The Virginia Electric and Power Co. yesterday paid a $31,900 fine imposed by the Nuclear Regulatory Commission for 30 violations discovered in an investigation of construction practices at the North Anna nuclear power plant.

Vepco called the fine "unnecessary, improper and unwarranted."

The investigation was begun in August after three unidentified individuals made charges of improper procedures, poor quality construction and other irregularities at the Nort Anna plant in Louisa County about 75 miles from Washington.

NRC spokesmen said the probe was divided into four phases and still is not complete. The fine was imposed on the basis of violations already found.

Vepco President T. Justin Moore Jr. said that although the company disagreed with the penalty it was not appealing because that action would not be in the "best interest" of Vepco and its customers.

Vepco now is in the position of having reveived the three largest fines ever imposed in civil actions by the NRC or its predecessor, the Atomic Energy Commission.

Vepco paid a $38,000 fine in 1973 for violations of government regulations. It has been told to pay a fine of $32,500 for making "material false statements" concerning the geologic fault beneath its North Anna plant, but has appealed that to the courts.

Most of the violations that caused the most recent, $31,900 fine involved pipe installation and improper welds, poor bolt supports and similar construction problems. However, the NRC staff report said it was more concerned about the "management weaknesses" that the violations revealed than the actual poor workmanship.

Ernst Volgenau, director of the NRC's Office of Inspection and Enforcement, said earlier he would not recommend that Vepco receive an operating license for North Anna until it demonstrated it had taken "corrective action" for its management problems as well as for the construction deficiencies.