10 × 20

Chapter III distribution calculation

one of the formulas on the motor wiring

1. use

according to motor capacity (kW) with branch circuit conductors directly determine the size cut-off mother, do not have to first calculate the current motor capacity, again selected section of the lines.

2. Mnemonics

aluminum insulated wire with the various cross section of the motor capacity (kW) of the addend relationship:

2.5 plus three, four plus four.

6 added 6, 25 - 5.

120 wires, with 100 numbers.

3. Help

the formulas is three-phase 380 volt motor wiring. Insulated aluminum wire for the wire (or plastic wire) through pipe laying. As the motor capacity rating more, therefore, formulas, in turn, said that that section of the wire with different range of motor capacity. The range is 'greater than the section number of the number of' to that.

do this, first understand the general motor capacity (kW) of the arrangement:

old capacity (kW) arranged as follows:

0.6 1 1.7 2.8 4.5 7 10 14 ; 2,028,405,575,100,125

new capacity (kW) arranged as follows:

0.7 1.1 1.5 2.2 3 4 5.5 7.5 ; 1,013,172,230,405,575,100

'2 .5 plus three 'said the 2.5 mm2 of aluminum insulated wire, through pipe laying, can add 3 with '2 .5' kilowatt electric motor. The maximum of 5.5 kW motor.

'4 plus 4 'is 4 square millimeters of insulating aluminum wire, through pipe laying, can with '4 plus four' kilowatts of electric motors. That is maximum with 8 kW (products only close to 7.5 kW) motor.

'6 added six 'is that from the beginning and after six mm2 can with' increased six 'kilowatts of electric motors. That is 6 mm2 can be equipped with 12 kW, 10 mm2 can be equipped with 16 kilowatts, 16 mm2 can be equipped with 75 kilowatts.

'25-5 'is that starting from 25 mm2, addend by the change in five of six. That is 25 mm2 can be equipped with 30 kW, 35 mm2 can be equipped with 40 kW, 50 mm2 can be equipped with 55 kW, 70 mm2 can be equipped with 75 kilowatts.
the number of wires assigned 100
'120 '(read' hundred and the number of wires assigned 100 ') is that large 100-kilowatt electric motor, lead cross-section would not be to' strengthen 'the relationship to go with motor, but 120 mm2 of wiring but can only be assigned a 100-kilowatt electric motor.

【Example 1】 7 kilowatts motor with section 4 for conductor (at '4 plus 4 ').

【Example 2】 17 kilowatts motor section 16 for conductor (plus 6 by '6 ').

【3】 28 kilowatts motor cases with cross-section of 25 square millimeters of wire (in '25-5 ').

slight margin over wiring. Therefore, even if slightly too little capacity (such as 16 mm2 with 23 kilowatts), or capacity while not over, but the environmental temperature is high, it can be applied. But the cross section of the wire, when the ambient temperature is high, is still big a change is appropriate. Such as 70 mm2 with 75 kilowatts could have, if the ambient temperature is high, a significant 95 mm2, conversion is appropriate. The 100 kW has been replaced with 150 mm2 is appropriate.


second power line through tube formulas


1. use

pipe threading, the general rule: all the wire cross section of pipe (including insulation, etc.) not more than an empty tube cross-section of 40 ‰. This calculation is too much trouble for this, the manual has compiled a table for use. Formulas only address the required diameter of three-phase motor wiring problem. At this time worn by the three tube sections with insulated wire.

2. Mnemonics

diameter welded steel pipe and worn by the three cross-sectional relationship between power lines:

20 through 4,6,

25 wearing 10

40 through 35.

first and second rotation number.

3. Help

formulas refers to the welded steel pipe (or thickness of steel), tube wall thickness of 2 mm or more, can be buried underground. It is different from wire pipe (or black iron lamp).

welded steel pipe with inner diameter of said specifications, the unit is millimeter. To use formulas, should first understand the specifications of welded steel tubes arranged.

15 20 25 32 40 50 70 80

(1) has identified three kinds of diameter were here to wear the wire section. 20 mm diameter which can wear two kinds of 4 and 6 mm2 cross section. The other two can only wear one kind of cross-section diameter, 25 mm inner diameter that is only a kind of cross section through 10 mm2,as fast you can eat, 40 mm diameter can only wear one kind of 35 mm2 cross section.

(2) 'One, two turns a few' what does that mean? Sentence formulas to solve the relationships of other diameter of the thread said. But it is difficult to understand. To this end, we ordered out and take a look at the whole relationship:

welded steel pipe diameter 152025324050 70 80

(mm)

can wear wire section 2.5 4,6 10 16,25 35 50,70 95 120,150

(mm)

can be seen from the table: 15 start from the smallest diameter, along the sequence, always wear one, two cross sections, alternately. This is the 'first and second rotation number'.

alone this memory may be more difficult if the complement (1) to remember, will be easier. Example, to read through 4,6 '20 ', could be associated with: 20 in front of 15, and wearing a kind of cross section, and that is next to 2.5; and 20, followed by 25, also wearing a kind of cross section should be next to the 10. Also, read to '25 wearing 10 'and '40 through 35' can also be caused by similar associations. This is more easily remembered.

actual use, is often known to the section of the three power lines, and pipe specifications calling for a decision. This argument in turn will make use of formulas.

【1】 3 cases of 70 mm2 power cable should be equipped with welded steel pipe 50 (from '40 through 35 'association to the back of the 50 will be Wear 50,70 two sections).

【Example 2】 3 16 mm2 power cable should be equipped with 32 welding steel (from '25 wearing 10 'association to the back, or '40 through 35 'association to the front, can set the diameter to 32).

wire through the tube for threading convenience, requires a certain diameter. However, in the wire and the distribution of the diameter, when the pipeline short or elbow is low, then longer than the pipe or elbow to be more easier. Therefore, at this time also with a smaller diameter. Approach is to lead cross-section as a small level, again with diameter. If originally equipped with 10 mm2 conductor pipe diameter 25 mm, as short or elbow pipes less, now look into is 6 mm2 wire, again with diameter of 20 mm can be changed.

last mention: 'wearing tube, 240', that is, three power lines can only be achieved through tube 240 the maximum security (ambient temperature 25 °). It was already used in 150 mm2 of wire and 80 mm diameter, construction difficulties, a further large even harder. Know this number will enable us to judge: When the line current is greater than 240 Ah, and a pipeline to impossible, we must use two or three lines to meet. This low-voltage power distribution room outlet circuit, often this phenomenon.

3, squirrel-cage motor protection devices with control formulas

1. use

under three-phase squirrel-cage motor capacity (kW), decided to switch and fuse in the melt of the current (security).

2. Mnemonics

three-phase squirrel-cage motors are equipped with switches, the melt (An) on the motor capacity (kW) of the multiple relationships:

switch activated by 6 kW.

melt protection, kW x 4.

3. Help

formulas referring to the 380 volt three-phase squirrel-cage motor.

(1) small squirrel-cage motor, when the start is not frequent, you can use steel switch (or other protective cover of the switch) direct start. Steel switch capacity (safety), should be for the motor 'kilowatts, about 6 times the' safe about it. This is because the starting current big reason. This starts the motor directly with the switch capacity, the maximum should not exceed 10 kilowatts to 4.5 kilowatts generally less.

【Example 1】 1.7 kilowatts motor switch start, with 15 steel safety switch. (By calculation 1.7 * 6 = 10.2 Security. But the steel switch manufactured according to certain specifications, (15,30,60 security, etc.), because the election of 15 can be secured. Following the same.

【Example 2】 5.5 kilowatts starting motor switch, with 30 steel safety switch (calculated as 33 security, should be equipped with 60 safety switch, but not much more than 30 security, economic and not jeopardize safety considerations, can 30 An election of).

【3】 7 kilowatts cases of motor start switch, with 60 steel safety switch. Not used for \
(2) squirrel-cage motor is usually used for short circuit protection fuse. However, the melt fuse current, but also start to consider to avoid high current. To this end, the general melt current motor can be \Specific use, the same steel switch as product specifications should be used. Introduced here will be limited. But Fuse (soft wire) grand unified specification is not, is still with the number that shown in Table 3-1.


Table 3-1

motor capacity (kW) - Melt to compute the current - the choice of the fuses, model / melt rated current


RL1-60 / 20

; RM10-60/20

4.5 4.5 × 4 = 18 RT0-50/30

; RC1A-30/20

; - / Fuse 13



; RL1-60/30

; RM10-60/35

7 7 × 4 = 28 ; RT0-50/30
; RC1A-30 / 30

; - / Fuse 10

fuse can be individually installed in the magnetic starter before the synthesis can be set with switches (eg, steel switch containing a fuse). Use of melt in use as a \If no short circuit, it may be not to avoid starting current. At this time, allowing for large a melt (if necessary also for large 2) but not more.

4, auto Release setting current selection formulas

1. use

under motor capacity (kW) or transformer capacity (KVA) directly decided Release setting current size of the (security).

2. Mnemonics


instantaneous motor, kW 20 times. (1)

instantaneous transformer, KVA 3 times. (2)

heat release, according to ratings. (3)

3. Help

automatically switch on the squirrel-cage motors used in power lines do not always operate to make the switch. If the operating frequency, can add strings of a contactor to operate. Automatic switching may take advantage of the electromagnetic release device (instantaneous) to do short-circuit protection, use one of the thermal tripping device (or delayed release device) to do overload.

(1) sentence Mnemonics means control of a squirrel cage motors (three-phase 380V) and automatically switch the instantaneous action of electromagnetic tripping device tuning current (security), can be \choice. For example: 10 kW motor, automatic switching transient electromagnetic tripping device tuning current of 200 movements Security (10 × 20). \As the specifications of automatic switches and Release more, here it is not that Release and specifications. \
some small capacity, large motor starting current, sometimes by \At this time, allow a little longer to take a little bigger, but less than 20% is appropriate.

(2) sentence formulas is the post-distribution transformers, distribution transformers later, as a master switch with automatic switching, the instantaneous movement of its magnetic trip setting current device (safety), can be \three times the number of \For example: of 500 KVA transformer, as a master switch, the automatic switching transient electromagnetic Release 1500 action tuning current safety (500 × 3).

(3) for the motor or transformer overload protection and thermal over-current release, or delayed release device can set current motor or transformer rated current selection. Such as the 10 kW motor, the rectifier 20 safety; 40 kW motor, the tuning current of 80 safety; 500 KVA transformer, the current setting of 750 An. Specific choices, also allow slightly larger, it is appropriate not to exceed 20 ‰.

5, according to the tonnage crane decision switch and circuit distribution formulas

1. use

slip on the crane power supply wires and switches can be directly under the crane tonnage, the size of the decision, removed from the calculation of some intermediate links.

2. Mnemonics

2 吨 30, 5-ton 6,

15 - 100, 75 2.

wire section, a per tonne basis,

overhead crane, a large one.

3. Help

formulas applicable to the general use of the crane factory, voltage 380 V, three phase.

(1) the formulas that 'the decision by tonnage, the size of switching power supply (An) '. In front of each section of the Arab code that crane tonnage, followed by Chinese characters corresponding switch numbers indicate size of (security), but omitted a digit, such as '5 t 6 'is '5 t 60' omission, '75 2 'is '75 tons 200' of the omission, the general was easy to judge. Decision to switch according to formulas:

2 tons and the following 30 safety

5 吨 60 safe

15 吨 100 safe

75 吨 200 safe

in the middle of the tonnage of the crane, such as the 10-ton crane, a large tonnage may be similar switches, and that is the election of 100 security.

(2) the formulas that the decision by the tonnage supply wire (through the tube) cross-section size.

'section of the lines per tonne basis', is that the cable car tonnage can choose similar (or larger) size of the wire. If the optional 3-ton crane similar to the 4 mm2 wire. 5-ton crane desirable 6 mm2 of. But the 'big one overhead crane', that is not 5-ton bridge crane to take 6 mm2, and should take 10 mm2 of.

more options than the cable car wire motor according to 'the motor wire' of the formulas should be equipped with smaller wires. Such as the 5-ton overhead crane, electric motor about 23 kilowatts, according to formulas added 6 '6 ', should be equipped with 10 mm2 of. This is because the crane is usually used in short, stopping a long time, repeated short-time work system is the reason. Similar equipment are welding. Shorter time were electric magnetic flaw detector and so on. The wiring for such equipment, can get smaller.

final supplementary to talk about the welder branch of the distribution. Welding arc and resistance welding are usually divided into two major categories, including resistance welding (welding, spot welding, seam welding, etc) then use the time to be shorter. As mentioned above, on which wiring can be smaller, specific practices; first volume change (lower), can \(x 0.5), and then it changes the capacity for distribution.

【Example 1】 32 KVA AC arc welding machine, press the 'arc Bazhe', the 32 × 0.8 = 25.6, the distribution can be changed when the capacity of 26 kVA. When connected with 380 volts single phase, according to 26 × 2.5 = 65 security distribution.

【Example 2】 50 KVA spot welder, according to 'solder and a half,' the 50 × 0.5 = 25, you can at 25 kVA power distribution. When 380 volts single phase, by 252.5 = 62.5, or 63 security distribution.