The fundamental voltage Equation 2.2 applied to two coils with N1 and N2 turns and negligible resistance and leakage flux gives the following rms voltages V1 and V2 on two sides of the transformer (ignoring the negative sign):
= . (5.1)
Ignoring small power loss in core and coils, the conservation of energy require the volt-ampere (power) balance on two sides, that is, V1 · I1 = V2 · I2, and also the ampere-turns balance, that is, I1 · N1 = I2 · N2, leading to
= = . (5.2)
Although these relations are for the ideal transformer, they give fairly accurate results in practical transformers as well. The above transformer relations in rms values are emphasized in words below:
• Voltage ratio = turn ratio of the two coils. • Current ratio = reciprocal (flip) of the turn ratio of the two coils. • Volt-ampere product (VA or kVA or MVA) and power on both sides are
equal. • Ampere-turn products (magnetomotive force) on both sides are equal.