United StatesPrimary and Secondary Transformer Voltage
Transformer Voltage.
Transformer Primary Voltage.
Primary voltage is the voltage applied to the terminals of the primary winding of a transformer. The energy applied to the primary must be in the form of a changing voltage which creates a constantly changing current in the primary, since only a changing magnetic field will produce a current in the secondary. A transformer consists of at least two sets of windings wound on a single magnetic core. There are two main purposes for using transformers. The first is to convert the energy on the primary side to a different voltage level on the secondary side. This is accomplished by using differing turns counts on primary and secondary windings. The voltage ratio is the same as the turns ratio. The second purpose is to isolate the energy source from the destination, either for personal safety, or to allow a voltage offset between the source and load.If the primary has fewer turns than the secondary, you have a step-up transformer that increases the voltage.
If the primary has more turns than the secondary, you have a step-down transformer that reduces the voltage.
If the primary has the same number of turns as the secondary, the outgoing voltage will be the same as what comes in. This is the case for an isolation transformer.
In certain cases, one large coil of wire can serve as both primary and secondary. This is the case with a variable auto-transformers. The transformer may be considered as a simple two-wheel 'gearbox' for electrical voltage and current. The primary winding is analogous to the input shaft and the secondary winding to the output shaft. In this comparison, current is equivalent to shaft speed, voltage to shaft torque. In a gearbox, mechanical power (speed multiplied by torque) is constant (neglecting losses) and is equivalent to electrical power (voltage multiplied by current) which is also constant. The gear ratio is equivalent to the transformer step-up or step-down ratio. A step-up transformer acts analogously to a reduction gear in which mechanical power is transferred from a small, rapidly rotating gear to a large, slowly rotating gear: it trades current (speed) for voltage (torque), by transferring power from a primary coil to a secondary coil having more turns. A step-down transformer acts analogously to a multiplier gear in which mechanical power is transferred from a large gear to a small gear: it trades voltage (torque) for current (speed), by transferring power from a primary coil to a secondary coil having fewer turns.
Transformer Secondary Voltage.
Secondary voltage is the coil winding supplying the output voltage. The output voltage of a transformer varies some with varying load resistances, even with a constant voltage input. The degree of variance is affected by the primary and secondary winding inductance, among other factors, not the least of which includes winding resistance and the degree of mutual inductance (magnetic coupling) between the primary and secondary windings. For power transformer applications, where the transformer is seen by the load as a constant source of voltage, it is good to have the secondary voltage vary as little as possible for wide variances in load current. The measure of how well a power transformer maintains constant secondary voltage over a range of load currents is called the transformer's voltage regulation. It can be calculated from the following formula: “Full-load” means the point at which the transformer is operating at maximum permissible secondary current. This operating point will be determined primarily by the winding wire size and the method of transformer cooling. One main reason for changing the secondary voltage is for compensation when the incoming line voltage changes. By using automatic equipment, the secondary voltage that serves the load will remain basically constant, or regulated, should the line voltage fluctuate. To avoid a continual voltage hunting condition a voltage tolerance limit is maintained, usually from a half volt to a few volts. A transformer is an electrical device constructor of two or more coils that are linked together by magnetic flux. If a voltage is applied to the first coil, magnetic flux will be created. If the magnitude of the applied flux changes, then the flux being generated will also change. This changing flux will link the primary and secondary coil and induce a voltage across the secondary windings. The concept of inducing voltage across a secondary coil using changing voltage in a primary coil is called mutual inductance or flux linkage.- Go back to the previous page.
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