21-04-2012, 10:47 AM
GUIDE FOR SELECTION OF SWITCHYARD EQUIPMENT
3_3%2520selection%2520of%2520switchyard%2520equipment-Part-III.pdf (Size: 964.12 KB / Downloads: 177)
Substation Equipment
Outdoor step up substation at hydroelectric stations comprises of main equipment,
ancillary equipment and switchyard structures. Selection of power transformers and
circuit breakers is discussed in section 2 and 3. However special requirement for selection
of facility required for handling of transformers and supporting structures for circuit
breakers are discussed.
References and Codes
IS: 9921Part 1 to 5 – Alternating currents disconnectors (isolators) and earthing switches
rating, design, construction, tests etc.
IS: 2705 Part 1 to 4 – Current transformer
IS: 3156 Part 1 to 4 – voltage transformer
IS: 3070 part 1 to 3 – Lightning arrestors
IS: 2544 – Porcelain insulators for system above 1000 V
IS: 5350 – Part III – post insulator units for systems greater than 1000
IS: 5621 – Hollow Insulators for use in electrical equipment
IS: 5556 – Serrated lock washers – specification
IEC: 186 – Voltage transformer
1.2 Seismic Consideration
Forces caused by earthquake which may occur for the seismic intensity of the zone
concerned should be taken into account. Stresses resulting after including these loads
should not exceed permissible stresses.
Bus bars
The out door bus-bars are either of the rigid type or the strain type.
In the rigid type, pipes are used for bus-bars and also for making connections among the
various equipments wherever required. The bus-bars and the connections are supported
on pedestal insulators. This leads to a low level type of switchyard wherein equipment as
well as the bus-bars are spread out. Since the bus-bars are rigid. The clearances remain
constant. However as the bus-bars and connections are not very high from the ground, the
maintenance is easy. Due to large diameter of the pipes, the corona loss is also
substantially less. It is also claimed that this system is more reliable than the strain bus.
This type is however not suitable for earthquake prone area due to rigidity.
The strain type bus bars are an overhead system of wires strung between two supporting
structures and supported by strain type insulators. The stringing tension may be limited to
500-900 kg. depending upon the size of the conductor used. These type of busbras are
suitable for earthquake prone areas.