Common sense of copper bar selection

Common sense of copper bar selection

1 Introduction

Busbars, also known as busbars or current-carrying buses, are a type of conductor that carries current. It is mainly used for collecting, distributing and transmitting electrical energy in switchgear and control equipment to connect primary equipment. According to the statistics of relevant data, most of the short-circuit accidents occur directly or indirectly at the busbar. Busbar failure is one of the most serious faults among electrical equipment failures. Therefore, the correct selection and application of the bus is extremely critical.

This article makes a preliminary analysis, calculation and summary of several aspects related to busbars in medium voltage 3.6kV-40.5kV switchgear and control equipment.

2 Types of busbars

In indoor switchgear and control equipment copper bending machine, the busbars are divided into rectangular, circular, D-type, U-shaped, etc. according to the cross-section. Among them, the rectangular busbars of the same cross-section have lower resistance and larger heat dissipation surface than the circular, D-type, U-type, etc. For reasons such as high current carrying capacity, rectangular busbars are most widely used in voltage levels of 40.5kV and below. Circular and D-type busbars have good skin effect and good anti-corona effect. They are also used, but the connection is more complicated. U-shaped bus is generally used in equipment with large current and high force effect requirements, such as generator outlet switchgear. 

Its rated current is large, generally reaching above 5000A, and its rated peak withstand current (IP) is large, generally above 50kA. According to the material, it can be divided into copper bus bar, aluminum bus bar, and iron bus bar. Among them, copper bus bar has the largest current-carrying capacity, good corrosion resistance and force effect, and is the most widely used. Aluminum busbars are also used in low current, non-coastal and non-petrochemical systems. The use of iron busbars is mainly for economic considerations, and is mainly used in PT connection lines. According to the natural state, it can be divided into hard bus and soft bus. The soft bus is mainly used in places where the connection is inconvenient and can absorb some force effects, such as inside the circuit breaker.

3 Current carrying capacity of bus

3.1 Definition of the current carrying capacity of the bus: The current carrying capacity of the bus refers to the effective value of the current that the bus can carry under the specified conditions.

Note: The main indicator of the specified conditions is temperature. For indoor switchgear and control equipment, the upper limit of the ambient temperature is 40°C and the lower limit is -25°C.