Overview

Metro power supply system (MPSS) mainly includes external power supply, main transformer substation, traction power supply system and LV transformation and distribution system. LV distribution system provides LV power for all M&E equipment required for metro operation (excluding traction loads). Generally, LV distribution system is composed of LV part of step-down substation and HVAC control in terms of function. The power supply of HVAC Control Room is from LV part of step-down substation. LV part of step-down substation mainly provides power for other equipment except ventilation and air-conditioning equipment in stations (including communication, signal, lighting, fire control, integrated monitoring, automatic fare collection (AFC) and escalator). LV part of HVAC control mainly provides power for ventilation and air-conditioning equipment (including various fans, air valve, cooling tower and chiller unit).

Electrical loads such as communication, signal and fire control belong to special critical primary load. In order to increase power supply reliability, primary load must be supplied by dual power supply and double circuit as per Clause 15.1.6 in GB 50157-2013 Code for Design of Metro.

Application Overview

In the practical application, dual-power automatic transfer switch (hereinafter referred to as ATS) is mainly arranged at relevant positions of environmental control system (ECS) primary load distribution cabinet, terminal power switch box, uninterruptible power system (UPS) and emergency power system (EPS) so as to ensure power supply continuity for critical equipment. PC-level ATS of SATS s g series and SATS s d series provided by Sfere can meet requirements of metro power distribution.

ATS Application of Environment Control Distribution Cabinet

Considering metro stations are characterized by centralized location, complicated control and high requirements for automatic system with many ventilation and air-conditioning equipment (about 40% of station power consumption), generally A-end and B-end HVAC Control Rooms are respectively arranged at both ends of stations adjacent to environmental control room so as to realize power supply for and control of ventilation and air-conditioning equipment.

The power supply of HVAC Control Room is from LV part of step-down substation. A-end HVAC Control Room, for example, provides power for primary loads by 2 dual-power switching devices after being connected with 4 circuits of power supply via different buses of step-down substation; and provides power for secondary and tertiary loads after being separately connected with power supply in step-down substation. In case 2 ATSs are adopted, primary loads can be grouped for load balance. Generally, the capacity of each set of ATS is controlled about 400 A.

Since ECS has such inductive loads as fan which has relatively high requirements of ATS, it is recommended that special PC-level ATS of SATS s g series should be adopted.

AC-33B (high inductive load and motor loads GB/T 14048.11-2016); it can protect three-phase motor and three-phase load by detecting phase sequences of 2 circuits of power supply so as to avoid load damages caused by inconsistent phase sequences of main and standby power supply; when the switch is faulty, watchdog relay can detect and give alarms so that staff can timely replace the switch to prevent possible accidents; since on-load operation can be conducted no matter of automatic, electric and manual operation, reliable transfer can be achieved in any cases; self-cleaning contact can avoid surface oxidation which easily occurs and then causes poor contact and heating in that one circuit of ATS is always exposed to air due to infrequent transfer; 0 position locking can be applied to nonfirefighting loads. During the maintenance and overhaul of such loads, this function will ensure the safety of maintainers; this product has modular design which can ensure power supply continuity without bypass devices by replacing control module or drive module with convenient removal under energized condition; mechanical and electrical double interlock ensures that power supply of two circuits cannot be connected simultaneously; delay, overvoltage / undervoltage and frequency can be detected and adjusted.

ATS Application of Power Switch Box

For primary loads such as escalators, fire-fighting pumps, main drainage pumps, flooding-proof doors and lighting in public area, two circuits of power supply are generally introduced near such loads respectively from two busbars of the substation, and power switch box is arranged at the ends of 2 circuits of power supply to achieve uninterruptible power supply. The adjacent primary loads can share one power switch box.

Considering such equipment have relatively small load current and part of equipment are inductive loads, it is recommended that special PC-level ATS of SATS s d series should be adopted.

AC-33B (high inductive load and motor loads GB/T 14048.11-2016); it can protect three-phase motor and three-phase load by detecting phase sequences of 2 circuits of power supply so as to avoid load damages caused by inconsistent phase sequences of main and standby power supply; when the switch is faulty, watchdog relay can detect and give alarms so that staff can timely replace the switch to prevent possible accidents; since on-load operation can be conducted no matter of automatic, electric and manual operation, reliable transfer can be achieved in any cases; self-cleaning contact can avoid surface oxidation which easily occurs and then causes poor contact and heating in that one circuit of ATS is always exposed to air due to infrequent transfer; 0 position locking can be applied to nonfirefighting loads. During the maintenance and overhaul of such loads, this function will ensure the safety of maintainers; integrated transfer switch (small current) has no other wiring except power detection line, which greatly reduce the possibility of wiring error and line faulty; mechanical and electrical double interlock ensures that power supply of two circuits cannot be connected simultaneously; delay, overvoltage/undervoltage and overfrequency / underfrequency can be detected and adjusted.

ATS Application of Uninterruptible Power System (UPS)

Currently, UPS (decentralized or centralized power supply) is basically arranged for such weak current system as communication, signal, ISCS, automatic fire alarm, environment and equipment monitoring, AFC, access control and automatic fire extinguishing in metro. For weak current system (most computer's loads), the power supply is generally from two busbars, transferred automatically at the end and then transmitted to UPS input end.

According to UPS loads and power supply modes, when ATC with rated current not more than 160 A is required for front end of UPS, special PC-level ATS of SATS s d series is recommended; when ATC with rated current more than 160 A is required for front end of UPS, special PC-level ATS of SATS s g series is recommended.

AC-33B (high inductive load); it can avoid load damages caused by inconsistent phase sequences of main and standby power supply by detecting phase sequences of 2 circuits of power supply; when the switch is faulty, watchdog relay can detect and give alarms so that staff can timely replace the switch to prevent possible accidents; since on-load operation can be conducted no matter of automatic, electric and manual operation, reliable transfer can be achieved in any cases; self-cleaning contact can avoid surface oxidation which easily occurs and then causes poor contact and heating in that one circuit of ATS is always exposed to air due to infrequent transfer; 0 position locking can be applied to nonfirefighting loads. During the maintenance and overhaul of such loads, this function will ensure the safety of maintainers; mechanical and electrical double interlock ensures that power supply of two circuits cannot be connected simultaneously; delay, overvoltage / undervoltage and overfrequency / underfrequency can be detected and adjusted.

ATS Application of Emergency Power System (EPS)

Generally, the EPS used in metro, with input of two-circuit three-phase power supply, AC output and hot spare operation, provides power for emergency lighting and excavation indicator in stations as well as lighting in underground areas, and the inverter is in hot standby status (no-load inversion).

According to EPS capacity, when ATC with rated current not more than 160 A is required, special PC-level ATS of SATS s d series is recommended; when ATC with rated current more than 160 A is required, special PC-level ATS of SATS s g series is recommended.

AC-33B (high inductive load and motor loads GB/T 14048.11-2016); it can protect three-phase motor and three-phase load by detecting phase sequences of 2 circuits of power supply so as to avoid load damages caused by inconsistent phase sequences of main and standby power supply; when the switch is faulty, watchdog relay can detect and give alarms so that staff can timely replace the switch to prevent possible accidents; since on-load operation can be conducted no matter of automatic, electric and manual operation, reliable transfer can be achieved in any cases; self-cleaning contact can avoid surface oxidation which easily occurs and then causes poor contact and heating in that one circuit of ATS is always exposed to air due to infrequent transfer; 0 position locking can be applied to nonfirefighting loads. During the maintenance and overhaul of such loads, this function will ensure the safety of maintainers; mechanical and electrical double interlock ensures that power supply of two circuits cannot be connected simultaneously; delay, overvoltage/undervoltage and overfrequency/underfrequency can be detected and adjusted.

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