Tree-trunk main wiring system diagram a

Circuit breakers should be installed at 6-10kV bus sections . However, when one of the following conditions applies, an isolating switch or load switch or isolating contact
group can be installed.
    1) Manual switching of power supply during an accident can meet the requirements;
    2) No load operation is required;
    3) There is no requirement for relay protection or automatic devices
    4) There are fewer outgoing circuits.
    Installation of power supply switches of transformers in substations: For example, if a tree trunk power supply is used, as shown in Figure 15-8, protected switching equipment should be installed
. For radial power supply, an isolation switch or load switch should be installed. When the transformer is adjacent to the high-voltage distribution room, the switch does not need to be installed.
    When the low-voltage bus tie circuit breaker adopts the self-turning method, it should meet the following requirements: it should be equipped with position selection switches with three states: "self-turning and self-resetting", "self-turning and resetting", and "self-turning and deactivating"
. The self-turning delay of the low-voltage bus tie circuit breaker is O~ls. When the low-voltage main circuit breaker opens due to fault, automatic closing of
the bus tie circuit breaker is not allowed. The main circuit breaker and the bus tie circuit breaker on the low-voltage side should be electrically interlocked and must not be operated in parallel to the grid.
  When the emergency power supply (such as a diesel generator set) is connected to the low-voltage power distribution system of the substation, an interlock should be set up between the emergency power supply and the external power supply, and it must not be operated in parallel with the grid.
Avoid confusion with foreign power billing. There must be some caution in wiring . Flexibility to ensure that some important loads can be supplied with power under non-accident conditions .