4 Selection of the switching equipment

Calculation of continuous-current currents from the side of G1, G2 and G3:

We calculate the aperiodic component of the SC current:

,

where T_а = 0,16 s for generator with power 12 МW,

where for all modern switches.

Heat pulse of SC:

where t_off = (0,1+0,185) s for generator power 32 МW.

The conditions for selecting switching devices: high-voltage switches and disconnectors, as well as their catalog data are given in table 3.

Table 3 - Selection of switching e

Selection conditions	Calculation data	Reference data
		Switch VVU-35А-40/2000 U3	Disconnector RND-35/2000 U1
Udes ≥ Un	Udes = 35 кV	35кV ≥ 35 кV	35 кV ≥35 кV
Inom ≥ Imax	Inorm= А Imax= А	2000 А ≥1314,025 А	2000 А ≥1314,025 А
Ioff≥	=11,262 kА	40 кА≥ 11,262 кА	-
Id ≥ is	is = kА	102 кА ≥ 31,216 кА	80 кА ≥ 31,216 кА
I2ther·tther ≥ Bк	Bк = кА2 s	4800 кА2 с ≥ 67,728 кА2 с	3969 кА2 с ≥ 67,728 кА2 с

5 Drawing up a simplified schematic diagram of the chpp

Taking into account the peculiarities of the electric receivers, the power supply circuit, as well as the large number of connections to the busbars for the main switchgear of the CHP, a feasibility study may be provided for a circuit with two busbar systems, in which each element is connected through a fork of two busbar disconnectors, work on both one and the other bus system. The scheme is in working order: the generators are connected to the first busbar system, from which group reactors and communication transformers are fed. The working bus system is partitioned by a switch and a reactor, the purpose of which is the same as in a circuit with a single bus system. The second bus system is redundant, the voltage is normally not present. Both bus systems can be interconnected by bus couplers that are normally disconnected.

With a voltage of 35 kV, the line shutdown will be short, since the duration of repair of the switches is small. During this period, a reserve is used over the network to provide power to consumers. At voltages of 110 kV and higher, the duration of repair of switches, especially air, increases and it becomes unacceptable to disconnect the circuit for the entire repair time, therefore the circuit is only used for 35 kV switchgears.

The following busbar systems are selected for tires:

- 110 kV circuit with two working and bypass bus systems;

- 35 kV circuit with three working and bypass bus system;

- 10 kV circuit with two busbar systems.