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Types of Current Transformer
Types of Current Transformer
A current transformer (CT) is a type of instrument transformer designed to produce an alternating current in its secondary winding proportional to the incoming primary current.current transformer 5a They are used in conjunction with standard ammeters to provide a safe way of monitoring electrical currents without breaking the circuit. There are a number of different types of current transformers, and each has its own advantages and disadvantages. Some are better suited for certain scenarios than others.
Unlike the voltage transformer we looked at previously, a CTs primary winding never has more than one or a few turns and is connected in series with the conductor it is attached to giving rise to it also being sometimes referred to as a series transformer.current transformer 5a The secondary current is rated at a standard 1A or 5A for ease of measurement. The primary winding can be constructed of a single flat turn, a coil of heavy duty wire wrapped around a core or as a Toroidal, Doughnut or Bar type.
These are designed to be mounted on the load conductor and insulated from the high operating voltage of the system to which they are attached.current transformer 5a The current flowing in the primary of the CT is sensed by a magnetic field around the conductor and transmitted to its secondary via the core. This produces a secondary current which is proportional to the current being carried in the primary and is used to measure or monitor a variety of conditions including overcurrent, undercurrent, peak and average current.
As an alternative to the above two main types, there are also handheld clamp meter CTs which are designed to wrap around the conductor that they are being used on and can be opened and closed without disconnecting it.current transformer 5a These are useful for measuring currents in situations where access to the cable is not possible, or a quick measurement reading can be required.
A bar-type CT with 1 turn on its primary and 160 turns on its secondary is typically used in combination with a 0-1 A or 0-5 A ammeter.current transformer 5a This combination provides a maximum secondary current that will cause a full scale deflection on the ammeter when the primary is at its rated current. This relationship is determined by the CTs ‘window’ or its internal ratio and may be modified slightly by passing the primary through its window more than once thereby changing its turns ratio. This is particularly useful when a primary current needs to be increased or decreased by a significant amount.
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