What Is a Ring Circuit?

In order to improve the reliability of power supply, so that users can obtain power from two directions, the power supply network is usually connected in a ring shape. This type of power supply is referred to as ring power supply for short. Ring power supply refers to the power supply mode in which the power source and the load point are connected by a power line. The ring-shaped power supply can improve the reliability of power supply. When any section of the line in the ring fails, the faulty section is removed by the switch, which will not affect the power supply to the load point; it can reduce voltage loss and power loss, improve power quality and economics of power supply Sex. However, the relay protection and operation of ring power supply are more complicated.

Ring power supply is a power supply method in which the power supply, power lines, and users are closed into a ring.

This power supply mode can make the power supply between the power sources mutually reconciled. When any line segment in the ring fails, other lines can supply power, which can keep users' power consumption unaffected. This kind of power supply is usually used for important users to improve power supply reliability. Circular power supply is more economical than dual-loop radiant power supply. However, the relay protection device, electric energy metering, and dispatching operation of the ring-shaped power supply method are relatively complicated. And when the fault occurs, the power transmission path changes, so the voltage quality is poor. ^[1]

In large DC networks, the main advantage of a ring-shaped power supply network is to save cables, but its operation switching is more complicated and it is more difficult to find ground fault points. Due to the long path of the ring-shaped power supply network and the large voltage drop of the cable, it is mostly used in medium and small capacity power plants and substations. Its design principles are as follows:

(1) According to the layout and nature of various electrical equipment (such as 220, 110kV power distribution devices and main control rooms, factory power distribution devices, furnace control panels, etc.), various electrical loads (such as control signal power) , Closing network of circuit breakers, etc.), each of which constitutes an independent double-loop ring-shaped power supply network. Normally, it should run in open loop. When one branch circuit fails, it does not affect the normal operation of the entire network.

(2) Generally, two feedback lines are led from the DC main screen, which are respectively connected to the two ends of the power distribution device or other power supply network, and are connected to two of the bays or screens via a knife switch, and then the power supply network is connected in series And in the appropriate place, use the power engineering DC system design manual knife switch segmentation. When a certain ground or other fault occurs in an intermediate network, the fault segment can be broken down in order to quickly identify the fault point and eliminate the fault in time. At this time, it will not affect the normal operation of other power supply target networks.

If the power distribution devices are separated by many distances, the DC main screen can be used to connect three feedback lines, and a feedback line is introduced at the middle interval of the power distribution device to divide into two networks.

(3) The cross section of the power supply cable should be calculated and selected according to the distance from a feedback line to the furthest distance from an electrical equipment.

(4) Electric motors such as DC lubricating oil pumps for steam turbines and hydrogen-cooled DC sealed oil pumps can be powered by two DC feeders. The units are connected by knife switches to form a ring network. When the number of small indoor demagnetizing switches or branch switches for generators in the main factory building is small, they can also be connected according to the above power supply method. If there are a large number of units, the network can be independently formed and powered by a dual-circuit power supply.

(5) Other direct current electrical equipment, such as accident lighting, backup power for telecontrol communication devices, constant lighting in the main control room, and DC test power for electrical test rooms, are generally powered by a single loop. ^[2]

(1) Ring power supply has the following advantages:

1) Reliable power supply: It can better ensure uninterrupted power supply to users.

2) Economical operation: The wire can be used reasonably.

3) Flexible operation: it can run better in various situations.

(2) The loop power supply has the following disadvantages:

When a fault occurs near one end of the power supply, the power is completely supplied by the other end. Excessive voltage and power loss may also cause overload of the unfaulted line. Therefore, it must be fully considered when designing. ^[3]

In AC 10KV power distribution systems such as industrial and mining enterprises, residential quarters, ports and high-rise buildings, because of the small load capacity, the high-voltage circuits are usually controlled by load switches or vacuum contactors, and are equipped with high-voltage fuse protection. This system usually adopts a ring-shaped power supply, and the high-voltage switchgear used is generally called a ring network cabinet. In addition to the ring-shaped power supply to the power distribution station, its high-voltage bus must also pass through the current through the ring-shaped power supply network (that is, the current supplied to the adjacent power distribution station through the bus of the power distribution station). Choose according to the sum of the load network's load current and the ring network crossing current to ensure that the high-voltage bus is not under load during operation.