Differentiation of Types of Current Transformers

Current transformers classified by purpose

According to their different purposes, current transformers can roughly be classified into two categories:

Measurement current transformers (or measurement windings of current transformers): These provide current information about the power grid to measurement and metering devices within the normal range of working current.

Protective current transformers (or protective windings of current transformers): These provide information about fault currents in the power grid to relay protection devices and other equipment during power grid failures.

Measurement current transformers are used to measure large alternating currents but need to be converted into more uniform currents for secondary instrument measurement purposes. Since the voltage on the line is relatively high, it would be dangerous to measure it directly. The CT (current transformer) plays the role of current conversion and electrical isolation. It is a sensor for measuring the electrical current information of the primary loop in the power system, measurement instruments, and relay protection secondary devices. The CT (current transformer) converts high current into low current in proportion. The primary side of the CT (current transformer) is connected to the primary system, and the secondary side is connected to measurement instruments, relay protection devices, etc.

Protective current transformers are classified into:

Overload current transformers,
Differential current transformers,
Ground protection current transformers (zero-sequence current transformers).

Protective current transformers are mainly used in conjunction with relay devices to provide signals for cutting off the fault circuit when faults such as short circuits and overloads occur in the line, in order to ensure the safety of the power supply system.

Current sensors classified by insulation medium:

Dry-type current transformers. These are insulated by immersion treatment with ordinary insulating materials and paint.
Potting current transformers. These are molded from epoxy resin or other resin mixtures.
Oil-immersed current transformers. These are insulated with insulating paper and insulating oil and are generally used for outdoor purposes.
Gas-insulated current transformers. These have a main insulation composed of gas.

Current sensors classified by installation method:

Pass-through current transformers. These are used to pass through screen plates or walls.

Pillar-type current transformers. These are installed on a surface or pillar and serve as both a first-circuit conductor pillar-type CT (current transformer) and an electrical conductor.

Busbar-type current transformers. These are a type of CT (current transformer) that is directly mounted on the insulating sleeve of the busbar without a primary conductor or primary insulation.

Current sensors classified by principles:

Electromagnetic current transformers: These current transformers realize current transformation according to the principle of electromagnetic induction.

Electronic current transformers.

Development direction:

Due to problems such as saturation, nonlinearity, and narrow frequency band, electronic-type current transformers are gradually becoming popular. Electronic-type current transformers generally have the advantages of magnetic saturation resistance, low power consumption, and wide frequency band.

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