Switchgear assemblies types

Low voltage switchgear and controlgear assemblies. Type tested and partially type tested assemblies 8623 (Part-1) 1993 BS EN 60439 1/1994... 

The bus system of a switchgear assembly, its interconnecting links and wires are the protected type components, whereas an interrupter (breaker, switch or a fuse) may be a protecting or protected type, depending upon their application and location in the circuit. A contactor and an OCR are therefore protected devices in the same context, for they provide no short-time protection. A protecting device may become protected when it is also provided with a back-up protection. 

The fault ctirrents also develop electrodynamic foi ces, Fii, as in equation (28.4) due to the sub-transient d.c. component. These forces play an important role in the meehanical design of the interrupting device, the load-bearing and mounting structuies for the interrupter and the bus system, and the hardware used in a switchgear assembly. All such mechanical parts, supports and hardw-are should be adequate to withstand such forces when they arise, A procedure to arrive at the ideal size of the current-carrying components, mounting structure, type of supports and hardware cte, is discussed in detail in Example 28.12. 

In the cubicle construction of a switchgear assembly the busbar chamber is normally located at the top of the assembly and runs through the length of it. It is usually suitable for extension, through fish joints at either end, if required at a later date. For installations having top cable entry, the busbar chamber may also be located at the bottom of the assembly or the depth of the panel increased, with an additional shroud between the top busbar chamber and cable chamber. From these main busbars are tapped the vertical buses for each vertical panel. Manufacturers may adopt different practices for horizontal and vertical busbar arrangements to economize on their cost of production. We illustrate the most common types of busbar arrangements. 

Wet test While an indoor type switchgear assembly requires only a dry power frequency voltage withstand test, the outdoor type switchgear assembly also needs a wet test under wet conditions to check the external insulation. For the test procedure refer to lEC 60060-1. 

This will be carried out under similar parameters of room condition and the type of test voltage wave to those for a switchgear assembly (Section 14.3.5). The current in each phase should be within 2% of the specified test value (rated current). 

Figs 6.72 and 6.73). Sparking components (e.g. fuses, contactors, circuit breakers) inside or parts not complying with the temperature class of the assembly are individually protected by an independent type of protection (for the most part in a flameproof housing). More recently, attempts have been made to introduce pressurized switchgear assemblies onto the market (Fig. 6.19). In the USA, the classic solution has been a flameproof enclosure with the conduit technique, see Fig. 6.83. 

Depending upon their application, a switchgear or a controlgear assembly can be one of the following types ... 

In outdoor type switchgear or controlgear assemblies the normal practice is to provide a double door in the front to house the front panel and protect the door knobs, meters, lights, pushbuttons, reset knobs or other accessories mounted on the door and thus prevent water or dust leaking through joints, knockouts and fitments etc. It is also recommended to have a canopy on the top of the enclosure to protect the panel from direct rain. Figures 13.6 and 13.28 illustrate this type of construction. 

Below we discuss briefly the constructional requirements and general manufacturing practices for cubicle-type switchgear and controlgear assemblies, and the electrical and the mechanical design considerations to comply with the above design parameters and service conditions. 

Cubicle type switchgear can be constructed in many different arrangements depending upon a variety of requirements. For example the following aspects may be important for a particular plant, environmental protection, ease of access to internal parts, ease of terminating cables, fixed or withdrawable switching devices, maintainability and level of personnel skill, cost and economics, expected life duration of the product, fitness for its purpose. The switchgear industry is very competitive and so it is essential to clearly specify what is required in the form of assembly and its construction. Otherwise a false or unsatisfactory decision may be made mainly based on a cost comparison. 

Switchgears can serve as main secondary service equipment, as main primary service equipment, and as load center equipment when located near load concentrations. The assembly and its devices provide for the control and distribution of electricity to utilization or subdistribution equipment. Most switchgear manufactured since 1955 has been metal-enclosed, dead-front, free-standing type, with its circuit protective devices enclosed each in its own compartment. For certain types of load applications, the protective devices are group-mounted in separate cubicles instead of individual compartments. 

Checking throughout the assembled switchgear or motor control centre for completeness and conformity to approved drawings, including name/data plates, types and ratings of equipment with corresponding identification labels both inside and on the front panel... 

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