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Maxwell's CONDIS® grading and coupling high voltage capacitors
November 30, 2009 - Maxwell is the world leader in high voltage capacitor technology due to first-in-class products' quality and reliability, excellent electrical & mechanical strength resulting in long lifetime and its ability to respond to individual customer requirements. Additional strengths are intensive R&D activities to maintain our market position as well as the leadership role in setting HV capacitor standards.
Application of CONDIS® grading and coupling high voltage capacitors
Maxwell's CONDIS® high voltage capacitors are mainly used as grading or coupling capacitors in circuit breakers of transmission and distribution network switchyards as well as generator breakers of power plants. High voltage capacitors may be used either for live tank breakers where the breakers are installed outdoor and thus the insulation is done by air (AIS), or for dead tank breakers and GIS circuit breakers where the capacitors are installed in the gas insulated breaking chamber.
Grading capacitors are used to distribute the voltage uniformly in the interrupting chambers of the circuit breaker. For voltages of 550kV and above typically 2 chamber breaker designs are used. The capacitors are installed in parallel to the breaking chambers. In addition to the voltage distribution function grading capacitors allow to reduce the voltage increase during the breaker opening. Furthermore, they also protect the breaker from a re-ignition during opening.
Coupling capacitors are used on dead tank breakers, generators or any other HV equipment to limit the over-voltage coming from a short distance fault on a low capacitive line. Estimates indicate that approximately 60% of the electric utility grid above 245kV employs circuit breaker rated at 40kA as interrupting short-circuit current, with most of the balance rated at 63 kA. Upgrading from 40 kA to 63 kA is accomplished by adding a single coupling capacitor, and provides increased protection for the circuits. Systems rated up to 80 kA have also been made available in the last few years for areas with very high power generation capability.
Features of CONDIS® grading and coupling high voltage capacitors
Maxwell offers coupling and grading capacitors for life and dead tank circuit breakers with porcelain and composite insulators as well as for GIS circuit breaker with glass fibre reinforced tubes. All insulators are in full compliance with the international standard IEC60815.
Porcelain insulators are standardized and equipped with alternating long-short sheds. Main advantage of porcelain insulators are Maxwell's experience gathered over the past few decades with such insulators, the high mechanical strength as well as the bio-degradable basic material used.
Composite insulators consist of fibre-reinforced epoxy cylindrical tubes with a Silicon rubber coating and integrated sheds. The electrical and mechanical properties of the composite insulators exceed those of porcelain and synthetic materials. The Silicon rubber coating maintain its excellent hydrophobic properties and hence resistance to creepage currents over decades of operation. They are ideally suited for use in polluted areas like cities. Key advantages of composite compared to porcelain type high voltage capacitors is their reduced weight resulting in an easier handling as well as their fail-safe behaviour in case of a catastrophic failure. Composite capacitors are explosion-proof.
Maxwell offers a full range of porcelain and composite capacitors for life tank and dead tank circuit breakers with nominal voltages from 9 up to 250kV and capacitances starting from 200pF. Several fixing methods are available for porcelain and composite type capacitors. The Maxwell's standard fixing solution allows a fixation independent of the flange diameter, interchangeability of old and new CONDIS capacitors and full compatibility between porcelain and composite insulator type high voltage capacitors. Flange diameters vary from 210, 230 and 255mm for porcelain type as well as 160 and 210mm for composite type capacitors.
GIS capacitors are dedicated to various types of gas insulated switchgears, and the design is therefore customer specific. Components for GIS circuit breakers need to withstand tough environments with extreme temperature variations, dust as well as pollution and need to fulfil the confined space requirements.
GIS capacitors with nominal voltages up to 500kV and capacitances above 200pF are available. Standard flange diameter are 100, 120, 140 and 174mm. Flanges, tubes and field distribution will not be changed going forward, allowing a backward compatibility with former technologies.
CONDIS® products are specifically known in the market for their low partial discharge and tan delta loss levels. Other key features are a mechanical strength of up to 40g regarding vibrations and mechanical shocks and cantilever strength from 5 to 25kNm for porcelain and composite type capacitors. With its superior electrical and mechanical characteristics CONDIS® capacitors meet the specifications of all circuit breaker manufacturers worldwide.
Based on its proprietary and automated manufacturing process and equipment Maxwell is able to offer the flexibility required to produce customized high voltage capacitors according to the customer's specification.
Range of life and dead tank as well as GIS type grading and coupling capacitors
CONDIS® technology
Maxwell applies CONDOR (CDOR), the company's latest technological development using aluminium foil capacitors with polypropylene-paper mixed dielectric, impregnated with synthetic oil. Within high voltage capacitors are over 100 flat windings connected in series. For optimal performance and longevity these elements must be identical, as any variations in one element will place added load on that element, and eventually cause it - and consequently the entire unit - to fail.
Maxwell is the only supplier of high-voltage components in the world to completely automate its winding and assembly process, and thus has the unique ability to manufacture the elements within each unit to be identical. Also as a result of this fully automated process, the company is the only manufacturer of high voltage capacitors to perform a quality check on each individual element as it is wound, in addition to testing the fully assembled final product.
Key element of Maxwell's proprietary CDOR technology is the automated stacking and series connection of the flat windings through welded connections between the individual windings. This allows the suppression of aluminium connections and manual soldering external to the windings, a design still used today as standard technology by competitors. Maxwell applies this cost intensive technology for the other product families called CDCT and CDHT.
In order to keep pace with the increasing market demand for high voltage capacitors and to ensure our market share of more than 60% Maxwell recently put in operation the 4th so-called BOBDOR line, a new fully automated winding and assembly line with in-line quality controls.
In addition to the additional winding and assembly line Maxwell invested heavily in new processes and manufacturing equipment for drying, tightness test and impregnation. All these investments combined result in a drastic reduction in throughput time.
Lower weight, shorter lead-time, higher quality and reliability, less variation of the electrical performance, high temperature stability, and small size of active parts resulting in lower capacitor cost as well as superior integration into the designs of the customer are among the guaranteed advantages of the CDOR technology.
In the late 1980's two major customers, Siemens and ABB, began using CONDIS® high voltage capacitors in their live and dead tank, as well as GIS circuit breaker systems. Siemens switched from another supplier as a result of quality issues, and ABB began using CONDIS® products exclusively when they closed their own high voltage capacitor unit in the late 1990's. Today, almost all OEM worldwide are buying Maxwell high voltage capacitors.
Quality and testing
A reputation for high quality is key to Maxwell's future. Therefore the company invests heavily in the constant improvement to its entire organization. The brand name CONDIS® has thus become a synonymous for highest quality for the major manufacturer of circuit breakers worldwide.
As part of our quality process, all CONDIS® capacitors are individually tested in routine testing for several electrical performance parameters such as capacitance, tan delta, partial discharges and voltage levels. The capacitance measurement ensures no winding element has a breakdown. The particle discharge measurement ensures the capacitor has no defect that potentially could destroy the capacitor later during operation. The different voltage tests eliminate the risk of failure during the first period of service. All tests are done according to IEC and ANSI standards.
Maxwell's type tests cover or exceed the most severe conditions taken from all available international and customer specific standards. This allows us to offer products that cover all customer specifications.
Author
Adrian Schneuwly, Sr. Dir. Business Development, Sales & Marketing
For More Information Contact
Sandra Baeriswyl
Marketing Manager
Maxwell Technologies SA
CH - 1728 Rossens
Switzerland
Phone: +41 26 411 8626
Fax: +41 26 411 8506
www.maxwell.com
sbaeriswyl@maxwell.com
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