［ Development of Rotating Machinery-Based System Products ］

Model Change of Gas Engine
Alternator
Keywords

High efﬁciency, Light-weight design, Analytical technologies

Abstract

In the large market of medium-speed engine generating systems, there is aconstant and stable demand for gas engines. While we are diligently working toincrease our market presence in this ﬁeld, we recently conducted a modelchange on a gas engine alternator in order to meet the various demands of ourcustomers.
Compared with our conventional models, we aimed to improve alternator
efﬁciencies and a light-weight design. By applying various analysis technologies, we conducted an optimal design, a study on strength, and a review onperformance. In addition, we made a 10MVA class prototype and conducted veriﬁcation tests, compared the analytical results, and conducted conventional
tests such as temperature rise test, measurement of losses, insulation test, as
well as other various tests. We veriﬁed the design analysis and product performance. As a result, we realized more than 10% light-weight design than 0.2%
efﬁciency gain (under 100% load at the rated power factor) by comparing theconventional model and the prototype.

1 PrefaceIn the ﬁeld of medium-speed engine generating systems, gas engine generating systems maintain a stable demand as it offers high combustion
efﬁciencies and low CO2 emission. We have manufactured and supplied a variety of engine alternators. We recently made a model change of anengine alternator in order to increase sales in overseas markets.
In order to realize an improvement of performance (efﬁciency) and a light-weight design compared with the conventional model, we took research
on an optimal design, thermos-ﬂuid analysis, andmechanical strength analysis in order to reﬂect themeasured results into a design for new modelchange. This paper introduces our approach using
various analytical technologies and the results ofdesign comparison veriﬁcation using a prototype.

2 Details of Improvements
2.1 Attaining Higher Efﬁciency
To realize a higher efﬁciency, we made improvements primarily focusing on the reduction of copper

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Noriyuki Koshizuka,
Daisuke Muramatsu

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and mechanical losses because they make up alarge part of the total losses.
As a measure to reduce copper losses, wereviewed the method of forming the armature winding. The number of coils is decreased and thecross-sectional area is increased. As such, we created a design to reduce copper losses in armaturecoils. As a measure to reduce mechanical loss, it isimportant to reduce cooling air volume. This measure is disadvantageous, however, for cooling efﬁciency. As such, we created a new design using
thermos-ﬂuid analysis and conducted an optimal
wind-volume design in consideration of the temperature rise in windings. In this way, we studied theminimal windage loss possibility by reducing thesize of the cooling fan blades.

2.2 Light-Weight Design
The reduction of the alternator weight effects
the quantity of all materials used. This results in the
reduction of environmental loads and the enhancement of the competitiveness of product sales. For
alternator characteristics, the total quantity of winding wires and core used is dependent on the performance speciﬁed for the alternator. As such, weevaluated the structure of the rotor and stator as key
units of the entire alternator, down to individual components.
In this assessment, we adopted a Value Engineering (VE) approach so that existing components
can be examined from various angles and foundpoints for improvement while satisfying the requiredfunctions. The reviewed results were reﬂected in thelatest alternator design. In so doing, we streamlined
the number of required components, simpliﬁed thestructure design, and realized a light-weight design.

3 Examination of the Design throughAnalysis
3.1 Fluid Analysis and Thermal Analysis
Most mechanical loss is in the alternator windage loss. In order to reduce windage loss, it is mosteffective to decrease the volume of cooling air. We
analyzed in order to reduce the wind volume, whileconsidering winding temperatures. The result of thisanalysis was reﬂected in the design of the cooling
fan blades.
For analytical software, we used the ANSYS.
With this software, air ﬂows and temperature distribution before and after the model change werevisualized. In so doing, we found design issues andstudied possible measures to correct. As a result,
we realized the reduction of the total mechanicalloss by 40% by lowering the wind volume while satisfying the required conditions for satisfying winding
temperatures. Fig. 1 shows the result of ﬂuid analysis and Fig. 2 shows that of thermal analysis.

Fig. 1Result of Fluid Analysis

The result of ﬂuid analysis into the generator interior is shown.
The rotating state of the rotor is visualized in order to make theﬂows visible in the armature.

3.2 Mechanical Strength Analysis andEigenvalue Analysis
When the plate thickness and materials to be
used are reviewed and the design policy is greatly
modiﬁed, it is necessary to carefully conﬁrm resultant reliability. For this purpose, we used analyticalsoftware for evaluation.
The rotor was conﬁrmed to have sufﬁcientstrength, even under the condition of over-speed atwhich the revolving speed is greater than the rated
level. The operating condition for the generator wasbased on the Daily Start and Stop (DSS) system. A
cyclic load was continuously exerted on the rotor. The
analysis and evaluation were, therefore, carried out
in regard to strength against fatigue. It became clearthat there is no problem in this subject. Fig. 3 shows

Fig. 2

Result of Thermal Analysis

The distribution of temperature rises inside the alternator is shown.
The temperature rises in windings were analyzed so that the obtained data can be reﬂected in the design for the cooling fan blades.

Fig. 3Result of Rotor Pole Strength Analysis

The analytical result of the rotor magnetic pole is shown in regard to the 1/16 analytical model. Based on the obtained result, weconﬁrmed that there is no problem in strength against over-speed.

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the result of rotor pole strength analysis and Fig. 4
shows that of cooling fan blade strength analysis.
In general, the stator gives rise to a resonancephenomenon when the natural frequency of thecomponent parts coincides with the vibrational frequency of the engine being a prime mover and thealternator itself. Such a phenomenon leads to theoccurrence of abnormal vibration or alternator damage. For this reason, we analyzed and evaluated inorder to check that the natural frequency is far different from the vibrational frequency. We conﬁrmed
there is no problem. Fig. 5 shows the result ofeigenvalue analysis for brackets and Fig. 6 showsthat of eigenvalue analysis for the stator as a whole.
Based on these analytical results, we reduced thetotal generator weight by more than 10% comparedwith conventional model of a similar size, without
sacriﬁcing quality.

4 Veriﬁcation by a Prototype
We made a 10MVA class prototype to perform
a veriﬁcation test and a performance test in order toverify the matters checked by the analysis results.
In examining winding temperatures, we performed a temperature rise test. We conﬁrmed thattemperature rises in both stator and rotor windings atthe estimated full load conditions will be below the temperature rise limit speciﬁed by a relevant standard.
We also conﬁrmed an efﬁciency gain by morethan a design target value of 0.2%. Fig. 7 shows acomparison of losses with a conventional model.

Fig. 6Fig. 4

Result of Cooling Fan Blade Strength Analysis

The analytical result of cooling fan blade strength is shown. We
conﬁrmed that there is no problem in strength against overspeed.

Result of Eigenvalue Analysis for the Stator asa WholeThe result of eigenvalue analysis on the entire alternator stator isshown. The natural frequency value was sufﬁciently different
from that of the vibrational frequency. As such, we conﬁrmed that
there is no frequency problem.

Armature loss
Field loss
Mechanical loss

Loss

Stray losses
Core loss

Conventional modelFig. 5

Result of Eigenvalue Analysis for the Brackets

The result of eigenvalue analysis for the bracket unit is shown.
The natural frequency is sufﬁciently different from the vibrationalfrequency and this suggests freedom from any problem.

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Fig. 7

Model change

Comparison of Losses

The comparison of losses with conventional versions is shown.
Compared with conventional model, we achieved over a 0.2%
efﬁciency gain.

Log Magnitude (m/s) ^2. RMS

View：3D View (Complex)
BLK：Result 01
Freq：12.5Hz

1E＋03

M#1 Cross spectrum 1A：2A100
1010.1
0.01

Fig. 9050100（Hz）

150200Result of Natural Frequency Measurement byHammering Test

The result of natural frequency measurement by bracket hammering test is shown. Comparing with the result of analysis, weconﬁrmed that there is no problem in analytical accuracy.
Fig. 8Result of Measurement in Vibration Mode by
Hammering Test

The result of measurement in vibration mode by bracket hammering test is shown.

For the veriﬁcation of natural frequency, wemeasured actual frequency by performing a hammering test. Comparing the actually measured values with the result of analysis, we conﬁrmed that
there is no problem in analytical accuracy. Fig. 8
shows the result of measurement in vibration modeand Fig. 9 shows the result of natural frequency
measurement by hammering test.

5 Postscript
After performing various analysis and veriﬁcation tests by a prototype, we realized a modelchange for higher efﬁciency and a light-weight
design. Going forward, we will continue to makeefforts to introduce advanced technologies and thelatest analytical technologies so that we can supply
high-performance and highly reliable products toour customers.
・All product and company names mentioned in this paper are
the trademarks and/or service marks of their respective owners.

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