Skip to main content

Electrical Machine Design (equations)


DC Machine


Induction Machines

Synchronous Machines

Output Equation Pa=CoD2Ln, where Pa=P/h for generators, Pa=P for motors For Single Phase
Q=2.22 f Bm Ai Kw Aw d 10-3
For Three Phase
Q=3.33 f Bm Ai Kw Aw d 10-3
Q=CoD2 L ns
KVA Input Q=
HP * 0.746 / Cos f * h
Q=CoD2 L ns
KVA Input Q=
HP * 0.746 / Cos f * h
For Turbo alternators
Q=1.11Bavac KwsVa2 L 10-3/ns
Output Coefficient Co=Bav ac* 10-3 where Bav-magnetic loading and ac - electric loading DNA Co=11 Kws Bav ac 10-3 Co=11 Kws Bav ac 10-3
Choice of Magnetic Loading
Flux Density in Teeth Frequency of Flux Reversals Size of machine DNA Magnetizing current, Flux Density, Iron loss Iron loss, Stability, Voltage Rating, Parallel Operation, Transient ShortCircuit current
Choice of Electric Loading
Temperature rise,
speed of machine, Voltage, Armature reaction, Commutation
DNA Overload Capacity, Copper losses, Temperature rise, Leakage Reactance Copper loss, Synchronous reactance, Temperature rise, Stray Load losses,
Voltage rating
Flux Density
Yoke – 1.3 to 1.6 Wb/m2
Pole – 1.2 to 1.7
Air Gap – 0.4 to 0.6
Armature teeth – 1.5 – 2.2
Armature core – 1.0 to 1.5
1. 0 to 1.4 wb/m2 for Distribution Transformer
1.2 to 1.5 for power Transformers
Stator tooth
1.3 to 1.7 Wb/m2
Rotor tooth
1.3 to 1.7 Wb/m2
Current Density
Large Machine with strap wound conds – 4.5A/mm2
Small M/c with wire wound conds – 5A/mm2
High speed - 6 to 7A/mm2
General - 4 to 7A//mm2
1.1 to 2.2 A/mm2- small Tr..
2.2 to 3.2 – large power Tr..
5.4 to 6.2 – Large power Tr with Forced circulation
In rotor bar 4 to 7A/mm2 Current density in armature conductor
d = 3 to 5A/mm2
Main Dimension D- Diameter of the armature, L- Armature Length Hw (Height of window) and Ww (width of Window) D –diameter of stator bore
L- Length of Stator core
D –diameter of stator bore
L- Length of Stator core
L/τ Ratio
0.45 to 1.1
b/τ =0.64 to 0.72
(for Square pole face and Square Pole Section)
DNA minimum cost L/t =1.5- 2
good pf L/t = 1 – 1.25
good h L/t =1.5
overall design L/t =1
best pf t =Ö0.18L
L/t = 0.6 to 0.7
L/t = 1 to 5
Choice of Number of Poles Frequency Between 25 to 50 HZ
Current per parallel path is limited to 200A.
The Armature MMF Should not be large.
For Bolted pole
Va = 50 m/s
Dovetail & T Head
Va=80 m/s
Length of Air Gap lg=(0.5 to 0.7)* ac* τ * 1.6*106 Bg Kg DNA Lg= 0.2 + 2ÖDL
Lg=0.2 + D
Lg=(1.6ÖD) – 0.25
M/c with open type slots
L g/t = 0.01 to 0.015
M/c with maximum o/p
L g /t = 0.02
Turbo Alternator
Lg=0.5SCR act Kf10-6/Kg Bav
Slot Information Slot Area = Conductor area/ slot space Factor DNA Stator Slot Pitch Yss=p D/Ss Values of Stator slot pitch
Yss < 25mm – Low Volt M/c
Yss < 40mm – for 6KV & less
Yss < 60mm - m/c upto 15kV
Tooth Information DNA DNA width of stator tooth
Wts min = fm / 1.7(Ss/p) Li
Width of rotor tooth
Wtr min = fm / 1.7(Sr/p) Li
Core D=Di+2dc+2ds
Di Inner Dia.of armature
dc Depth of core
ds Depth of slot
Square Core Kc = 0.45
Two stepped core Kc = 0.56
Three stepped core Kc=0.6
Kc – core area factor = Ai/d2
Depth of stator core
dcs = fm / 2 Bcs Li
Depth of rotor core
dcr = fm / 2 Bcr Li
Armature MMF/Pole Up to 100Kw- 5000 or less
100 to 200Kw- 5000 –7000
500 to1000Kw 7500-10000
over1500Kw –Upto 12,500
Armature MMF/pole
ATa = 2.7 Ip Tph Kws / p
Field MMF
ATf =SCR * Ata
Dispersion Coefficient DNA DNA s = Im/Isci
Im-Magnetizing current
Isci – ideal Short ckt current
Short Circuit Ratio
DNA DNA DNA The ratio of field current required to produce rated voltage on OC to field current required to circulate rated current at SC.
SCR = 1/Xd
Slot Loading DNA DNA Slot Loading = Zss Is
Conds/slot Zss=6Ts/Ss
Stator Conds = Ss Zss
Additional Information Current/Parallel path = Ia/p
For Wave Winding Ia/2
number of tubes =
[(Pi +Pc/q)-12.5 St] /8.8p dt lt
Rotor Bar current
Ib = 0.85 6Is Ts/Sr
End ring current
Ie=Sr Ib/p p
(Ss-Sr) should not be equal to
0,±p, ±2p, ±3p, ±5p, ±1, ±2, ±(p±1) ±(p±2)
Current thru the conductor
Iz = Iph/a
Peripheral Speed
Va = p D ns
DNA - Data Not Available (Data or the concept may not be there).
Reference: Electrical Machine design by A. K Sawhney


  1. sir,
    your work is excellent, but if we consider in design aspect, you should mention nomenclature also, other wise different text books will follow different nomenclatures.

    1. Hmm Yes. But I prepared this 13 years back, I think it still works. Now I am in Computer Science and Engg. So Lost the touch in this subject.


Post a Comment

Popular posts from this blog

Installation of NS2 (ns-2.35) in Ubuntu 20.04

Installation of NS2 (ns-2.35) in Ubuntu 20.04 LTS Step 1: Install the basic libraries like      $] sudo apt install build-essential autoconf automake libxmu-dev Step 2: install gcc-4.8 and g++-4.8 open the file using sudo mode $] sudo nano /etc/apt/sources.list Include the following line deb bionic main universe $] sudo apt update $] sudo apt install gcc-4.8 g++-4.8 Step 3:  Unzip the ns2 packages to home folder $] tar zxvf ns-allinone-2.35.tar.gz $] cd ns-allinone-2.35/ns-2.35 Modify the following make files. ~ns-2.35/ Change @CC@ to gcc-4.8 change @CXX@ to g++-4.8 ~nam-1.15/ ~xgraph-12.2/ ~otcl-1.14/ Change in all places  @CC@ to gcc-4.8 @CPP@ or @CXX@ to g++-4.8 open the file: ~ns-2.35/linkstate/ls.h Change at the Line no 137  void eraseAll() { erase(baseMap::begin(), baseMap::end()); } to This void eraseAll() { this->erase(baseMap::begin(), baseMap::end()); } All changes made Step 4: Open a new termi

Installing ns-3.34 in Ubuntu 20.04

This post shows how to install ns 3.34 in Ubuntu 20.04 LTS Prerequisites: Fresh installation of Ubuntu Version 20.04 LTS  ns3.34 can be downloaded from here Follow the video link for complete step by step instructions on the installation.  This version fixes the compilation issues of (bug in ns3.33)  Issue the following commands after opening a terminal  $ sudo apt update $ sudo apt install g++ python3 python3-dev python-dev pkg-config sqlite3 python3-setuptools git qt5-default gir1.2-goocanvas-2.0 python3-gi python3-gi-cairo python3-pygraphviz gir1.2-gtk-3.0 ipython3 openmpi-bin openmpi-common openmpi-doc libopenmpi-dev autoconf cvs bzr unrar openmpi-bin openmpi-common openmpi-doc libopenmpi-dev tcpdump wireshark libxml2 libxml2-dev Unzip or untar the ns-allinone-3.34.tar.bz2 in the home folder (in my case its /home/pradeepkumar) $ cd ns-allinone-3.34/ $ ./ --enable-examples --enable-tests  Once the installation is completed, you may get an output show

Installation of ns3 in Windows 10 and Windows 11 OS using WSL (Windows Subsystem for Linux)

This post shows how to install ns-3.33 in Windows 10 through WSL (Windows Subsystem for Linux) This posts works for Windows 11 also (I have tested it on a Windows 11 ISO and it works the Same way as mentioned in the following post.) This post will work for ns-3.3x version. Prerequisites : Install Windows Subsystem for Linux with GUI: Please refer the following video  System Information: OS used: Windows 10 and WSL (Ubuntu 20.04) GUI: XServer for Windows NS3 Version: ns-3.33 See the following complete video on how to install ns3 in Windows 10 Step 0 : Open XLaunch Step 1 :  Open WSL using PowerShell and open it as Administrator Command:/  wsl $ xfce4-session The GUI of Ubuntu Opens within Windows 10 OS. Step 2 : Download ns3 from website through Mozilla Firefox browser Step 3: Open a Terminal  $ sudo apt update $ sudo apt install build-essential autoconf automake libxmu-dev python3-pygraphviz cvs mercurial bzr git cmake p7zip-full python3-matplotlib python-tk python3-dev qt5-q