Primary and Secondary 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.