Busbar parts that do not require busbar thermal and electrodynamic effects verification

Busbar parts that do not require busbar thermal and electrodynamic effects verification

 

(1) Adopt fuse protection and connect to the bus bar under the fuse (except current-limiting fuse) copper busbar cut punch bend machine.

(2) Busbar in voltage transformer circuit.

(3) The transformer capacity is 1250KVA and below, and the voltage is 12KV and below, so as not to damage the busbar due to failure. It is mainly used for busbars in non-important electricity consumption places.

(4) Parts that are not exposed to thermal effects and electrodynamic effects, such as the connection wires and sealing wires of surge arresters.

5 Bus selection

5.1 Selection of main bus

The general principle of main busbar selection is to meet the rated current requirements of the main incoming circuit breaker. After selecting the main busbar according to the rated current, check the thermal and electrodynamic effects according to the previous calculation.

5.2 Selection of the next busbar

The selection principle of the next busbar is to determine the current carrying capacity of the busbar according to the rated current of the switchgear and control equipment, and at the same time check whether it meets the requirements of the system's rated short-time withstand current and rated peak withstand current. The rated current of the switchgear and control equipment is the lowest rated current of all the primary equipment in the equipment, usually the rated current of the current transformer.

5.3 A few points to note

(1) According to the provisions of GB3906-1991, the minimum current-carrying capacity of busbars in switchgear and control equipment should have a margin of 10% relative to the rated current.

(2) Under normal circumstances, considering the heat dissipation and increasing the load capacity for the future, the main bus bar in the design drawing is generally larger. At this time, it should be manufactured in strict accordance with the drawing, and the bus bar specifications cannot be reduced at will.

(3) Choose a model with a larger bus width for the same cross-sectional area as much as possible. If you can choose TMY80×6 but not TMY60×8, it is mainly conducive to heat dissipation.

(4) When the operating environment temperature of the switchgear and control equipment is slightly higher than the specified temperature, it is necessary to fully consider whether the current carrying capacity of the bus is sufficient.

GB311.1-1997 "Insulation Coordination of High Voltage Transmission and Transformation Equipment" stipulates:

When the temperature is higher than 40℃, the rated insulation voltage should be multiplied by the temperature correction coefficient Kt=1+0.0033(T-40);

General: Each increase in ambient temperature by 3°C increases the test voltage by 3%. When the ambient temperature increases by 1°C, the rated current should be reduced by 1.8%.

The minimum span when the commonly used rectangular busbars are arranged relative to the thickness direction of the busbars

The minimum span when the commonly used rectangular busbars are arranged relative to the thickness direction of the busbars

 

  For example: for a 31 copper busbar bending machine.5kA system, ich takes 80kA, such as for KYN28-12 switchgear a=27.5cm, for TMY100×10 and LMY100×10

Then: L copper MAX≤755 (mm).

L aluminum MAX≤530 (mm).

It can be seen from the calculation that for the 31.5KA system, if the relative arrangement of the 100×10 bus width direction is adopted, if other factors are ignored in the theoretical calculation, the bus support must be controlled within 755mm (530mm), which is 800mm for the cabinet width Switchgear is unrealistic in terms of application. Therefore, this method is generally seldom used in 12KV and 40.5KV switchgear and control equipment, but in low-voltage equipment for structural considerations and to reduce occupied space, it is often used in the side entry line and tie line.

According to the above formula, for several common data, such as the distance between the busbars 210mm, 275mm (12KV voltage grade products) 350mm, 400mm, 460mm (40.5KV voltage grade products), the table is summarized as follows:

The minimum span (mm) when commonly used rectangular busbars are arranged relative to the thickness direction of the busbars:

Short circuit capacity kA/4s 31.5 40

Distance (mm) 210 250 275 350 460 210 250 275 350 460

TMY

100×10 Theoretical value 2100 2280 2400 2700 3100 1680 1830 1900 2160 2475

Recommended value 1800 1800 1800 2200 2200 1400 1400 1400 1800 1800

TMY

80×10 theoretical value 1680 1830 1900 2160 2475 1340 1460 1530 1725 1980

Recommended value 1400 1400 1600 1800 1800 1200 1200 1200 1400 1400

TMY

80×8 theoretical value 1500 1630 1710 1930 2210 1195 1300 1370 1540 1770

Recommended value 1200 1200 1400 1400 1800 1000 1000 1000 1200 1400

TMY

60×6 theoretical value 970 1060 1110 1255 1440

Recommended value 800 800 800 1000 1000

LMY

100×10 theoretical value 1475 1610 1690 1900 2185 1180 1290 1350 1525 1750

Recommended value 1200 1200 1200 1400 1600 1000 1000 1000 1200 1400

LMY

80×10 theoretical value 1180 1290 1350 1525 1750 945 1030 1080 1215 1395

Recommended value 1000 1000 1000 1200 1400 800 800 800 1000 1000

LMY

80×8 theoretical value 1050 1150 1205 1360 1560 845 925 970 1100 1250

Recommended value 800 800 1000 1000 1200 800 800 800 800 1000

    (Table 2)

The minimum span (mm) when commonly used rectangular bus bars are arranged relative to each other in the width direction of the bus bar:

Short-circuit capacity KA/4S 31.5 40

Distance (mm) 275 400 460 275 400 460

TMY

100×10 theoretical value 755 910 980 605 730 780

Recommended value 600 800 800 600 600 600

Bus electrodynamic effect

Bus electrodynamic effect

 For the 31.5kA/4S system, the minimum cross-sectional area of the grounded copper busbar is:

S=330×86.7% =287mm2

Calculated according to the above formula, corresponding to various rated short-time withstand currents, corresponding to several commonly used rated short-time withstand currents in switchgear and control equipment, the minimum cross-section of the busbar and the minimum specifications of the copper busbar and aluminum busbar used are shown in Table 1 :

    Table 1

Busbar kA/4s 25 31.5 40 63 80

Specification of copper busbar in equipment 50×6 60×6 80×6 or 60×8 80×10 100×10

Specification of grounding copper busbar 50×5 50×6 50×8 80×8 80×10

Specification of aluminum busbar in equipment 80×6 or 60×8 80×8 100×8 or 80×10

Copper busbar in equipment

Minimum cross-section (mm2) 260 330 420 660 840

Aluminum bus bar in the equipment

Minimum cross-section (mm2) 425 540 685 1075 1365

4.2 Electrodynamic effects of busbars

The bus bar is a conductor that carries current. When a current flows, it will inevitably produce a force on the bus bar. The force exerted by the bus on the current is related to the current, the shape of the bus, and the distance between the buses. Busbars placed in parallel are the most common in switchgear.

Determine the maximum span of the busbar (the maximum distance between the two supports) according to the rated peak withstand current

Principle: The acting stress acting on the busbar kg/cm≤ the allowable stress of the busbar hydraulic busbar cutting punching bending machine in india.

Formula: js=1.76L2ich2×10-3/aW≤y

In the formula: js—acting stress acting on the bus, kg/cm2;

Y—The maximum stress of the bus bar is allowed, 1400 when the bus bar is copper, and 700 when the bus bar is aluminum;

L-support distance between busbars (cm);

A—the distance between each other (cm);

W——Rectangle bus section coefficient, cm3;

Ich—rated peak withstand current, (kA)

According to the above formula:

The maximum span of the copper busbar is L copper MAX≤(1400aw 103/1.76 ich2) 1/2= 892(aw)1/2/ ich

The maximum span of the aluminum bus bar is L aluminum MAX≤(700aw 103/1.76 ich2)1/2= 631(aw)1/2/ich

Coefficient of rectangular bus section:

For the horizontally arranged three-phase bus, when the bus is laid flat; or for the vertically arranged three-phase bus, when the bus is placed upright: (that is, the thickness direction of the bus is opposite, the force effect is good at this time)

W1 = 0.167bh2; where h is the bus width (cm) and b is the bus thickness (cm). Substitute W into the above formula to get

L copper MAX≤365h（ab) 1/2/ ich

L aluminum MAX≤258h（ab) 1/2/ ich

For example: for a 31.5kA system, ich takes 80kA, such as for KYN28-12 switchgear a=28, for the maximum span of TMY100×10 and LMY100×10 type busbars. The busbar width is 100/10=10cm, and the thickness is 10/10=1cm.

L copper MAX≤240 (cm).

L aluminum MAX≤170（cm）

For the horizontally arranged three-phase bus, when the bus is placed upright; or for the vertically arranged three-phase bus, when the bus is laid flat: (that is, the width direction of the bus is opposite, the electrodynamic effect is not good at this time)

W2 = 0.167b2h;

Then: L copper MAX≤365b（ah) 1/2/ ich

L aluminum MAX≤258b（ah) 1/2/ ich

Busbar ampacity calculation

Busbar ampacity calculation

 

 I4=2.45Id

In the formula, I4 is the current carrying capacity of the four-layer copper busbar (A).

Note: Two-layer and above copper bars mean that there is an air gap between the two-layer busbar equal to the thickness of the busbar.

The conversion relationship between the bus at an ambient temperature of 40℃ and an ambient temperature of 25℃ is:

I40=0.85I25

In the formula, I40 is the current carrying capacity of the bus at 40℃ (A); I25 is the current carrying capacity of the bus at 25℃ (A).

The conversion relationship between the download traffic of copper busbars and aluminum busbars of the same specification under the same ambient temperature conditions is:

IAl=ICu/1.3

In the formula, ICu is the current carrying capacity of the copper bus; IAl is the current carrying capacity of the copper bus.

For example, according to the above formula, the current carrying capacity of the TMY100×10 bus is:

Single layer: 100×18.5 = 1850A. The search manual is 1860A. This data is based on the “High Voltage Distribution Device Regulations” issued by the Ministry of Water and Electricity of China Industry Press.

Double layer: 2 (TMY100×10) current carrying capacity is:

1850×1.58=2923(A); [Check manual is 2942A];

Three layers: 3 (TMY100×10) current carrying capacity is:

1850×2=3700A [Check the manual for 3780A]

All the above calculations are quite close to the data in the manual, and the busbar ampacity can be calculated according to the above formula.

3.4 Description

(1) The above calculation formula is applicable to bus bars of 120×12 and below specifications.

(2) For the current-carrying capacity of the shaped bus, it is recommended to use economic current density for calculation.

4 Thermal and electrodynamic effects of busbars

4 busbar punching cutting.1 Thermal effect of bus

4.1.1 The thermal effect of the bus bar refers to the thermal effect that the bus bar can carry under the specified conditions due to the flow of current. In switching equipment and control equipment, it refers to the rated short-time withstand current (IK) carried by the busbar within the specified time under the specified use and performance conditions.

4.1.2 Determine the minimum cross section of the bus according to the rated short-time withstand current

According to the formula in GB3906-1991 "3.6-40.5kV AC metal-enclosed switchgear and control equipment" [Appendix F]: S=(I/a)(t/θ)1/2 to determine the minimum cross section of the bus bar.

In the formula:

S—Minimum cross section of bus bar, mm2;

I-- rated short-time withstand current, A;

A—Material coefficient, copper is 13, aluminum is 8.5;

T-- rated short-circuit duration, s;

Θ—Temperature rise (K), generally 180K for bare conductors and 215K for 4s duration.

For the 31.5kA/4S system, the minimum cross-sectional area of the copper busbar is:

S=(31500/13)×(4/215)1/2=330 mm2

The relationship between the minimum cross-sectional area of the aluminum bus and the minimum cross-sectional area of the copper bus is:

SAl=1.62SCu

In the formula, SAl is the minimum cross-sectional area of the aluminum bus; SCu is the minimum cross-sectional area of the copper bus.

For the 31.5kA/4S system, the minimum cross-sectional area of the aluminum bus is:

SAl=1.62×330 =540 mm2

According to the provisions of 7.4.3 in DL404-1997 "Technical Conditions for Ordering Indoor AC High Voltage Switchgear", the grounding busbar and the cross-section of the conductor connected to it should be able to calculate 87% of the rated short-circuit breaking current of the nameplate. The minimum cross-sectional area of the ground bus under the short-circuit capacity of the system (short-circuit time is 4S).

Relationship between busbar layout and current carrying capacity

Relationship between busbar layout and current carrying capacity

 

The current carrying capacity of the busbar is higher than that when it is placed horizontally. Generally, when the busbar is laid flat and the width is less than 60㎜, the current carrying capacity is 0.95 times that of the vertical bus, and when the width is greater than 60㎜, the current carrying capacity is the vertical 0.92 times, this is because the heat dissipation performance when standing is better than when laying flat.

3.3 Carrying capacity value

According to the different materials of the bus, the current carrying capacity is also different at the same temperature. In the switchgear and control equipment, the rectangular copper bus bar is the main rectangular aluminum bus bar. Its current carrying capacity value can generally be found according to various design manuals. Based on many years of experience, the author summarizes the simple calculation formula of the busbar current carrying capacity (AC) when standing upright through the statistics of the busbar current carrying capacity in various manuals.

Current carrying capacity Id(A) of single-layer rectangular copper busbar at 40℃:

Id = k (b+8.5) h

In the formula, b is the thickness of the busbar (mm); h is the width of the busbar (mm); k is the coefficient (A/mm).

The relationship between the current-carrying capacity of the double-layer copper busbar and the single-layer busbar at 40℃

I2=(1.56～1.58) Id

In the formula, I2 is the current carrying capacity (A) of the double-layer copper bus; Id is the current carrying capacity (A) of the single-layer copper bus Bus duct manufacturers. 1.56～1.58 is the coefficient, generally 1.58 for 100×10 bus; 1.57 for 80×10, 1.57 for 60×6, and 1.56 for 60×6.

The relationship between the current carrying capacity of the 3-layer copper busbar and the single-layer copper busbar at 40℃ is:

I3=2Id

In the formula, I3 is the current carrying capacity of the four-layer copper busbar (A).

At 40℃, the relationship between the current carrying capacity of the 4-layer copper busbar and the single-layer copper busbar is (this type of option is not recommended, it is best to use a special-shaped busbar instead)

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.

Insulation powder film forming defects and solutions

Insulation powder film forming defects and solutions

 

The problems that occur during the use of insulating powder are summarized below for reference.

   1. The gloss of the coating film is insufficient: the baking time is too long during curing; the temperature is too high; other harmful gases are mixed in the baking; the surface of the workpiece is too rough; the pre-treatment method is not properly selected copper busbar benders.

   2. Discoloration of the coating film: repeated baking several times; other gases mixed in the oven; excessive baking during curing.

3. Orange peel on the surface of the coating film: the thickness of the sprayed coating is uneven; the atomization of the powder is not good, and the spray gun has powder accumulation; the curing temperature is low; the powder is damp, the powder particles are too coarse; the workpiece is grounded poorly; the baking temperature is too high High; the coating is too thin.

   4. Dimples in the coating film: improper handling, impure oil removal; source contamination, compressed air deoiling, incomplete water removal; uneven workpiece surface; contamination by dust or other impurities.

   5. Bubbles appear on the coating film: after the surface treatment of the workpiece, the moisture is not completely dried, leaving the pretreatment residual liquid; degreasing, rust removal is not complete; the underlying volatiles are not removed; the surface of the workpiece has pores; the powder coating is too thick.

   6. Uneven coating film: uneven powder spraying; the distance between the spray gun and the workpiece is too close; the high-voltage output is unstable.

   7. The coating film has poor impact strength and adhesion: the phosphating film is too thick; the curing temperature is too low, the time is too short, so that the curing is not complete; the bottom metal is not cleaned; the coating will reduce the adhesion after being immersed in water.

8. Pinholes in the coating film: the air contains foreign objects and residual oil; the voltage of the spray gun is too high, causing the coating to break down; the distance between the spray gun and the workpiece is too close, causing the coating to break down; the coating is too thin; the coating film is not sufficiently cured .

   9. A small amount of sand particles appear on the surface of the coating film: the spray is clogged or the air flow is not good; the atomization of the spray gun is not good; there is powder dripping in the powder spraying room; other debris contaminates the surface of the workpiece.

   10. The coating is off: the surface of the workpiece is not well treated, and the degreasing and rust removal are not complete; the output voltage of the high-voltage electrostatic generator is insufficient; the workpiece is poorly grounded; the air pressure is too high when powdering;

11. Uneven powder supply: the powder supply tube or powder spraying tube is blocked, and the powder adheres and hardens at the nozzle; the air pressure is insufficient and the pressure is unstable; the air compressor is mixed with oil or water; the fluidization of the powder supply is unstable, There is too little powder in the powder feeder; the powder supply tube is too long, and the resistance increases when the powder flows.

  12. Powder flying and poor adsorption: the electrostatic generator does not have insufficient high voltage; the workpiece is not well grounded; the air pressure is too large;

  13. The amount of powder spraying is low: insufficient air pressure, insufficient air volume; too high air pressure, the proportion of air in the mixture of powder and flow is too high; water vapor and oil pollution are mixed in the air space; the spray gun head is partially blocked.

  14. The powder spray tube is blocked: Due to the material of the powder spray tube, the powder is easy to adhere to the wall of the tube; the output tube is heated, causing the powder Lin in the tube to agglomerate; the powder conveying tube is bent and distorted; the powder is mixed with more granular impurities.