# Transformer current and voltage relationship Transformers change the voltage of the electrical signal coming out of the voltage of alternating current is the direct relationship between the. Know the primary current to hook a transformer up to the right size circuit The current will depend on two factors: the voltage of the power. Relationship between voltage, current and frequency in a transformer Transformer is a static device which is used to step up or step down the voltage. So it only.

Figure below Turns ratio of This is a very useful deviceindeed.

### TURNS AND VOLTAGE RATIOS

With it, we can easily multiply or divide voltage and current in AC circuits. At either end both the generator and at the loadsvoltage levels are reduced by transformers for safer operation and less expensive equipment. A transformer that increases voltage from primary to secondary more secondary winding turns than primary winding turns is called a step-up transformer.

Conversely, a transformer designed to do just the opposite is called a step-down transformer. Figure below Transformer cross-section showing primary and secondary windings is a few inches tall approximately 10 cm.

This is a step-down transformer, as evidenced by the high turn count of the primary winding and the low turn count of the secondary. As a step-down unit, this transformer converts high-voltage, low-current power into low-voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary due to the increase in current. In case you were wondering, it is possible to operate either of these transformer types backwards powering the secondary winding with an AC source and letting the primary winding power a load to perform the opposite function: Transformers are often constructed in such a way that it is not obvious which wires lead to the primary winding and which lead to the secondary.

There is usually significant to the numbering of the wires H1 versus H2, etc. Any device that could output more power than it took in would violate the Law of Energy Conservation in physics, namely that energy cannot be created or destroyed, only converted.

## Step-up and Step-down Transformers

As with the first transformer example we looked at, power transfer efficiency is very good from the primary to the secondary sides of the device.

The practical significance of this is made more apparent when an alternative is considered: Figure below Motor generator illustrates the basic principle of the transformer. Refer to figure Part A of the figure shows a transformer whose primary consists of ten turns of wire and whose secondary consists of a single turn of wire. You know that as lines of flux generated by the primary expand and collapse, they cut BOTH the ten turns of the primary and the single turn of the secondary. This means that if the voltage applied to the primary winding is 10 volts, the counter emf in the primary is almost 10 volts. Thus, each turn in the primary will have an induced counter emf of approximately one-tenth of the total applied voltage, or one volt.

Since the same flux lines cut the turns in both the secondary and the primary, each turn will have an emf of one volt induced into it.

The transformer in part A of figure has only one turn in the secondary, thus, the emf across the secondary is one volt. The transformer represented in part B of figure 10 has a ten-turn primary and a two-turn secondary. Since the flux induces one volt per turn, the total voltage across the secondary is two volts. Notice that the volts per turn are the same for both primary and secondary windings. Since the counter emf in the primary is equal or almost to the applied voltage, a proportion may be set up to express the value of the voltage induced in terms of the voltage applied to the primary and the number of turns in each winding. This proportion also shows the relationship between the number of turns in each winding and the voltage across each winding.

### How to Calculate Transformer Primary Current | Sciencing

This proportion is expressed by the equation: Notice the equation shows that the ratio of secondary voltage to primary voltage is equal to the ratio of secondary turns to primary turns. The equation can be written as: The following formulas are derived from the above equation: If any three of the quantities in the above formulas are known, the fourth quantity can be calculated. A transformer has turns in the primary, 50 turns in the secondary, and volts applied to the primary Ep.

What is the voltage across the secondary E s? There are turns of wire in an iron-core coil. If this coil is to be used as the primary of a transformer, how many turns must be wound on the coil to form the secondary winding of the transformer to have a secondary voltage of one volt if the primary voltage is five volts? The ratio of the voltage 5: Sometimes, instead of specific values, you are given a turns or voltage ratio. In this case, you may assume any value for one of the voltages or turns and compute the other value from the ratio.

For example, if a turn ratio is given as 6: The transformer in each of the above problems has fewer turns in the secondary than in the primary. As a result, there is less voltage across the secondary than across the primary.

The ratio of a four-to-one step-down transformer is written as 4: A transformer that has fewer turns in the primary than in the secondary will produce a greater voltage across the secondary than the voltage applied to the primary.