Why we are use 11KV / 22KV / 33KV / 66KV / 110KV / 230KV / 440KV this type of ratio. Why can’t we use other voltage ratio like 54KV / 99KV etc?

Why we are use 11KV / 22KV / 33KV / 66KV / 110KV / 230KV / 440KV this type of ratio. Why can’t we use other voltage ratio like 54KV / 99KV etc?

When an alternator generates voltage, we always use a multiple of 1.11 because for a pure sine wave the FORM FACTOR is the  ratio of rms value of voltage or current with the avg. value of voltage or current and for pure sine wave rms value of current is Imax/root '2' and avg. value is 2Imax/pie and which comes out to be 1.1;

We can't have a combination of other then a multiple of 1.11*.
So we can see all the voltages are made inevitably multiple of this value (1.1, which is the form factor of ac wave).

Also it provides us the best economic construction of step up and step down transformers.


* In the case of a Square Wave ie. a digital wave, the RMS and the average value are equal; therefore, the form factor is 1.

 

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Different type of motors...

Different type of motors.....

Squirrel Cage Motor

 

Electric Motor

An Electric motor is a machine which converts electric energy into mechanical energy. Its action is based on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force whose direction is given by Fleming’s Left-hand Rule and whose magnitude is given by F = BIl Newton.

Types of AC Motors

Classification Based On Principle of Operation:

(a) Synchronous Motors.

1. Plain

2. Super

(b) Asynchronous Motors.

1. Induction Motors:

(a) Squirrel Cage

(b) Slip-Ring (external resistance).

2. Commutator Motors:

(a) Series

(b) Compensated

(c) Shunt

(d) Repulsion

(e) Repulsion-start induction

(f) Repulsion induction

Classification Based On Type of Current:

1. Single Phase

2. Three Phase

Classification Based On Speed of Operation:

1. Constant Speed.

2. Variable Speed.

3. Adjustable Speed.

Classification Based On Structural Features:

1. Open

2. Enclosed

3. Semi-enclosed

4. Ventilated

5. Pipe-ventilated

6. Riveted frame-eye etc. 

Types of DC Motor

Most common DC motor types are-

1. Permanent-magnet motors
2. Brushed DC Motor

a.       DC shunt-wound motor

b.      DC series-wound motor

c.       DC compound motor

                                                              i.      Cumulative compound

                                                            ii.      Differentially compounded

d.      Permanent magnet DC motor

e.       Separately excited

3. Brushless DC Motor
4. Coreless or ironless DC motors
5. Printed armature or pancake DC motors
6. Universal motors

 

 

 

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How to choose transformer rating?

 How to choose transformer rating?

When an installation is to be supplied directly from a MV/LV transformer and the maximum apparent-power loading of the installation has been determined, a suitable rating for the transformer can be decided, taking into account the following considerations:

• The possibility of improving the power factor of the installation
• Anticipated extensions to the installation
• Installation constraints (e.g. temperature)
• Standard transformer ratings.

3-phase transformer

The nominal full-load current In on the LV side of a 3-phase transformer is given by:



where:

• P_a = kVA rating of the transformer
• U = phase-to-phase voltage at no-load in volts (237 V or 410 V)
• I_n is in amperes

Single-phase transformer

For a single-phase transformer:



where

• V = voltage between LV terminals at no-load (in volts)

Simplified equation for 400 V (3-phase load)

• I_n = kVA x 1.4

The IEC standard for power transformers is IEC 60076.

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