Current transformers are key devices used for measurement and protection in power systems. Their core function is to proportionally convert high current into low current, facilitating instrument monitoring or relay protection. Insert-type current transformers are widely used in shipbuilding, wind power generation, and other applications with high space and efficiency requirements due to their convenient installation and ability to operate without disconnecting the main circuit. This article uses the MBS AG ASK 21.3 model as an example to analyze its technical principles and applicable scenarios.
Technical Principles and Core Parameters
The working principle of a current transformer is based on the law of electromagnetic induction. When a high current flows through the primary winding, a proportional current is induced in the secondary winding, achieving current "reduction" and isolation. The ASK 21.3 model uses a split core design, a non-intrusive structure, and can be directly inserted into existing cables or busbars without disconnection.
This model has a rated current of 40A and a current ratio of 30:0.05, meaning that a 30A primary current corresponds to a 0.05A secondary output, with an accuracy class of 1 (error ≤ ±1%). Its threaded mounting and black box packaging balance mechanical stability and environmental adaptability.
Design Features and Applicable Scenarios
The split core structure of the ASK 21.3 is its core advantage. Traditional closed-core transformers require disconnecting the circuit for installation, while the split core can directly encase the conductor, significantly reducing downtime, making it particularly suitable for retrofitting existing equipment. The threaded mounting design further simplifies the fixing process, making it suitable for space-constrained ship hulls or wind turbine nacelles.
In shipbuilding, this model can be used to monitor the current of the main propulsion motor or power distribution system, ensuring equipment overload protection; in wind power generation, it can provide real-time feedback on the generator output current, assisting converter control. Its imported parts status and batch number management (e.g., batch 43245) meets the traceability requirements of industrial equipment.
Usage and Precautions
During installation, ensure the conductor completely passes through the core window to avoid measurement errors due to poor contact. The secondary side load impedance should be strictly controlled within the rated range (usually ≤5Ω), otherwise it will affect accuracy or even damage the equipment. Furthermore, the secondary side must never be open-circuited, otherwise high voltage will be generated, endangering safety. This model has a minimum packaging quantity of 1 unit, supporting single-item purchasing, suitable for small-scale applications or spare parts replacement. Its black encapsulation material is flame-retardant and can withstand a wide temperature range of -40℃ to 85℃, but prolonged exposure to highly corrosive gases or liquids should be avoided.
Technical Differences from Standard Models
Compared to traditional closed-core current transformers, the ASK 21.3's split-core design sacrifices some permeability (approximately 10%-15%), but gains significantly improved installation efficiency. Its 30:0.05 current ratio configuration is more suitable for low to medium current applications (such as 40A rated current), while high current applications require models with a higher ratio.
In terms of packaging, the boxed design provides dust and moisture protection compared to bare-packaged models (such as some industrial-grade products), but is slightly larger. Users need to weigh the advantages and disadvantages based on their actual installation space and protection requirements.