FAQ -- Answers to Frequently Asked Questions

How is a transformer's rated capacity calculated?
Single-phase -- Capacity (VA) = Secondary voltage (V) x Secondary current (A)
Three-phase -- Capacity (VA) = Secondary voltage (V) x Secondary current (A) x 3
What is protection coordination for a transformer?
For safety, protective equipment must be installed on both the primary and secondary sides of a transformer. Select the primary-side equipment to protect against transformer inrush current and the secondary-side equipment to protect against electrical shorts.
What is transformer inrush current?
Depending on the phase when the power source is applied, the iron core may experience magnetic saturation, resulting in momentary flow of overcurrent. This is called "inrush current." It is normally a large current of up to around 15 to 30 times the rated primary current, and so care is required when selecting primary-side protective equipment.
Are any measures available to counter inrush current?
Because occurrence of inrush current is basically inevitable, we at Nunome Electric also offer inrush-reducing transformer products that suppress inrush current to about ten times the rated primary current.
What is electrostatic shielding?
Inserting a grounded shield plate between a transformer's primary and secondary coils makes intrusive noise caused by capacitance between these coils flow to ground, thereby blocking noise propagation. This is extremely effective in suppressing high-frequency signals such as noise.
What about grounding of the transformer?
For safety, this must be performed without fail. The required conditions in Japan and overseas differ according to the targeted standards.
What kinds of connections are available for three-phase transformers?
A wide variety are available, including, Scott connection, V-V connection, and V/reverse-V connection. You can select the appropriate connection type to match the usage load and conditions.
What is an auto-transformer?
An auto-transformer is a transformer that achieves compact size and light weight by sharing portions of the primary and secondary coils. This transformer also offers high efficiency and ?small? voltage regulation. One disadvantage is passing noise with no reduction because the primary and secondary sides are not insulated, and in some cases high voltage may be applied to the low-voltage side, which may cause accidents involving electrical shock or electrocution, or damage to the load equipment.
What are the features of noise-suppression transformers compared to noise filters?
Insulating the primary and secondary sides achieves large suppression of common-mode noise and low leak current.
Are transformers available for use overseas?
Basically, a transformer for use overseas must comply with the standards of the respective country of use. We offer product line-ups of UL-certified transformers for North America (the USA and Canada) and transformers certified by TUV as compliant with EN standards for Europe, which we believe can accommodate a considerably wide range of use.
Are UL-certified transformers available?
We at Nunome Electric offer a large number of product line-ups of transformers that have earned UL recognition. UL-recognized products are UL-certified at the component level, and you can use them to achieve compliance with the final standards.
What are CSA standards?
CSA standards are established by the Canadian Standards Association, Canada's national standards organization. However, almost all CSA standards are identical with UL standards, and we offer C-UL-certified products, which are certified by Underwriters' Laboratories as complying with CSA standards.
Are transformers available for Russia?
When exporting to Russia, products that comply with GOST R standards are required. We offer GOST R-certified product lines and invite you to tell us what specified you need.
Are JIS-compliant transformers available?
JIS standards are in the process of being modified for consistency with the standards of the International Electrotechnical Commission (IEC). Because of this, transformers that meet JIS standards can be considered equivalent if they are compliant with IEC standards.
Are transformers available for China?
Transformers are presently not covered by the standards of the China Compulsory Certification (CCC) program. If you are considering exports to China, we recommend using products that are compliant with IEC standards.
Are RoHS-compliant transformers available?
Our transformers can be made to comply with the EU's Restriction of Hazardous Substances Directive (RoHS). Please inform us of this requirement when you place your order.