FAQ | Feb 28,2023
According to their purpose, current transformers can be roughly divided into two categories:
Current transformers for measurement (or measuring windings of current transformers) : provide current information of the power grid to measuring and metering devices within the normal working current range.
Current transformer for protection (or protection winding of current transformer) : in the state of power grid fault, to provide the relay protection device with power grid fault current information.
Classified by insulating medium
1. Dry type current transformer: It is made of ordinary insulating materials and treated by dipping paint as insulation.
2. Castable current transformer: current transformer moulded by epoxy resin or other resin mixed materials.
3, oil-immersed current transformer: by insulating paper and insulating oil as insulation, generally outdoor type.
4. Gas insulation current transformer: The main insulation is composed of gas.
Classified by installation mode
1. Penetrant current transformer: current transformer used to pass through the panel or wall.
2, pillar type current transformer: installed on the plane or pillar, as a primary circuit conductor pillar of the current transformer.
3. Bushing current transformer: It is a current transformer directly installed on the insulated bushing without primary conductor and primary insulation.
4: busbar type current transformer: no primary conductor but primary insulation, directly installed on the bus used in a current transformer.
Classification by principle
1. Electromagnetic current transformer: current transformer that realizes current conversion according to the principle of electromagnetic induction.
2. Electronic current transformer:
For example, (1) Optical current transformer refers to the use of optical devices as measured current sensors, optical devices are composed of optical glass, all optical fibers, etc.
(2) hollow coil current transformer. Also known as Rogowski coil current transformer. The hollow coil is usually made of enamelled wire evenly wound on the ring skeleton. The skeleton is made of non-ferromagnetic materials such as plastics and ceramics. The relative permeability of the skeleton is the same as that of the air, which is a significant feature of the hollow coil different from the current transformer with iron core.
(3) Core coil type low power current transformer (LPCT). It is a development of the traditional electromagnetic current transformer. Based on the design of high impedance resistance, the saturation characteristics are improved under very high primary current, the measurement range is expanded, and the power consumption is reduced. It can measure overcurrent and full offset short-circuit current with high accuracy without saturation. The measurement and protection can share a low-power current transformer with core coil, whose output is voltage signal.
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