Ohm's Law can be used to explain the behavior of current transformers (CTs) and potential transformers (PTs) in electrical circuits. Ohm's Law states that the current passing through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance of the conductor.
Current Transformers (CTs):
CTs are used to step down high current levels to measurable levels suitable for instrumentation and protection devices. According to Ohm's Law, the current (I) in a CT's secondary winding is directly proportional to the voltage (V) across its secondary winding and inversely proportional to the secondary winding's resistance (R).
Mathematically, Ohm's Law for the secondary winding of a CT can be expressed as:
I (secondary current) = V (secondary voltage) / R (secondary winding resistance)
CTs are designed to have very low resistance in their secondary winding, which means the current in the secondary circuit will be directly proportional to the voltage across the winding. This allows accurate current measurement and protection functions, as the secondary current mirrors the primary current (the current flowing through the primary winding).
Potential Transformers (PTs):
PTs are used to step down high voltage levels to a standardized lower voltage level suitable for instruments and meters. Again, applying Ohm's Law, the current (I) in the PT's secondary winding is directly proportional to the voltage (V) across its secondary winding and inversely proportional to the secondary winding's resistance (R).
Mathematically, Ohm's Law for the secondary winding of a PT can be expressed as:
I (secondary current) = V (secondary voltage) / R (secondary winding resistance)
Similar to CTs, PTs are designed with very low resistance in their secondary winding, ensuring that the current in the secondary circuit accurately represents the voltage across the primary winding. This allows voltage measurement and instrumentation at reduced voltage levels for various applications.
In summary, Ohm's Law helps us understand the relationship between voltage, current, and resistance in the secondary windings of both current transformers (CTs) and potential transformers (PTs). By maintaining low resistance in their secondary windings, these transformers ensure that the secondary current accurately reflects the primary current (for CTs) or primary voltage (for PTs), allowing for reliable measurement and protection in electrical systems.