The retrofit in medium voltage systems is a main stream activity of PPMEO from the creation of the company. To date, our team has successfully completed many projects in this segment, earning the company’s place and establishment on the market as a reliable and preferred partner.
The medium voltage switchgear, as well as the apparatus in masonry classical cells are composed of different components, with specific service lifetime. Based on such criteria they can be divided into three groups:
1. Stationary components: metal cabinets and panels, current and voltage transformers, insulators, busbars and supporting elements, which generally age with a slower rate;
2. Moving components: commutating and switching apparatus. Circuit breakers (and disconnectors in masonry cells) are exposed to the effects of electrical arching and in their drives, mechanically stressed and normally working under tension details ware off with time.
Despite the physical aging, commutating apparatus are also rapidly aging morally. There are constantly new technologies under development and products with better and better characteristics become available. For example, regarding circuit breakers smaller dimensions and weight, increased mechanical resource, higher short circuit breaking current, lack of gas or oil leakage during commutation, minimal service necessity, higher reliability and safety in operation are part of ever improving general application capabilities. Such are the new generation of vacuum and SF6 breakers;
3. Secondary components are represented by relay protections, control systems, electrical monitoring and alarm signaling devices etc. These components age morally at a much more rapid rate than physically.
The modernization of classical masonry cells that PPMEO provides includes:
- Preparing a design project for refurbishment of the cell and bay.
Refurbishment of circuit breaker, refurbishment of disconnectors, refurbishment of instrument transformers, new support structures for C.B.s, I.T.s, S.A.s., refurbishment of supporting and transition insulators, refurbishment of surge arrestors and HV fuses, refurbishment of the front panel and cell’s doors, refurbishment of busbar system, cleaning and refreshment of busbar system and cell structure.
Preparation of a design project for refurbishment of the cell. Complete retrofit with exchange of equipment and materials for secondary wiring and respective devices: relay protection unit; wirings, auxiliary switching and signaling relays, position indicators, metering units, switches for control, fuses, interlocks, terminals etc; secondary cables, for current and voltage circuits, circuit breaker and interlocks for disconnectors; new single line diagram on the control panel door, with light position indicators for the respective apparatus (C.B., disconnectors); Delivery and installation of Energy meter implemented in bay control panel or in special dedicated cabinet.
Retrofit of medium voltage switchgear
PPMEO has the technical potential, the know-how and the experience to retrofit and to modernize various types of medium voltage switchgear, which are in service in Bulgaria.
The retrofit process includes:
Preparation of design project, refurbishment of circuit breaker’s truck, new support structure for the circuit breaker, instrument transformers etc.;
Delivery and exchange of minimum oil or air blown type of breaker with vacuum or SF6 one according to customer preferences (ABB, Siemens, Schneider or else), instrument transformers, surge arrestors etc.;
Manufacturing and exchange of the busbar system, new primary contact terminal clamps, refurbishment or manufacturing of new compartment doors or covers.
The constructional changes required for implementation of the new circuit breaker in the existing panel are executed directly onto the truck, which allows with the use of spare truck minimal outage time. The company sends a team on site for technical inspection and coordination of the job. The modernization is performed in factory conditions and guarantees full compliance with the local and international standards. Manufacturing of a new truck is also possible if required.
Secondary wiring includes:
Refurbishment of low voltage compartment, with delivery and exchange of secondary wiring for control, signaling, current and voltage circuits, new terminals MCBs, auxiliary relays etc.;
Delivery of new and exchange of existing relay protection of various producers such as ABB, Siemens, Schneider, Rocon etc., according to customer preferences; Connection of MV cables, with preparation of cable terminations. Testing, commissioning and putting in service of the new apparatus and devices.
PPMEO has developed a variety of technical solutions for various types of switchgear.
Power cube - cassettes for circuit breakers. Using pre manufactured power cube, the circuit breakers could easily be build in existing switchgear panels or masonry cells. The Power cubes’ main features are limited dimensions, weight, built in mechanical and electrical interlocks, earthing switch etc. They are factory tested, which guarantees functionality and parameters compliant with the international standards. Power cubes are being produced with various electrical ratings and can match toughest of requirements.
PPMEO performs a retrofit of the various types of switchgear panels that have many years of operation in Bulgaria, such as:
Russian types: K – 37, KRU2 – 10, K – XII, K – XIII, K – XXVI, K – XXVII, KP – 10/50, KE – 10
Bulgarian types: K3 – 02
Ex. East German types: CSIM
Polish types: RSW – 10/6
Advantages of switchgear retrofit:
- Increased reliability and safety during operation;
- Cost saving effect – the price of retrofit is significantly lower, compared to the investment for a new panel and also saves maintenance costs;
- Extending the service life of the panels with some 20-25 years;
- Easy upgrade of the equipment to a level for application of a new SCADA system.