Machines Practice 7
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ScribdTranslationsMachines Practice 7
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ScribdTranslationsAUTONOMOUS UNIVERSITY OF NUEVO LEÓN
SCHOOL OF MECHANICAL AND ELECTRICAL ENGINEERING
Raul Alejandro Puente Fernandez
Mat: 1581121
Time: V3
Maestro: Gerardo Treviño Castro
Electric Machines Lab
Practice #7
Standard NEMA numbering, terminal identification for
three-phase induction motors with 9 terminals
NEMA standard numbering, identification of
terminals for three-phase induction motors of 9
terminals
OBJECTIVE:
Identify the terminals and the pole-phase groups of an induction motor and
to know the normalized numbering (NEMA).
THEORETICAL FRAMEWORK
Three-phase motors can be differentiated by the number of terminals
what they have; obviously this number must be a power of 3. The
NEMA (National Electrical Manufacturers Association) classifies
to the motors according to the number of terminals and the most common are those of
3, 6, 9 and 12 terminals.
To number the electrical diagram of the motor, NEMA says that
the terminals are numbered clockwise from the outside
inward into the phases.
9 terminal motor
This type of motor can be connected either
like a giant star or like two
stars in parallel; the delta connection not
It is used. It can work with two voltages.
of service:
•For 220 V it is connected as 2 Y in
parallel.
For 440 V it is connected as a star
giant.
The identification of the terminals of your
this would be left as:
Procedure
The procedure we will follow will be valid as long as the
motor has a winding in American star type with nine
terminals. In the standardized numbering established by the NEMA
terminals 10, 11, and 12 are part of the neutral that is internally
connected with the motor, we still need to identify the nine terminals
missing.
Using the ohmmeter, continuity will be checked between a
terminal and the rest. If it only has continuity with one other, that gives us
It will indicate that it is one of the outer sections of the winding.
either (1-4) or (2-5) or (3-6); but if it has continuity with two of the
remaining terminals, this will indicate to me that it is the central terminal and
We list their terminals with (7-8-9). Subsequently, the other ones are located.
winding sections.
So far we have identified the central star
and the three pairs of terminals but we don't know
which is which, that is, which is (1-4) or (2-5) or (3-6).
To identify these terminal pairs, the following is followed
this procedure.
Feed the inner star with a minimum voltage of
approximately 10% of the motor's nominal voltage.
2. Connect one of the unknown sections in series with the star.
3. Measure the voltages at the supposed terminals (1 to 8) and (1 to 9)
COMPARISON
If the voltages V1 and V2 are equal and greater than the applied voltage, the coil
connected is the correct one.
If the voltages V1 and V2 are equal and lower than the applied voltage to the coil
connected is the correct one, but it is connected upside down, that is to say
1 is 4 and
4 is 1
If the voltages V1 and V2 are different from each other, one greater and the other lesser than
the feeder, the coil is incorrectly connected: is 7 8 or is it 9.
REPORT:
What precautions should be taken when supplying voltage to the star?
internal to the test?
R= Do not create a short circuit by making improper connections, we must
carefully inspect the connections. It should be taken into account the
identification of the terminals and measuring devices that are being
using, to be sure that they are the correct ones and also to stop
be careful when doing the practice, make sure an accident doesn't happen.
Can the previous procedure, or something similar, be used to identify
the 12 terminals of a star and double star connection motor
parallel?
Yes, this was just an example but it can be done.
How could the pole-phase groups be reviewed and their correct connection in a
deriving poles resulting from two speeds?
R=Could the pole-phase groups be reviewed by connecting them in a certain way?
distinct and according to the data obtained, compare them with the new ones and
from there determine and/or draw conclusions about it.