6 Transformers

Core

Ferromagnetic material that is capable of conducting a magnetic field. iron is a common material.

Isolation Transformer

Has a primary and secondary windings that are physically and electrically isolated. it is Magnetically coupled, not electrically coupled. Since there is no electrical connection between the primary and secondary, the transformer is basically a Filter between the two.

Power loss by a transformer is converted into ______________ and must be dissipated by the transformer.

Heat

When sizing a transformer size should you pick a model that has a higher or lower VA rating?

Higher

Transformer Input and Output Relationship

Ideally, the output of a transformer should be the same as the input power. However, due to the construction, there is usually some amount of power loss. the power In equals the power Out plus any losses.

How can you tell if the coils have been shorted to the core?

If a resistance is shown between any coil and the core.

Advantages of a transformer

Improves efficiency of the transfer of energy from one coil to another by using a core to concentrate the magnetic Field.

Advantage of a transformer

Improves the efficiency of the transfer of energy from one coil to another by using a core to concentrate the magnetic field. the primary Coil creates a magnetic field that is concentrated by the core and induces a voltage in the secondary Coil. the voltage induced in the secondary Coil can then be used to drive a load.

Regarding Control transformers if the line voltage is 240 VAC how must the 2 primaries be connected?

In Parallel

Regarding Control transformers, if the supplied line voltage is 480 VAC how must the primaries be connected?

In Series

When checking for shorts you should measure what between the primary and secondary coils?

Infinite resistance

TVs make use of this type of transformer to protect the electrical components from voltage spikes on the main power lines.

Isolation Transformer

Proper ventilation ensures

Maximum service life and operating efficiency from the transformers.

Is it okay to select a transformer with a VA rating much higher than the rating you need? Why?

No, the higher you go the less efficient the transformer will be.

Autotransformers are used frequently by whom to provide voltage regulation to large power lines.

Power companies

Regarding Isolation Transformers, voltage spikes that might occur on the primary are greatly _____________ or ______________ in the secondary

Reduced, Eliminated

Heat build up does what to a transformer?

Reduces the life and eventually destroys the transformer.

Control transformers with the primaries connected in parallel have the _________ turn ratio as a single primary.

Same

Undersizing a transformer can result in what?

Serious damage to machinery and/or fire.

If the machine does not have devices like motors with high in-rush characteristics, what is more important than in-rush current?

Steady-state current

Step Down Line Voltage

Takes the voltage down, allowing a 110/120 volt device to be used with a 220/240 volt electrical outlet.

If you apply a primary voltage that is different that it's rating

The transformer's efficiency will be lower

The connection of the primaries in a control transformer determines what?

The turns Ratio of the input and output

What's the most important guideline to use when sizing a transformer?

To select a transformer that safely and efficiently provides the maximum current that can be drawn by a load.

Autotransformers

Uses only one coil for the primary and secondary. it uses special connections on the coil called taps to produce the different ratios and voltages.

Occurs when there is a difference between the number of times each if the coils is wound around the core.

Voltage difference between primary and secondary Coil.

Principle of mutual Inductance

When two electrical coils are placed near each other, AC electrical current flowing in one coil induced and AC Voltage in the second coil. Occurs because the electrical current creates a magnetic field around the first coil which in turn induced a voltage in the second coil.

With a perfectly balanced load, the current in the grounded conductor (the tap) is _________ because the common currents returning from each side of the transformer actually cancel each other.

Zero

What to measure to look for opens in coils?

the resistance of each coil should be checked

Common application of a transformer with a center tap

- Central air - Water heater - Clothes Dryer

120 VAC transformer applications

- Electrical outlets - Lighting System

Information needed to size a transformer

- Input Voltage available - Output Voltage desired - Output current required, both in-rush and steady state

Types of Transformers

- Isolation Transformers - Autotransformers

2 ways to determine if a transformer has failed

- Measure input and output voltages - Check the transformer with an ohmmeter

Transformer components

- Primary coil - Secondary coil - Core

Steps used to calculate the actual current load

1 - calculate secondary VA 2 - Assume primary VA equals secondary VA 3 - Calculate the actual current load

The control transformer is used to reduce the main or line voltage of __________ or _____________ to a control voltage if 120 VAC

240 VAC, 480 VAC

A transformer operates at it's highest efficiency when you use what?

A load that is equal to the rated load shown in the specifications.

Center Tap Transformer

A tap that splits a secondary in half

Control Transformer

A type of transformer that is often used to reduce voltage front the main power line in the plant to a lower voltage that operates a machines electrical control system. Most common type of control transformer has 2 primary coils and one secondary.

Control Transformers with the primaries connected in series ________ the turns of the primaries together

Add

Transformer

An electrical device that converts AC electricity from one voltage level to another.

Primary Coil

An electrical wire wrapped around the core. the transformer input.

Secondary Coil

An electrical wire wrapped around the core. the transformer output.

Tap

An extra lead found on the second coil. Connected at a point between the ends of the coil so that you can get a different output voltage from the transformer. This is because it uses a reduced number of turns in the secondary coil.

What can be used to check for opens in coils, shorts between coils or coils shorted to the core without any power applied to the transformer?

An ohmmeter

120 VAC loads should always be _________ as closely as possible between the 2 legs of the transformer.

Balanced

While the primary to secondary ratio determines the output voltage, it also determines the __________. Because the input power and output power are always equal, if the voltage goes up, __________ goes down

Current

In-rush current

Devices (machines with motors) draw their maximum current when they first start; therefore it is the critical value to consider when selecting the transformer.

Common application of a transformer with a center tap

Distribution Transformer