Excessive voltage deviation affects the function and life of electrical equipment
The electrical counterparts of the building know that the appropriate input voltage of the electrical equipment is the rated voltage of the same value as the nominal voltage of the power distribution system. The electrical equipment can guarantee the normal function and the rated voltage within the specified voltage range. Service life.
If you measure the voltage at the terminal of the power supply, the measured value is often not its rated voltage, but slightly higher or lower. This deviation is called the voltage deviation.
The building electrical design specification and the electrical product standard stipulate that as long as the voltage deviation value is within the specified range, it is suitable for the operation of the electrical equipment. The voltage deviation of the general electrical equipment in China is ± 5 %.
When the voltage is high, the motor will increase in temperature due to the increase in core iron loss; when the voltage is low, the motor will increase in temperature due to the increase in copper loss in the winding. The shaft power output is proportional to the square of the input voltage. As long as the voltage deviation is not more than ± 5 %, the motor can still guarantee its rated shaft power output without exceeding its allowable temperature rise without shortening its service life. Motors in developed countries have a voltage deviation of ± 10% due to their superior material quality.
The self-resetting over-voltage and under-voltage protection specified by some electrical codes in China not only has the danger of self-resetting, but the over-voltage action setting value is 270 V, and the positive voltage deviation is as high as + 22.7%, which greatly exceeds the value of ± 5 %. It is difficult to guarantee the normal function and service life of the electrical equipment.
In summary, excessive voltage deviation will affect the function and life of the electrical equipment, which is a major indicator of the quality of electrical power. Measures should be taken to reduce the voltage deviation in the design and installation of building electrical. It is called voltage regulation.
Regrettably, in the current design and installation acceptance of China, the voltage adjustment has not been given due attention, resulting in some undue losses of users in the use of electricity. The author does not know much about this. I would like to throw a brick to attract jade, state a hole of insight, for peer criticism, and also draw the attention of peers to start discussions.
Causes of voltage deviations in utility grids and electrical installations
Voltage deviations are caused by voltage losses in the utility grid and user electrical devices. The percentage value of voltage loss can be simply calculated by the formula (PR+QX) / U2, where P and Q are the active load and the lag reactive load in the system respectively, and R and X are the resistance and inductive reactance in the system respectively. , U is the nominal voltage of the grid and the device. In the formula, QX generates a voltage loss much larger than PR, so the grid and the device should have sufficient adjustable lead reactive power to reduce the voltage loss caused by QX in the mode, and play the voltage adjustment function of the power system.
Before China's reform and opening up, the deviation of power consumption voltage was large. The main reason was that the state's economic situation was not good at that time, and the power grid and equipment lacked the leading reactive power.
Voltage adjustment of 10 kV distribution transformer voltage regulating switch
The user distribution transformer nameplate usually has a mark such as 10 kV ± 5 % / 0.4 kV. It shows that the transformer is used in a grid of 10 kV nominal voltage with a secondary side no-load line voltage of 400 V. In order to adapt the number of turns of the primary winding to the line voltage level of the 10 kV grid, a non-exciting voltage regulating switch (hereinafter referred to as regulating voltage) for adjusting the number of windings of the rated voltage of 5 % under unpowered conditions is provided in the primary winding. switch).
Figure 1 shows the wiring diagram of the voltage regulating switch of the primary winding of the star-connected line. The three voltage regulating switches are interlocked: when the 10 kV line voltage is too high, adjust the switch to the + 5 % position to increase Winding turns; when the voltage is low, adjust to -5 % position to reduce the number of winding turns, so that the no-load output voltage of the secondary winding of the transformer is close to 230 / 400 V, which plays a role in voltage regulation. If the regulator switch is 2 × 2. 5 %, the voltage can be adjusted to be finer.
The voltage regulating switch is set on the high voltage side of the transformer because the current on the high voltage side is small, which is convenient for the production of the voltage regulating switch. It can also be seen from Fig. 1 that the distribution transformer of the primary side winding is a star-shaped junction, and the voltage regulating switch is located at the low end of the winding voltage, has a low voltage level, and has a simple structure and is easy to manufacture. The situation is much more complicated if the windings are triangular. This is probably one of the reasons why the former Soviet Union widely used Y, yn12 junction distribution transformers.
Incorrect voltage regulator switch position increases voltage deviation
In order to use the input voltage of the electrical equipment not to exceed the specified voltage deviation value, two conditions must be met: one is to make the voltage loss of the low-voltage distribution line drawn from the transformer within a reasonable range, which is the work of the electrical device designer; The position of the voltage regulating switch of the primary winding of the distribution transformer should be compatible with the voltage level of the 10 kV incoming line at the transformer. The turns ratio of the two windings makes the secondary side output voltage of the secondary side close to 230 / 400 V, full load voltage. Close to 220 / 380 V, this is the work of electrical installation and inspection personnel.
In the author's many years of work experience, it is found that there are many reasons for the excessive voltage deviation of the electrical equipment. The latter condition is not satisfied, that is, the position of the voltage regulating switch of the distribution transformer is incorrect.
For example, a factory's contact welder (resistance welder) often fuses the solder joints of the precious welds, making the welds waste. The author found on the scene that the input voltage of the welder was too high, and the reason why the input voltage was too high was that the position of the voltage distribution switch of the distribution transformer was incorrect. After changing the switch position from 0 to + 5 % position, the welder will work normally and no more waste will be produced.
This voltage deviation caused by the incorrect position of the transformer voltage regulating switch is too large, which affects the normal production situation. I have seen it in some factories.
The reason why the distribution transformer regulating switch position is incorrect
Depending on the distance between the 10 kV user and the regional substation, some 10 kV power supply lines have higher voltages and some are lower. For this reason, the 10 kV incoming line voltage should be detected during the construction and acceptance of the user's distribution substation, and the position of the transformer regulating switch should be correctly selected, as shown in Figure 2, to ensure the appropriate output voltage level on the secondary side of the transformer.
Regrettably, this extremely important step is often not taken seriously by construction and acceptance. For example, the author's house is located in the middle of the distribution line. The measured power voltage is actually 237 V, and the deviation is + 8 %. It is conceivable that the voltage deviation of the first-end house will exceed + 10%. The position of the voltage regulator switch is definitely not correct.
In this large value overvoltage for many years, the life of electrical equipment must be shortened to a considerable extent. Sadly, the household suffers from unnecessary loss but has no knowledge of it. This situation can be quite common.
In the construction and installation of substations, it is generally unwilling to change the position of the transformer regulating switch. The reason is that the operation is improper, and the contact resistance of the contact of the voltage regulating switch is increased to cause local overheating. In fact, this can be completely avoided. After adjusting the position of the pressure regulating switch, the experienced electrician always rotates the handle of the pressure regulating switch and then rotates it back and forth a little to make the contact better and avoid the overheating of the contact. Rather than adjusting the voltage regulator switch correctly, the voltage deviation is too large, but it is extremely irresponsible to the user.
Mistaken version of the title title qualification exam questions misleading on the voltage adjustment concept
A colleague gave the author a review of the 2014 design qualification exam, which was reproduced as follows:
A workshop substation is equipped with a transformer of 1 600 kVA, 10 kV ± 2 × 2. 5 % / 0.4 kV and an impedance voltage of 6%. The low-voltage busbar is equipped with a 300 kvar shunt compensation capacitor, which is fully input when normal.
Problem: The maximum voltage loss from the substation low voltage bus to the remote equipment distribution line is 5%, the minimum voltage loss to the near-end equipment feeder line is 0.95%, and the transformer full-load voltage loss is 2%. The electrical equipment allows voltage deviations within ± 5 %. Calculate and judge which of the transformer taps: a. + 5%; b. 0; c. - 2. 5 %; d. - 5 %.
I can't answer this question after reading the exam questions. The position of the transformer voltage regulating switch only needs to adapt to the voltage level of the 10 kV incoming line, as shown in Figure 2 of this paper.
Make the output voltage of the secondary side of the transformer meet the nominal voltage requirement of the low-voltage electrical equipment, that is, the no-load output voltage of the secondary side of the transformer is 230 / 400 V. Under this premise, the low-voltage system is correctly designed, the voltage loss is verified, and the electric equipment is used. The input voltage deviation is not more than ± 5 %. The position of the transformer voltage regulating switch has nothing to do with some technical parameters of the low-voltage power distribution system. The choice of the position of the transformer voltage regulating switch in the test is determined by the data of the low-voltage power distribution line, so that the examinee can carry out complicated calculations, which is obviously wrong.
This error test explains the gap in the theoretical level of voltage regulation in China's building electrical, and it is this improper test that prompted the author to dedicate this article, calling on peers to pay attention to the test of voltage level and voltage adjustment in building electrical.
Inspection of voltage levels should be added in construction acceptance specifications
The voltage level of the electrical equipment is too high or low, which does not endanger personal safety, but it affects the function and life of the electrical equipment for many years. This long-term adverse effect is often not noticed because it is not noticed by people. Unfortunately, China's building electrical construction acceptance specification and even the verification (Verification) chapter of IEC 60364 standard have not proposed the voltage level of electrical equipment. It is required to let the excessive voltage deviation harm the electrical equipment, which is a problem that needs to be highly valued in the construction and acceptance of building electrical construction.
When discussing the chapter of the IEC 60364 standard inspection in China's IEC / TC 64 focal point committee, the author proposes that the IEC should supplement the test of the voltage level of the electrical device every time, but it does not attract attention every time and does not discuss it. Reflect this suggestion.
At a building electrical exchange meeting in China in April 2014, Mr. Tison, Chairman of IEC / TC 64, accepted an exclusive interview with China's "Building Electrical" magazine. He euphemistically said: "TC64 has not heard too much voice from China." "China has hardly participated in the development of the consensus of IEC 60364." As a member of the IEC / TC 64 standard for many years, I am grateful to Mr. Tison for his expectations.
The above-mentioned proposal IEC / TC 64 supplements the requirements for building electrical equipment voltage level inspection as an example. China does not have no "sound", but the communication channels are not smooth enough. IEC / TC 64 does not hear some "sounds" from China. In recent years, China's IEC / TC 64 focal point committee has done a lot of useful work for the introduction and transformation of international standards for building electrical.
Mr. Tison's expectation shows that there are still some shortcomings in China's centralized work. The author sincerely hopes that China's IEC / TC 64 centralized work will be on the basis of achievements, reflecting China's "voice". A lot of work involved in the development of the IEC 60634 standard, to enhance the international reputation of China's building electrical.
The electrical counterparts of the building know that the appropriate input voltage of the electrical equipment is the rated voltage of the same value as the nominal voltage of the power distribution system. The electrical equipment can guarantee the normal function and the rated voltage within the specified voltage range. Service life.
If you measure the voltage at the terminal of the power supply, the measured value is often not its rated voltage, but slightly higher or lower. This deviation is called the voltage deviation.
The building electrical design specification and the electrical product standard stipulate that as long as the voltage deviation value is within the specified range, it is suitable for the operation of the electrical equipment. The voltage deviation of the general electrical equipment in China is ± 5 %.
When the voltage is high, the motor will increase in temperature due to the increase in core iron loss; when the voltage is low, the motor will increase in temperature due to the increase in copper loss in the winding. The shaft power output is proportional to the square of the input voltage. As long as the voltage deviation is not more than ± 5 %, the motor can still guarantee its rated shaft power output without exceeding its allowable temperature rise without shortening its service life. Motors in developed countries have a voltage deviation of ± 10% due to their superior material quality.
The self-resetting over-voltage and under-voltage protection specified by some electrical codes in China not only has the danger of self-resetting, but the over-voltage action setting value is 270 V, and the positive voltage deviation is as high as + 22.7%, which greatly exceeds the value of ± 5 %. It is difficult to guarantee the normal function and service life of the electrical equipment.
In summary, excessive voltage deviation will affect the function and life of the electrical equipment, which is a major indicator of the quality of electrical power. Measures should be taken to reduce the voltage deviation in the design and installation of building electrical. It is called voltage regulation.
Regrettably, in the current design and installation acceptance of China, the voltage adjustment has not been given due attention, resulting in some undue losses of users in the use of electricity. The author does not know much about this. I would like to throw a brick to attract jade, state a hole of insight, for peer criticism, and also draw the attention of peers to start discussions.
Causes of voltage deviations in utility grids and electrical installations
Voltage deviations are caused by voltage losses in the utility grid and user electrical devices. The percentage value of voltage loss can be simply calculated by the formula (PR+QX) / U2, where P and Q are the active load and the lag reactive load in the system respectively, and R and X are the resistance and inductive reactance in the system respectively. , U is the nominal voltage of the grid and the device. In the formula, QX generates a voltage loss much larger than PR, so the grid and the device should have sufficient adjustable lead reactive power to reduce the voltage loss caused by QX in the mode, and play the voltage adjustment function of the power system.
Before China's reform and opening up, the deviation of power consumption voltage was large. The main reason was that the state's economic situation was not good at that time, and the power grid and equipment lacked the leading reactive power.
Voltage adjustment of 10 kV distribution transformer voltage regulating switch
The user distribution transformer nameplate usually has a mark such as 10 kV ± 5 % / 0.4 kV. It shows that the transformer is used in a grid of 10 kV nominal voltage with a secondary side no-load line voltage of 400 V. In order to adapt the number of turns of the primary winding to the line voltage level of the 10 kV grid, a non-exciting voltage regulating switch (hereinafter referred to as regulating voltage) for adjusting the number of windings of the rated voltage of 5 % under unpowered conditions is provided in the primary winding. switch).
Figure 1 shows the wiring diagram of the voltage regulating switch of the primary winding of the star-connected line. The three voltage regulating switches are interlocked: when the 10 kV line voltage is too high, adjust the switch to the + 5 % position to increase Winding turns; when the voltage is low, adjust to -5 % position to reduce the number of winding turns, so that the no-load output voltage of the secondary winding of the transformer is close to 230 / 400 V, which plays a role in voltage regulation. If the regulator switch is 2 × 2. 5 %, the voltage can be adjusted to be finer.
The voltage regulating switch is set on the high voltage side of the transformer because the current on the high voltage side is small, which is convenient for the production of the voltage regulating switch. It can also be seen from Fig. 1 that the distribution transformer of the primary side winding is a star-shaped junction, and the voltage regulating switch is located at the low end of the winding voltage, has a low voltage level, and has a simple structure and is easy to manufacture. The situation is much more complicated if the windings are triangular. This is probably one of the reasons why the former Soviet Union widely used Y, yn12 junction distribution transformers.
Incorrect voltage regulator switch position increases voltage deviation
In order to use the input voltage of the electrical equipment not to exceed the specified voltage deviation value, two conditions must be met: one is to make the voltage loss of the low-voltage distribution line drawn from the transformer within a reasonable range, which is the work of the electrical device designer; The position of the voltage regulating switch of the primary winding of the distribution transformer should be compatible with the voltage level of the 10 kV incoming line at the transformer. The turns ratio of the two windings makes the secondary side output voltage of the secondary side close to 230 / 400 V, full load voltage. Close to 220 / 380 V, this is the work of electrical installation and inspection personnel.
In the author's many years of work experience, it is found that there are many reasons for the excessive voltage deviation of the electrical equipment. The latter condition is not satisfied, that is, the position of the voltage regulating switch of the distribution transformer is incorrect.
For example, a factory's contact welder (resistance welder) often fuses the solder joints of the precious welds, making the welds waste. The author found on the scene that the input voltage of the welder was too high, and the reason why the input voltage was too high was that the position of the voltage distribution switch of the distribution transformer was incorrect. After changing the switch position from 0 to + 5 % position, the welder will work normally and no more waste will be produced.
This voltage deviation caused by the incorrect position of the transformer voltage regulating switch is too large, which affects the normal production situation. I have seen it in some factories.
The reason why the distribution transformer regulating switch position is incorrect
Depending on the distance between the 10 kV user and the regional substation, some 10 kV power supply lines have higher voltages and some are lower. For this reason, the 10 kV incoming line voltage should be detected during the construction and acceptance of the user's distribution substation, and the position of the transformer regulating switch should be correctly selected, as shown in Figure 2, to ensure the appropriate output voltage level on the secondary side of the transformer.
Regrettably, this extremely important step is often not taken seriously by construction and acceptance. For example, the author's house is located in the middle of the distribution line. The measured power voltage is actually 237 V, and the deviation is + 8 %. It is conceivable that the voltage deviation of the first-end house will exceed + 10%. The position of the voltage regulator switch is definitely not correct.
In this large value overvoltage for many years, the life of electrical equipment must be shortened to a considerable extent. Sadly, the household suffers from unnecessary loss but has no knowledge of it. This situation can be quite common.
In the construction and installation of substations, it is generally unwilling to change the position of the transformer regulating switch. The reason is that the operation is improper, and the contact resistance of the contact of the voltage regulating switch is increased to cause local overheating. In fact, this can be completely avoided. After adjusting the position of the pressure regulating switch, the experienced electrician always rotates the handle of the pressure regulating switch and then rotates it back and forth a little to make the contact better and avoid the overheating of the contact. Rather than adjusting the voltage regulator switch correctly, the voltage deviation is too large, but it is extremely irresponsible to the user.
Mistaken version of the title title qualification exam questions misleading on the voltage adjustment concept
A colleague gave the author a review of the 2014 design qualification exam, which was reproduced as follows:
A workshop substation is equipped with a transformer of 1 600 kVA, 10 kV ± 2 × 2. 5 % / 0.4 kV and an impedance voltage of 6%. The low-voltage busbar is equipped with a 300 kvar shunt compensation capacitor, which is fully input when normal.
Problem: The maximum voltage loss from the substation low voltage bus to the remote equipment distribution line is 5%, the minimum voltage loss to the near-end equipment feeder line is 0.95%, and the transformer full-load voltage loss is 2%. The electrical equipment allows voltage deviations within ± 5 %. Calculate and judge which of the transformer taps: a. + 5%; b. 0; c. - 2. 5 %; d. - 5 %.
I can't answer this question after reading the exam questions. The position of the transformer voltage regulating switch only needs to adapt to the voltage level of the 10 kV incoming line, as shown in Figure 2 of this paper.
Make the output voltage of the secondary side of the transformer meet the nominal voltage requirement of the low-voltage electrical equipment, that is, the no-load output voltage of the secondary side of the transformer is 230 / 400 V. Under this premise, the low-voltage system is correctly designed, the voltage loss is verified, and the electric equipment is used. The input voltage deviation is not more than ± 5 %. The position of the transformer voltage regulating switch has nothing to do with some technical parameters of the low-voltage power distribution system. The choice of the position of the transformer voltage regulating switch in the test is determined by the data of the low-voltage power distribution line, so that the examinee can carry out complicated calculations, which is obviously wrong.
This error test explains the gap in the theoretical level of voltage regulation in China's building electrical, and it is this improper test that prompted the author to dedicate this article, calling on peers to pay attention to the test of voltage level and voltage adjustment in building electrical.
Inspection of voltage levels should be added in construction acceptance specifications
The voltage level of the electrical equipment is too high or low, which does not endanger personal safety, but it affects the function and life of the electrical equipment for many years. This long-term adverse effect is often not noticed because it is not noticed by people. Unfortunately, China's building electrical construction acceptance specification and even the verification (Verification) chapter of IEC 60364 standard have not proposed the voltage level of electrical equipment. It is required to let the excessive voltage deviation harm the electrical equipment, which is a problem that needs to be highly valued in the construction and acceptance of building electrical construction.
When discussing the chapter of the IEC 60364 standard inspection in China's IEC / TC 64 focal point committee, the author proposes that the IEC should supplement the test of the voltage level of the electrical device every time, but it does not attract attention every time and does not discuss it. Reflect this suggestion.
At a building electrical exchange meeting in China in April 2014, Mr. Tison, Chairman of IEC / TC 64, accepted an exclusive interview with China's "Building Electrical" magazine. He euphemistically said: "TC64 has not heard too much voice from China." "China has hardly participated in the development of the consensus of IEC 60364." As a member of the IEC / TC 64 standard for many years, I am grateful to Mr. Tison for his expectations.
The above-mentioned proposal IEC / TC 64 supplements the requirements for building electrical equipment voltage level inspection as an example. China does not have no "sound", but the communication channels are not smooth enough. IEC / TC 64 does not hear some "sounds" from China. In recent years, China's IEC / TC 64 focal point committee has done a lot of useful work for the introduction and transformation of international standards for building electrical.
Mr. Tison's expectation shows that there are still some shortcomings in China's centralized work. The author sincerely hopes that China's IEC / TC 64 centralized work will be on the basis of achievements, reflecting China's "voice". A lot of work involved in the development of the IEC 60634 standard, to enhance the international reputation of China's building electrical.
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