Building Electrical Engineering – The Difference Between High-Voltage Incoming and Outgoing Switchgear

10kV high-voltage switchgear includes: 10kV high-voltage outgoing switchgear, 10kV high-voltage incoming switchgear, 10kV high-voltage ring main unit, PT cabinet, and metering cabinet. The terms "incoming switchgear" and "outgoing switchgear" differ by only one character; their differences and functions are significant.

Incoming switchgear – This is the switchgear that receives power from an external source.

Generally, it receives 10kV power from the power grid. This 10kV power is then transmitted to the 10kV busbar through the switchgear; this switchgear is the incoming switchgear. In substations with voltage levels of 35-110kV and above, the incoming switchgear refers to the transformer's low-voltage (10kV) switchgear. That is, the first cabinet connecting the low-voltage output of the transformer to the initial terminal of the 10kV busbar is called the incoming switchgear, also known as the transformer's low-voltage incoming switchgear.

The incoming line switchgear is the main switchgear on the load side. This switchgear bears the current carried by the entire busbar. Because it connects the main transformer to the low-voltage side load output, its role is crucial. In terms of relay protection, when a fault occurs on the low-voltage side busbar or circuit breaker of the main transformer, the overcurrent protection on the low-voltage side of the transformer trips the incoming line switchgear to clear the fault. A fault on the low-voltage side busbar also relies on the backup protection on the low-voltage side of the main transformer to clear the incoming line switchgear. The transformer differential protection also clears the low-voltage side circuit breaker, i.e., the incoming line switchgear.

In a 110kV substation, the switch parameters for the low-voltage incoming line switchgear differ from those of other switchgear. Its rated current is 3150A～4000A, and its rated breaking current is 31.5～40kA. The parameters of the 10kV bus tie switchgear are the same as those of the incoming line switchgear.

Outgoing line switchgear—this is the switchgear that distributes electrical energy from the busbar.

Power is transmitted from the 10kV busbar to the power transformer via a switchgear; this switchgear is one of the 10kV outgoing switchgear units. An outgoing switchgear is installed on the low-voltage side of the transformer, transmitting power through this switchgear to the low-voltage busbar. Several other low-voltage switchgear units are then installed on the low-voltage side to distribute power to various points of use. These low-voltage switchgear units are all outgoing switchgear units.

If a low-voltage system is introduced from nearby, the low-voltage switchgear connected to the incoming line is also an incoming switchgear unit, only at a lower voltage. Switchgear units extending from the low-voltage busbar are also outgoing switchgear units. Therefore, incoming switchgear units can be high-voltage or low-voltage, and similarly, outgoing switchgear units can be high-voltage or low-voltage.