How to Select the Distribution Transformer for the Rural Power Grid Upgrading

HIMALAYAL - SHANGHAI - CHINA

There is a variety of power transformers, so it is not easy to select a suitable transformer for upgrading the rural power grid. How to select the distribution transformer for upgrading the power grid is briefly discussed.     

The distribution transformer is essential to upgrade the rural power grid, the loss of which accounts for about 55% of low-voltage loss of rural power grid. Here, we explore the selection of distribution transformer.  



1. Select the capacity of distribution transformer reasonably

The selection principle is comprehensive consideration of load property, available load value and development scale. Methods include optimal load coefficient method, comprehensive cost analysis method, optimal benefit method and the ration of main transformer capacity to distribution transformer etc. The standard for selecting the capacity is to meet the actual load maximum; if the room needs to made, it had better be less than 10%; a seasonal and exclusive distribution transformer shall be selected according to two times average load.  

Now, new low-loss transformers are being used to replace energy-consuming transformers in the distribution system, reducing the iron loss by 40% or so. The economic benefit is remarkable due to large quantities of distribution transformers and great load change. Hence, we believe that how to take full advantage of transformer capacity without doing damage to normal lifespan of transformer should form the main basis for selecting the capacity of distribution transformer.   

2. Select the number of distribution transformer reasonably  

Based on the rural power grid featured by users scattered all over the rural area, strong load density and intervals, a lot of electricity-supply methods can be employed, such as single-phase transformer, parent-child transformer and transformers in parallel. Substations or industrial and mining companies generally use the parent-child transformer, with the parent transformer set according to the maximum load while low load condition for child transformer. 

By doing so, the utilization of distribution transformer is greatly improved and no-load loss is reduced. In rural areas, some distribution transformers are in low-load operation for most of the time during one year except short-time peak load. Under that circumstances, the parent-child transformer or transformer in parallel can also be used for some special users. When the load changes significantly, the transformer with different capacities are put into use based on the principle of minimum electricity loss.   

3. Select a Reasonable Model of Transformer  

The S11 series of 10kV power transformer is a low-loss product produced in China. Its winding is wound by copper wire, with the body and insulation adopting new design and processes. It is the first choice for rural power grid upgrading. The documents issued by the official organization require that energy-consuming distribution transformers cannot be purchased, installed and used. The low-loss distribution transformer is recommended for new users.    

4. Select a Fine Operation Mode of Transformer 

The increase in load should be taken into account in upgrading the rural power grid. It is common practice to make a certain room, so the capacity of transformer tends to be larger. However, there is great difference between peak and valley, which requires us to make the most of rural power system features to avoid the over-load or light-load. The two transformers run in parallel at load peak while one transformer is on-load and the other stops running at low load. The operating transformer load is always at or close to optimal service area through adjusting the operation mode of transformer. In this way, the aim of reducing the active power loss of distribution transformer can be achieved and economic operation of the whole rural power grid is realized.  

5. Guarantee the Balance of Three Phase Load 

The rural distribution transformer runs in light-load and no-load manner for a long time during one year, resulting in great three-phase imbalance. The imbalance in three-phase load distribution will lead to imbalanced voltage and greatly increase the power loss. When three-phase load reaches the maximum imbalance, active power loss of transformer is three times active power loss with three-phase load balance. Hence, try to balance three-phase load and make adjustment in time if the imbalance exceeds the limit.   

6. Improve the Power Factor of Power Grid

In rural power grid, the low power factor of low-voltage electrical grid and great power loss have an impact on the operation of lines and transformers. As we all know, when the transformer outputs certain active power, the required capacity is inversely proportional to power factor. Therefore, the improvement of power factor means the reduction of required capacity. The importance of power factor improvement shall be recognized. Moreover, the power factor of the whole power grid is enhanced by means of installing reactive compensation devices in order to save the electricity and reduce the loss.