Silicone rubber for large power plant generators

WACKER  presented a new electrically conductive silicone rubber at this year’s CWIEME coil winding, insulation and electrical manufacturing exhibition,  ELASTOSIL® N 9189, a product developed for sealing and bonding applications, prevents operational damage in generators. WACKER also highlighted ELASTOSIL® N 2076. The electrically insulating silicone rubber protects electric coils from harmful environmental influences. This year’s CWIEME took place in Berlin, Germany, from June 3 to 5.

ELASTOSIL® N 9189 is a non-sag compound that becomes free flowing under shear force. The product is formulated to be tin-free and falls into the category of so-called one component RTV-1 silicone rubber grades that cure at room temperature on exposure to atmospheric humidity. Only alcohol is released during curing. The cured rubber has a medium Shore hardness and can withstand temperatures of up to 230°C over a long period.

This rubber adheres to multiple materials commonly used in the electrical engineering sector and does not require specially pretreated surfaces. Another feature of the material is its electrical conductivity. The specific volume resistivity of the cured rubber is 10 ohm-centimeters. This means that ELASTOSIL® N 9189 conducts electrical currents better than seawater and just as well as a 10-percent saline solution. This allows electrical charges to be dissipated very well from the surface of other materials.

ELASTOSIL® N 9189 is predestined for use in generators found in large power plants. Their stator windings are usually composed of copper bars. These winding segments, known as Roebel bars (composite conductors), are installed in the slots of the stator laminations. Extremely high electrical field strengths occur at the slot ends during operation and can trigger corona discharges. If no field-control countermeasures are taken, the discharges can damage the primary insulation of the copper bars in the long term. Bonding the copper bars at the slot exits with ELASTOSIL® N 9189 optimizes the electrical field and potential distribution, thus protecting the stator from malfunctions.

The new product is tin-free and only releases alcohol during curing. It therefore offers significant processing advantages, particularly in terms of occupational health and safety. ELASTOSIL® N 9189 is superior to its predecessor ELASTOSIL® N 189 in terms of electrical conductivity and mechanical properties. Th latter will therefore be replaced by the new grade.

ELASTOSIL® N 2076 – self-leveling and flame-retardant

ELASTOSIL® N 2076 also belongs to the class of one-component RTV-1 silicones, which cure at room temperature. As with ELASTOSIL® N 9189, ELASTOSIL® N 2076 likewise only releases alcohol during curing.

Another special feature of ELASTOSIL® N 2076 are its self-leveling properties. The product that was developed as a coating material for electric coils can be applied by dipping. This is particularly advantageous when coating choke coils, transformer coils or end windings of relatively small drive motors. The cured silicone layer is resistant to weathering, UV and heat and is electrically insulating. It permanently protects the electric coils from moisture, dirt and deposits.

ELASTOSIL® N 2076 is formulated to be flame-retardant and meets the requirements of European standard EN 45545-2, which applies to fire safety in rail vehicles.