What is the European power distribution system and the US power distribution system?

What is the European power distribution system and the US power distribution system?

Transmission and distribution systems in Europe and North America are similar: facing central power stations, using a high-voltage transmission grid and a series of 3-5 voltage layers, including a customer service layer. Use a variety of special standard voltages and equipment types, such as 400kV and 345kV, or star-grounded and delta-grounded. European power systems typically operate at 50Hz, while US power systems operate at 60Hz. This difference, while important, is not fundamental. In general, the system structure of the two continents and the regions of the world that follow these two standards.

What is the European power distribution system and the US power distribution system?
Electric power distribution

The main difference between the US and European systems is in the distribution layer. Service voltages in Europe are mostly 240V (~416V phase-to-phase) and 120V in the US (208V phase-to-phase), this is a 2:1 ratio that creates a significant difference in design limits, resulting in different services and main feeders Floor. Typically, power at 2 times the voltage allows 2 times the distance to be transmitted, which means that power distributed at the service voltage can cover 4 times the ground area. So, for this reason alone, the service transformers in the European power system are about 4 times the size and 1/4 the number of service transformers in the US power system, again, this situation makes the three-phase service layer (0.416kV phase-to-phase) distribution The use of electrical wires becomes practical and economical. The US power system uses 208V phase-to-phase service circuits and wiring only when users require three-phase 208V power. In the case of equal losses and voltage drops, the distance of power transmission in a three-phase line is about 2 times that of a single-phase line, and multiplying the distance by 2 times becomes 4 times, and this ratio or the effectively covered ground area reaches 16 times. As a result, the European power system uses fewer and larger service transformers. In the European power system, the usual capacity of service transformers is 250~1500kV.A, while in the United States it is 15~100kV.A.

①The branch layer in the American system
The 120V voltage can deliver power to the user, but the distance is limited, and the limited distance and small service transformers require primary voltage branch lines in the US power system. Branch lines, stubs, or line segments are tapped from the main feeder and represent the terminal portion of the process where electrical energy travels from the substation to the customer in the US system. The spur lines are directly connected to the main trunk and operate at the same voltage rating. A series of branch lines tap off from the main feeder and travel through the community, each delivering power to dozens of homes.

Usually, spur lines are not branched, many spur lines are single-phase or two-phase, and all three-phase are only used for relatively large power demands or situations where three-phase service must be provided to some customers. Typically, single-phase and two-phase spurs are alternated, as shown below, the distribution planner tries to balance the load as much as possible with different phases of the main feeder.

Under normal circumstances, the branch line is a small single-phase branch line to transmit 10kV.A~2MV.A electric energy. When spur lines need to carry large amounts of power, planners will typically use all three phases, with relatively small wires for each, rather than single-phase and large wires. This method avoids serious load imbalance at the point where the branch line is connected to the main feeder. If the “large branch” power demand is distributed across all three phases, the flow, load and voltage will remain more stable.

Branch lines (wooden poles) can be overhead lines or underground cables. Unlike main feeders and transmission lines, single-phase branch lines are sometimes directly buried. In this case, the cable is placed in a plastic sheath (much like a vacuum cleaner hose), a trench is dug, the armored cable is laid in the trench and properly buried. In many cases, directly burying branch lines is no more expensive than underground cables.

② Tree system and ring system
Another difference between the US power system and the European power system is the layout of the primary distribution lines. In the United States, branching is usually used for wiring, commonly referred to as “dendrillic” or tree-like layouts. A circuit leaves a substation and is branched and re-branched, so a circuit as a whole has one origin and many destinations. There may be as many as 6 termination points, which can be connected to other circuit termination points through normally open switches for emergency backup and field switching. In contrast, Europe typically uses loop feeders, where a loop can be powered from two points (both ends) and operate as a closed loop or in connection with an open connection point. In practice, neither paradigm is absolute. The US power system occasionally uses loop feeders, and tree feeder layouts also exist in European power systems, at least in rural areas.

What is the European power distribution system and the US power distribution system?
Tree system and ring system

To a certain extent, the small number of larger service transformers in the European power system dictates this layout. To a certain extent, however, the way distribution lines are laid out in the US and European systems is just a matter of practice: it has been done in the past, and it works.

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