Introduction

Ring type power supply open loop operation can ensure the reliability of power supply; backup power is switching. Medium terminal power distribution scheme is kind of integrated substation whose volume is small, weight is light, cable is plug type connection after unified planning for cable, HV switches, CB and transformers of power distribution system in industrial area and civil buildings. It is fully insulated. After using it, 10kV medium voltage can be connected with load center so that power consumption of cable and operation cost is decreased and power distribution design of industry and civil buildings is simplified. After using substation integrated automatic system, the transferring ability for relay protection and backup power is increased so that the power supply reliability is enhanced and operation modes are flexible.

Characteristics

The advantages of this scheme are：no need power supply switching for ground lighting, EPS setting to stop gas power discharging light interrupting can be avoided when switching power; meet the requirements for match continuity and emergency lighting; save money; temporary diesel generator unit can be borrowed.  This scheme is common used in Europe and American large-scale stadium.

Solution I

This scheme is used for industries and civil buildings without important loads. If use one circuit of cable with more integrated substations like trunk type to supply power so that 10kV medium voltage will be connected with load center. Once there is accident on cable, the more closer to accident place, the larger power-off area will be. After the cable is maintained, the power can be recovered. If use two circuits of cable operated in parallel, the cost will be increased but power consumption will be decreased. Once there is accident on one cable, plug out the fault cable from integrated substation after power off, then recover the power. The power can be recovered during maintenance, therefore, the power interruption time is shortened.

This scheme is used for medium/small size of industries and civil buildings with important loads. The ring type unit consists of two circuits of cables to supply power. The operation modes are: bustie switch is NORMAL CLOSE, one circuit of power is in operation, another one is backup. Or bustie switch is NORNAL OPEN, two circuits of power are in operation at the same time. The power comes from 10kV busbars. According to relay protection and backup power switching, open loop operation or close loop operation is allowed. When one cable has accident, it will be isolated after the action of protection. The power interruption will not happen in close loop operation. The power can be recovered in short time through backup power switching during open loop operation.

This scheme is used for large/medium size of industries and civil buildings with important loads. According to the requirements of power supply department or user, open loop or close loop operation can be adopted to ensure reliability of power supply. Use integrated power supply scheme and integrated substation, the substation design can be simplified, construction schedule can be quickened and power consumption will be decreased.

With the development of substation relay protection technology, the technologies of power supply and power distribution devices and relay protection are improved too. After the appearance of integrated power supply schemes and integrated substations, the reliability of ring net unit power supply can be ensured. The length of cable can be shortened and the amount of switchgears can be decreased when using ring net unit power supply, which is important for power supply systems in cities and large/medium size companies.