<P> If the burden resistance is much less than inductive impedance of the secondary winding at the measurement frequency then the current in the secondary tracks the primary current and the transformer provides a current output that is proportional to the measured current . On the other hand, if that condition is not true, then the transformer is inductive and gives a differential output . The Rogowski coil uses this effect and requires an external integrator in order to provide a voltage output that is proportional to the measured current . </P> <P> Ultimately, depending on client requirements, there are two main standards to which current transformers are designed . IEC 61869 - 1 (in the past IEC 60044 - 1) & IEEE C57. 13 (ANSI), although the Canadian and Australian standards are also recognised . </P> <P> Current transformers are used for protection, measurement and control in high - voltage electrical substations and the electrical grid . Current transformers may be installed inside switchgear or in apparatus bushings, but very often free - standing outdoor current transformers are used . In a switchyard, live tank current transformers have a substantial part of their enclosure energized at the line voltage and must be mounted on insulators . Dead tank current transformers isolate the measured circuit from the enclosure . Live tank CTs are useful because the primary conductor is short, which gives better stability and a higher short - circuit current rating . The primary of the winding can be evenly distributed around the magnetic core, which gives better performance for overloads and transients . Since the major insulation of a live - tank current transformer is not exposed to the heat of the primary conductors, insulation life and thermal stability is improved . </P> <P> A high - voltage current transformer may contain several cores, each with a secondary winding, for different purposes (such as metering circuits, control, or protection). A neutral current transformer is used as earth fault protection to measure any fault current flowing through the neutral line from the wye neutral point of a transformer . </P>

What is the use of ct and pt