Bus system

To operate the MPI or LPI equipment at stable and reprodncable inspection conditions modern units are equipped with a monitoring and control system called "Quality Assurance Package" (termed QAP). The QAP System is ba.sed on an industrial PC with a bus system and field sensors. It ensures that process parameters important for the reproducability of the MPI or LPI are controlled an held between defined limits by a central computer system. It can be adapted to any old system, as well as integrated into new systems. 

Table 13.1 Rated voltages and frequencies for metal enclosed bus systems also applicable for switchgear assemblies...

If two sections are joined together to have a common vertical bus system, say. Sections 3 and 4, then the rating of the common bus will be ... 

This is a simple calculation to determine the maximum symmetrical fault level of a system, to select the type of equipment, devices and bus system etc. But to decide on a realistic protective scheme, the asymmetrical value of the fault current must be estimated by including all the likely impedances of the circuit. 

Figure 13.18 Fault level of tap-offs of a bus system under cumulative influence of two power sources...

Table 13.12 Derating for higher altitudes for metal enclosed switchgear assemblies and bus systems...

The rating of cuiTcnt-carrying equipment (switchgear assemblies, such as for the main bus system), devices (breakers, switches and contactors) and components (connecting links and wiring etc.) is defined by two parameters ... 

The mechanical endurance of the current-carrying parts of all the equipment, bus system, deviees and components, used in a particular circuit as well as the load-bearing members and supports on which they are mounted. The electrical parts of a device (breakers and switches, etc.) are the responsibility of the component manufacturers. The manufacturer of the switchgear assembly is responsible for the busbar systems, metallic links and wires. 

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. 

If the short-time lating of the interrupting device is higher than the fatilt level of the system, which is the case with modern interrupting devices, the fault level of the system alone will prevail for the busbars, components and hardwaie. For example, for a system fault level of. SO kA. if the interrupter used is of 65 kA short-time rating, the bus system and all associated components w ill be designed for 50 kA onlv. 

Figure 13.29 A power distribution scheme illustrating the procedure to assign fault level to a device, component or a bus system...

We discuss in detail in Chapter 28, the procedure to design a bus system, including its mounting and supporting structure and hardware for a required fault level. 

A separate control wireway may also run through the same busbar chamber, with suitable segregation or shrouding between the main bus and the control bus. This arrangement can be seen in Figures 13.2 and 13.7. The control bus system may be required for one or more auxiliary supplies for the following auxiliary services. 

The switchgear assembly, its components and the bus system must be designed for the rated voltage and frequency. 

ANSI C-37/20C specifies this rating only for metal-clad switchgear assemblies and not for metal-enclosed bus systems,... 

The selection process of power cables is almost the same as that of a bus system discussed in Section 28.3. For simplicity we consider only the basic data for selection which would suffice the majority of applications. For accurate calculations a similar approach will be essential as for the bus systems (Chapter 28). For site conditions and laying arrangements which may influence the basic rating of a cable, corresponding derating factors have also been provided. The information covered here will be useful to users to meet their cable requirements, although the data may vary marginally for different manufacturers. For more data on cables, not covered here, reference may be made to the cable manufacturers. 

All electrical equipment are designed for a specific BIL, as indicated in Tables 11.6, 13.2, 14.1, and 32.1(A) for motors, switchgears and bus systems respectively, and Tables 13.2 and 13.3 for the main power system (line clearances and insulators). If the actual severity of a prospective surge, i.e. its amplitude and/or rise time or both, is expected to be higher than these levels (higher amplitude and lower rise time) the same must be damped to a safe level, with the use of surge arresters, surge capacitors or both as discussed later. 

The criteria to determine the safe protective level of an arrester are the BIL of the equipment, as shown in Table 11.6 for motors. Tables 13.2 or 14.1 for switchgears, Table 32.1(A) for bus systems, and Tables 13.2 and 13.3 for all other systems. Motors have a comparatively lower BIL, but they are not connected directly on an outdoor... 

For the theory of neutralization of the magnetic effect on the conductor in a non-magnetic shielding, refer to the continuous enclosures for isolated phase bus systems discussed in Section 31.2.2. As a result of non-magnetic shielding there will be no saturation of the iron core and the V-I characteristic of the reactor will remain almost linear. 

A three-phase fault somewhere in the bus system, without reactive compensation and ignoring the line impedance, can reach a level of... 

Carrying Power Through Metal-enclosed Bus Systems... 

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