One, current estimation of electrical equipment: when you know the power of the electrical equipment can estimate its rated current:
Three-phase motor rated current according to the motor power 2 times, that is, each kilowatt multiplied by 2 is the rated current of the current flow, such as a three-phase motor rated power of 10 kilowatts, then the rated current of 20 amps. This way of estimating the three-phase squirrel-cage asynchronous motor, especially the closest four, for other types of motors can also be
Single-phase 220V motor current per kilowatt calculated by 8A
Three-phase 380V welder current per kilowatt counted by 2.7A (with a motor-type DC welder should be counted according to the 2A per kilowatt
Single-phase 220V welder per kilowatt counted by 4.5A
Single-phase 220V welder per kilowatt counted by 4.5A. kW by 4.5A
Single-phase incandescent lamps, tungsten iodine lamps per kilowatt current according to 4.5A
Note: Dysprosium lamps commonly used on the construction site for the 380V power supply (only two phase wires, a ground), the current per kilowatt in accordance with the 2.7A
Second, the three-phase motor rated current calculation of the different voltage levels
Mnemonic: capacity divided by the number of kV, multiplied by a factor of point seven six. The quotient multiplied by the coefficient of point seven six.
Description:
(1) the mnemonic is applicable to any voltage level of three-phase motor rated current calculation. By the formula and the mnemonic can be illustrated by the capacity of the same voltage level of different motor rated current is not the same, that is, the number of voltage kilovolts is not the same, remove the same capacity, the resulting "quotient" is not the same, not the same quotient to multiply by the same coefficient of 0.76, the resulting value of the current is not the same. If the above mnemonic is called a general mnemonic, it can be derived from the calculation of 220, 380, 660, 3.6kV voltage rating motor rated current special calculation mnemonic, with special calculation mnemonic calculation of a three-phase motor rated current, capacity kilowatts and current amperage relationship directly multiplier, eliminating the capacity divided by the number of kilovolts, the quotient multiplied by the coefficient of 0.76.
Three-phase two hundred and two motor, kilowatts three point five amps.
Commonly used three hundred eight motors, one kilowatt two amps.
Low-voltage six hundred and six motors, one kilowatt one point two amps.
High voltage three thousand volt motor, four kilowatts one amp.
High voltage six thousand volt motor, eight kilowatts one amp.
2) When using the mnemonic, the capacity unit is kW, the voltage unit is kV, and the current unit is A. This must be noted.
(3) the coefficient of 0.76 in the mnemonic is to take into account the motor power factor and efficiency and other calculations to get a comprehensive value. Power factor of 0.85, efficiency is not 0.9, these two values are more suitable for tens of kilowatts above the motor, on the commonly used 10kW motor appears to be larger. This will have to use the mnemonic c calculated motor rated current and motor nameplate labeled value has an error, this error on the motor below 10kW according to the rated current first switch, contactor, wire, etc. has little impact.
(4) the use of mnemonic calculation skills. Calculate the rated current of commonly used 380V motor with the mnemonic, first with the motor connected to the power supply voltage 0.38kV number removed 0.76, quotient 2 to multiply the capacity (kW) number. In case of larger capacity 6kV motor, capacity kW number is exactly 6kV number of multiples, then the capacity divided by the number of kilovolts, the quotient multiplied by 0.76 coefficient.
(5) error. By the mnemonic coefficient of 0.76 is to take the motor power factor of 0.85, efficiency of 0.9 and calculated so that the calculation of different power factor, efficiency of the motor rated current there is an error. Derived from the mnemonic c 5 special mnemonics, capacity (kW) and current (A) multiples, is the voltage level (kV) number divided by 0.76 coefficient of the quotient. Specialized mnemonics easy to calculate, but should be noted that the error will increase. Generally larger number of kilowatts, the calculated current is slightly larger than that on the nameplate; while the number of kilowatts is smaller, the calculated current is slightly smaller than that on the nameplate. In this regard, when calculating the current, when the current up to more than ten amps or tens of amps, it is not necessary to count to the decimal point. Can be rounded up and five, only take the whole number, so both simple and does not affect the practical. For smaller currents can also be counted to a decimal.
Three, measured current capacity
Measured no-load current without nameplate motor, estimate its rated capacity
Mnemonic:
No license plate motor capacity, measured no-load current value,
Multiply by ten and divide it by eight to calculate the number of kilowatts near the level of rating.
Explanation: the mnemonic is no nameplate three-phase asynchronous motor, do not know its capacity kilowatts is how much, can be measured by measuring the motor no-load current value, estimate the motor capacity kilowatts of the method.
Four, known transformer capacity, the voltage level side of the rated current
Mnemonic:
Capacity divided by the voltage value, the quotient multiplied by six divided by ten.
Description: applicable to any voltage level.
In the daily work, some electricians are only involved in one or two voltage levels of the transformer rated current calculation. Simplify the above mnemonic, it can be deduced to calculate the rated current of each voltage level side of the mnemonic:
Capacity coefficient multiplied to seek.
Five, known transformer capacity, quick calculation of its first and second protection fuse (commonly known as fuse) current value
Mnemonic:
Distribution of high-voltage fuse, capacity and voltage compared to seek.
Low-voltage transformer fuse, capacity multiplied by 9 divided by 5.
Description:
The correct choice of fuse is very important for the safe operation of the transformer. When only the fuse for transformer high and low voltage side protection, the correct choice of fuse is more important. This is an electrician often encountered and to solve the problem.
Six, measured the secondary side of the power transformer current, calculate the load capacity carried
Mnemonic:
Knowing the secondary pressure, measured current for kilowatts.
Voltage level four hundred volts, one ampere zero point six kilowatts.
The voltage level of three kilovolts, one ampere four point five kilowatts.
Voltage rating six thousand volts, one amp whole nine kilowatts.
Voltage rating ten kilovolts, one ampere fifteen kilowatts.
Voltage rating thirty-five thousand, one amp fifty-five kilowatts.
Description:
Electricians in their daily work, often encountered in the higher authorities, managers, etc. asked about the operation of the power transformer, the load is how much? Electricians themselves often need to know how much the transformer load. Load current is easy to know, directly look at the distribution device set up on the ammeter, or with the corresponding clamp-type ammeter to know, but the load power is how much, can not directly see and measure the knowledge. This will need to rely on this mnemonic calculations, otherwise the conventional formula to calculate, both complex and time-consuming.
Seven, measured incandescent lighting line current, calculate its load capacity
Lighting voltage two hundred and two, one an two hundred and twenty watts.
Description: industrial and mining enterprises, lighting, mostly 220V incandescent lamps. Lighting power supply line refers to the line from the distribution panel to each lighting distribution box, lighting power supply trunk line is generally three-phase four-wire, load for the following 4kW available single-phase. Lighting distribution line refers to the line from the lighting distribution box to the illuminator or socket and other lighting facilities. Regardless of whether the power supply or distribution lines, as long as the current value of a phase line measured with a clamp-type ammeter, and then multiplied by 220 factors, the product is the load capacity of the phase line. Measure the current for the number of capacity, can help electricians quickly adjust the lighting trunk line three-phase load capacity imbalance, can help electricians analyze the distribution box to protect the fuse is often melted, the reason for the distribution of wire heating and so on.
Eight, known 380V three-phase motor capacity, overload protection for its thermal relay element rated current and set current
Mnemonic:
Motor overload protection, thermal relay hot element;
No. current capacity two and a half times, twice the number of kilowatts set.
Description:
(1) motor easily overloaded, due to starting or self-starting conditions are serious and may start failure, or need to limit the starting time, should be equipped with overload protection. Long-term operation of unmonitored motor or 3kW and above, it is also appropriate to install overload protection. Overload protection device is generally used thermal relay or circuit breaker delay overcurrent detector. Currently our production of thermal relays for light load starting, long period of work or intermittent long-term work of motor overload protection.
(2) thermal relay overload protection device, the structural principle is very simple, can be selected to adjust the thermal element is very delicate, if the level of selection of large will have to be adjusted to the low limit, often resulting in the motor to stop, affecting the production, increasing the maintenance work. If the level of selection of small, only to the high limit adjustment, often motor overload does not act, or even burn the motor. (3) the correct calculation of 380V three-phase motor overload protection thermal relay, still need to find out the same series of models of thermal relay can be installed with different rated current of the thermal element. Thermal element rating current according to "two times the number of kW rating"; thermal element rated current according to "two and a half times the capacity of the number of current" calculated selection; thermal relay type specifications, that is, its rated current value should be greater than or equal to the rated current value of the thermal element.
Nine, measured without nameplate 380V single-phase welding transformer no-load current, calculated based on the rated capacity
Mnemonic:
Three hundred and eight welder capacity, no-load current multiplied by five.
Single-phase AC welding transformer is actually a special-purpose step-down transformer, compared with the ordinary transformer, its basic working principle is more or less the same. In order to meet the requirements of the welding process, the welding transformer works in a short-circuit state, requiring a certain arc voltage during welding. When the welding current increases, the output voltage drops sharply, when the voltage drops to zero (i.e., the secondary side of the short-circuit), the secondary side of the current is not too large, etc., that is, the welding transformer has a steeply falling external characteristics, the welding transformer's steeply dropping external characteristics are obtained by the reactance coils generated by the voltage drop. No-load, because there is no welding current through the reactor coil does not produce voltage drop, the no-load voltage is equal to the secondary voltage, that is to say, the welding transformer no-load and ordinary transformer no-load the same. The no-load current of the transformer is generally about 6%~8% of the rated current (the state regulations no-load current should not be greater than 10% of the rated current). This is the theoretical basis of the mnemonic and formula.
Ten, conductor capacity calculation mnemonic (1)
Conductor capacity and cross-section of the wire, but also with the wire material, type, laying method and ambient temperature, etc., affecting a number of factors, the calculation is also more complex. A variety of conductor capacity can usually be found from the manual. But the use of mnemonics with some simple calculations, it can be directly calculated, do not have to check the table.
1. mnemonic Aluminum insulated wire capacity and cross-section of the multiplier relationship
10 under the five, 100 on the two,
25, 35, four, three boundaries, .
70, 95, two and a half times.
Pipe-through, temperature, eight or nine percent off.
Bare wire plus half.
Copper wire upgrades count.
Description The mnemonic for the various cross-section of the current-carrying capacity (ampere) is not directly pointed out, but with the cross-section multiplied by a certain number of times to indicate. This will be commonly used in China wire nominal cross-section (mm2) is arranged as follows:
1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185......
(1) the first sentence of the mnemonic pointed out that the aluminum core insulated line capacity (A), can be multiplied by the cross-section of the multiplier. ), can be calculated by multiples of the cross-section. Mnemonic in the Arabic digital representation of the cross-section of the wire (square millimeters), the Chinese character numbers that multiples. "means that the cross-section in the 10 below, the flow-carrying are five times the value of the cross-section. "100 on two" (read hundred on two) means that the cross-section of more than 100 load capacity is two times the value of the cross-section. Cross-section of 25 and 35 is four times and three times the division. This is the mnemonic "25, 35, four or three boundaries". And cross-section of 70, 95 is two and a half times. From the above arrangement can be seen: in addition to 10 below and 100 above, the middle of the wire cross-section is every two specifications belong to the same kind of times.
For example, aluminum core insulated wire, the ambient temperature is not greater than 25 ℃ when the calculation of the current-carrying capacity:
When the cross-section of 6 square millimeters, the calculated current-carrying capacity of 30 amps;
When the cross-section of 150 square millimeters, the calculated current-carrying capacity of 300 amps;
When the cross-section of 70 square millimeters, the calculated current-carrying capacity of 175 amps;
From the above arrangement, it can also be seen that: In addition to 10 and more than 100, in addition to the intermediate conductor is the same multiple of each two specifications. >From the above arrangement can also be seen: the multiplier decreases with the increase in cross-section, at the junction of the multiplier shift, the error is slightly larger. For example, the cross-section of 25 and 35 is four times and three times the demarcation, 25 is four times the range, it is calculated according to the mnemonic for 100 amps, but according to the manual for 97 amps; and 35 is the opposite, according to the mnemonic for 105 amps, but check the table for 117 amps. However, this does not affect the use of a lot. Of course, if you can "count", in the selection of wire cross-section, 25 does not let it full to 100 amps, 35 can be slightly more than 105 amps will be more accurate. Similarly, 2.5 mm2 wire position in five times the beginning of the actual more than five times (up to 20 amps or more), but in order to reduce the loss of electrical energy within the wire, usually do not have to such a large current, the manual is generally only marked 12 amps.
(2) The next three phrases deal with changing conditions. "through the pipe, temperature, eight, 90% discount" means: if it is laid through the pipe (including groove boards and other laying, that is, the wire plus a protective jacket layer, the unidentified exposed), after calculation, and then 20% discount; if the ambient temperature exceeds 25 ℃, after calculation, and then 90% discount, if both through the pipe, the temperature is more than 25 ℃, then 80% discount and then 90% discount, or simply according to a time! Discount 70% calculation.
On the ambient temperature, as a rule, is the average maximum temperature of the hottest month of summer. In fact, the temperature is variable, in general, it affects the wire current-carrying is not very large. Therefore, only for certain temperature workshop or hotter areas more than 25 ℃, only when the discount is considered.
For example, the aluminum core insulated wire in different conditions to calculate the flow:
When the cross-section of 10 square millimeters through the tube, then the current-carrying capacity of 10 × 5 × 0.8 ═ 40A; if the high temperature, then the current-carrying capacity of 10 × 5 × 0.9 ═ 45A; if it is a high temperature through the tube and, then the current-carrying capacity of 10 × 5 × 0.7 ═ 35A.
(3) for bare aluminum wire, the mnemonic pointed out that "bare wire plus half," that is, after the calculation and then add half. This refers to the same cross-section of bare aluminum wire and aluminum core insulated wire comparison, the current-carrying capacity can be increased by half.
For example, the calculation of bare aluminum wire capacity:
When the cross-section of 16 square millimeters, the capacity of 16 × 4 × 1.5 ═ 96 amps, if the high temperature, the capacity of 16 × 4 × 1.5 × 0.9 = 86.4 amps.
(4) for the copper conductors of the current-carrying capacity, the mnemonic pointed out that "the copper line upgraded to count", that is, the order of the cross-section of copper conductors to upgrade the order of a level, and then calculated according to the corresponding conditions of the aluminum line.
For example, the cross-section of 35 square millimeters of bare copper wire ambient temperature of 25 ℃, the calculation of the current-carrying capacity of: 50 square millimeters of bare aluminum wire upgraded to 50 × 3 × 1.5 = 225A.
For cables, the mnemonic is not introduced. General directly buried high-voltage cables, by and large, can be used directly in the first phrase of the relevant multiplier calculation. For example, 35 square millimeters of high-voltage armored aluminum core cable buried in the ground for the 35 × 3 = 105 A. 95 square millimeters of about 95 × 2.5 ≈ 238 A.
Three-phase four-wire system in the zero line cross-section, usually selected for the phase line cross-section of about 1/2. Of course, it should not be less than the minimum cross-section permitted by the mechanical strength requirements. In the single-phase line, because the zero line and phase line through the same load current, so the zero line cross-section should be the same as the phase line cross-section.
Eleven, conductor capacity calculation of mnemonic (2)
Aluminum insulated conductor capacity and cross-section of the multiplier relationship
Estimation of the mnemonic:
Two point five under the multiplied by nine, up minus a number of smooth go.
Thirty-five times three point five, double into a group minus point five.
Conditions have changed plus discounting, high temperature 90% off copper upgrade.
Through the number of roots of two, three, four, eight, seven, six discount full load flow.
Description: (1) this section of the mnemonic for a variety of insulated wire (rubber and plastic insulated wire) of the current-carrying capacity (safety current) is not directly pointed out, but "cross-section multiplied by a certain number of times" to indicate that, through the heart of the calculation. From Table 5 3 can be seen: the multiplier decreases with the increase in cross-section.
"2.5 multiplied by nine, up minus one to go with the number," said 2.5mm 'and the following cross-section of various aluminum core insulated wire, the flow rate of the cross-section of the number of about 9 times. Such as 2.5mm 'wire, the current-carrying capacity of 2.5 × 9 = 22.5 (A). From 4mm' and above the conductor's capacity and cross-section of the number of multiples of the relationship is along the line number up, the multiplier decreases one by one l, that is, 4 × 8, 6 × 7, 10 × 6, 16 × 5, 25 × 4.
"Thirty-five times three point five, double double group minus point five", said the 35mm" conductor capacity for the number of sections of 3.5 times, that is, 35 × 3.5 = 122.5 (A). From 50mm' and above, the conductor, its capacity and the number of multiples of the cross-section relationship between the number of two two line number into a group, the multiplier in turn minus 0.5. That is, 50, 70mm' conductor capacity for the number of cross-section of 3 times; 95, 120mm" conductor capacity is the number of its cross-section of 2.5 times, in turn, analogous to the number of the cross-section of the conductor, the number of the cross-section of 2.5 times. 5 times, and so on.
"Conditions have changed plus discount, high temperature 90% copper upgrade". The above mnemonic is an aluminum core insulated line, laying in the ambient temperature of 25 ℃ under the conditions. If the aluminum core insulated line laying in the ambient temperature is higher than 25 ℃ for a long time in the region, the conductor capacity can be calculated according to the above mnemonic calculation method, and then discount can be; when the use of non-aluminum but copper insulated line, it is the capacity of the same specifications than the aluminum line is slightly larger than that of some of the mnemonics can be calculated as described above than the aluminum line to increase the number of a line of the capacity of the line. Such as 16mm' copper wire capacity, can be calculated according to 25mm2 aluminum wire.
Twelve, electrical construction power inspection with low-voltage tester pen mnemonic
Low-voltage tester pen is a commonly used by electricians to assist the safety appliances. Used to check whether the 500V conductor or a variety of electrical equipment shell charged. An ordinary low-voltage tester, can be carried around, as long as the principle of mastering the tester, combined with the familiar principles of electrician, the flexible use of many skills.
(1) determine the alternating current and direct current mnemonic
Pen judgment AC and DC, AC bright DC dark,
AC neon tube through the body bright, DC neon tube bright end.
Instructions:
First of all, inform the reader that the use of low-voltage power test pen before, must be confirmed in the charged body test test; in the absence of confirmation of the power test pen normal before, shall not be used. Discriminate between AC and DC power, it is best to make a comparison between the "two power", so it is very obvious. Measurement of alternating current neon tube at the same time the two ends of the light, measurement of direct current neon tube only one end of the pole light.
(2) determine the positive and negative DC mnemonic:
The electric pen to determine the positive and negative poles, observe the neon tube to be careful,
The front end of the bright is negative, the back end of the bright for the positive pole.
Instructions:
The front end of the neon tube refers to the tip end of the electric pen, neon tube back end refers to the end of the hand, the front end of the bright for the negative pole, and vice versa for the positive pole. Test should be noted: the power supply voltage of 110V and above; if the person and the earth insulation, a hand touching the power supply of any pole, the other hand holding the people's pen, the pen metal head touched the power supply was tested another pole, neon tube front pole bright, the power supply is negative; if the neon tube is neon tube rear pole bright, the power supply is positive, which is based on the unidirectional flow of DC and the flow of electrons by the negative to the positive pole of the principle of mobility.
(3) to determine whether the DC power supply grounded, positive and negative grounding difference mnemonic
Transformer DC coefficients, electric pen touch does not light;
If the light is near the tip of the pen, the positive pole has a ground fault;
If the light is close to the end of the finger, the ground fault is in the negative pole.
Explanation:
Power plants and substations of the DC coefficient, is insulated from the ground, people stand on the ground, with a tester pen to touch the positive or negative, neon tubes should not be bright, if bright, then the DC system has a grounding phenomenon; if bright in the end near the tip of the pen, is the positive ground; if bright in the end of the finger, is the negative grounding.
(4) to determine the same phase and different phase mnemonic
Judgment of the two lines of the same different, two hands each holding a pen,
two feet and the ground phase insulated, the two pens are touching a line,
Watch a pen with the eyes, not light the same as the different phase bright.
Description:
This test, remember that the two feet and the ground must be insulated. Because most of our country is 380/220V power supply, and transformers generally use the neutral point directly to ground, so do the test, the human body and the earth must be insulated, to avoid constituting a circuit, so as to avoid misjudgment; test, the two pens are bright and do not light up the same display, so only look at a can be.
(5) determine the 380/220V three-phase three-wire power supply line phase line ground fault mnemonic
star connection three-phase line, the electric pen touched two bright,
the remaining one brightness is weak, the phase of the conductor has been grounded;
If it is almost no light , the metal grounding fault.
Description:
The secondary side of the power transformer are generally connected to the Y-shaped, three-phase, three-wire system in the neutral point is not grounded, with a tester pen touching the three phase wires, there are two than the usual slightly brighter than the brightness of the other on the brightness to be weaker, it is indicated that the brightness of the weak phase line with grounding phenomenon, but it is not too serious; if the two are very bright, and the remaining one is almost invisible bright, is the this phase line has a metal ground fault.
More about the engineering/service/procurement category of the tender writing production, enhance the winning rate, you can click the bottom of the official website customer service free consultation:/#/?source=bdzd