Lab2 (11314693)

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)


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


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)




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)


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


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)


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.

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Lab2 (11314693)