Electrical Thumb Rules-(Part-5)

Standard Size of Transformer (IEEE/ANSI 57.120):

Single Phase Transformer

Three Phase Transformer

5KVA,10 KVA,15 KVA,25 KVA,37.5 KVA,50 KVA,75 KVA,100 KVA,167 KVA,250 KVA,

333 KVA,500 KVA,833 KVA,1.25 KVA,1.66 KVA,2.5 KVA,3.33 KVA,5.0 KVA,6.6 KVA,8.3 KVA,10.0 KVA,12.5 KVA,16.6 KVA,20.8 KVA,25.0 KVA,33.33 KVA

3 KVA,5 KVA,9 KVA,15 KVA,30 KVA,45 KVA,75 KVA,112.5 KVA,150 KVA,225 KVA,300 KVA,500 KVA,750 KVA,1MVA,1.5 MVA,2 MVA,2.5 MVA,3.7 MVA,5 MVA,7.5MVA, 10MVA ,12MVA,15MVA,20MVA ,25MVA, 30MVA,37.5MVA ,50MVA ,60MVA,75MVA,100MVA

 Standard Size of Motor (HP):

Electrical Motor (HP)

1,1.5,2,3,5,7.5,10,15,20,30,40,50,60,75,100,125,150,200,250,300,400,450,500,600,700,

800,900,1000,1250,1250,1500,1750,2000,2250,3000,3500,4000

 Approximate RPM of Motor

HP

RPM

< 10 HP

750 RPM

10 HP to 30 HP

600 RPM

30 HP to 125 HP

500 RPM

125 HP to 300 HP

375 RPM

 Standard Size of Motor (HP):

Electrical Motor (HP)

1,1.5,2,3,5,7.5,10,15,20,30,40,50,60,75,100,125,150,200,250,300,400,450,500,600,700,

800,900,1000,1250,1250,1500,1750,2000,2250,3000,3500,4000

 Motor Line Voltage:

Motor (KW)

Line Voltage

< 250 KW

440 V (LV)

150 KW to 3000KW

2.5 KV to 4.1 KV (HV)

200 KW to 3000KW 3.3 KV to 7.2 KV (HV)
1000 KW to 1500KW 6.6 KV to 13.8 KV (HV)

 Motor Starting Current:

Supply

Size of Motor

Max. Starting Current

1 Phase < 1 HP 6 X Motor Full Load Current
1 Phase 1 HP to 10 HP 3 X Motor Full Load Current
3 Phase 10 HP 2 X Motor Full Load Current
3 Phase 10 HP to 15 HP 2 X Motor Full Load Current
3 Phase > 15 HP 1.5 X Motor Full Load Current

Motor Starter:

Starter

HP or KW

Starting Current

Torque

DOL <13 HP(11KW) 7 X Full Load Current Good
Star-Delta 13 HP to 48 HP 3 X Full Load Current Poor
Auto TC > 48 HP (37 KW) 4 X Full Load Current Good/ Average
VSD   0.5 to 1.5 X Full Load Current Excellent
Motor > 2.2KW Should not connect direct to supply voltage if it is in Delta winding

 Impedance of Transformer (As per IS 2026):

MVA

% Impedance

< 1 MVA

5%

1 MVA to 2.5 MVA

6%

2.5 MVA to 5 MVA

7%

5 MVA to 7 MVA

8%

7 MVA to 12 MVA

9%

12 MVA to 30 MVA

10%

> 30 MVA

12.5%

 Standard Size of Transformer:

Standard Size of Transformer

KVA

Power Transformer (Urban)

3,6,8,10,16

Power Transformer (Rural)

1,1.6,3.15,5

Distribution Transformer

25,50,63,100,250,315,400,500,630

 

 

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About Jignesh.Parmar
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 14 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

7 Responses to Electrical Thumb Rules-(Part-5)

  1. Kaustubh Wasave says:

    Hello Sir,
    I am a huge fan of yours. I recently ran into your blog and have been hooked since. Your blog contains all vital information that an electrical engineer, like me, needs to know and I thank you for the pain that you took to make it available for everyone. I have one request, if its not too much for you, can you please explain relay coordination in an industry or substation using an example?
    Thank you and keep up the good work. We’ll always look up to you for inspiration.

  2. Sandeep Ayyagari says:

    Hello Sir,
    Thanks for your great support in Electrical ,please let me know the Magnetizing current in a Transformer and basic tests to be conducted before charging the Transformer ,and Standard Tolerances to be followed for Transformer Selection ,and General Transformer Erection Procedure, and Pre Commissioning Checks,Check List for Smother Maintenance.

  3. Luis Zorrilla says:

    Jignesh,

    Thanks a lot for your Blog. I have a question for you:

    What is the impact of modeling or not modeling the static wire in a Transmission, Distribution line? I am doing a model for a transmission line and I want to know how much details I need to have to have reasonable results.

    Regards

  4. P.Ashokan says:

    Hello Sir,

    could you say Which Standards You are used in above All the details.
    Thanking you,
    P.Ashokan
    Chennai

  5. why in a.c power cable like to delta shape? please tel me sir.

    thanking you,
    Mintu kr. pandit
    Howrah/ W.B

  6. why in a.c power cable like to delta shape? please tel me sir,

    thanking you
    mintu kr. pandit
    Howrah / W.B

  7. Engr. Ghazanfar Ali Khan says:

    How rating of tertiary winding winding is formulated, calculated?

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