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Do you have the Power Receiving System which can meet your requirements?

Power supply system separates the power supplied from the main line, and it is required that the total power supply system can be operated safely without extending the trouble at the lower system to the upper system. This is called “Protective Coordination”. In case the secondary circuit was shut down by the breaker or earth leakage breaker due to the trouble of short-circuit or leakage, it is important to keep the influence safely to the minimum. In case there is a limit with the breaker on the power supply side in the former plant facility, it is required to reduce the influence of insulation and noise by installing a transformer in the lower system. However, when changing the existing equipment to the new one, the higher power consumption than that of the former one may be required because the higher productivity and machine function are expected with the new facility.

If the machine or equipment requires the bigger capacity, the diameter of the installation cables and the capacity of the circuit breaker supplying power should be made to the bigger ones from the time of wiring the main line. However, when the transformer is located in the secondary side circuit in the equipment design, it is necessary to select the breaker which has the bigger capacity than the rated current to protect the transformer.

In the age of energy saving, the power receiving breaker of the machine or equipment is required to have the rated current as close to the actual rated current as possible. It generates the magnetizing inrush current with transformer, and it depends on the transformer design. In case of the transformer having the capacity of several 10KVA, the magnetizing inrush current can be several times to ten times, and in case of the transformer with the smaller capacity of several VA, it will amount to 20 to 30 times.

Regarding the approval test for the standard, in case of CE-Marking, it is important to get the approval test by a Notified Body. In such case as pressure vessel, the inspection by a notified body is indispensable. However, in case of general industrial machine, the self-declaration for CE-Marking is acceptable. For the self-declaration, it is conditioned that the product is inspected by the authorized organization for the approval test and the standard is to be understood firmly with the product. This is the reason why there might be a considerable gap between Japan and Europe on the understanding of safety..

Magnetizing inrush current can be changed in the basic design of the transformer. However, generally speaking, in order to miniaturize the transformer size, it is possible to make the transformer core smaller by increasing the magnetic flux density in the core, and the smaller transformer size overall can be advantageous in the cost. However, on the contrary, it is to be noted that the magnetizing current is getting higher.

This can be indicated in the proportional relationship as follow;

(Magnetizing inrush current) higher ∶ lower = (Transformer cost) lower ∶ higher

Because the receiving power in the low voltage circuit has the lower voltage and the current value is getting higher, and it causes the higher construction cost to exchange the existing breaker with the new one. It is possible to specify the most appropriate power receiving system by considering the cost difference between the construction cost and the upgrading cost of the transformer to that for the lower magnetizing inrush current.

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