Answer: The theory of foreign electrician apprentice's reality table refers to that foreign electrician leads the apprentice to conduct on-the-spot investigation and practical operation in practical work to verify and apply theoretical knowledge. As an important part of power system, overhead lines play a key role in practice.

Overhead line refers to a power transmission method used in the process of power transmission and distribution, and the power transmission line is suspended in the air through brackets (such as telephone poles). The purpose of describing the table theory with the apprentice is to combine the theoretical knowledge learned by the apprentice with the practical work, including the installation, maintenance and overhaul of overhead lines.

From a professional point of view, overhead lines have the following important functions:

1. transmission capacity: overhead lines can effectively transmit electricity from power plants to user terminals to meet people's demand for electricity. The reasonable design and construction of overhead lines can ensure the stable transmission and supply of electric energy.

2. Economy: Compared with buried lines, the construction and maintenance costs of overhead lines are relatively low. Overhead lines are convenient to hang and maintain, and easy to patrol and maintain. This makes overhead lines widely used in urban and rural power grid construction.

3. Reliability: Overhead lines have certain wind resistance, disaster resistance and external interference resistance, and can be used under different climatic and environmental conditions. At the same time, the decentralized arrangement of overhead lines can also improve the reliability of the system. Once a fault occurs, it can be repaired by maintaining or replacing the corresponding line.

Summary: The practical purpose of the theory of realistic table of foreign electrician apprentice is to combine the theoretical knowledge learned by apprentice with practical application, and verify and apply it in overhead line work. As a part of power system, overhead lines play an important role in transmission capacity, economy and reliability. Through in-depth understanding and practice of overhead lines, foreign electricians and apprentices can better master practical application skills and make contributions to the safe operation and sustainable development of power systems.