Single Phase Transformer VS Three Phase Distribution Transformer

Single Phase Transformer VS Three Phase Distribution Transformer

This paper starts with the structure and parameters of single phase distribution transformer and three phase distribution transformer, and compares the engineering cost, electrical energy loss, construction and occupied space, noise, voltage quality, power supply reliability, etc. According to the operation situation, the application sites of the two distribution transformers are summarized, and some suggestions for the selection of the power supply mode are put forward.

Pad-mounted Transformer

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Dry-type Transformer

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Pole Transformer

TypeCSP type Frequency: 50/60Hz; Rated Power: 5~167kva

Dry-type Transformer

Frequency: 50/60Hz Rated voltage:10kv, 20kv,30kv Rated Power: 400~2500kva

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At the same time, Daelim can also provide you with three-phase transformers: pad mounted transformer, dry type transformer and various types of Oil immersed transformers.

Table of Contents

At present, low-voltage power distribution generally adopts 220/380V three-phase four-wire system for power supply, and the neutral point is directly grounded. This low-voltage power distribution method using three phase distribution transformers has many disadvantages:

① The power supply radius is long and the line loss is large. According to incomplete statistics, the line loss rate of medium and low voltage distribution networks is generally around 6% to 10%, and even more than 15% in some areas;

② The power supply radius is long, the voltage drop is large, and the “low voltage” problem is serious, which affects the quality of electricity consumption of residents;

③three phase distribution transformers have large losses and noise, which cannot guarantee the green economic operation of distribution transformers.

In order to solve these problems, some countries have already used the single-phase power supply mode, which introduces 10kV lines into the load center, and supplies power according to the principles of small capacity, dense distribution, and short radius, which not only reduces line losses, but also improves power quality and power supply reliability.

Therefore, the proper promotion of single phase distribution transformers is very necessary.

In this paper, single-phase and three phase distribution transformers are studied from the aspects of principle and technical parameters. Through the investigation and actual operation experience of single phase distribution transformers, the suitable places for application of two distribution transformers are summarized, and the power supply The choice of mode raises several caveats.

Structure comparison of single-phase and three phase distribution transformers

Three phase transformer wiring method

three phase distribution transformers are common in daily production and life. Common wiring methods include Dyn11 and Yyn0, as shown in Figure 1. The single phase distribution transformer usually uses II0 wiring, and the low-voltage side is divided into two ways: three-tap and four-tap, as shown in Figure 2.

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Wiring method of single phase transformer

In Figure 2(a), a1 and a2 are the phase (fire) lines, x is the zero line, the low-voltage side winding is a single winding and the middle tap is grounded when in use, forming two windings, and the voltage ratio of the high and low voltage sides is 10kV/±0.22 kV. In Figure 2(b), a1 and a2 are phase (fire) wires, x1 and x2 are zero wires, the low-voltage side winding is a double winding, and there is no electrical connection between the two windings. The voltage ratios are all 10kV/0.22kV.

Comparison of loss parameters of single-phase and three phase distribution transformers

pad mounted transformer buzzing

In the case of using the same material, the single phase distribution transformer of the same capacity has smaller no-load and load losses than the three phase distribution transformer, so it can better meet the needs of energy saving and consumption reduction.

Taking the commonly used 100kVA and 50kVA distribution transformers as an example, the comparison of their losses is shown in Table 1 and Table 2.

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From the data in Table 1 and Table 2, it is not difficult to find that, taking the distribution of 50kVA capacity as an example, the total loss of the transformer is equal to the no-load loss plus the load loss, the total loss of the single phase distribution transformer is 895W, and the total loss of the three phase distribution transformer is 895W. The loss is 953W.

If calculated according to the annual operation of 8 000h, the electric energy saved by a single phase distribution transformer in one year is (953-895) × 8 000 = 464 (kWh).

Comparison of engineering cost and power loss of single-phase and three phase distribution transformers

800 kva three phase transformer from daelim

For a distribution network project with the same capacity installed, the total power loss of a single phase distribution transformer (total power loss = transformer loss + low-voltage line loss, transformer loss = transformer iron loss + transformer copper loss) is less, and the project cost is less high, but in the long run, single phase distribution transformers are more economical to operate.

Although the cost of single-phase transformation is relatively high, after several years of making up for lost electricity costs, from a long-term perspective, single-phase power supply is more economical.

Construction and space occupied comparison of single-phase and three phase distribution transformers

pole sinlge phase distribution transformer

Compared with the three phase distribution transformer, the single phase distribution transformer is smaller in size and can be installed on the original pole without additional poles, which is very convenient for on-site construction and transformation.

In addition, there are only two high-voltage incoming lines for single phase distribution transformers. Therefore, in some narrow areas of the line corridor, the size of the overhead line crossbar can be appropriately reduced on the premise of meeting the safety distance, which reduces the difficulty of construction and reduces the space occupied.

Construction and space occupied comparison of single-phase and three phase distribution transformers

pole transformer from daelim

Compared with the three phase distribution transformer, the single phase distribution transformer is smaller in size and can be installed on the original pole without additional poles, which is very convenient for on-site construction and transformation.

In addition, there are only two high-voltage incoming lines for single phase distribution transformers. Therefore, in some narrow areas of the line corridor, the size of the overhead line crossbar can be appropriately reduced on the premise of meeting the safety distance, which reduces the difficulty of construction and reduces the space occupied.

Construction and space occupied comparison of single-phase and three phase distribution transformers

three phase dry type distribution transformer

Compared with the three phase distribution transformer, the single phase distribution transformer is smaller in size and can be installed on the original pole without additional poles, which is very convenient for on-site construction and transformation.

In addition, there are only two high-voltage incoming lines for single phase distribution transformers. Therefore, in some narrow areas of the line corridor, the size of the overhead line crossbar can be appropriately reduced on the premise of meeting the safety distance, which reduces the difficulty of construction and reduces the space occupied.

Noise comparison of single-phase and three phase distribution transformers

three phase pad mounted transformer from daelim

Experiments and practices show that, compared with ordinary three phase distribution transformers, the noise of single phase distribution transformers is significantly reduced, and the distribution transformers with seamless wound iron core structure are particularly prominent in noise reduction.

Voltage quality comparison of single-phase and three phase distribution transformers

Because single phase distribution transformers use medium-voltage lines to directly “enter the home”, compared with three phase distribution transformers, the power supply radius is greatly reduced, the voltage drop is reduced, and the voltage quality is significantly improved.

Comparison of power supply reliability of single-phase and three phase distribution transformers

Single Phase Pad Mounted Distribution Transformer (2)

The single phase distribution transformer is adopted, and the number of users per transformer is reduced, which can effectively improve the reliability of power supply;

At the same time, single phase distribution transformers are easier to install and exchange than three phase distribution transformers, and the accident handling time can be greatly shortened;

In addition, the high and low voltage three-phase coils of three phase distribution transformers are assembled together. Any problem with one phase coil will cause the entire transformer to be paralyzed, resulting in power outages in the entire station area, while single phase distribution transformers will not have such problems. .

How to choose a distribution transformer?

Three-phase pole-mounted transformers

Through the above comparison, and according to the actual application of single phase distribution transformers and three phase distribution transformers, the application places of the two are summarized as follows:

1) In areas where single-phase loads are concentrated, such as residential areas, single phase distribution transformers can be preferred.

At present, the electricity consumption type of urban residential quarters is basically lighting electricity or single-phase power electricity (such as air conditioners, refrigerators and other household appliances), and has the condition of “high voltage to the home”.

According to the residential design and load distribution, the power supply mode of one single phase distribution transformer in one building or one single phase distribution transformer in one unit can be adopted to shorten the power supply radius of the low-voltage network as much as possible, and control it not to exceed 100m.

2) The rural line is different from the city, there are no concentrated residential quarters and residential buildings, and the electricity consumption is small, and it is in the area without three-phase load.

Generally, it is completely possible for natural villages to configure a small-capacity single phase distribution transformer with relatively concentrated residents, and with the further growth of rural electricity load, its economic benefits will also be rewarded by reducing line losses.

However, there are many three-phase electrical equipment such as water pumping and threshing in rural areas, and some small-capacity three phase distribution transformers must be installed.

Therefore, in rural areas, the application of single phase distribution transformers must be carried out together with three phase distribution transformers according to the actual local electricity consumption, and reasonably planned based on the principles of “small capacity, dense distribution, and short radius”.

3) single phase distribution transformers can be used in residential areas and markets with serious electricity theft. The high-voltage power supply is “to the home”, which can not only prevent the phenomenon of electricity theft caused by the random pulling of low-voltage wires, but also facilitate the assessment of line losses in the sub-line and sub-station areas.

4) Encourage small industrial users to switch from using electricity under the original comprehensive transformer to using electricity from special transformers. With the popularization and application of single phase distribution transformers, some two-phase small industrial users or commercial users can install dedicated single phase distribution transformers.

Under the guidance of electricity consumption policy and electricity price policy, it will become more and more common for industrial users to install special transformers.

In this way, it is possible to separate residential lighting power and small industrial three-phase power power, and appropriately replace three phase distribution transformers with single phase distribution transformers to reduce the loss of public low-voltage lines and comprehensive transformers.

At the same time, the load of the comprehensive transformer can be balanced, and the user’s voltage can be more stable.

What should be paid attention to when choosing a distribution transformer?

pole mounted transformer product tests

When choosing a power supply method, make a good plan and budget, and do not be blind. The following points should be noted:

1) The single-phase power supply method is the same as the three-phase four-wire system, which is a more reasonable power supply method. In the transformation of the distribution network, measures should be taken according to the actual situation and local conditions, and it should not be “one size fits all”.

2) A long-term plan must be considered in the circuit design. The low-voltage distribution network must be built once, and the transformer capacity must be selected reasonably, and the load rate must be increased to recover the investment as soon as possible.

The main advantage of single phase distribution transformer power supply is for single-phase load, so it is necessary to investigate and analyze the load composition and its geographical environment, try to separate the single-phase load from the three-phase power load and make the transformer as close to the load point as possible.

3) When implementing the single-phase power supply mode, the power supply mode of “small capacity, densely distributed points, short radius, and high load rate” should be preferred. Only in this way can the loss reduction benefit of the single-phase power supply mode be brought into play.

For residential areas with simple single-phase loads, the suspended single phase distribution transformers are used for decentralized power supply, which has the characteristics of simple wiring, convenient maintenance, high voltage quality, low low-voltage line loss, and small interaction between users.

4) No matter what method is used to supply power, try to keep the three-phase load balance. If the unbalance of the three-phase load is too large, the unbalance of the three-phase current will increase, which will not only affect the voltage quality, but also increase the line loss of the 10kV distribution network.

Conclusion

With the continuous deepening of the power reform, the competition for power supply in the distribution network will become increasingly fierce. It is an inevitable requirement to improve the power quality of users, reduce the power loss of enterprises, and realize the optimal power supply mode.

Each power supply company can adopt single-phase or three phase distribution transformer power supply mode according to local conditions according to the load density and distribution characteristics of the distribution network in its jurisdiction to achieve optimal power supply.

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