A motor problem

Q) A 25 HP 6 Pole 50 Hz 3 phase 960 rpm at full load. I 2 = 35 A, Allowing 250 W as Cu loss in SC gear . 1000 W = Mech losses.
How much is r2?
Ans)

Q) 440 V , 50 Hz, 6P, 3 phase, 

Ans) F2 = 100/60 

Factors to Be considered in Design

Transformer Design

• Calculation of leakage reactance.
• Core dimension.
• Window Dimension.
• Frame Size
• Conductor turns, size.
• Cruciform dia etc.
• Hw/Ww, Kw, Stacking Factor

Motor Design

• Main dimensions. ( alternator)
• Speed Limitations (alternator)
• Air gap length, Tph etc.(alternator)
• SCR L/T (alternator).
• Bar etc of Induction Motor.

Limitation of design

• Saturation
• Temperature Rise
• Insulation
• Efficiency
• Mechanical Parts
• Commutation
• Power Factor
• Consumers Spec
• Standard Spec

Machine Design Facts

Q) Why electrostatic machines are not used and not electromagnetic machines are used?

Ans) Because of use of maximum energy density funda.

Q) What is Basic Structure of machine:

Ans:

• Magnetic Circuit
• Electrical Circuit
• Dielectric Circuit
• Thermal Circuit
• Mechanical Circuit

considering all above a successful designer brings out an economic and technical compromise.

What we use for Magnetic calculations

1. Basic Formula etc.

2. Total mmf calculation

• mmf for airgap
• Net length of iron
• mmf for teeth
• real & apparent flux densities

3. Leakage calculation

Motor Design

Some questions answered.

Q)What is the difference between Screw Compressor and Reciprocating Compressor?
Ans) Screw Comp. is a constant torque load device. The output( i.e. air flow is also const.). unlike reciprocating comp, current of Screw Comp is much less fluctuating.

Q)Why three intermediate tap positions ( 11A,11B and 11C) are provided?
Ans) For Mechanical convenience.

Q) What re three MODES of CB/Feeder?
Ans) 1.Service :- Both Control and Power Supply will be there.
2.Test :- Only control Supply and no power supply.
3.Isolation:-Neither Control Now Power Supply.

Q)Where you find two diaphragms in transformer?
Ans) In the EXTRA VENT provided just below level og conservator.

Some "matching" problem on electrical machines

Interpoles-------------Commutation in DC machines
Three pt starter ..........D Shunt motor
Dummy coils..................Wave winding
Equalising Ring.............Lap Winding