In addition to measurement, the most important function of current transformers widely used in power systems is relay protection. Protection current transformers have different accuracy levels according to different protection designs and different relay action principles adopted by the power system. For example, the steady-state protection accuracy level (P level) reflects the steady-state short-circuit current, and the transient protection accuracy level (TP level) reflects the short-circuit transient current.
One of the performance indicators of protection current transformers is to ensure that the primary current multiples when the error does not exceed the specified value, which is called the accuracy limit coefficient. This is what we usually call the maximum primary current multiples that guarantee the composite error requirements. Generally, there are 5/10/15/20/30, etc. The accuracy level of the protective current transformer is rated by the maximum allowable composite error percentage specified for the accuracy level under the rated accuracy limit primary current, and the letter "P" is used to indicate protection. The general accuracy levels are 5P and 10P. In actual work, the accuracy limit coefficient of the protective current transformer is usually written after the accuracy level, for example: 5P20 means that the composite error of the transformer is 5% and the accuracy limit coefficient is 15.
The basic identification letter of the transient protection characteristic level is "TP". According to the different requirements for the error characteristics, a corresponding letter is added after TP to distinguish: TPS, TPX, TPY, TPZ, etc. There are different requirements for different protection levels, and the design and use are very different.
Since the core section of the protective current transformer is generally large, once the secondary circuit of the transformer is open, the secondary winding of the transformer will generate a very high open circuit voltage. The high voltage will endanger the safety of people and equipment; at the same time, the high saturation of the core will A large residual magnetism is generated in the iron core, which increases the error. If the circuit is open for a long time, the saturated iron core may also overheat and cause a greater accident. Therefore, when using a protective current transformer, the secondary output terminal of the transformer must be reliably connected to the load. When the load is not connected, the output terminal should be reliably short-circuited, and the short-circuited wire must have a sufficient cross-sectional area to avoid the large secondary current generated when the primary current is too large to fuse the wire, causing the secondary circuit to open and appear high voltage.
Low-voltage protective current transformers are relatively large in size and mass due to the need to ensure the necessary overload current. When installing and fixing, a reliable product fixing solution is required.

The protective transformer series includes rectangular protective current transformers suitable for copper busbar installation and circular protective power transformers suitable for cable installation. The accuracy levels are 5P and 10P; the accuracy limit coefficients are 5/10/15/20/30, etc. The rated load varies from 3VA to 50VA according to the secondary current and transformation ratio. It can be flexibly selected according to the input characteristics of the equipment.

Naming: 

Color code:
0: black; 3: red; 6: blue; 8: gray;
The shell color specified by the customer is coded and classified according to the main color of the color system;
Normal use and installation conditions:

*Working voltage: ≤660V.
*Ambient temperature: -20℃~＋55℃.
*Ambient humidity: Relative humidity is not more than 80%.
*Altitude: not more than 3000m.
*Atmospheric conditions: There is no serious pollution, corrosive and explosive media in the atmosphere.
*Working frequency: 50-60 Hz.
*Storage temperature: -30℃~＋85℃.
*Insulation and heat resistance: E grade.
*Installation conditions: Indoor.
*Environment without significant frequent vibration and impact.