The transmission system is the link between the power plant and the load. In the power system network, transmission lines cover a large area. Studying and designing the transmission network is the most important task.
Overhead transmission lines have three constants resistance (R), inductance (L) and capacitance (C). These parameters are uniformly distributed over the entire length of the transmission line. The resistance and inductance form a series impedance. For single-phase lines, the capacitance exists between the conductors and also between the conductors and nature. For three-phase transmission lines, the capacitance forms a shunt path that runs the length of the transmission line. Therefore, the capacitance effect complicates the modeling and calculation of transmission lines.
Overhead transmission lines are divided into three types depending on how capacitance is considered.
When the line length reaches approximately 50 km, the line is considered a short transmission line. The line voltage is completely below 20 kV. The capacitance effects in short overhead lines are ignored. Because of the small length and the low voltage, the capacitive effect is minimal. Therefore, in short, in overhead transmission lines, the capacitive effect is negligible. Therefore, only resistance and inductance are considered when designing, modeling and studying the performance of short lines.
When the line length is between 50 and 150 km and the line voltage is between 20 and 100 kV, such overhead lines are considered medium transmission lines. In such lines, capacitive effects cannot be ignored. Therefore, the capacitive effect must be included when studying the performance of the line.
Depending on the distribution of capacitive effects, dielectric transmission lines are further divided into three parts; the end condenser method, the nominal T method and the nominal PI method.
End condenser method
In this method, the line capacitance is concentrated at the receiving or load end of the transmission line.
Nominal T method
In this method, it is assumed that the capacitance of the line is concentrated at the midpoint the line. Half of the resistance and inductance are concentrated on the sides.
Nominal PI method
In this method, the capacitance of each conductor is divided into two halves. One half is at the transmitting end and the other half is at the receiving end.
When the length of a transmission line exceeds 150 km, the line is considered a long transmission line. In this type of transmission line, the voltage exceeds 100 kV. For the modeling and design of long overhead transmission lines, the capacitive effects are considered to be uniformly distributed over the entire length of the line. A rigorous approach is used to solve the mathematical model of long transmission lines.
1. What is overhead line fitting?
Overhead line fittings are accessories used to support overhead wires and overhead systems in overhead construction and are available in different manufacturing standards to suit different environmental and voltage requirements.
2. What is the standard for hot-dip galvanizing testing?
There are several standards for testing hot-dip galvanizing of overhead line fittings, for example, Asian markets such as Malaysia and Indonesia, test hot-dip galvanizing according to ISO 1461. For South America, they test for hot-dip galvanizing according to ASTM 123.
3. Can I get a sample before I place an order?
Yes, of course. Confirming samples before mass production is a necessary step. If the type of overhead line fitting you need is in stock, the customer only needs to cover the courier cost and the sample is provided free of charge. If you need a new sample made from your drawing, you should charge for the sample.
4. If a new design is made, who will charge for it?
If you do not accept our current power connector types, the manufacturer will usually charge for the tooling. The manufacturer will make new tooling based on your design and the new tooling belongs to you. The manufacturer simply helps you take care of the tooling in our factory. If you have paid, the manufacturer can also refund your tooling costs if you order a certain quantity.
5. What is the delivery time for overhead line accessories?
If the overhead line parts you need are in stock, they will be shipped immediately after you pay for them. If the one you need is not in stock, it will take 20 days to make the 1*20 container and further confirm if you need to make a new tool for it.
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