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IS 13529 (1992): Guide on Effects of Unbalanced Voltages on
the Performance of Three-Phase Cage Induction Motors [ETD
15: Rotating Machinery]
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Indian Standard
GUIDE ON EFFECTS OF UNBALANCED
VOLTAGES ON THE PERFORMANCE
OF
THREE-PHASE
CAGE INDUCTION
MOTORS
UDC 6213133330253: 621317321
BUREAU
MANAK
OF
BHAVAN,
BIS 1992
INDIAN
9 BAHADUR
NEW DELHI
October
I992
STANDARDS
SHAH
ZAFAR
MARG
110002
Price Group
Rotating
Machinery
Sectional
Committee,
ET 15
FOREWORD
This Indian
the Rotating
Council.
Standard
was adopted by the Bureau of Indian Standards,
after the draft finalized by
Machinery
Sectional Committee had been approved by the Electrotechnical
Division
When the line voltages applied to a three-phase cage induction
motor are not equal,
the stator
windings
will also be unequal.
A small percentage voltage unbalance
much larger percentage current unbalance.
the currents in
will result in a
The application
of unbalanced
voltages to a three-phase induction
motor introduces
a negative
sequence voltage, and this produces in the air gap a flux rotating against the rotation of the rotor,
thus tending to produce high currents. A small negative sequence voltage may produce
currents
in
the windings
considerably
in excess of those present
under
balanced
voltage
conditions.
Consequently,
the temperature
rise of the motor operating
at a particular load and percentage
voltage unbalance
shall be greater than for the motor operatmg
under the same conditions
with
balanced voltage.
In the preparation
of this standard,
assistance has been derived from IEC Pub 892 ( 1987 ) Effects
of unbalanced
voltages on the performance
of three-phase cage induction
motors, issued by the
International
Electrotechnical
Commission
( 1EC ).
IS 13529: 1992
Indian Standard
GUHDE ON EF~FECTS OF UNBALANCED
N THE PE
ORMANCE OF
VOLTAGES
THREE-PHASE
CAGE INDUCTION
MOTORS
5 CALCULATION
UNBALANCE
1 SCOPE
1.1 This standard
provides
effects of unbalanced
voltages
of three-phase
cage induction
guidance
on
the
on the performance
motors.
1.2 For general information,
a list of standards
in
covering
cage induction
motors
is given
Annex A.
2 REFERENCE
STANDARDS
The standards
given in
adj:lncts to this standard.
Annex
B are necessary
OF PERCENTAGE
5.1 The percentage voltage unbalance
may easily
be determined
by a motor user from -the voltage
readings of the three phases.
It is calculated
by
the following formula:
Percelilage
voltage unbalance
Maximum voltage deviation
from average ioltage
=
x 100
Average voltage
5.1.1 Example
3 TER,%IINOLOGY
Tile
terms
defined
in
IS
1885 ( Part 35) : 1973
shall apply.
4 EFFECTS OF UNBALANCED
ON PERFORMANCE
The effects
performance
of unbalanced
are as follows:
VOLTAGES
voltages
Percentage
voltage unbalance
on
currents
at normal
operatitig
speed
shall be greatly unbalanced
to the order of
approximately
six to ten times the voltage
unbalance.
The
The locked-rotor
currents
shall
be unbalanced
to the same degree
that
the
voltages are unbalanced,
but the lockedrotor apparent
power shall increase only
slightly;
b) Torques
The locked-rotor,
pull-up
and breakdown
torques
are decreased
when the voltages
are unbalanced.
If the voltage unbalance
should be extremely
severe, the torques
might not be adequate for the application;
c) Full- Loud Speed
motor
the
voltages; and
5
= -x
215
motor
a) Currents
The full-load
With voltages of 220 V, 215 V and 210 V, the
average voltage is 215 V, and the maximum
voltage
deviation
from
the avera~ge is 5 V.
Therefore:
speed is reduced slightly when
operates
with
unbalanced
4 Noise and Vibration
100 = 23 percent.
5.1.2 The true negative
sequence
voltage component may be up to 18 percent
higher than the
value obtained from the formula.
5.1.3 The above formula
is given for the convenience
of the motor user, and is only
an
approximation
of the percent negative
sequence
voltage component.
A more accurate determination can be made with the aid of symmetrical
components.
5.1.4 For voltage unbalances
study of the negative sequence
currents is necessary.
over 5 percent, a
component
of the
6 DERATING OF MOTOR
OVERHEATPKG
TO PREVENT
4.1 Voltages should be virtually balanced (see 3.2
of IS 325 : 1978 ). In
some
applications
a
greater
unbalance
than
that
permitted
by
IS 325 : 1978 may be unavoidable,
and
some
derating
of the motor might be necessary
to
reduce the possibility of damage from overheating.
Noise and vibration may increase
with an
increase in voltage ( and current ) unbalance.
The vibration could be detrimental
to the motor or to the entire drive system.
hOrE - Derating might not be necessary when a
motor is designed to operate (under rated conditions )
at temperatures lower than those in accordance with
IS 325 : 1978.
IS 135#9: 1992
6.2 Ty ical values of derating of single speed
three-p Rase cage induction motors rated up to
6<0 V are shown in Fig. 1. For motors of
different types and for rated outputs larger than
630 kW, the derating curve may be different and
the manufacturer should be consulted or operatemperature
measurements
should
be
ting
examined.
7 OVERLOAD PROTECTION
DERATED MOTORS
DEVICES FOR
7.1 Where a motor is derated for operation on
unbalanced voltages, the selection and setting of
the overload protection device should take into
account the combination of the derating factor
applied to the motor and the increase in current
7.2 In the absence of specific information, it is
recommended that overload protection devices be
selected and/or adjusted at the minimum value
that does not result in tripping for the derating
factor and voltage unbalance that applies.
7.3 Where unbalanced voltages are likely, it is
recommended that the user install overload protection devices that are responsive to maximum
current rather than average current.
1
VOLTAGE
Fir;.
resulting from the unbalanced voltages. This is
a complex problem involving the variation in
motor current as a function of load and voltage
unbalance, in addition to the characteristics of
the overload protection device relative to maximum current or average current.
3
UNBALANCE
4
(PERCENT)
TYPICAL DBRATING FACTOR Due TO UNBALANCED VOLTAGES
IS 13529:1992
ANNEX A
( Clause 1.2)
LIST OF tNDIAN
IS No.
324 : 1978
STANDARDS
ON INDUCTION
IS No.
Title
Three-phase induction
(fourth revision )
7538 : 1975
motors
Textile motors : Part 1 Loom
2972
(Part 1): 1979 motors (first revision )
Textile motors : Part 2
2972
(Part 2) : 1979 motor8 (first revision )
8151 : 1976
Card
8789 : 1978
Textile motors : Part 3 Spinframe
motors
( .first
(Part 3): 1979 ning
revision )
2972
3682 : 1966
Flameproof alternating current
motors for use in mines
4029 : 1967
Guide for testing
induction motors
9283 : 1979
9628 : 1980
three-phase
12066 : 1986
MOTORS
Title
Three-phase
squirrel
cage
induction motors for centrifugal
pumps for agricultural application
Single-speed Ihree-phase induction motors for driving lifts
Values of performance characteristics for three-phase induction motors
Motors for submersible pump
sets
Three-phase induction motors
with type of protection n
Three-phase induction motors
for machine tools
ANNEXB
( Clause 2 )
LIST OF RELEVANT
IS No.
INDIAN STANDARDS
IS No.
Title
Three-phase induction motors
(fourth revision )
vocabulary :
Electrotechnical
1885
(Part 35 ) : I973 Part 35 Rotating machinery
electrical
machines
4722 : 1992
Rotating
(first revision )
325 : 1978
Title
12802 : 1992
Temperature rise measurement
of rotating electrical machines
12824 : 1989
Type of duty and classes of
rating
assigned to rotating
electrical machines
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