CORROSION CONDITION APPRAISAL FOR UNDERGROUND BINDINGS OF AIR TRANSMISSION LINES SUPPORTS

                         

Микитинский М.С.

 кандидат технических наук

КОРРОЗИОННАЯ ОЦЕНКА СОСТОЯНИЯ ПОДЗЕМНЫХ КРЕПЛЕНИЙ ОПОР ВОЗДУШНЫХ ЛИНИЙ ЭЛЕКТРОПЕРЕДАЧИ

                                                                                                                               Аннотация

Автором проекта проведены аналитические расчёты, разработан прибор и предложен метод интерпретации глубины коррозионных повреждений узла крепления оттяжек опор высоковольтных линий. Образец прибора был испытан на линии напряжением 300 киловольт в одном из регионов России.                                                                                    

Ключевые слова: анкерный узел, коррозия, опора ЛЭП

Mikitinsky M.S.

Ph.D.

CORROSION CONDITION APPRAISAL FOR UNDERGROUND BINDINGS OF AIR TRANSMISSION LINES SUPPORTS

                                                                                                                                   Abstract 

Author of  the project  carried out analytical  calculations , instrument   elaborations and corrosion depth interpretation propositions of stretches binding bundle of  high voltage lines. The device example has been tested on voltage 330 kV line in one region of Russia.                                             

Keywords: anchor bundle, corrosion, electric line support

Introduction                                                                                                                         

The supports with stretches on high voltage line in all industrial countries there are. The underground stretches binding are represented an anchor junction of U–shape bolt with half- round loop, what to steel armature is boiled.

In spite of rate period for underground bindings, also support the whole, is established in 30 – 50 years, on some lines already after 20 years a certain “extractions” of  U–shape bolts are observe. The cause is underground corrosion of bolt and loop (together) on support stretch of 220–500 kV lines.

These  occurrences usual number of countries such Russia, Finland, USA.

Results of researches                                                                                                        

- The identification  the degree (depth) corrosion is possible by connecting of resistance instrument  to the  tails of U–shape  bolt above ground surface

- Electric resistance of U–shape  bolt (0.01 Ω) and resistance of contact (0.1 Ω) do not let determine the change of resistance caused by corrosion  if the DC was applied

- At the frequency 1.6 MHz electric current penetrates metal on depth 10 mm. This way it gets to the corrosion–injured of the bolt surface

- For this frequency of electric current the resistance of U–shape  bolt (length 5m, diameter 36mm) is equal to 1.5 Ω (the absence of corrosion); 4.5 Ω (the depth of corrosion 2.5mm); 2-3 Ω (the depth of corrosion  5mm)

- The real corrosion for U–shape bolts, taken from the ground, has confirmed the correct interpretation of the electrical impedance

Operations and facility 

- Probationer bolt is connected to the measuring instrument (points m-n) by short copper insolate conductors

- The regulator of the sensitivity is set to least possible value

- By rotation of variable condencer (C)  tried to get the minimal level of zero indicator

- By rotation of variable resistor (R) tried to get zero level of zero indicator

- The regulator of the sensitivity is set to next value

- Record last value on the variable resistor scale

- Calculate interpretation of electrical resistance of depth corrosion of the anchor bolt lower parts.

 Fig.1. The measurement block represents bridge–T         Fig.2. The external appearance (L, r are determined when m – n are shorted)                          of instrument example