Vibration Specifications Standards Electrical Motors With
Alarm Limits
Electrical Motor Requirements
Motors will be defined by four (4) categories:
Standard motor.......Utility Operations
Special motor..........Semi-Finish Operations
Precision motor.......Finish Operations
Other motor............Per agreement by vendor and Lockheed
Martin
The frequency range for motor certification will be from
Fmin = 0.3 X Running Speed (synchronous speed) to Fmax =
120,000 CPM (2,000 Hertz)
Alternating current motors will be tested
at rated voltage and frequency, and no load. Single speed
alternating current motors will be tested at synchronous
speed. A multi-speed alternating current motor will be tested
at all its rated synchronous speeds. Direct current motors
will be tested at their highest rated speed. Series and
universal motors will be tested at operating speed.
Note: The required deflection is inversely proportional
to the speed squared.
MOTOR ISOLATION
Method of Motor Isolation for Measuring Vibration Place
the motor on an elastic mounting so proportioned that the
up and down natural frequency shall be at least as low as
25 percent of the test speed of the motor. To accomplish
this it is required that the elastic mounting be deflected
downwards at least by the amounts shown in the Following
table due to the weight of the motor. When a flexible pad
is used the compression shall in no case be more than 50
percent of the original thickness of the flexible pad; otherwise
the supports may be too stiff.
MOTOR SYNCHRONOUS SPEED(RPM)
ISOLATION PAD COMPRESSION(INCHES)
900 1
1200 9/16
1800 1/4
3600 1/16
7200 1/64
Note: The required deflection is inversely proportional
to the speed squared.
MOTOR ISOLATION
Method of Motor Isolation for Measuring Vibration
All new and rebuilt motors shall conform to the vibration
limits specified when tested in accordance with this specification.
CRITICAL SPEED
Completely assembled motors shall have a percentage separation
between the rotor shaft first actual critical speed and
the rated motor speed as specified:
ROTOR DESIGN FIRST ACTUALCRITICAL
SPEED LOCATION
Rigid Shaft At least 25% Above Rated Motor Speed
Flexible Shaft Maximum of 85% of Motor Speed
LIMITS
All electrical motors defined by NEMA Standard MG-1-1993
Section I "Classification . According to Size,”
Small (fractional), Medium (integral) and Large Machines,
shall meet the following requirements:
The Velocity Amplitude (Inch/sec-Peak) of any line of resolution,
measured at bearing locations in any direction shall not
exceed the Line-Amplitude Band Limit values specified in
and graphed when determined in accordance with using the
frequency range defined
The Acceleration Overall Amplitude (g's Peak) at bearing
locations in any direction (ref. Section 4) shall not exceed
the Band-Limited Overall Amplitude Acceptance Limit values
specified and graphed when determined in accordance with
Section using the frequency range defined.
ELECTRICAL MOTOR CERTIFICATION
The amplitude of vibration at bearing locations in any
direction shall not exceed the values listed.
Vibration signatures of velocity and acceleration, and
a listing of the maximum peak velocity in each band for
vibration measurements taken at position 1 horizontal, position
2 vertical, and position 3 axial shall be submitted as part
of the motor certification. The data shall be identified
with the Motor Serial Number, Frame Number, Model Number,
Horsepower and Synchronous speed.
The motor nameplate shall carry the following designation:
Vibration data and signatures must be submitted with the
motor to the Maintenance Engineering Department or other
authorized representative before acceptance of the motor
will be authorized.
Motors not meeting the certification shall be rejected.
Figure 1 Maximum Allowable Vibration Limits for Electric
Motors
