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DESIGN OF �ELECTROMAGNETS

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TOPICS TO BE COVERD

  • Introduction.
  • Application of electromagnets.
  • Construction.
  • Types of electromagnet.
  • Design of coil.
  • Lifting magnets.
  • Design equation.
  • Steps for design of various magnets.

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BASIC PRINCIPLES:

  • When a current carrying coil is wound on magnetic material like iron, that iron piece becomes electromagnet.
  • this process is called electromagnetism.

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APPLICATIONS OF ELECTROMAGNETS:

  • Electrical measuring instruments.
  • Lifting magnets.
  • Magnetic clutches.
  • Electric bells.
  • Electric clocks.
  • Circuit breakers.
  • Relays.
  • Electric valves.
  • Telephone receiver.
  • Ac / dc machines.

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FUNCTIONS OF ELECTROMAGNETS:

  • For lifting, pulling & holding purposes.
  • For lifting heavy loads, larger size electromagnets are used.
  • For holding purposes, like relay, valves etc, small size electromagnets are used.

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TYPES OF ELECTROMAGNETS:

  • 1) TRACTIVE TYPE:
  • These electromagnets are solenoids and used to produce mechanical movement in the armature to do work.
  • Can be operated by ac or dc supply.
  • Used in bells, valves, relays, telephone receivers, buzzer, magnetic switches.

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TYPES OF ELECTROMAGNETS:

  • 1) PORTATIVE TYPE:
  • These electromagnets are used for holding purpose.
  • Operated on dc supply only.
  • Used in lifting magnets, magnetic clutches.
  • Magnetic separators.

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DESIGN OF ELECTROMAGNETIC COIL:

  • Coils are circular in shape & rectangular in cross section area.

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DEIGN OF ELECTROMAGNET COIL:

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DEIGN OF ELECTROMAGNET COIL:

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outer

inner

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DEIGN OF ELECTROMAGNET COIL:

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DEIGN OF ELECTROMAGNET COIL:

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DEIGN OF ELECTROMAGNET COIL:

  • CALCULATION OF RESISTANCE OF COIL & SIZE OF CONDUCTOR:

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DEIGN OF ELECTROMAGNET COIL:

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DEIGN OF ELECTROMAGNET COIL:

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Ambient temperature is 20°.

At 20°, resistivity is 0.01734 ohm/m/mm²

& alfa zero is 0.00393 / °c

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DEIGN OF ELECTROMAGNET COIL:

  • MMF REQUIRED:

Total AT = AT for airgap + AT for iron part.

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DEIGN OF ELECTROMAGNET COIL:

  • TOTAL WINDING AREA:

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DEIGN OF ELECTROMAGNET COIL:

  • TOTAL WINDING AREA:

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DEIGN OF ELECTROMAGNET COIL:

  • TEMPERATURE RISE OF COIL:

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DEIGN OF ELECTROMAGNET COIL:

  • TEMPERATURE RISE OF COIL:

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DEIGN OF ELECTROMAGNET COIL:

  • TEMPERATURE RISE OF COIL:

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DEIGN OF ELECTROMAGNET COIL:

  • SPACE FACTOR , Sf:

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DEIGN OF ELECTROMAGNET COIL:

  • SPACE FACTOR , Sf:

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DEIGN OF ELECTROMAGNET COIL:

  • SPACE FACTOR , Sf:

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DEIGN OF ELECTROMAGNET COIL:

  • SPACE FACTOR , Sf:

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DEIGN OF ELECTROMAGNET COIL:

  • SPACE FACTOR , Sf:

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DEIGN OF ELECTROMAGNET COIL:

  • Numerical-1:
  • A coil is wound on a former has outside diameter of 80 mm and inside diameter of 30 mm. The height of the coil is 100 mm.

Calculate:

  • The winding depth, total winding area, length of mean turn.
  • Space factor & no. of turns when conductors are bed & do not bed.

The coil is wound with 35 SWG, s.c.c. copper wire having an area of 0.0357 mm², a bare diameter of 0.213 mm and diameter with insulator of 0.313 mm.

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DEIGN OF ELECTROMAGNET COIL:

  • Numerical-1 data :

Do = 80 mm

Di = 30 mm

Hc = 100 mm

a = 0.0357 mm

d = 0.213 mm

d1 = 0.313 mm

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Dc = 25 mm

Aw = 2500 mm²

Lmt = 173 mm

Sf = 0.3635, 0.4195

T = 25455, 29376

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DEIGN OF ELECTROMAGNET COIL:

  • Numerical-2:
  • Prove that, with given overall dimensions, temperature rise, cooling co-efficient and space factor, the maximum mmf that can be produced by an exciting coil is impendent of the supply voltage.

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MAGNETIC FORCE OR PULL:

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MAGNETIC FORCE OR PULL:

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MAGNETIC FORCE OR PULL:

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MAGNETIC FORCE OR PULL:

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INDEX NUMBER:

  • shape of electromagnet depends upon two factor:
  • 1) force of magnet
  • 2) linear displacement of armature called STROKE.

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  • for a constant value of flux density B in air gap, the area of working gap of magnet is proportional to the force.

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INDEX NUMBER:

  • From above, index number is given by:

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  • It is an index of the shape of an electromagnet.

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LIFTING MAGNETS:

  • TYPES OF LIFITING MAGNETS:

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  • Flat-faced armature type.
  • Horse shoe type.
  • Plunger type.

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FLAT-FACED ARMATURE TYPE:

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FLAT-FACED ARMATURE TYPE:

  • It has two working gaps.
  • These gaps are magnetically in series & mechanically in parallel.
  • This type of magnets are large in size & made of cast iron.
  • Force varies inversely as the square of airgap.
  • Used to produce large force in relatively small distance.

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FLAT-FACED ARMATURE TYPE:

  • DESIGN EQUATION:

1) Force equation:

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2) MMF equation:

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FLAT-FACED ARMATURE TYPE:

  • DESIGN EQUATION:

3) Heating equation:

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4) Voltage equation.

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

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  • Following specification are given for design of magnets.
  • Required force.
  • Stroke or length of air gap.
  • Max. temp. rise.
  • Supply voltage.
  • excitation. (continuous or intermittent)

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

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Step1: Calculate the radius of central limb or innr pole, r1

Cacluate index number:

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From index number find flux density from graph.

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

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Step 1: Calculate the radius of central limb or inner pole, r1 :

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

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Step 2: Calculate total MMF required.

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MMF required for iron part is negligible.

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

Step 3: Calculate height of coil & radius r2.

From the temperature rise we can calculate the value of hc.

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

Step 3: Calculate height of coil & radius r2.

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dc = r2-r1

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

Step 4: Calculate radius r3, & thickness t1, t2.

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

Step 5:Calculate diameter of conductor or wire.

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

Step 6:Calculate the number of turns:

No. of turns corresponding to the insulated conductor d1 are calculated in height wise & depth wise of the exciting coil after making certain allowances for the insulation.

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

Step 6:

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

Step 7:Calculate total resistance of coil:

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Step 8:Calculate current in coil:

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FLAT-FACED ARMATURE TYPE:

  • DESIGN STEPS:

Step 9:Calculate actual value of total MMF:

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Step 10:Calculate actual temperature rise of the coil:

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HORSE SHOE TYPE:

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Magnetic path

Yoke

Airgap

Armature

D

dc

t

W

hc

r1

r2

t1

t2

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HORSE SHOE TYPE:

  • D = distance between two pole centres.
  • r1 = radius of pole core.
  • r2 = radius of pole core + winding.
  • t1 = thickness of armature.
  • t2 = thickness of yoke.
  • t = thickness of pole face.
  • W = width of pole face.
  • dc = depth of coli.
  • hc = height of coil.

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HORSE SHOE TYPE:

  • It has two working gaps.
  • It is a bipolar type electromagnet.
  • This type of magnets are small in size.
  • Force varies inversely as the square of airgap.
  • Used to produce small force.

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HORSE SHOE TYPE:

  • DESIGN EQUATION:

1) Force equation:

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2) MMF equation: