Current transformers are used to step down current in a very predictable fashion with respect to current and phase. They are generally used as inputs to current instruments.
Instrument transformers are used to step-down current or voltage to measurable values. They provide standardized, useable levels of current or voltage in a variety of power monitoring and measurement applications.
Resistors are electrical components that oppose the flow of either direct or alternating current. They are used to protect, operate, or control circuits.