35kV Substation Design

1. Construction Scale
It is recommended to install two main transformers. The capacity of a single main transformer is 5000kVA. 3150kVA, 8000kVA, and 10000kVA are optional. There are 2 to 4 outgoing circuits for the 35kV substation and 12 outgoing circuits for the 10kV substation. Capacitive reactive power compensation capacity is 20% to 30% of the main transformer capacity.

2. Primary Electrical Part
2.1 Main Electrical Wiring

The main electrical wiring method of substation should be determined according to the substation's status in the power grid, number of outlet circuits, equipment features, load characters, and other conditions.

For the 35kV substation, internal bridge or single - bus sectionalizing connection can be adopted. For the 10kV substation, it would be better to use single - bus sectionalizing connection.

2.2 Power Distribution Unit
The 35kV substation can be outfitted with the outdoor open-type AIS power distribution unit and it is appropriate to equip the 10kV substation with the indoor switch cabinet.

2.3 Short-Circuit Current Level
The short-circuit current level for both 35kV and 10kV substations is designed as 31.5kA. In practical engineering design, this value should be checked according to the actual conditions.

2.4 Selection of Main Electrical Equipment

35kV substation 10kV substation
Oil immersed transformer Dry type transformer
AIS Withdrawable switchgear

3. Secondary Electrical Part
Designed to be unattended, the 35kV substation adopts computer monitoring system to complete the real-time monitoring and control of all equipment in the substation. Data are collected and processed uniformly, and resources are shared. Electrical analog quantity is collected by AC sampling. The whole substation is equipped with a unified set of GPS time system.

Centralized arrangement is adopted for the secondary major equipment. The 10kV part adopts integrated protection and control device which is installed in the corresponding switch cabinet. A set of computer-controlled high-frequency switching AC power supply is adopted and a group of valve regulated lead acid battery is attached.

Domestic microprocessor-based protection devices are used. They are connected to the monitoring and control system through the communication ports. Necessary hardware access points are provided.

4. Drainage, Fire Protection, Heating and Ventilating
City tap water or deep well water is used in the substation. The separate drainage system is adopted and the portable fire extinguisher is used for the fire protection of main transformers.

Natural ventilation and mechanical ventilation are adopted. Air conditionings are set in the secondary electrical equipment room.

5. Environment Protection
The oil discharged from the main transformer or other equipment with oil in accidents is led to the dedicated oil pool. After oil-water separation, the water is discharged into the storm sewer.

Green measures should be taken according to the local conditions, so as to reduce routine maintenance and management workload and save investment.