An off-load tap changer (OLTC) or De-Energized Tap Changer (DETC) allows the output voltage to be adjusted by changing the taps in the transformer using a control device. As the name implies, these types of tap changers require that no load be connected to the transformer or that the transformer be completely de-energized before any switching maneuver.

ASP has been actively involved in the original development of industry reference standards, contributing to the evolution of best practices in tap changer technology. Our expertise and commitment to excellence have helped shape the benchmarks that define performance and reliability in this field.

Today, all our devices are fully compliant with IEC 60214-1, ensuring that our products meet the highest international standards for safety, efficiency, and durability.

In addition, ASP is ISO 9001:2015 certified, reflecting our dedication to continuous improvement, quality management, and customer satisfaction. This commitment to excellence reinforces our position as a trusted partner for power industry professionals worldwide.

We take pride in the French origin of our products, as demonstrated by the following:

• Our products are entirely designed and engineered in-house by our dedicated R&D team, ensuring innovation and technical excellence.

• The vast majority of our suppliers are based in France.

• We manufacture most of the key components of our tap changers ourselves in our sole factory in France, including moving and fixed contacts, shafts, moving and fixed bars, brackets, and pinions.

• All tap changers are fully assembled in our French facility.

We would be delighted to welcome you for a visit to our plant.

The tap changer you should select depends on various features such as:

• Maximum tension class
• Maximum intensity
• Number of positions required
• But also any other feature necessary for your device you think is relevant

You can use the technical forms to define your tap changer and contact us by email :  contact@appareils-precision.fr

Yes, if you are looking for an off-load tap-changer with features that are not presented in our online catalog, we can design and manufacture it for you.

Indeed, we can modify different parts of the devices presented, such as:

• Dimensions
• Distance between phases
• Number of positions, phases, and stages
• Localization of the control device: cover/wall/side wall of the transformer
• Silver plating for the moving and / or fixed contacts

We can help you if you need any explanation for handling the tap changer. For instance, if a change is required for your project or even an adjustment, our design team is ready to answer your questions

Indeed, we have numerous instructions, procedures, and guides we can email you. For years, we have been creating instructions in response to our customers’ requests. Now we have many resources we can provide you if needed.

Feel free to contact our team by email for instructions or advice regarding the products you have purchased. Please indicate the order confirmation number and the device number in question in your email.

If the transformer is to be used in extreme weather conditions, such as corrosive environments or low temperatures (down to -50°), here is information that could be helpful:

• The aluminum parts located outside the Transformer (steering wheel, handle, control unit…), can be provided with anodic oxidation and a primary coat of paint.
• The steel parts located outside the transformer are zinc-plated by default, nevertheless, they can be provided in stainless steel.
• The O-rings are, by default, in Nitrile or Viton (FPM), but they can also be provided in silicone for extreme temperatures

Our tap changers are compatible with following oils :

• Mineral oils
• Synthetic oils
• FR3 natural ester dielectric (we recommend to use a higher class voltage for the tap changer when using this oil)
• Natural ester oils
• Synthetic ester oils (Midel)

The temperature limits of our devices are determined by the materials used in their construction, including plastics, Bakelite paper, and seals. Based on the manufacturer’s recommendations, our equipment is designed to operate within a temperature range of -55°C to +110°C.

For optimal performance and durability, we advise adhering to these limits to prevent any material degradation or potential malfunction. If you have specific environmental constraints, feel free to contact us for guidance on the best solutions for your application.

Drying Process & Tightening Recommendations

Proper drying of our devices is a crucial step to ensure their optimal performance.

We recommend the following drying conditions : maximum temperature of 110°C for 8 to 12 hours.

TAP CHANGERS: HM, HZ, FII, FII-HI, HI, and HT

Following the drying process, we recommend tightening the screws and nuts that are directly connected to insulating material components (such as paper and phenolic resin laminates) according to the specifications below:

• Metal screws and nuts:

• M5 → Tightening torque: 5 N.m

• M6 → Tightening torque: 9 N.m

• Glass-fiber reinforced epoxy screws and nuts (Permaglas):

• M8 → Tightening torque: 5 N.m

• M10 → Tightening torque: 7 N.m

• M12 → Tightening torque: 9 N.m

 Note: Glass-fiber reinforced epoxy screws and nuts (Permaglas) are not glued in our workshops.

All our devices are compatible with the use of a padlock (not provided).

The allowable size varies depending on the device family and the type of operating control devices.

For distribution tap changer, the shackle of the padlock must have a diameter between 5 and 8 mm.

For medium and power tap changers, up to 9mm.

We recommend that the tap changer be operated several times on a full range of taps once a year to ensure that any deposits are removed from the contact area.

In case annual maintenance is not possible and the tap changer has not been used for many years, it is recommended to operate the tap changer approximately 20 times on a full range of positions before changing the tap.

Measuring the resistance of the phases before and after the self-cleaning maintenance operation described above would help check its efficiency.

Yes, on request, we are willing to provide you with 3D models of the tap changer.

Do not hesitate to ask us by email.

Indeed, if it is easier for you that we organize transportation with a French forwarder, we are willing to do so.

We are used to international trade since we have been exporting our products since 1961, therefore you can ask us if necessary.