b'18 Partner News Spring 2024EnterpriseCurrent Transformers - getting to the coreJacques Beecher MIET, Electrical Engineer with Eta Projects, highlights the basic operating principles and emphasises the importance of correctly selecting current transformers in electrical systems.In standard domestic applications, the3. This periodic change of magnetic flux primary current, typically less than 100within the core induces a changing Amps, can be directly measured by thepotential difference (voltage) in the types of meters shown in Figures 1 and 2,secondary winding.known as whole current meters. However, in commercial or industrial settings where4. Providing that the secondary winding is higher currents are expected and energyclosed, an alternating current directly monitoring and/or protection is required,proportional to the primary current is Current Transformers (CTs) are used. produced.The purpose of a CT is to take a large5. By connecting an ammeter in the primary current and produce a secondarysecondary circuit, the secondary current current directly proportional to it. Thiscan be measured. Assuming the CT ratio current is much lower in value and canis known, it is possible to measure the therefore be more safely, easily, andprimary current indirectly through useaccurately measured. The fundamentalof the CT.principles of a current transformer areFigure 1: Analogue Domestic Meterillustrated in Figure 3 and operate as follows.It must be noted that it is extremely important that this secondary winding is 1.The primary alternating current flowsmaintained closed. In the event of an open through a conductor, generatingcircuit in the secondary winding under load, an electromagnetic field around itdangerously high voltages between the perpendicular to the currents direction.terminals is produced. For safety purposes, Due to nature of alternating current,it is advisable to install a CT shorting block this electromagnetic field continuouslywith CTs to prevent such situations from reverses direction. arising.2. The primary conductor passesCurrent Transformer types vary depending through the central core of the CT,on the application and required function. For which is constructed from a magneticexample, Solid core CTs are a permanently material. As the core is exposed toinstalled and are mostly used for metering the electromagnetic field, it becomesand protection in switchgear. Whereas Split-magnetized, generating a magnetic fluxcore or Clamp-on CTs are used in temporary within the core. applications for example in power qualityFigure 2: Digital Domestic Meter'