ELECTROMAGNETIC DEVICES - eng

Electromagnetic relay.
Generator.
Transformer.

A relay is an electrical switch that opens and closes under the control of another electrical circuit.
The switch is operated by an electromagnet to open or close one or many sets of contacts.

How it works!

A relay has at least two circuits. One circuit can be used to control another circuit. The 1st circuit (input circuit) supplies current to the electromagnet.
When the switch is closed, the electromagnet is magnetized and attracts one end of the iron armature.
The armature then closes the contacts (2nd switch) and allows current to flow in the second circuit.
When the 1st switch is open again, the current to the electromagnet is cut, the electromagnet loses its magnetism and the 2nd switch is opened. Thus current stops flowing in the 2nd circuit.

Generator can be modified to an a.c generator by replacing its commutators with two (separate) slip rings. The two slip rings rotate in tandem with the armature. 
Carbon brushes connect the armature to the external circuit. The armature is initially at the vertical position. 

Describe and explain a rotating-coil generator and the use of slip rings

Supplement

Hmmm – now this is getting a bit more challenging! Let’s go through this step-by-step.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

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Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

http://nurshiyaam.wordpress.com/

Magnets, producing a magnetic field.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

http://nurshiyaam.wordpress.com/

Magnets, producing a magnetic field.

Coil, made of insulated copper wire, rotated in the magnetic field by turning the shaft.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

http://nurshiyaam.wordpress.com/

Magnets, producing a magnetic field.

Coil, made of insulated copper wire, rotated in the magnetic field by turning the shaft.

Slip rings are fixed to the coil and rotate with it.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

http://nurshiyaam.wordpress.com/

Magnets, producing a magnetic field.

Coil, made of insulated copper wire, rotated in the magnetic field by turning the shaft.

Slip rings are fixed to the coil and rotate with it.

Brushes (normally carbon) rub against the slip rings.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

Slip ring detail

Brushes keep the coil connected to the outside part of the circuit.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

Slip ring detail

Brushes keep the coil connected to the outside part of the circuit.

As the coil rotates, it cuts magnetic field lines, so an EMF is generated, and a current flows.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

Slip ring detail

Brushes keep the coil connected to the outside part of the circuit.

As the coil rotates, it cuts magnetic field lines, so an EMF is generated, and a current flows.

The slip rings keep the coil in contact with the brushes throughout the rotation, and as a result the current flows in alternate directions, producing an alternating current (AC).

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

N

S

100



0


-100

Current (mA)

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

N

S

100



0


-100

Current (mA)

1

1

= maximum forward current

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

N

S

100



0


-100

Current (mA)

1

1

= maximum forward current

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

N

S

100



0


-100

Current (mA)

1

1

= maximum forward current

2

2

= maximum reverse current

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

N

S

100



0


-100

Current (mA)

1

1

= maximum forward current

2

2

= maximum reverse current

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

N

S

100



0


-100

Current (mA)

1

2

The maximum EMF can be increased by:
Increasing the number of turns on the coil.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

N

S

100



0


-100

Current (mA)

1

2

The maximum EMF can be increased by:
Increasing the number of turns on the coil.
Increasing the area of the coil.
Using a stronger magnet.

Supplement

“In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.” – wikipedia.

AC generators are also called alternators.

To build a generator we need two things:
A magnetic field
A moving wire

N

S

100



0


-100

Current (mA)

1

2

The maximum EMF can be increased by:
Increasing the number of turns on the coil.
Increasing the area of the coil.
Using a stronger magnet.
Rotating the coil faster.

A simple transformer

SOFT IRON CORE

A simple transformer

SOFT IRON CORE

12V

AC Input Voltage (Primary) V1

Primary input coil 5 turns n1

A simple transformer

SOFT IRON CORE

12V

AC Input Voltage (Primary) V1

Primary input coil 5 turns n1

Secondary output coil 10 turns n2

24V

AC Output Voltage (Secondary) V2

This is an example of a STEP-UP transformer – the voltage is increased between the primary and secondary coils.

A simple transformer

SOFT IRON CORE

12V

AC Input Voltage (Primary) V1

Primary input coil 5 turns n1

Secondary output coil 10 turns n2

24V

AC Output Voltage (Secondary) V2

This is an example of a STEP-UP transformer – the voltage is increased between the primary and secondary coils. In a STEP-DOWN transformer, the voltage is decreased.

A simple transformer

Why does this happen?

A simple transformer

Why does this happen?

When AC flows through the primary coil, it sets up an alternating magnetic field in the soft iron core and, therefore, in the secondary coil. This changing field induces an alternating voltage in the secondary coil.

A simple transformer

Why does this happen?

When AC flows through the primary coil, it sets up an alternating magnetic field in the soft iron core and, therefore, in the secondary coil. This changing field induces an alternating voltage in the secondary coil.

Provided all field lines pass through both coils, and there is no heat loss, the following equation applies:

Output voltage = turns on output coil
Input voltage turns on input coil

V2 = n2
V1 n1

A simple transformer

V2 = n2 x V1
n1

n2 = V2 x n1
V1

V1 = n1 x V2
n2

n1 = n2 x V1
V2

Eg. A transformer has 20 turns on the primary coil (input) and 10 turns on the secondary coil (output). If the input voltage is 50 volts, what is the output voltage?

A simple transformer

V2 = n2 x V1
n1

n2 = V2 x n1
V1

V1 = n1 x V2
n2

n1 = n2 x V1
V2

Eg. A transformer has 20 turns on the primary coil (input) and 10 turns on the secondary coil (output). If the input voltage is 50 volts, what is the output voltage?

V1 = 50, n1 = 20, n2 = 10

V2 = 10 x 50 = 25 V
20

The voltage has been reduced from 50V to 25V. This is an example of a STEP-DOWN transformer.

A simple transformer

A simple transformer

The changing current in the primary coil( a.c) produces magnetic field in the core that is in phase with the current in the primary coil.
T he magnetic field form the primary threads through the secondary coil. Since the flux is changing, by Faraday’s law, induced e.m.f is directly proportional to the rate of change of magnetic flux linkage and thus induced e.m.f will be alternating at the same frequency as the current in the primary coil.