Leppert Nutmeg

The challenge

Leppert-Nutmeg, Inc., of Connecticut, USA, provides electromechanical services and electric motor sales within New England and throughout the world. The company was contracted to carry out a rewind of a Westinghouse hydroelectric generator at FirstLight Power’s Stevenson Dam hydroelectric power station on Connecticut’s Housatonic River.

The 8333 kVA generator, which has been in service for over 100 years, operates for decades between rewinds, meaning every aspect of the rewind process must be highly controlled to maximise operational life.

The solution

The hydropower market has stringent requirements for the rewind of generators, covering materials, processes and testing. As such, Leppert Nutmeg required a coil manufacturing partner who could be relied upon to work within the given specifications to produce a set of coils that would meet the high standards of manufacturing and testing. With previous experience working with Houghton International, Leppert Nutmeg knew they would be capable of meeting these requirements.

The technical teams at Houghton International and Leppert Nutmeg worked in collaboration to produce a coil design that followed the specifications provided by the operator, whilst also modernising the design with updated materials and drawing on Houghton International’s extensive expertise to optimise the design. This included upgrading the coil insulation system from class B to class F for better dielectric strength and a longer service life.

Houghton International manufactured a full set of 288 (+ 2 spare) 6.6kV coils using their HiDRO coil design, specifically developed to meet the design specifications of hydro applications. Houghton International’s AutoCoil software was used to produce 3D coil designs and slot build drawings to clearly communicate the coil design and ensure accurate fit.

The coils were subject to extensive testing. Sample coils were tested for Voltage Endurance (VE) for 1200 hours, three times longer than required by the IEEE 1043 standard, which extrapolates to over 30 years in service. After VE testing, the coils passed further electrical testing, including Tan Delta and Partial Discharge tests, giving confidence in service life surpassing 30 years of operation.

All coils were subject to HiPot, Interturn and Tan Delta testing prior to dispatch and further testing recommendations were provided to the customer for testing during and after winding.

The coils were vacuum sealed and packaged inside a moisture-proof crate for transport to the USA and additional winding materials were supplied with the coils.