIN THANT S/N: 11314693
Load Current, IL(A) Load Capacitance C(µF) VR (Theoretical) % VR (Practical)%
0.38 10 -22.06 -17.98
0.75 20 -44.1 -28.77
1.7 40 -88.22 -41.5
Table 6 Voltage Regulation Theoretical Vs Practical (CL)
Figure 6 Voltage
Regulation
Theoretical Vs
Practical (CL) -100
-80
-60
-40
-20
0
0 0.5 1 1.5 2
Vo
ltag
e R
egu
lati
on
(%
)
Load Current(A)
Voltage Regulation Vs Current load (Capacitive load)
Voltage Regulation(Theoretical)
Voltage Regulation(Practical)
Name: AUNG MIN THANT S/N: 11314693
V. Lab Report
3. Discuss the results and offer quantitative theoretical explanations of any differences between
calculated and measured results.
We are technically ignoring the value of Ra (armature resistance) in this lab due to
synchronous reactance greater than armature resistance (Xs >>Ra). When I worked out
Voltage Regulation of resistive load, Ra was not considered at all.
Observation of figure 1 (Open Circuit Test), the linear graph is illustrated from the origin to
0.52A. After 0.52A, non-linear region is started to the end of 2.5A because the motor reaches
the saturated point after the excitation current. Moreover, the synchronous reactance would
alter according to the motor passes the saturated point. The experimental result is quite similar
to the theoretical result although there is a bit of human and equipment errors.
My group and I have measured the short circuit current (Isc) at the rotor current 2.5A, the
voltage 87.76 Vphase. And, the graph was plotted as Figure 2. According to practical result,
there is an identical answer between theory and experiment.
The terminal voltage increases together with the resistance. Increasing voltage and resistance
decreases the current. The practical result can be computed by using Ea = Va + jXsIa.
Obviously, Ea is greater than Va in all different types of resistors which lead to positive
voltage regulation. Figure 4 shows that the experimental result is quite close to the theoretical
point of view. The analysis is quite achievable.
The terminal voltage and current raise together the increment of capacitive value. The reason
is because the higher amount of energy can be stored into capacitor which gives higher
terminal voltage per phase. There are a lot of differences between theory and experiment in
voltage regulation due to taking the wrong values.
There are some uncertainties in my results due to human and equipment errors. Human errors
are mainly caused by not obeying sequential steps and taking values in a wrong time.
Equipment error could be the rectifier does not work at all. Room temperature also needs to
consider while we are doing the lab in order to achieve the reasonable results.