AC and DC Machinery: EMF Equation of DC Generators and Transformer Configurations, Slides of Electric Machines

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AC and DC Machinery

The EMF Equation of DC generator

Faraday’s Law

The magnitude of the voltage is directly proportional to the rate of flux being cut. Voltage per conductor: Voltage per Path:

Technically we can just simplify this as : :Where this flux is equivalent to line per seconds. Conversion factor: 1 voltage of emf can be produced by 1× 10 ^ - 8 lines / seconds

Note: use this formula when flux is in lines and time is in seconds.

So what were be able to get is the voltage per conductor and we know that the armature is slotted where the conductor rotates and each of them cuts magnetic flux. It means each of those conductor will be induced in voltage, but before that we have to understand that this armature windings are divided in several parallel path. This parallel path depends on the kind of armature windings connections. Parallel path- number of circuit traced by the circuit in armature windings as it enters on brush and leaves the other brush. For lap winding : a = p×m where: m= plex or the degree of multiplicity p= number of poles a= number of parallel paths

This refers to the voltage in every parallel path that will also refer to the total that is induced or created by DC generator. For wave windings : ( the number of parallel path is two) a= 2 × m Frog leg windings : ( equivalent to twice the number of poles that you have) a= 2 × p

Sample problem: Calculate the average voltage in a moving conductor if it cuts 3.5×10^6 line in 1/50 seconds. Given:

Note: It is important to remember that transformers do not generate electrical power; they transfer electrical power from one AC circuit to another using magnetic coupling. The core of the transformer is used to provide a controlled path for the magnetic flux generated in the transformer by the current flowing through the windings, which are also known as coils. There are four primary parts to the basic transformer. The parts include the Input Connection, the Output Connection, the Windings or Coils and the Core. Input Connections - The input side of a transformer is called the primary side because the main electrical power to be changed is connected at this point. Output Connections - The output side or secondary side of the transformer is where the electrical power is sent to the load. Depending on the requirement of the load, the incoming electric power is either increased or decreased. Winding - Transformers have two windings, being the primary winding and the secondary winding. The primary winding is the coil that draws power from the source. Core - The transformer core is used to provide a controlled path for the magnetic flux generated in the transformer. The core is generally not a solid bar of steel, but rather a construction of many thin laminated steel sheets or layers.

TRANSFORMER CONFIGURATIONS

• There are different configurations for both single-

phase and three-phase systems.

• Single-phase Power - Single-phase transformers are

often used to supply power for residential lighting,

receptacle, air-conditioning, and heating needs. Single

phase transformers can be made even more versatile

by having both the primary winding and secondary

winding made in two equal parts. The two parts of

either winding can then be reconnected in series or

parallel configurations.

Three-phase Transformers - Three-phase

transformers have six windings; three primary and

three secondary. The six windings are connected by

the manufacturer as either delta or wye. As

previously stated, the primary windings and

secondary windings may each be connected in a

delta or wye configuration. They do not have to be

connected in the same configuration in the same

transformer. The actual connection configurations

used depend upon the application.

TYPES OF TRANSFORMERS

• POWER TRANSFORMER

• A power transformer is used primarily to couple electrical energy from a power supply line to a circuit system, or to one or more components of the system. A power transformer used with solid state circuits is called a rectifier transformer. A power transformer's rating is given in terms of the secondary's maximum voltage and current-delivering capacity.

• DISTRIBUTION

TRANSFORMER

• A pole-type distribution transformer is used to supply relatively small amounts of power to residences. It is used at the end of the electrical utility's delivery system.

• AUTOTRANSFORMER

• The autotransformer is a special type of power transformer. It consists of a single, continuous winding that is tapped on one side to provide either a step-up or a step-down function. This is different from a conventional two-winding transformer, which has the primary and secondary completely isolated from each other, but magnetically linked by a common core. The autotransformer's windings are both electrically and magnetically interconnected.