Lab 4 3-Phase Synchronous Machine by xbc10147

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									EE 332 Lab Manual                            Lab 4                  3-Phase Synchronous Machine


          Lab 4: 3–Phase Synchronous Machine
                                                                        
Goals                                             induces a voltage E in the armature circuit.
                                                                
                                                  Note that E is an ac phasor quantity, fully
   To review power factor principles             described as
                                                                     
   Review and familiarisation with three–                           E  Ee  
                                                                          ˆ j  t           (4.1)
    phase systems                                 The rms magnitude of the induced voltage, E,
   To understand the modes of operation of       is often referred to as the “excitation” and the
    synchronous machines                          phase angle,, is referred to as the “load
   To understand how synchronous machines        angle”. The excitation of the armature is often
    may be connected to the power system          dealt with as an independent variable. In
                                                  reality, it is a function of the field winding,
Introduction                                      field circuit design and speed of rotation.
                                                  The steady-state behaviour of a synchronous
This lab will consider the operation of           machine may be described using the per-phase
synchronous machines as both motors and           equivalent circuit models shown in Fig. 4-1
generators. You will investigate the ability of   and Fig. 4-2. Notice that the only difference
synchronous machines to consume or supply         between the models is the definition of the
VARs to the power system, independent from        direction of positive current flow: out of a
the direction of power flow. Limits on the        generator and into a motor. The diagrams
performance of the machines will also be          represent one phase of the machine, with V, E
explored. Note that the theory refers to round-   being phase voltages, Ra the armature
rotor machines; saliency is beyond the scope of   resistance and XS the synchronous reactance.
the course.

Theory
Synchronous machines are similar to DC
machines in that: they have a field winding and
an armature winding; a dc current is passed
through the field winding to produce flux; the
                                                  Fig. 4-1 Synchronous generator per-phase equivalent
flux from the field winding induces a voltage                        circuit model
in the armature winding. However, unlike DC
machines: the field winding is on the rotor and
the armature winding is on the stator; the
armature winding is an ac winding.

          Armature Circuit
For the majority of the analysis of synchronous
machine behaviour, we are only concerned             Fig. 4-2 Synchronous motor per-phase equivalent
with the armature circuit. We assume that there                       circuit model
is a field winding that produces a flux which

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EE 332 Lab Manual                                   Lab 4                   3-Phase Synchronous Machine
In many machines, it is reasonable to assume            having zero phase angle, and the current,
that XS >> Ra and resistance can be neglected.          synchronous reactance voltage drop and
In this case, Fig. 4-1 and Fig. 4-2 can be              excitation voltage are drawn relative to the
replaced with Fig. 4-3 and Fig. 4-4                     terminal voltage. If positive power flows in the
                                                        same direction as positive current then the
                                                        phase angle of current relative to terminal
                                                        voltage, , must be in the range:
                                                                        90    90       (4.4)
                                                        Constructing a phasor diagram, it becomes
                                                        clear that
                                                                     
                                                           E leads V in a generator, and
                                                                   
    Fig. 4-3 Simple generator per-phase circuit            E lags V in a motor
                                                        The four basic shapes of phasor diagram for
                                                        the circuits in Fig. 4-3 and Fig. 4-4 are shown
                                                        in Fig. 4-5, Fig. 4-6, Fig. 4-7 and Fig. 4-8. It
                                                        can be seen that the terminal power factor is a
                                                        function of the magnitude of the excitation. If
                                                        |E|>|V| in a generator, then for (4.2) to hold, the
                                                        power factor must be lagging. Similarly, if
      Fig. 4-4 Simple motor per phase circuit           |E|<|V| then the power factor must be leading.

Generating vs. Motoring
Viewing the circuit models, the only obvious
distinction between motoring and generating is
the defined direction for positive current.
Writing down the voltage loop equation for a
generator from Fig. 4-3 results in (4.2).
                   
                E  V  jI a X S          (4.2)                 a
Writing down the voltage loop for a motor
from Fig. 4-4 results in (4.3).
                         
                V  E  jI a X S     (4.3)                  Fig. 4-5 Over-excited generator. |E| >|V|, lagging
                                                                              power factor
In the physical system, the distinction between
motor and generator is related to power flow.
If power flows from the mechanical system,
through the machine to the electrical system,
the machine is operating as a generator. If
power flows from the electrical system,
through the machine to the mechanical system,
the machine is operating as a motor. To help                                 a
understand the operation of a synchronous
machine, it is usual to use phasor diagrams.
                                                            Fig. 4-6 Under-excited generator. |E|<|V|, leading
The terminal voltage of the phase is defined as                              power factor

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EE 332 Lab Manual                                  Lab 4               3-Phase Synchronous Machine
                                                       development for military applications. In
                                                       typical synchronous generators and medium-
                                                       large size synchronous motors, the rotor field
            a                                          is created using a DC field winding. Unlike a
                                                       DC machine field winding, the field winding is
                                                       rotating at synchronous speed; this creates the
                                                       difficulty of how to create the rotor DC field
                                                       current. Two possible options are available:
                                                       1. Use slip rings and carbon brushes to supply
                                                          the DC current from an external source.
 Fig. 4-7 Over-excited motor. |E|>|V|, leading power   2. Generate an ac voltage on the shaft by
                       factor
                                                          using an additional stationary field winding
                                                          and rotating conductors. Then rectify the
                                                          induced ac voltage over the rotating
                                                          conductors to DC, with diodes mounted on
                                                          the rotor. No slip rings and brushes are
                                                          needed for this case.
      a
                                                       The first option is often popular as the initial
                                                       capital cost is lower. This is offset by higher
Fig. 4-8 Under-excited motor. |E|<|V|, lagging power   operating costs as maintenance is required on
                       factor
                                                       the brushes and slip rings. The second option is
                                                       often used in larger machines. A small ac
For a motor, it can be seen that for (4.3) to          generator called a brushless exciter has its
hold, an over-excited generator must have a            armature circuit mounted on the shaft of the
leading power factor. From these observations,         rotor, and its dc field circuit mounted on the
and knowledge of a typical power system, one           stator. The generated AC current is then
can state that the majority of synchronous             rectified directly on the rotor using a 3-phase
machines will be operated with |E|>|V|. (Most          rectifier.
loads on the power system are lagging, so
                                                       In this lab manual If represents the DC currents
generators must generate the VARs required
                                                       in different windings depending on the type of
by the system, also operating at lagging power
                                                       exciter. For synchronous machines with
factor. Most times when a synchronous motor
                                                       brushes, If represents the rotor field current
is used, it is operated at leading power factor to
                                                       supplied directly from an external source. For
help improve the overall power factor at a
                                                       brushless synchronous machines, If represents
site.) Note that in this lab, we will assume that
                                                       the DC current in the field circuit mounted on
the supply is an infinite bus: |V| is constant, f is
                                                       the stator.
constant.

                Field Circuit                                    Torque and Power
                                                       Equations to approximate power and torque
The field of synchronous machine can be
                                                       can be found from the simplified phasor
created either by a winding or a permanent
                                                       diagram. It can be seen in Fig. 4-9 that the load
magnet. Permanent magnet machines have
                                                       angle and power factor angle are related by
typically been small motors, although large
multi-MW machines are currently under                                E sin   I a X S cos        (4.5)

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EE 332 Lab Manual                               Lab 4                 3-Phase Synchronous Machine
                                                     It can be seen in Fig. 4-10 that for a generator.
                                                                       Q  3VI sin             (4.12)
                                                                        3VE         3V 2
                                                                   Q       cos                (4.13)
                                                                         XS          XS
                                                     For a motor, due to the change in direction of
    a
                                                     positive current,
                                                                        3V 2 3VE
                                                                   Q           cos            (4.14)
                                                                         XS   XS
           Fig. 4-9 Phasor diagram angles
                                                     Re-plotting the data from Fig. 4-10 to plot
Using the definition for voltamps and power in       power on the positive x-axis and VARs on the
a 3-phase system:                                    positive y-axis, it is possible to plot the
                     S  3VI               (4.6)     operating chart of a synchronous machine,
                   P  S cos              (4.7)     shown in Fig. 4-11.
where V and I represent phase quantities.
Substituting (4.5) into (4.6), (4.7) gives
                      3VE
                 P        sin            (4.8)
                       XS
Using the mechanical power equation
                    Pmech  m              (4.9)
and noting that in a synchronous machine
mechanical speed equals synchronous speed,
                         4 f
              m   s               (4.10)
                           p
results in the torque equation
                      3VE
                           sin           (4.11)
                      X S s
Note that f is frequency in Hz, p is the number         Fig. 4-11 Synchronous machine operating chart
of poles in the machine. Using (4.8) the phasor
diagram of Fig. 4-9 can be scaled to give            A machine can operate anywhere within the
power and VARs, shown in Fig. 4-10.                  following limits:
                                                     1. Stator heating limit; Smax. Set by the
                                                        maximum allowable armature current
                                                     2. Rotor heating limit; Emax. Set by the
                                                        maximum allowable field winding current.
                                                     3. Prime mover limit; Pmax. The maximum
                                                        power available from the mechanical
                                                        system.
                                                     4. Static stability limit, =90. The limiting
                                                        case of (4.8).
          Fig. 4-10 Phasor Diagram Power

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EE 332 Lab Manual                              Lab 4                3-Phase Synchronous Machine
Finally, the case where the armature resistance
is not negligible must be considered. In this
case, the terminal electrical power is given by
               Pt  3VI cos 
                                           (4.15)
               Pt  3VLL I L cos 
and the armature losses are given by
                  Pscl  3I a2 Ra         (4.16)
The relationship between electrical terminal
                                                             Fig. 4-12 Synchronization circuit
power and the mechanical power depends on
whether the machine is a motor or generator.
For a generator                                     Depending on the state of the lamps,
                Pmech  Pt  Pscl     (4.17)        differences in the voltage conditions across the
                                                    contacts can be determined.
For a motor                                         The possible voltage conditions and lamp
                 Pmech  Pt  Pscl        (4.18)    states are listed below.
Torque can be found from the mechanical             1. All conditions are met. The lamps will
power using (4.9).                                     flash in union at a very low frequency
                                                       equal to the difference between the
                                                       generator and system frequencies.
                                                    2. Phase sequencing is incorrect. The lamps
       Parallel Operation of                           will flash at different times. This can be
      Synchronous Generators                           corrected by interchanging two of the
                                                       machine phases.
The majority of synchronous generators are          3. There is a big difference between the
operated in parallel with other generators.            generator and system frequencies. The
Most generators are connected to a power grid.         lamps will flash in unison at a high
Exceptions to grid connection include                  frequency. In this case, adjust the speed of
emergency generators and remote sites                  the generator to reduce the frequency of the
(including communities in the north, logging           lamps.
and drilling camps), though these situations        4. Voltage magnitudes are different. The
often have a number of generators in parallel.         lamps will glow steadily. The brightness of
When connecting generators to a system with            the lamps is a function of the voltage
an existing voltage certain conditions must be         difference. Increase or decrease the
fulfilled:                                             excitation to reduce the intensity of the
1. The RMS line voltages must be equal.                lamps.
2. The phase sequences should be consistent.        5. Phase angles are not equal. The lamps will
3. The connection must be made at or near an           glow steadily. It is unlikely that the
   instant when the two voltages are in phase.         generator and system will have exactly the
4. The generator frequency must be slightly            same frequency and constant phase angle
   higher or lower than the system frequency.          error.

The simplest method to meet these conditions
is to use synchronization lamps connected
across the contactor, as shown in Fig. 4-12.

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EE 332 Lab Manual                              Lab 4                3-Phase Synchronous Machine
  Starting a Synchronous Motor
Synchronous machines only produce torque at
synchronous speed. Generators are usually
brought to synchronous speed by the
mechanical system, but starting motors is more
challenging. Many synchronous motors are
constructed with an induction cage on the
rotor. This allows the motor to start from
standstill and accelerate to synchronous speed.
Once the motor is at synchronous speed, the
field winding can be turned on and the
machine acts like a synchronous motor. Other
options include placing a small induction
motor on the same shaft as the synchronous             Fig. 4-13 Synchronous machine open and short
machine. The induction machine accelerates                            circuit test data.
the synchronous machine to synchronous              of short circuit armature current with field
speed with no load attached. Once at                current is recorded. Typical plots of o/c voltage
synchronous speed, the synchronous machine          and s/c current are shown in Fig. 4-13.
is energised and a load applied via a               Open circuit phase voltage (also the excitation)
mechanical clutch. A final option involves          is given by
using a variable frequency supply to slowly
accelerate the machine to the desired operating                      E  2 N  fˆ
                                                                                 c             (4.19)
synchronous speed.                                  At lower field current levels, the field current-
                                                    flux relationship is linear and terminal voltage
                                                    rises linearly with field current. As the field
  Open and Short Circuit Tests                      current increases during the open circuit test,
The accurate determination of synchronous           saturation occurs and the incremental rate of
reactance is non-trivial. Synchronous reactance     change of voltage with field current is reduced.
depends not only on field current, but also load    During the short circuit test, the flux produced
angle, armature current and armature                by the armature winding acts against the field
reactance. However, if we assume that it is         winding flux, reducing the total flux in the
possible to linearize the system about the rated    machine and preventing saturation. As a result,
voltage, and that armature reaction always          short circuit armature current increases linearly
opposes the rotor magnetic field, then it is        with field current. Now, during the short
possible to derive an estimate of the               circuit, test, the per phase equivalent circuit
synchronous reactance based on open circuit         model may be drawn as in Fig. 4-14.
and short circuit tests.
During an open circuit test, the machine
operates at synchronous speed and the
variation of line-line voltage with field current
is recorded. During a short circuit test, the
terminals are short circuited and the variation                   Fig. 4-14 Short Circuit




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EE 332 Lab Manual                                  Lab 4                  3-Phase Synchronous Machine
It can be seen that                                     controlled using a variable speed drive to
                                E                       obtain the required torque and speed.
                      XS                      (4.20)
                               I a sc
More strictly:
                                                        Lab Procedure
                               Eoc  I f   
                 XS I f                     (4.21)   Safety
                               I a sc   I 
                                          f
                                                           Re-read the safety rules from lab 1. It will
A plot of synchronous reactance as a function
                                                            only take a minute and could save you
of field current is shown on the graph in Fig.
                                                            from serious injury.
4-13. It can be seen that even using these
                                                           Make sure that your circuits are always
simple assumptions synchronous reactance is
                                                            checked before energizing the circuit
nonlinear. An approximation is possible if the
system is linearized about the rated terminal              This lab requires the on-bench generation
voltage for the machine. To find XSsat as shown             of ac and dc voltages. Remember that the
in Fig. 4-13, the following procedure is used:              generated voltages are not protected and
                                                            exercise extreme caution when creating
1. Find the field current that will produce                 your circuit and carrying out your
   rated open circuit terminal voltage, Ifr                 measurements.
2. Find the short circuit armature current Iafr
   that corresponds to the field current Ifr.           Open Circuit Test
3. Find the reactance given by
                         V                              In this test you will use a Fluke 25 as an
                 X Ssat  rated            (4.22)
                          I a fr                        ammeter (10A connection) to measure DC
                                                        field current, a Fluke 87 to measure speed and
It should be noted that this reactance is an            a Fluke 43B power analyzer to measure ac
approximation. It is based on the assumption            quantities. Connect the circuit for the DC
that armature reaction opposes rotor flux. As a         machine panel and synchronous machine panel
result, the approximation should be best when           as shown in Fig. 4-15 and Fig. 4-16. On the
generating with a lagging power factor.                 DC machine panel, set the DC drive speed
                                                        control to zero (counter clockwise) and current
Lab equipment                                           control to maximum (clockwise).

Some of the synchronous machines in the lab
have a nameplate that states star (wye)
connection; others have a nameplate that states
delta connection. However, all machines used
in this lab are wired with a wye connection.
Most of the machines sets in the lab are 4-pole
machines, with synchronous speed of 1800
rpm.
In this lab, the DC machine is used to drive the
synchronous machine when generating and
load the synchronous machine when motoring.
When generating, the DC machine is                               .
                                                            Fig. 4-15 DC panel wiring for open circuit test

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EE 332 Lab Manual                                Lab 4              3-Phase Synchronous Machine
                                                     slowly reduce the speed and make sure that the
                                                     field current remains constant throughout this
                                                     test. Record the speed and open circuit line-
                                                     line voltages at 200rpm steps from 1800 rpm to
                                                     200rpm.
                                                     Turn the synchronous machine field winding
                                                     variac to zero, reduce the DC drive speed to
                                                     zero and once the machine have stopped, turn
                                                     off the supplies and de-energize the bench.


                                                     Short Circuit Test
   Fig. 4-16 Synchronous machine panel wiring:       Do not adjust the DC panel wiring. Connect
                 open circuit test                   the synchronous machine panel as shown in
                                                     Fig. 4-17 and clamp the Fluke 43B current
Turn the DC field winding rheostat fully             probe to the spade connector lead at the short
counter-clockwise. On the synchronous                circuited synchronous machine terminals. Turn
machine panel, make sure the field winding           the probe on to 10mV/A and check the probe
variac is set to zero and (if present) make sure     settings on the meter are also at 10mV/A and
the field winding switch is set to 0-24V.            that the probe is properly zeroed. Check that
Connect the Fluke 87 to the BNC output on the        both the DC machine and synchronous
induction machine panel and set the reading to       machine field windings are at their minimum
“Hz”. Have your circuit and settings checked.        settings, the DC drive current limit is at its
Energise the bench and turn on the DC                maximum and the speed control is set to zero.
machine field supply. Press the green start          Have your circuit and settings checked.
button on the DC machine panel and use the           Turn on the DC machine field winding and
speed control knob to slowly increase the            press the green start button on the DC machine
speed to the rated speed of the synchronous          panel. Use the speed control to accelerate the
machine (1800rpm). Turn on the synchronous           synchronous machine to rated synchronous
machine field winding. Making sure that the          speed. Turn on the synchronous machine field
speed is constant, slowly increase the               winding supply. Making sure that the speed
synchronous machine field variac setting and         remains constant, slowly increase the
record the field current (Fluke 25) and open         synchronous machine field current while
circuit line-line voltage (Fluke 43B) at 30V         carefully monitoring the short circuit current.
increments from 30V to 300V. The speed may
change while changing the field current; adjust      Record the field current and the short circuit
the speed control knob on DC machine panel           armature current as it increases in 2.5A steps,
to keep the speed constant throughout this test.     up to a maximum of 17.5A. Return the
                                                     synchronous machine variac to zero, reduce
                                                     the DC drive speed to zero and once the
Speed Test                                           machines have stopped, turn off the supplies
                                                     and de-energize the bench.
Adjust the synchronous machine field winding
variac until the line-line voltage is
approximately 208V. Record the field winding
current. Use the DC drive speed control to
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EE 332 Lab Manual                                Lab 4               3-Phase Synchronous Machine
                                                     Turn on the DC machine field winding, press
                                                     the green start button on the DC machine panel
                                                     and slowly accelerate the machines until they
                                                     are rotating slightly faster (e.g. 1815rpm) than
                                                     synchronous speed.
                                                     Turn on the field winding for the synchronous
                                                     machine and adjust the field winding current
                                                     until the line-line voltage reads 208V. Turn on
                                                     the switch to see the synchronization lamps. At
                                                     the moment the flashing lamps become dark,
                                                     press the green start button on the synchronous
                                                     machine panel to connect the synchronous
                                                     machine to the supply.
   Fig. 4-17 Synchronous machine panel wiring:
                 short circuit test                  Turn the DC drive current control to a
                                                     minimum (counter clockwise), the speed
                                                     control to a maximum (clockwise) and increase
Generator Load Tests                                 the DC machine field current to its maximum
                                                     setting.
Do not adjust the DC panel wiring. Connect           In the follow constant excitation test and
the synchronous machine panel as shown in            constant power test, you will need to adjust the
Fig. 4-18. Clamp the Fluke 43B current probe         real power and reactive power frequently. To
to measure the line 1 current and insert the         get the required real power, you will need to
Fluke 43B voltage probes to measure the line-        adjust the DC drive current control on the
                                                     DC machine panel. To get the required
                                                     reactive power, you will need to adjust the
                                                     field current of the synchronous machine by
                                                     turning the variac on the synchronous
                                                     machine panel. The two adjustments are not
                                                     independent. You may turn the DC drive
                                                     current knob and the variac back and forth to
                                                     reach the required real and reactive power.
                                                     Constant Excitation
                                                     Making sure that the Fluke 43B is on the 3
                                                     power setting, adjust the DC drive current
                                                     control to set the synchronous machine
                                                     terminal power to zero. Increase the
   Fig. 4-18 Synchronous machine panel wiring:       synchronous machine field current by
                generator load test                  adjusting the variac on synchronous machine
line voltage across the two other lines. Check       panel until the armature current is
that both the DC machine and synchronous             approximately 10A. Record the field current,
machine field windings are at their minimum          armature current, line-line voltage, power,
settings, the DC drive current limit is at its       VAR, VA and power factor. Keep that field
maximum and the speed control is set to zero.        current constant by adjusting the variac while
Have your circuit and settings checked.              slowly increasing the current control setting on


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EE 332 Lab Manual                            Lab 4                3-Phase Synchronous Machine
the DC drive to repeat the measurements at
1.0kW intervals up to 4.0kW.
Constant Power
Re-adjust the synchronous machine field
winding until the generator is producing 4kW
and 4kVAR at a lagging power factor. Record
the field current, armature current, line-line
voltage, power, VAR and VA. Slowly reduce
the synchronous machine field winding current
and repeat the measurements at 1kVAR
intervals until the machine is producing
4kVAR at a leading power factor. Reduce the
DC drive current setting until the synchronous
machine power is nearly zero, and then adjust
the synchronous machine field current until the
armature current is minimized. Press the stop
button on the synchronous machine set.            Fig. 4-19 DC machine panel wiring: motor load test
Reduce the synchronous machine field current
to zero. Turn off the 1-phase and 3-phase         Try to adjust the DC machine field current to
supplies on the DC machine panel and              get the synchronous machine input power of
synchronous machine panel and de-energize         2.5kW. If the input power cannot reach 2.5kW,
the bench.                                        you can change the number of load resistors
                                                  and adjust the DC machine field current in the
          Motor Load Tests                        meanwhile until the input power reads 2.5kW.
                                                  Increase the synchronous machine field
Do not adjust the synchronous machine panel       winding current until the synchronous machine
wiring. Add a parallel-connected load box to      power factor is approximately 0.6 leading. The
the terminals of the DC machine armature, as      input power may change when you are
shown in Fig. 4-19. Make sure that all the        adjusting the power factor. You can readjust
switches are in the “off” position. Check that    the DC machine field current to return to
both the DC machine and synchronous               2.5kW. Record the synchronous machine
machine field windings are at their minimum       armature current, line-line voltage, power, VA,
settings, the DC drive current limit is at its    VAR and power factor. Slowly reduce the
maximum and the speed control is set to zero.     synchronous       machine       field     current.
Have your circuit and settings checked.           Maintaining the power at 2.5kW by adjusting
Start the DC machine and synchronize the          the DC machine field current, repeat the
synchronous machine with the supply, as in the    readings at power factors of approximately 0.8
generator load tests. Switch off the 3-phase      leading, unity, 0.8 lagging, 0.6 lagging. Reduce
supply to the DC drive.                           the DC machine field to its lowest setting,
                                                  switch off the load resistors, adjust the
Turn the DC machine field current to its          synchronous machine field until the armature
maximum setting, then, switch on resistors on     current is minimized then switch off the supply
the load box until the input power to the         to the synchronous machine. De-energize the
synchronous machine is around 2.5kW.              bench.


Revised Winter 2008                       4-10
EE 332 Lab Manual                                Lab 4                3-Phase Synchronous Machine

Lab Report                                            Questions
No formal lab report is required. Hand in             1. From the Open Circuit Voltage vs. Field
copies of all spreadsheets, graphs, calculations         Current plot explain why a phase voltage is
and questions. The report is due one week after          present when the field current is zero.
the lab date.                                         2. Why does the Open Circuit Voltage vs.
                                                         Field Current graph start to level off once it
Calculations                                             reaches a certain magnitude?
                                                      3. Considering the plot of open circuit voltage
Once you have recorded your data, download
                                                         vs. speed, is the machine excited using
the spreadsheet for lab 4 from the website at
                                                         brushes or a brushless exciter? Explain
www.ece.ualberta.ca/~ee332/. Enter your
                                                         your choice.
measurements into the spreadsheet. The
spreadsheet will automatically calculate all the      4. Look at the Short Circuit Current vs. Field
required information, and plot all the required          Current graph. Why is the relationship
graphs. Print a copy of the spreadsheet                  between short circuit current and field
Analysis and all the graphs.                             current linear?
                                                      5. Explain the shape of the generator armature
Sample Calculations                                      current vs. field current plot at constant
                                                         power.
The following sample calculations must be             6. Explain the shape of the generator E loci
handed in with your results:                             and P-Q plots at constant field current and
1. Calculate Xs (sat) for the data closest to VLLoc      constant power, respectively.
   = 208V.                                            7. Explain the shapes of the motoring current
2. Calculate the load angle () and excitation           and reactive power plot at constant power.
   (E) for the case where P = 4kW, Q =                8. Explain the shapes of the motoring E and I
   4kVAR (in constant power generator test).             loci at constant power.
   You may need linear interpolation to
                                                         (Hints for question 5 ~ 8: You may need to
   calculate Xs for this question.
                                                         use phasor diagrams and relevant equations
3. Draw the phasor diagrams for the above                to analyze the trends of those curves.)
   case. Include Ia, V, E, IaXs,  and  in your
   drawings.
4. Draw the phasor diagram for motor
   operation at 0.8 lagging power factor.




Revised Winter 2008                          4-11
EE 332 Lab Manual                             Lab 4                 3-Phase Synchronous Machine
Name:                                                     ID #                SECTION #

                   EE332 Lab 4: Pre–Lab Questions
1. What are the goals of this lab?



2. Is an over excited generator operating with leading or lagging power factor?


3. In the open circuit test, what do you use to set the speed of the synchronous machine?




4. In the open and short circuit tests, do you supply electrical power to stator winding of the
   synchronous machine?


5. What range of current do you expect in the short circuit test?


6. Under what conditions should you close the contact to connect the supply to the synchronous
   machine?



7. What is used to control the flow of power to the synchronous machine when it is acting as a
   generator?



8. How is the synchronous motor loaded?



9. How is the reactive power flow to/from the synchronous machine controlled?



10. Which meters are used in this lab?




Revised Winter 2008                        4-12
EE 332 Lab Manual                          Lab 4                      3-Phase Synchronous Machine
Name:                                                         ID #                       SECTION #
Name:                                                         ID #
Name:                                                         ID #

                                   Measurements
    Table 4-1 Open Circuit Test                          Table 4-4 Constant Excitation
        If (A)        VLL (V)         If           Ia          VLL         P             Q     S
                                     (A)           (A)         (V)        (kW)     (kVAR)    (kVA)




                                                          Table 4-5 Constant Power

                                      If           Ia          VLL         P             Q     S
                                     (A)           (A)          (V)       (kW)     (kVAR)    (kVA)
  Table 4-2 Open Loop Speed Test
    nm (rpm)          VLL (V)




                                                              Table 4-6 Motoring
    Table 4-3 Short Circuit Test
        If (A)         Ia sc (A)      If           Ia          VLL         P             Q     S
                                     (A)           (A)          (V)       (kW)     (kVAR)    (kVA)




Revised Winter 2008                   4-13

								
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