Medium voltage air insulated metal-clad switchgear internal arc-proof
BVK-A-12 / 17.5 / 24
- Introduction
- Standards
- Normal operating conditions
- Degrees of protection
- Electrical characteristics of the switchgear
- Safety of the switchgear
- Vacuum circuit breakers and contactors
- Internal arc resistance
Introduction
The BVK-A is a medium voltage metal-clad switchgear for indoor installation. Compartments in the units are separated by means of metal partitions, and parts under voltage are freestanding. The switchgear is modular and installed by composing standard units one to another in a coordinated manner. The switchgear is easy to configure and choice of apparatus and instruments is very wide.
The performance of the air isolated switchgear with withdrawn equipment allows user:
- high availability and reliability section,
- complete safety for the personnel of the section,
- minimal maintenance,
- inability to improper handling,
- quick and easy installation.
Standards
The switchgear and main apparatus contained therein shall be subject to the following standards:
- IEC 62271-1 for general application,
- IEC 62271-200 for the switchgears,
- IEC 62271-102 for the earthing switches,
- IEC 60071-2 for coordination of insulation,
- IEC 62271-100 for the circuit-breakers,
- IEC 60044-1 for the current transformers,
- IEC 60044-2 for the voltage transformers.
Normal operating conditions
The switchgear rated characteristics are guaranteed under the following ambient conditions:
- minimum ambient temperature: -5°C,
- maximum ambient temperature: +40°C,
- maximum relative humidity: 95%,
- maximum altitude: 1000 m,
- presence of normal, non-corrosive and unpolluted atmosphere.
The switchgear must also be installed in ambient with the following characteristics:
- inside masonry or prefabricated structures,
- suitable for containing electrical apparatus,
- closed and not accessible to the public,
- only utilisable by personnel in charge of the electrical installation.
Degrees of protection
Degrees of protection of the switchgear are in accordance with the Standard IEC62271-200. BVK-A switchgears are normally supplied with the following standard degrees of protection:
- IP40 external housing,
- IP20 inside the compartments.
Electrical characteristics of the switchgear
| Rated voltage | kV | 10 | 13.8 | 20 |
| Rated insulated voltage | kV | 12 | 17.5 | 24 |
| Rated power frequency withstand voltage 1 min. | kV | 28 | 38 | 50 |
| Rated lightnng impulse withstand voltage | kV | 75 | 95 | 125 |
| Rated frequency | Hz | 50/60 | 50/60 | 50 |
| Rated short-time withstand current 3s up to | kA | 31.5 | 31.5 | 25 |
| Peak withstand current up to | kA | 81.9 | 81.9 | 62.5 |
| Internal arc withstand current | kA [1s] | 31.5 | 31.5 | 25 |
| Rated busbars current up to | A | 3600* | 3600* | 2500 |
|
Rated branch current |
A | 630 1250 1600 2000 2500 3600* |
630 1250 1600 2000 2500 3600* |
630 1250 1600 2000 2500 |
The typical unit of BVK-A consists of up to a maximum of seven compartments segregated from each other by means of metal partitions (incoming/outgoing unit with measurements shown in the figure). There are two versions of the units by way of closing the door of the CB and feeder compartment – with bolts and central handle.
Safety of the switchgear
The BVK-A switchgear is equipped with all interlocks and supplies necessary for insuring a high degree of safety and reliability for personnel and the installation. The interlocks are performed with keys, padlocks or interlock magnets.
Standard safety interlocks (compulsory)
 |
Interlock | Condition | ||
| 1 | A | Racking in/out the apparatus | Apparatus closed | |
| B | Closing the apparatus | Undefined position of the truck | ||
| 2 | A | Racking in the apparatus | Apparatus connector disconnected | |
| B | Disconnecting the apparatus connector | Truck in service or undefined position | ||
| 3 | A | Closing the earthing switch | Truck in service or undefined position | |
| B | Racking in the apparatus | Earthing switch closed | ||
| 4 | A | Opening door of apparatus compartment | Apparatus in service or undefined position | |
| B | Racking in the apparatus | Opened door of apparatus compartment | ||
| 5 | A | Opening door of cable compartment | Earthing switch open | |
| B | Opening the earthing switch | Opened door of cable compartment |
Vacuum circuit breakers and contactors
|
The BVK-A switchgear is equipped with vacuum circuit-breakers that today occupy important place in all sectors of primary distribution. Vacuum circuitbreakers cover the entire scope of parameters of the switchgear and therefore the whole range of applications. The BVK-A switchgear is developed in cooperation with the ABB and one of the reasons for the cooperation were the vacuum circuit-breakers. Tens of years of experience gathered in the development and application of vacuum chambers are now reflected in the range of ABB's circuit-breakers, which are characterized by their exceptional electrical and mechanical characteristics, very long lifetime without the need for maintenance, compactness and using highly innovative construction techniques. The ABB develops and produces a complete range of vacuum chambers for use in circuit-breakers, contactors and in all medium voltage applications. |
|
Internal arc resistance
During development of modern medium voltage switchgear, in the foreground must be the safety of personnel and therefore the BVK-A is designed and tested to provide an internal arc caused by short-circuit current equalled to maximum amount of short withstand current. Tests show that the metal casing of the BVK-A switchgear is capable of protecting the personnel working in the vicinity of the switchgear in case of failure to grow in the internal arc.
The parameters of each specific switchgears must be very carefully designed in terms of exhausting hot gases and incandescent particles to ensure and retain the safety of the personnel. The BVK-A switchgear is equipped with complete series of solutions in order to satisfy all requests when the exhausting is possible inside the room, also when exhausting is not possible inside as the case with installations on ships. The BVK-A construction offers complete passive protection against the effects of a failure due to the inner arc during the period from 1s to current 25kA.
With metal-clad apparatus the probability of an internal arc occurring is very low because it is designed and constructed to prevent these faults and guarantees maximum personnel safety. In fact, it is able to resist the overpressures caused by the arc and is fitted with exhaust ducts to channel the gases generated and therefore prevent damage to the personnel and equipment.
Standard solution - excerpt on two sides
How is the figure shown above, it is necessary to satisfy the requirements of a minimum of 3m high room where the switchgear is built. Also it is advisable that the openings of the chimney of the switchgear are moved away a minimum of 850mm, and it is the best to excerpt outside the room, that is in the area out of danger for people and equipments. In this case, the openings must be properly protected to prevent any water, dust, animals or other foreign bodies from entering.
The extensions must consist of a duct made of metal material (able to resist a minimum pressure of 60 kPa) with a cross-section at least the same as the output cross-section of the extensions already applied to the switchgear, with bends with the widest possible radius and suitably supported.
