Vibration Severity of EA

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Vibration Severity & Noise Limit For Diesel Generating Sets

Dr. R. Sharma

&

S. N. Misra

Abstract :Vibration, its effects, analysis and vibration severity levels (as per various standards) are discussed in

this note specially with reference to the Diesel Generating Sets. Further to this the salient provisions of G.S.R.

371(E) dated 17th

May 2002 , Environment (Protection) second Amendment Rules, 2002 are also discussed.

1.0 Introduction :Vibration

Abnormal large vibration level of a machine always implies a symptom of bad production in

assembly line viz. mechanical or electrical unbalance, deformation of core or shaft, loose

parts etc. Abnormal vibration will introduce large stress on machine construction itself, or

connected equipment and thus ultimately the service life. Therefore, some vibration limits are

specified in order to avoid MTBF (Mean Time Between Failure).Before vibration criteria is introduced, some vibration terminology and concepts are

explained following vibrating spring-mass system.

From physical and mathematical derivation we have,

Vibration displacement, x = XSin t

Vibration velocity, v =dt

dx= X Cost ; and

Vibration acceleration, a =2

2

dt

xd= - 2 x ;

Where

is the rotating angular velocity,

x is the root mean square (r.m.s.) displacement,X is the peak displacement, peak to peak value ,

T is the period (= 2/t), and

f is the frequency (=1/T) .

1.1 Vibration Severity

Vibration severity defined as a comprehensive and simple characteristic unit for describing

the vibratory state of a machine is used as the basis of classification and, on the basis of

theoretical considerations and practical experience, the root mean square value of vibration

velocity has been chosen as the unit of measurement for indicating vibration severity.

Vibration Severity is a generic term which designates a value, such as a maximum, average

or other significant numerical value descriptive of a vibration. The vibration severity of amachine is defined as the maximum of r.m.s. value of the vibration velocity measured at

significant point of a machine such as a bearing, mounting point etc.

1.2 Vibration Analysis

Vibration measurement systems fall into the following categories:

Single Value Methods

Hand Held meters


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BSNL Electrical Zone Patna 2

SPM Units

Acoustic Emission Units

Vibration Pens

4-20mA sensors

Time Frequency Methods

Hand Held Data-collectorsOn line systems

1.2.1 Single Value Measurements

The variety of single value measurements is endless, from the ISO filtered levels mentioned

in ISO 10816 [1] to the magic numbers offered by some of the technology vendors;

promising to solve all of your plant condition problems within one simple solution. ISO

10816-3 is summarised as a supporting appendix to this text.

Please note single value methods are either generic or specific. The generic case is where

a value will indicate the presence of a problem but cannot categorise the problem into a

specific fault (e.g. Unbalance, looseness, misalignment, cavitation etc.). The specific methodsconcentrate on issues such as bearing faults and try to eliminate the influence of other faults

through the use of algorithms and electronic design.

The following table outlines the more common types of measurement with comments on

applications and a brief technical description of the method.

Single Value Method Summary

Method Description Applications

ISO Filtered Velocity 2Hz 1kHz filtered

Velocity

Works as a general condition

indicator.

SPM Carpet and Peak related tothe demodulation of a

sensor resonance around

30kHz.

One of the better single valuebearing indicator methods.

Some problems on larger

bearings and gear units.

Acoustic Emission Distress & dB,

demodulates a 100kHz

carrier which is sensitive

to stress waves.

Better general indicator than

ISO velocity, without the ISO

comfort zone.

Vibration Meters / pens Combine velocity,

bearing and acceleration

techniques (sometimes

include thermal)

Look for ISO Velocity,

envelope & high frequency

acceleration for best

performance.

4-20mA sensors Filtered data converted toDCS/PLC compatible

signal.

ISO velocity versionavailable, envelope version

still awaited.

Can be used to home in on

specific problems by special

order.

Single value vibration methods have two major advantages and only one real disadvantage;

these are low cost, simple interpretation and lack of accuracy respectively. The overall CM


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Impacts are created as a rolling

element collides with a damagedarea.

These impacts show as transients

within the time domain. TheDemodulator extracts these

transients.

Extracted impact frequencies are

then displayed on an envelope

spectrum (shown opposite)

system implications of single value methods are discussed within the later sections of this

text.

Single value data are easy to trend and interpret as shown by the inset plot below.

1.2.2 Time Frequency Measurements

This type of measurement involves the detection and display of specific components of a time

history sensor output. The use of specific frequency components lends itself to the detection

of faults down to a single mechanical component (e.g. bearing, gear, impeller).

Once again, various methods, techniques and signal conditioning systems are used to detect

specific components of the raw time history data.

1.2.2.1 Displacement (Low Frequency)

Where the measurement of absolute movement is required, measured using LVDTs or eddy

current probes. Particularly useful in detecting the relative position of a rotor versus a

structure and in the diagnosis of plain bearing faults through the use of orbit plots.

1.2.2.2 Velocity (Mid Frequency)

The most commonly used method for fault identification, mainly due to the scalar

consistency of the method (i.e. 25mm/s is high almost irrespective of the machine type). Used

to detect signs of mechanical problems in the frequency range 20Hz 2000Hz. Detection

capabilities cover the following fault conditions.

Unbalance, Misalignment, Looseness, Resonance, Cavitation, Blade problems, Turbulence

1.2.2.3 Acceleration (High Frequency)

Amplitude Demodulation Methods

Used to extract impacts from the standard acceleration spectra through the extraction of the

amplitude-modulated component and the display of the demodulated components within an

auto-spectrum plot.


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There are two main types of envelope measurement, namely:

Band Pass Filtered Enveloping

Allows the time history associated with the excitation of a specific frequency band pass

through to the demodulator circuit. This method avoids the possibility of phase cancellation

and is better at isolating the transient activity.

High Pass Filtered Enveloping

Sets a High Pass filter and allows all measured time data above the HP filter pass to the

demodulator, this method is regarded as less effective by vibration practitioners.

General Acceleration

Where rotating machine related frequency components are expected above 2kHz, velocity

measurement is not accurate due to sensor noise levels. Acceleration time frequency analysis

tends to be used for the detection of fault components from: -

Any gear assembly (gearbox, timing gear, gear pump)

Where amplitude demodulation methods are not available (to detect a haystack

within the high frequency spectra)High speed screw assemblies.

Turbochargers

Blading problems on turbo-machinery

High frequency resonances

Detection of gear and rub related transients

1.3 Conclusion

From the above analysis it may be seen that the vibrations generated by the engine are

complex and contain harmonics of 1.5, 3, 5 or more times the fundamental frequency of the

vibration. The generator will be subjected to this vibration which will result in the generator

being subjected to vibration levels higher than those derived from the generator itself. Thus it

becomes imperative to specify the limit of vibration severity for rotating machineries.

Accordingly, a summary table is appended herewith as Appendix I (Summary of ISO 10816-

3) and Appendix II (Summary of IS:12075-1987).

2.0 Introduction :Noise & Emission

People are becoming more aware of hurt of noise to human beings in recent years and thus

give more demands on noise suppression. To evaluate how "large" a noise is, the acoustic

quantities can be expressed in two types of terms, sound power level and sound pressure

level.

SUMMARY Vibration

Combined Vibration Meter Low Cost and easy to use (look for ISO Vel &

Enveloped acceleration)

Acoustic Emission Meter Reasonable alternative Combined Vibration Meter (goodfor low frequencies)

Time Frequency (Datacollector) Required for specific and more accurate fault

diagnosis, choose band pass envelope method as bearing assessment technique.


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Sound power level, wL =10 log 10 )(0w

w

where

wL is the sound power level in decibel (dB)

w is power output from the sound source in watt

0w is the basic sound output, 10 12 watt, which is defined from the minimum audible sound

intensity of human ear, 10 12 watt /m 2 .

Sound pressure level (SPL), pL =10 log102

0

)(P

P=20 log 10 )(

0P

P

where

pL is the sound pressure level in decibel (dB);

P is the effective sound pressure in N/m 2 (Pa). (Physically equivalent to root-mean square

value of sound pressure function of time) ; and

0P is the basic sound pressure, 2*105 Pa, which is defined from the minimum audible sound

pressure of human ear .Human ears often have different hearing sense for different frequency components of the

sound with the same loudness. A correction function, A-weighting filter, is introduced in

noise-meter to correct the measured sound level in octave band to simulate human ears

hearing perception, and the unit is expressed as dBA. The A-weighting function curve and

adjusted values corresponding to center frequencies of octave band are shown as follows:

Centre

Frequency

(HZ)

Adjusted

Value (dBA)

Centre

Frequency

(HZ)

Adjusted

Value (dBA)

Centre

Frequency

(HZ)

Adjusted

Value (dBA)

31.5 -39 250 -9 2000 +1

40 -35 315 -7 2500 +150 -30 400 -5 3150 +1

63 -26 500 -3 4000 +1

80 -23 630 -2 5000 +1

100 -19 800 -1 6300 0

125 -16 1000 0 8000 -1

160 -13 1250 +1

200 -11 1600 +1

A-weighting function has large attenuation in low frequency range.

2.1 Provisions made in the Noise Protection Rules

With above backgrounds in mind the Government of India Vide para 94 has prescribed the

noise limit as follows:

2.1.1 Noise Limit for Diesel Generator Sets (upto 1000 KVA) manufactured on or

after the 1st

July 2003

2.1.1.1 The maximum permissible sound pressure level for new diesel generator (DG)

sets with rated capacity upto 1000 KVA, manufactured on or after the 1st

July, 2003 shall be

75 dB(A) at 1 metre from the enclosure surface.


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2.1.1.2 The diesel generator sets should be provided with integral acoustic enclosure

at the manufacturing stage itself

2.1.1.3 The implementation of noise limit for these diesel generator sets shall be

regulated as given in paragraph 3 below.

2.1.2 Noise limit for DG sets not covered by the above paragraph:

Noise limits for diesel generator sets not covered by paragraph , shall be as follows:

2.1.2.1 Noise from DG set shall be controlled by providing an acoustic enclosure or bytreating the room acoustically, at the users end.

2.1.2.2 The acoustic enclosure or acoustic treatment of the room shall be designed for

minimum 25 dB (A) insertion loss or for meeting the ambient noise standards, whichever is

on the higher side (if the actual ambient noise is on the higher side, it may not be possible to

check the performance of the acoustic enclosure/acoustic treatment. Under such

circumstances the performance may be checked for noise reduction upto actual ambient noise

level, preferably, in the night time). The measurement for Insertion Loss may be done at

different points at 0.5 m from the acoustic enclosure/room, and then averaged.

2.1.2.3 The DG set shall be provided with proper exhaust muffler with insertion loss of

minimum 25 dB(A).

2.1.2.4 These limits shall be regulated by the State Pollution Control Boards and the StatePollution Control Committees.

2.1.2.5 Guidelines for the manufacturers/users of Diesel Generator sets shall be as under

01 The manufacturer shall offer to the user a standard acoustic enclosure of 25 dB(A)

insertion loss and also a suitable exhaust muffler with insertion loss of 25 dB(A).

02 The user shall make efforts to bring down the noise levels due to the DG set, outsidehis premises, within the ambient noise requirements by proper siting and control measures.

03 Installation of a DG set must be strictly in compliance with the recommendations of

the DG set manufacturer.

04 A proper routine and preventive maintenance procedure for the DG set should be set

and followed in consultation with the DG set manufacturer which would help prevent noise

levels of the DG set from deteriorating with use.

2.1.3 Requirement of Conformance Labelling

(i) The supplier of the product must affix a conformance label on the product meeting the

following requirements :

(a) The label shall be durable and legible.

(b) The label shall be affixed on a part necessary for normal operation of the product and not

normally requiring replacement during the product life.

(ii) The conformance label must contain the following information

(a) Name and address of the supplier (if the address is described in the owners manual, it

may not be included in the label)


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(b) Statement "This product confirms to the Environment (Protection) Rules, 1986".

(c) Noise limit viz. 75 dB(A) at 1 m.

(d) Type approval certificate number.

(e) Date of manufacture of the product,

2.1.4 Authorised agencies for certification

The following agencies are authorized to carry out such tests as they deem necessary for

giving certificates for Type Approval and Conformity of Production testings of DG sets and

to give such certificates

i. Automotive Research Association of India, Pune

ii. National Physical Laboratory, New Delhi

iii. Naval Science & Technology Laboratory, Visakhapatnam

iv. Fluid Control Research Institute, Palghat

v. National Aerospace Laboratory, Bangalore

2.2 EMISSION LIMITS FOR NEW DIESEL ENGINES (UP TO 800 KW) FOR

GENERATOR SETS (CENSETS) APPLICATIONS

2.2.1 Emission Limits

The emission limits for new diesel engines up to 800 kw, for gensets applications shall be as

given in the Table below:

TABLE

Emission Limits (gAcw-hr) for Test CycleCapacityof Diesel

Engines

Date ofImplemen-

tation

NOx

HC 1CO IPM

SmokeLimit

absorption

coefficient,(WI) (at

full load)

Torque % WeightingFactors

1.07.2003 9.2 1.3 5.0 0.6 0.7 100 0.05Upto 19kw

1.07.2004 9.2 1.3 3.5 0.3 0.7 75 0.25

1.07.2003 9.2 1.3 5.0 8.5 0.7 so 0.30>19 kwupto 50 kw

1.07.2004 9.2 1.3 3.5 0.3 M 25 0.30

>50 kw

upto 260kw

1.07.2003 9.2 1.3 3.5 0.3 0.7 10 0.10

> 260

kw upto

800 kw

1.07.2004 9.2 1.3 3.5 0.3. 0.7,

2.2.2 Requirement of conformance labelling

(i) All the engines (individually or as part of the product) shall be clearly engraved Genset

Engine on the cylinder block.


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(ii) The engine or the product must be affixed with a conformance label meeting the

following requirements;

(a) the label shall be durable and legible;

(b) the label shall be affixed on a part necessary for normal operation of the engine or the

product and not normally requiring replacement during the life of the engine or the product.

(iii) The conformance label must contain the following information:

(a) name and address of the engine manufacturer or the engine or product importer (if theaddress is given in the owners manual, it may not be included in the label);

(b) statement that this engine or product conforms to the Environment (protection) Rules,

1986%

(c) type approval certificate number;

(d) date of manufacture of engine or in case of import, the date of import of the engine or the

product.

2.2.3 Compliance with BIS specifications

All engines up to 20 kw (individually or as part of the product) shall carry ISI mark and meet

relevant BIS specifications (IS 1000 1).

2.2.4 Authorised agencies for certification

The following agencies are authorized to carry out such tests as they deem necessary for

giving certificates of Type, Approval and Conformity of Production tests for Diesel engines

and to give such certificates

(i) Automotive. Research Association of India, Pune.

(ii) Vehicle Research and Development Establishment, Ahmednagar.

3.0 References

[1] ISO 10816-3 Mechanical Vibration Evaluation of machine vibration by

measurements on non-rotating parts.

[2] IS: 12075-1987 (Reaffirmed 1996) Mechanical Vibration of Rotating Electrical

Machines With Shaft Heights 56 mm and HigherMeasurement, Evaluation and Limits of

Vibration Severity.

[3] G.S.R. 371(E)- Environment (Protection) second Amendment Rules, 2002.


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Machines that are excluded from ISO 10816-3

Steam turbines with speeds > 1500rpm [ISO

10816-2]

Industrial Gas Turbines > 3MW [ISO 10816-4]

Hydraulic units [ISO 10816-5]

Machines Coupled to reciprocating parts [ISO

10816-6

Appendix 1 Summary of ISO10816-3

ISO 10816-3 Relates to the evaluation of velocity levels measured on the bearings of rotating

machinery. This standard supersedes the previous ISO 2372.

The measuring device must filter and sum the velocity energy between 2Hz and 1kHz, andthe standard only applies to machines with shaft speeds between 120rpm and 15000rpm.

The following Machines are included

Steam Turbines < 50MW speed < 1500rpm

Industrial Gas Turbines up to 3MW

Generators

Electric Motors

Rotary Compressors

Pumps (non reciprocating)

Blowers or Fans

(Not of lightweight or sheet metal construction)

The summary table inset below shows the maximum severity levels in mm/second and

inches/second RMS for the included machines above within the shown power ranges.

ISO 10816-3

CONDITION

Damage >0.18 > 0.28 >0.28 >0.43

Restrict

Operation 0.18 0.28 0.28 0.43

Unrestricted 0.11 0.18 0.18 0.28

New condition 0.06 0.09 0.09 0.14

Rigid Elastic Rigid Elastic

15kW- 300kW 300kW - 500MW

in/sec RMS

Maximum Allowable levels

ISO 10816-3

CONDITION

Damage >.4.5 > 7.1 > 7.1 >11.0

Restrict

Operation 4.5 7.1 7.1 11.0

Unrestricted 2.8 4.5 4.5 7.1

New

condition 1.4 2.3 2.3 3.5

Rigid Elastic Rigid Elastic

Maximum Allowable levels

mm/sec RMS

15kW- 300kW 300kW - 500MW


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Appendix 1I Summary of IS:12075-1987

IS 12075-1987 Relates to the evaluation of velocity levels measured on the rotating electrical

machinery.

The current practice followed internationally for measurements of vibration in V rms mode has

been adopted.This standard is not applicable to machines mounted in situ, three phase commutator

machines, three phase machines operated on single phase system and other coupled

machines.

Measurement of the vibration severity shall be made with the machine at no load and

uncoupled.

Derived values of vibration in displacement amplitude mode have been given for guidance of

those who do not have facility for Vrms

measurements.

The requirements for instruments for measuring vibration severity are covered in IS:11726-

1985.

Table I: LIMITS OF VIBRATION SEVERITY IN ROTATING ELECTRICAL

MACHINES MEASURED IN STATE OF FREE SUSPENSION

Shaft Height H, mm 56+ 1321500 upto

3000

600 to

1500

>1500

upto 3000

600 to

1500

>1500

upto 3000

Range of Speed,

RPM

Class of Vibration

SeverityRMS Value of Vibration Velocity, mm/s

Normal 1.8 1.8 1.8 2.8 2.8 4.5

Precision A 0.71 0.71 0.71 1.12 -- --

Precision B 0.45 0.45 0.45 0.71 -- --

Precision C 0.28 0.28 0.28 0.45 -- --

Table II: DERIVED VALUES OF VIBRATION SEVERITY IN ROTATING

ELECTRICAL MACHINES MEASURED IN STATE OF FREE SUSPENSION

Shaft Height H,

mm

56+ 132

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