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Preformed Windings are a global leader in the supply of high-quality diamond coils into the hydro industry.  We are so confident in our quality that we give our customers up to 10 years of warranty on our QualCoil coils.

The lowest Partial Discharge in the industry

Our extensive experience passing thermal cycle and voltage endurance testing at independent test facilities in addition to our CAD design process and state of the art manufacturing facilities and processes result in HV coils with the lowest Partial Discharge (Pd) in the industry.  We have manufactured thousands of hydro coils for customers globally up to 18kV and 95MW.

Understanding customer needs

Supplying the largest OEM’s such as GE Renewables and Andritz Hydro as well as leading independent hydro repair facilities, see what our customers say:

GE Renewables: “Preformed Windings have supplied many sets of high voltage coils to GE Renewables over the years. The quality of product and service is exceptional, and they are a trusted partner in our supply chain. We enjoy collaborative and cutting-edge research and development with Preformed Windings, which positions both organisations as thought leaders in the hydro industry. Their products offer significant benefits such as very low partial discharge and a long service life” (Global Commodity Leader, GE Renewables).

Andritz Hydro: “Preformed coils have successfully passed a rigorous set of qualification testing for Andritz Hydro. These tests included thermal cycling and voltage endurance to IEEE standards. We have had success using their coils. ”(Principal engineer, Andritz Hydro).

Magnetech: “The QC process is very effective resulting in zero rejects during a recent 468 slot rewind. The communication, technical support and order updates are very beneficial and make doing business across time zones transparent.” (General Manager, Magnetech).

Case study

Increasing the capacity of a coil

The challenge:

The end user wants to increase the capacity of their hydro generator from 12,000 kVA to 17,600 kVA whilst improving the operational condition of the machine, reducing maintenance requirements and extending the life of the asset.

The solution:

Preformed Windings and the service provider Sidewinders LLC worked closely together to redesign the coil utilising our 53 years of experience, our state of the art CAD system and the latest insulation technologies to design a coil suitable for the increased demand of the machine. The machine is being replaced with a superior quality that will ensure the lowest Partial Discharge levels and is the reason we offer 10 year warranties on our “QualCoil Life” coils

Positive feedback

Sidewinders LLC :  “Sidewinders LLC has used Preformed Windings for many years, and they are our preferred winding provider. Preformed Windings supplies exceptionally high quality HV diamond coils for hydrogenerators, along with 24/7 technical support. Preformed Windings’ engineers listen to each client’s needs and study the specific requirements of each project to provide precisely tailored solutions. Preformed Windings uses their position as trusted thought leaders in the industry to not simply manufacture replacement coils, but to substantially improve coil designs. Preformed Windings’ process and focus on continuous improvement results in superior machine performance that will endure for many years to come.”(Glen Peterkin, President and Technical Director, Sidewinders LLC).

Working with Sidewinders LLC

“It is a pleasure to work with industry experts such as Sidewinders LLC who offer exceptional levels of quality with a focus on customer service. The culture of integrity and honesty they maintain with suppliers and customers has afforded Sidewinders a fantastic reputation as a trusted, high-quality and value-leading partner in the aftermarket hydro repair industry around the world.”


For more information please contact:

James Stevens – Global Sales and Marketing Director – +44 (0)7825 092563 –

Stuart Whitfield – Hydro Expert – +1 800 5331 798  / +44 (0)7500 868778 –

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