1. Introduction
The subway station is generally divided into two underground floors. The underground floor is called the station hall floor, and the second floor is called the station platform. Each floor is divided into a common area and equipment areas at both ends. The public area is the area where passengers buy tickets and rides, and the equipment area is various professional equipment rooms, such as BAS, FAS, AFC (automatic ticket inspection), communication, signal, pump room, gas fire extinguishing, lighting distribution room, Environmental control room, environmental control room, traction/step-down substation, battery room, screen door management room, station control room, etc. The second phase of the Shanghai Rail Transit Pearl Line has a total of 17 underground stations and a ground vehicle section. The total length of the line is 22 kilometers. It is connected with the middle section of the first phase of the Pearl Line to form a loop.
The power supply system of the second phase of the Pearl Line uses a 110/35/10kV three-level voltage supply mode with centralized power supply, consisting of a main substation, a traction power supply system, a power distribution system and a power SCADA system. Two 110/35/10kV main substations are installed throughout the line to supply power to the traction power supply system (35kV) and the power distribution system (10kV). Since the subway traction and the station power are mostly first-class loads, each main substation is provided with two independent power sources by the urban power grid.
The power distribution system consists of a 10/0.4kV step-down substation, a low-voltage distribution system and a lighting distribution system. There are two large-scale stations in the step-down substation, which are bounded by the center of the station. Each substation provides half of the station and one half of the adjacent half of the load. The smaller station is set up to provide the entire station and the load power in the adjacent half of the two sides.
  2. Subway step-down substation design
2.1 main wiring
The whole line of step-down substation is divided into several power supply zones. Each power supply zone is from the 35/10kV main transformer of the main substation, and two 10kV power supplies are introduced nearby. A network switch is provided in each power supply zone, and the switch is disconnected during normal operation to form a 10 kV open dual-loop network power supply.
The two power supplies of each step-down substation are respectively introduced by the main substation or the adjacent busbars of 10kV adjacent to the step-down substation, connected to the two busbars, and one outlet is provided for each busbar of the step-down substation. The power supply supplies power to the adjacent step-down substation. The 10kV side wiring of the step-down substation adopts a single busbar segmentation type to set the busbar circuit breaker.
Two 10/0.4kV power transformers are provided in the step-down substation, which are connected to different 10kV busbars. The capacity of the transformer capacity meets one of the first and second loads that can afford the long-term load when one exits. Figure 1 shows the main wiring of the step-down substation.


Figure 1 Main wiring of step-down substation


2.2 mode of operation
In normal operation, the two 10kV incoming power supplies supply power to the two busbars respectively, the busbar circuit breaker opens, and the two busbars run in sections. When a bus line incoming power supply loses power, the incoming circuit breaker opens and the bus-coupled circuit breaker automatically closes.
The low-voltage busbar is a single-busbar segmented operation mode. When one power supply fails, the bus-segment segmentation switch is self-injected, and the other power supply power supply supplies the primary and secondary load power.
2.3 control, relay protection and automatic device
(1) Control
The step-down substation 10kV circuit breaker adopts SCADA remote control, substation centralized control and local control; 0.4kV incoming line, bus-coupled circuit breaker and three-stage load main switch adopt SCADA remote control and local control; The escalator feeder switch has a shunt release, and the shunt button is connected in parallel with the normally open contact of the FAS system output relay to enable the FAS system to disconnect it in case of fire.
(2) Relay protection
Relay protection should meet the requirements of reliability, selectivity, sensitivity and quick action, and strive to simplify the protection configuration; the protection of all levels of the power supply system should consider the cooperation relationship.
The relay protection device of the 10kV system of the step-down substation adopts a microcomputer-based comprehensive protection measurement and control unit to realize functions such as protection, measurement, information collection and control, interlocking and linkage between switches, communication, etc., and access through a fiber-optic Ethernet interface. The integrated automation system is uploaded to the control center, and the protection function is independent and independent of the network. The specific protection configuration is as follows:
10kV in and out line - line differential protection, over current protection, zero sequence current protection, over voltage protection, low voltage protection
10kV bus couple - time-limited current quick-break protection, zero-sequence current protection
Power transformer - current quick-break protection, over-current protection, overload protection, zero-sequence current protection, temperature protection (transformer internal protection), over-voltage protection, low-voltage protection
0.4kV low-voltage incoming line cabinet, female joint cabinet and environmental control first, second and third stage load feeder cabinets are equipped with overload, short-circuit transient, short-circuit delay and grounding protection, and other low-voltage cabinets are equipped with overload, short-circuit transient and grounding protection.
(3) Automatic device
The 10kV, 0.4kV bus-coupled circuit breaker sets the automatic input device/function, and the self-injection function can be input/exit in the local/far location.
The electric bus-connected circuit breaker used for the AC is set to automatically input and the incoming line is set to the self-recovery function.
The two-way AC incoming line for DC power is set to automatically input.
2.4 Measurement and measurement
All measurements and measurements of the substation are displayed locally in the switchgear and the main data is sent to the control center via the substation integrated automation system. The specific settings are as follows:
10kV in/out line current, 10kV bus voltage, primary side current/active power/active power of power transformer, secondary side current of power transformer, 0.4kV bus voltage, 0.4kV feeder current, incoming line current of AC system and busbar Bus voltage of the system used for voltage and DC.
2.5 Power factor compensation Active energy, power transformer secondary side current, 0.4kV bus voltage, 0.4kV feeder current, AC system incoming line current and bus voltage, DC power system bus