Some standard content:
National Standard of the People's Republic of China
Loading guide for oil-immersed power transformers
Loading guide for oil-immersed power transformers This standard is equivalent to IEC354·1991 "Loading guide for oil-immersed power transformers". 1 Subject content and scope of application
GB/T 15164—94
IEC354—1991
This standard specifies the limiting conditions for oil-immersed power transformers with loads exceeding the nameplate rating, the calculation method of the hot spot temperature of the windings under steady and transient conditions, and recommends mathematical models for temperature calculation and load tables and load diagrams for estimating the load conditions and life loss of various types of transformers.
This standard applies to the operation of oil-immersed power transformers with loads exceeding the nameplate rating. For electric furnace transformers with loads exceeding the nameplate rating, the user should negotiate with the manufacturer to determine their specific load diagrams. 2 Reference Standards
GB1094 Power Transformer
3 Terms and Symbols
3.1 Distribution Transformer
It is a transformer that reduces the network voltage to the voltage used by users, has independent windings, is cooled by natural oil circulation, has a maximum three-phase capacity of 2500kVA, a maximum single-phase capacity of 833kV+A, and a maximum voltage level of 35kV. 3.2 Medium Transformer
For transformers with independent windings, a three-phase rated capacity not exceeding 100MV·A or a capacity per column not exceeding 33MV·A, the rated short-circuit impedance (Z) shall meet the following requirements:
Where: W-—the number of core columns of the winding;
S,-rated capacity, MV.A.
For the equivalent capacity of autotransformers, see Appendix A. 3.3 Large transformers
Three-phase rated capacity exceeds 100 MV·A transformers, or short-circuit impedance (Z) exceeds the limit of 3.2. 3.4 Cyclic load
Cyclic load (usually one day), which is considered as the average aging amount within one cycle. It can be a normal load or a long-term emergency load.
3.5 Normal cyclic load
In cyclic load, the ambient temperature is high during a certain period of time, or a current exceeding the rated load is applied, but it can be compensated by the ambient temperature being low at other times, or a current under the rated load is applied. From the point of view of thermal aging, as long as the aging values in GB/T15164-94 approved by the State Administration of Technical Supervision on July 7, 1994 and implemented on January 1, 1995 with an aging rate greater than 1 can be compensated by the aging values with an aging rate less than 1, then this cyclic load can be considered to be equivalent to the rated load applied at normal ambient temperature. This principle can be used in long-term cyclic load operation. 3.6 Long-term emergency cyclic load This load is caused by the long-term withdrawal of some transformers in the system. Before the temperature rise of the operating transformer stabilizes, the withdrawn transformer cannot be put back into operation. This abnormal operation may last for weeks or even months, which will cause serious aging of the operating transformer, but the insulation should not be broken down (due to thermal degradation or reduced insulation strength). 3.7 Short-term emergency load
This load is caused by one or more accidents in the operating system, which seriously interferes with the normal load distribution of the system, causing the transformer to be seriously overloaded, causing the hot spot temperature of the conductor to reach a dangerous level, and may cause a temporary decrease in insulation strength. Nevertheless, compared with other methods, this short-term large load is still preferred. This load should occur as little as possible. Once it occurs, the load must be reduced quickly or the transformer must be withdrawn from operation as soon as possible to avoid transformer failure. The duration of this load should be less than the thermal time constant of the transformer and is related to the operating temperature before the load is increased. It should generally be less than 0.5h. 3.8 Technical symbols (used for temperature calculation) 3.8.1 Basic symbols
Annual change amplitude of daily average ambient temperature, K; change amplitude of each ambient temperature, K;
Ordinal number of the hottest day in a year;
Hot spot coefficient!
Load current, A;
Load factor (load current/rated current); relative aging value during a certain load period,
The ratio of load loss at rated current to no-load consumption; capacity, MV.A;
The number of hours of the hottest hour in a day; relative aging rate,
The number of cores of the winding;
The temperature difference between the winding and the oil, K;
·A certain month in a year (use Ding to calculate the aging and hot spot temperature throughout the year) t
Duration of peak load in the rectangular load diagram, h; short-circuit impedance, %;
Temperature, ℃;
Time constant;
ON indicates ONAN or ONAF cooling method;
indicates OFAF or FWF cooling method:
indicates ODAF or ODWF cooling method.
3.8-2 prefix
indicates temperature rise (to ambient temperature).
index (superscript symbol)
total loss to oil temperature rise exponential power;
current to winding temperature rise exponential power;
hot spot temperature applicable to OD cooling method. Subscript (general use)
about weighted ambient temperature;
GB/T 15164—94
M about ambient temperature used for hot spot temperature calculation; w
about winding;
about ambient temperature:
about hot spot temperature:
about coefficient used to calculate maximum hot spot temperature: about oil
indicates rated parameters (often the last subscript symbol): indicates temperature or temperature rise at time t1
indicates parameters of each generation.
Specific subscript for oil overflow (usually the first subscript symbol) refers to the oil at the top of the winding;
im refers to the average value of the oil inside the winding:
refers to the bottom of the winding, oil tank or heat converter; h
refers to the top layer in the oil tank;
om refers to the average value in the oil tank;
refers to the top of the heat exchanger:
em refers to the average value in the heat exchanger;
bt refers to the bottom oil temperature after t hours;
bhi refers to the bottom oil temperature at the beginning,
bu refers to the bottom oil temperature at the end.
Part I Summary
4 Effects of over-nameplate loads and their general limitations 4.1 Effects of over-nameplate loads
4.1.1 Factors affecting transformer life The actual life of a transformer is closely related to various accidents (such as overvoltage, short circuit in the system and sudden load, etc.). These accidents may occur alone or simultaneously. The following factors play a decisive role in the life of the transformer: a.
The severity of the accident (value and duration): b.
Transformer design and quality,
The temperature of each part of the transformer
The water content in the solid insulating medium and oil; The content of oxygen and other gases in the solid insulating medium and oil: The number, size and type of impurities.
The normal expected life value is based on continuous operation under normal ambient temperature and rated conditions. When the load exceeds the nameplate rating and (or) the ambient temperature is higher than the normal temperature, the transformer will be exposed to a certain degree of danger and aging will be accelerated. This guideline identifies these hazards and provides guidance on how to operate transformers over their nameplate ratings under limited conditions. 4.1.2 Hazards of transformers overloaded with nameplate ratings a.
The temperature of windings, clamps, leads, insulating oil and insulating parts will increase and may reach unacceptable levels. The leakage flux density outside the core will increase, causing metal parts coupled to this leakage flux to heat up due to eddy currents. The main flux, combined with the increased leakage flux, limits the overexcitation capacity of the core. With temperature changes, the moisture and gas content in solid insulation and oil will change d.
Bushings, tap changers, cable terminal connections and current sensors will also be subject to higher thermal stresses, affecting their structure and use..comGB/T15164-94
safety margins.
Therefore, with increasing current and temperature, the risk of premature transformer failure increases. These hazards may be direct short-term characteristics or may be caused by years of accumulated deterioration of the transformer. 4.1.2.1 Short-term danger
1. For short-term faults, the main danger is that bubbles may appear in high-field strength areas (such as windings and leads), causing the insulation strength to decrease. When the hot spot temperature suddenly rises above the critical temperature, bubbles may appear in the insulating paper. For transformers with normal moisture content, this boundary temperature is approximately between 110 and 160°C. This critical temperature will be further reduced as the moisture content increases. When large metal components heat up due to leakage magnetic flux, bubbles will appear on their surface (in the oil or in the solid insulation) (or due to oil oversaturation). However, these bubbles are usually generated in areas with low field strength, and only when they flow to high field strength areas will the insulation strength be significantly reduced.
The bare metal parts inside the transformer, if not in direct thermal contact with the organic insulating material, are in direct contact with the oil. Its temperature may rise rapidly, but should not exceed 180°C.
b. At higher temperatures, the mechanical characteristics of the transformer will deteriorate over time, which may reduce its short-circuit strength. c. The increased pressure inside the bushing may cause oil leakage and cause failures. If the temperature of the insulating medium exceeds 140°C, bubbles will also form inside the bushing arm.
The oil in the oil storage cabinet may expand and overflow. d.
e. The tap changer may not be able to cut off under large currents. 4.1-2.2 Long-term dangers
a. The thermal degradation process of the mechanical characteristics of the conductor insulation will be accelerated at higher temperatures. If the thermal degradation reaches a certain level, the effective life of the transformer will be shortened. Especially when affected by a system short circuit, the life loss of the transformer will be more serious. Its Other insulating materials, like structural parts and wires, may also age at higher temperatures. h.
Due to the high current flow, the contact resistance of the tap changer may increase. In severe cases, the contact point may overheat, affecting thermal stability.
d. The sealing material of the transformer may become brittle at high temperatures. When the load conditions drop to normal operating conditions, short-term hazards generally disappear. However, from a reliability perspective, they may have more serious consequences than long-term hazards.
This guideline analyzes both short-term and long-term hazards and limits the load capacity of the transformer. The load diagrams and load tables in this guideline are based on the relationship between the expected life of the mechanical properties of paper insulation and humidity and time, and the limit of the maximum hot spot temperature is based on the temperature that will immediately cause a failure. The maximum dangerous temperature is specified. 4.1.3 The effect of transformer over-nameplate load and the relationship between transformer capacity The effect of over-nameplate load is related to the size of the transformer capacity. If the capacity is the largest, there are a. Increased leakage flux density; b. Increased short-circuit stress;
Insulation volume affected by high field strength increases: d. It is more difficult to accurately determine the hot spot temperature. Therefore, when large transformers are over-nameplate rated, they are more susceptible to damage than small transformers, and the consequences of failure are more serious than those of small transformers. In order to make the transformer operate under the expected load conditions and control the operating hazards to an appropriate degree of danger, this guide divides the transformer into three types for consideration:
a. Distribution transformers only need to consider hot spot temperature and thermal degradation: b. The influence of leakage flux on medium-sized transformers is not critical, but different cooling methods must be considered; c. The influence of leakage flux on large transformers is large, and the consequences of failure are very serious. 4.2 General limits for loads exceeding the nameplate rating (current and temperature limits)..comGB/T 15164 94
For transformers exceeding the nameplate rating, it is recommended not to exceed any of the limits specified in Table 1, and the specific limits given in Chapters 5 to 7 must also be considered.
Table 1 Current and overflow limits for loads exceeding the nameplate rating Load type
Normal cyclic load current (per unit value) Hot spot temperature and temperature of metal parts in contact with insulating materials (°C) Oil layer ()
Long-term emergency cyclic load current (per unit value) Hot spot temperature and temperature of metal parts in contact with insulating materials (°C) Top oil temperature ()
Short-term emergency load current (per unit value)
Hot spot temperature and temperature of metal parts in contact with insulating materials (°C) Top oil temperature () Temperature of metal parts in contact with insulating materials () Top oil temperature ()
5 Specific limits for loads exceeding nameplate ratings
5.1 Specific limits for distribution transformers
5.1.1 Rating limits
Distribution transformers
Medium-sized power transformers
Large-sized power transformers
The distribution transformers covered by this guideline refer to transformers with a rated capacity of 2500kV+A and below (see 3.1). 5.1.2 Current and temperature limits
The load current, hot spot temperature and top oil temperature should not exceed the limits in Table 1. The top oil temperature and hot spot temperature limits for short-term emergency loads are not specified in the table because it is usually meaningless to control the duration of emergency loads on distribution transformers. It should be noted that when the hot spot temperature exceeds 140~160C, bubbles may be generated, thereby reducing the insulation strength of the transformer (4.1.2.1). 5.1.3 Accessories and other considerations
In addition to the windings, other parts of the transformer (such as bushings, cable terminal connections, tap changers and leads, etc.) may limit the operation of the transformer when the load current exceeds 1.5 times the rated current. Oil expansion and oil pressure will also limit the operation of the transformer. 5.1.4 Indoor transformers
When the transformer is used indoors, the rated oil temperature rise must be corrected due to the influence of the lower enclosure. This additional temperature rise is best determined by testing (see Section 10.5). 5.1.5 Outdoor environmental conditions
Wind, rain and sunshine will have some effect on the load capacity of distribution transformers, but since this effect is irregular, it is not practical to consider these factors.
5.2 Specific limitations of medium-sized power transformers
5.2.1 Medium-sized power transformers include three-phase transformers of 100MV·A and below, and their impedance limits shall comply with the provisions of Section 3.2.
5.2.2 Current and temperature limits
The load current, hot spot temperature, top layer oil temperature and the temperature of metal parts other than windings and leads shall not exceed the limits specified in Table 1. It should also be noted that when the temperature exceeds 140~160 (, bubbles will be generated, which may reduce the insulation strength of the transformer (see 4.1.2.1). 5.2.3 Accessories, supporting equipment and others
Except for the windings, other parts of the transformer (such as bushings, cable terminal connectors, tap changers and leads, etc.) may limit the operation of the transformer when the load current exceeds 1.5 times the rated current. Oil expansion and oil pressure may also limit the operation of the transformer. GB/T 15164—94
Similar considerations are necessary for equipment used in conjunction with the transformer (such as cables, circuit breakers and current sensors, etc.). 5.2.4 Short-circuit requirements
The transformer may not meet the short-circuit thermal requirements (based on a short-circuit duration of 2s as specified in GB1094.5) during or after operation at a load exceeding the nameplate rating. However, the duration of the short-circuit current in operation is, in most cases, less than 2s. 5.2.5 Voltage limits
In addition to the known limits on variable flux voltage regulation (see Chapters 3 to 5 of GB1094.4), the applied voltage should not exceed 1.05 times the rated voltage (main tap) or tap voltage (other taps) of any transformer winding. 5.3 Specific limits for large power transformers
5.3.1 Overview
For large power transformers, The additional restrictions related to leakage flux must be taken into account. Therefore, when inquiring or placing an order, the load capacity value required under specific operating conditions should be clearly stated (see Appendix C). As for thermal degradation of insulation, the same calculation method can be used for all transformers (and it is recommended to use a computer for calculation), based on the actual thermal resistance of the transformer, rather than the load table in Part III. According to the current state of transformer technology, large transformers are better to use more conservative and unique loading schemes than small transformers. From the perspective of the consequences of failure, it is very important to use highly reliable loading schemes for large transformers. Therefore, the following points should be fully taken into account: a. The combination of leakage flux and the main flux in the core column or yoke makes human-type transformers more susceptible to damage caused by overexcitation than small transformers, especially when the load value exceeds the nameplate rating. The increase in flux causes metal parts to heat up due to additional eddy currents. b.The consequences of the mechanical properties of the insulation material (which is a function of temperature and time) together with the damage caused by thermal expansion may be more serious for large power transformers than for small transformers. C. Since the hot spot temperature of other parts other than the winding cannot be obtained by the positive band temperature rise test, even if the transformer does not show abnormal band phenomenon in the test at rated current, it cannot be inferred that there will be no abnormal band phenomenon at a current exceeding the rated current. d. The hot spot temperature rise value of the winding exceeding the rated current calculated based on the temperature rise test results at rated current is less reliable for large transformers than for small transformers. 5.3.2 Limits of current and temperature
The load current, hot spot temperature, top oil temperature and the temperature of metal parts other than windings and leads shall not exceed the limits specified in Table 1. It should also be noted that bubbles may be generated when the temperature exceeds 140~160℃. It is possible to reduce the insulation strength of the transformer (see 4.1.2.1). 5.3.3 For accessories, supporting equipment and other considerations, see Section 5.2.3.
5.3.4 Short-circuit withstand requirements
See Section 5.2.4.
5.3.5 Voltage limits
See Section 5.2.5.
Part II Temperature calculations
6 Direct measurement of hot spot temperature
The temperature reached by the hottest winding is the most critical limiting factor of the transformer load, so every effort should be made to accurately determine this temperature value. Now, there are direct measurement methods (using optical fiber or similar devices). The direct measurement method is more accurate than the estimation method in Chapter 7.
7 Assumed thermal characteristics
7.1 Simplified description of thermal characteristics
The formulas given in this guideline are obtained on the basis of simplified thermal characteristics. The thermal distribution diagram shown in Figure 1 is assumed and is a simplified diagram of a very complex thermal distribution.
Top of winding
Ceramic winding
GB/T 15164—94
Temperature rise of oil in the sulphur layer
Average temperature rise of oil
Bottom temperature rise of oil
Hottest temperature rise
Average temperature rise of winding
Figure 1 Thermal distribution diagram of oil-immersed transformer
. The oil temperature in each winding increases linearly from bottom to top regardless of the cooling method. The temperature rise at any position of the winding increases linearly from bottom to top. This straight line is parallel to the straight line of oil temperature rise. The difference between the two parallel lines is the band number g (g is the difference between the average temperature rise of the winding and the average temperature rise of the oil measured by the resistance method). c. The hot spot temperature rise is higher than the average temperature rise at the top of the winding (Figure 1) because a margin must be left for the increase of stray losses. Since these factors are nonlinear, the difference between the hot spot temperature and the oil temperature at the top of the winding is used as 7Ig. The value of the hot spot coefficient H is related to the capacity of the transformer, the short-circuit impedance and the winding structure. It is approximately between 1.1 and 1.5. In the load diagram and load table of the third article, the distribution transformer takes 1.1. Medium and large transformers take 1.3. 7.2 The top oil temperature measured during the temperature rise test is different from the temperature of the oil at the top of the winding. This problem is more prominent in the transient state of sudden application of high current load. In fact, the top oil temperature is formed by the confluence of the oil flow circulating inside and outside each winding. For ON-cooled transformers, the difference between the windings is not obvious; therefore, the oil temperature at the top of the winding is equal to the top oil temperature in the oil tank. For transformers with ON and OD cooling, the oil temperature at the top of the winding is equal to the bottom oil temperature plus twice the difference between the average oil temperature inside the winding and the bottom oil temperature.
Due to the different oil flows, different cooling methods should be treated separately. For transformers with ON and OF cooling methods, the circulation of oil in the winding is considered to be driven by temperature differences, while for transformers with D cooling methods, the oil circulation rate is related to the oil pump and has nothing to do with the oil temperature. 7.3 For transformers with OF and OD cooling, a more accurate method should be used to calculate the average oil temperature. Because the hot spot temperature calculation is related to it (B1094.2 stipulates a feasible method to calculate this value, which is only used to correct the average temperature rise of the winding. This guideline prefers a new method (see Appendix B for this method) to calculate the average oil temperature from the temperature rise test results. 7.4 The time band of the winding is very small (5 to 10 minutes), even under short-term high load, it has little effect on the hot spot overflow. The minimum peak load time in the load table is specified as 30min 1 (see Chapter .), so in the calculation, this time constant is approximately regarded as equal to zero. 7.5 To calculate the hot spot temperature rise under continuous load, periodic load or other operating conditions, the original thermal characteristic data from different sources can be selected: a. Directly measure the hot spot temperature or the oil temperature at the top of the winding. Special temperature rise test results (if the hot spot temperature cannot be measured directly, only the hot spot coefficient H can be provided by the manufacturer):
b. Normal temperature rise test results;
c. Calculate the temperature rise under rated current.
GB/T 15164
Table 2 Example of thermal characteristic data for calculating the load table in Part III Distribution transformer
Axis index
Winding index
Loss ratio
Hot spot coefficient
Continental time constant
Environmental humidity
Hot spot temperature rise
Winding flat groove temperature rise
Temperature difference between hot spot and top of cable group oil
Average oil temperature rise
Winding top oil temperature rise
Bottom oil temperature rise
Note: For 0N cooling method, it is considered that>, equal to 8ar(h)| |tt||Table 2 provides examples of thermal characteristics and is the basis for the preparation of the load tables in Part III of this guideline. ON..
Power transformers
For large power transformers, if the measured value of the average winding temperature rise at rated current reaches a critical value (65K for ON and OF cold load methods and 70K for OD cooling method), the hot spot temperature rise at rated current may exceed 78K (the specific situation is related to the structural design of the transformer).
8 Hot spot temperature calculation equation
8.1 Steady-state temperature equation
8. 1.1 For transformers with natural oil circulation (ON) cooling, the hottest point temperature at any load is equal to the sum of the ambient temperature, the top oil temperature rise and the temperature difference between the hot spot and the top oil.
8 = 0. + A6.[1+RK7
8. 1.2 For transformers with forced oil circulation (OF) cooling +Hg.K
For (F cooling, the calculation method is based on the bottom oil temperature and the average oil temperature (see 7.2). The final hot spot temperature at any load is equal to the sum of the ambient temperature, the bottom oil temperature rise, the difference between the top oil temperature rise of the winding and the bottom oil temperature rise, and the difference between the hot spot temperature of the winding and the top oil temperature.
β = 0. + 48[1+RK*
8.1.3 Transformer with forced oil circulation guide (()D) cooling +2[m — oJK+ Hg,K
GB/T15164—94
For OD cooling, it is basically the same as OF cooling, but considering the change of wire resistance with temperature, a correction factor must be added:
=+ 0.15(0— h)(when K 1)
In the formula, - is the calculated value without considering the influence of wire resistance, and is calculated by formula (2): - is the hot spot temperature under rated conditions.
The user can ask the manufacturer for a more accurate formula. 8.1.4 Formula correction
Theoretically, some corrections should be made when using the above formula to calculate the final hot spot temperature. For example, when the temperature changes, the following load losses should be corrected:
b. The relationship between the pure resistance loss of the winding and the eddy current loss; c. The viscosity of the oil.
For ON and OF cooling methods, the oil viscosity will offset the influence of the change in wire resistance as the temperature changes. Therefore, the influence of the change in wire resistance is not considered in this guideline.
For OD cooling method, the effect of oil viscosity on temperature rise is small, and the influence of the change in wire resistance must be considered [see formula (3)]. 8.2 Transient temperature equation
Any change in load conditions is considered as a step function. The rectangular load diagram considered in the load table of Part 3 consists of an ascending step function and another descending step function with a certain time delay. For a continuously changing load, the step functions are applied in sequence at small time intervals. Therefore, a computer program is required to calculate the hot spot temperature (see Chapter 11). The oil temperature rise (e.g. bottom oil) after time t can be calculated using the following formula: A=+(bu)(1e-/)
Where: △——initial bottom oil temperature rise, K; △—steady bottom oil temperature rise of the applied load within time t, K; t. Oil time constant.
As the load increases, the temperature difference between the winding and the oil will rise to a new value according to the winding time constant. According to Section 7.4, this time constant can be neglected. The last term of formula (1) and the last two terms of formula (2) are assumed to correspond to the new load factor N.
9 Thermal aging of transformer insulation
9.1 Thermal aging law
If other influences are not considered, the insulation system is always subjected to chemical aging. This process is cumulative and can cause the insulation system to lose its insulating properties and cannot be used again. According to the Arrhenius law of chemical thermal aging, the life of the insulation system is expressed by the following formula: Life time = e(aT)
Where: a, P—constant
T—absolute temperature.
Within the limited temperature range, this relationship can be approximated by the single exponential form of the Mönzinger aging life: 5
Where: P-constant;
9-temperature, ℃.
GB/T 1516494
Life duration-e
Note: The Münsinger thermal aging rule is a simplified form of the Ahrens chemical thermal aging law. Within the temperature range specified in this guideline, the Münsinger rule still has sufficient accuracy and gives conservative thermal aging estimates. However, there is no simple and unique end-of-life criterion that can be used to accurately describe the remaining life of transformer insulation. However, it is practical to express the aging rate as the reciprocal of the Münsinger aging life formula. Aging rate-co&st · ers
The constant const in the above formula is related to many factors, such as the intrinsic quality of fiber products (composition of raw materials and chemical additives> and environmental parameters (water and free oxygen in the insulation system, etc.). However, the overflow variation coefficient P is independent of these factors and can be taken as a constant in the actual temperature range of 80-140°C. Its relationship with temperature is that the aging rate increases by 1 times for every 6K increase in temperature. This variation relationship is the basis of this guideline. The aging rate is related to the hot spot temperature of the winding. For transformers designed according to GB1094, the commonly used reference value of the hot spot temperature is 98°C at rated load and normal ambient temperature. This guideline stipulates that the relative aging rate at this temperature is equal to 1. At present, the insulation system of many transformers uses high-quality heat-resistant insulation materials. GB1094.2 does not consider this insulation level for oil-immersed transformers. The thermal characteristics and temperature rise limits can be considered according to the agreement between the manufacturer and the operating department. After the transformer uses high heat-resistant grade insulation, its expected normal life is based on a hot spot temperature of 110°C. 9.2 Relative thermal aging rate
For transformers designed according to GB1094, the relative thermal aging rate is 1 at a hot spot temperature of 98°C. This hot spot temperature corresponds to "operating at an ambient temperature of 20°C and a hot spot temperature rise of 78K". The definition of relative thermal aging rate is: V
Thermal aging rate under product
Thermal aging rate at 98°C
—20-98)6
This function represents the law of relative aging rate changing with hot spot temperature. Its change rate is as shown in the following table. 80www.bzxz.net
Relative aging rate
9.3 Calculation of life loss
GB/T15164—94
The life loss caused by running for several months, several days or several hours at a hot spot temperature of 98 is expressed in normal months, normal days or normal hours respectively.
If the load and ambient temperature remain unchanged during the operation period, the relative loss of life is equal to Vt (t represents the operating time). This also applies to constant operating conditions and changing ambient temperature (if weighted ambient temperature is used, see Chapter 10). In short, when both operating conditions and ambient temperature are changing, the relative aging rate changes with time. The relative aging value (or relative loss of life) in a certain load period is equal to: or
Where: n—the ordinal number of each time period (or time interval); N—the total number of time periods (or time intervals). 10 Ambient temperature
For outdoor air-cooled transformers, the actual air temperature shall be used as the ambient temperature. For indoor distribution transformers, the correction value for the ambient temperature is given in 10.5. For water-cooled transformers, the ambient temperature is the inlet water temperature, which varies less with time than the air.
If the peak load time exceeds several hours, the change in ambient temperature must be considered. The user can choose one of the following methods.
a. Weighted ambient temperature is used for thermal aging calculation. The average value of the maximum ambient temperature per month is used to calculate the maximum hot spot temperature (see 10.1 and 10.2).
b The actual temperature distribution diagram (10.3) can be used directly. The changing ambient temperature can be approximated by a double sine function (10.4). 10.1 Weighted ambient temperature for thermal aging calculation (e) If the ambient temperature changes significantly during the load cycle, a weighted value should be used in the thermal aging calculation because the weighted ambient temperature is higher than the arithmetic mean ambient temperature. The weighted ambient temperature is an assumed constant ambient temperature, and the insulation aging caused by it in a certain period of time is equivalent to the insulation aging caused by the actual changing ambient temperature in the same period (which can be a few days, a few months or even a year). For every 6K increase in temperature, the aging rate doubles, and the ambient temperature is considered to change according to a sinusoidal curve. The weighted ambient temperature is equal to:
= + 0.01(4)1 5
Where: Average ambient temperature
A is the temperature range during which the temperature values are read (the average value of the maximum value minus the average value of the minimum value). The correction factor for the average ambient temperature can be obtained from Figure 2. It is a graphical form of formula (9). ..com (9)
GB/T 15164—94
Figure 2 Calibration between weighted ambient temperature and average ambient temperature 10.2 Ambient temperature for hot spot temperature calculation 6m Weighted ambient temperature can be used for thermal aging calculation, but it cannot be used to verify the highest hot spot temperature reached during peak load. It is recommended to use the average value of the monthly maximum temperature. In view of the low probability of the occurrence of the absolute maximum value and the effect of the oil time constant, the absolute maximum temperature value is not used. 10.3 Continuously changing ambient temperature
When the calculation of thermal aging and hot spot temperature is limited to a few loads exceeding the nameplate rating, it may be more appropriate to use the actual ambient temperature change curve during the predetermined period. The ambient temperature change curve must represent a set of discrete values corresponding to the selected time interval of the load change.
10.4 Sinusoidal variation of temperature
When calculations are made over periods of many days or months, it is convenient to regard the ambient temperature variation as following two sinusoidal variations, the first representing the temperature variation over the whole year and the second representing the temperature variation at each stage. (T-TX)
= d + Acos
(D - DX) +(R or B.)cos
Annual average ambient temperature, S;
Annual variation amplitude of daily average ambient temperature, K: daily temperature variation amplitude used to calculate aging rate, K, daily temperature variation amplitude used to calculate maximum hot spot temperature, K; -The hottest day number in the year, D represents the number of a certain day in a year, such as February 1st is 32 days;.(10)
: The time sequence number of the hottest hour in the day, T represents the time sequence number of a certain hour in a day, such as 1:15 pm is 13.25 h.
To calculate these parameters, it is necessary to compile a computer program (as shown in Appendix D) and input the four temperature characteristics of each month of the year into the computer.
10.5 Ambient temperature correction when the transformer is running in an enclosure When the transformer is running in an enclosure, its temperature rise will increase by an additional value, which is about half of the temperature rise of the air in the enclosure. Tests show that the law of change of the additional temperature rise of the top layer oil with the load current is roughly similar to the law of change of the top layer oil temperature rise. Therefore, for transformers installed in an enclosure (such as a metal shell or a concrete room), △ in formula (1) should be replaced by the following. A - 4. + A(40..)
(11)℃.
GB/T 1516494
Life duration-e
Note: The Münsinger thermal aging rule is a simplified form of the Ahrens chemical thermal aging law. Within the temperature range specified in this guideline, the Münsinger rule still has sufficient accuracy and gives conservative thermal aging estimates. However, there is no simple and unique end-of-life criterion that can be used to accurately describe the remaining life of transformer insulation. However, it is practical to express the aging rate as the inverse of the Münsinger aging life formula. Aging rate-co&st · ers
The constant const in the above formula is related to many factors, such as the intrinsic quality of fiber products (composition of raw materials and chemical additives> and environmental parameters (water and free oxygen in the insulation system, etc.). However, the overflow variation coefficient P is independent of these factors and can be taken as a constant in the actual temperature range of 80-140°C. Its relationship with temperature is that the aging rate increases by 1 times for every 6K increase in temperature. This variation relationship is the basis of this guideline. The aging rate is related to the hot spot temperature of the winding. For transformers designed according to GB1094, the commonly used reference value of the hot spot temperature is 98°C at rated load and normal ambient temperature. This guideline stipulates that the relative aging rate at this temperature is equal to 1. At present, the insulation system of many transformers uses high-quality heat-resistant insulation materials. GB1094.2 does not consider this insulation level for oil-immersed transformers. The thermal characteristics and temperature rise limits can be considered according to the agreement between the manufacturer and the operating department. After the transformer uses high heat-resistant grade insulation, its expected normal life is based on a hot spot temperature of 110°C. 9.2 Relative thermal aging rate
For transformers designed according to GB1094, the relative thermal aging rate is 1 at a hot spot temperature of 98°C. This hot spot temperature corresponds to "operating at an ambient temperature of 20°C and a hot spot temperature rise of 78K". The definition of relative thermal aging rate is: V
Thermal aging rate under product
Thermal aging rate at 98°C
—20-98)6
This function represents the law of relative aging rate changing with hot spot temperature. Its change rate is as shown in the following table. 80
Relative aging rate
9.3 Calculation of life loss
GB/T15164—94
The life loss caused by running for several months, several days or several hours at a hot spot temperature of 98 is expressed in normal months, normal days or normal hours respectively.
If the load and ambient temperature remain unchanged during the operation period, the relative loss of life is equal to Vt (t represents the operating time). This also applies to constant operating conditions and changing ambient temperature (if weighted ambient temperature is used, see Chapter 10). In short, when both operating conditions and ambient temperature are changing, the relative aging rate changes with time. The relative aging value (or relative loss of life) in a certain load period is equal to: or
Where: n—the ordinal number of each time period (or time interval); N—the total number of time periods (or time intervals). 10 Ambient temperature
For outdoor air-cooled transformers, the actual air temperature shall be used as the ambient temperature. For indoor distribution transformers, the correction value for the ambient temperature is given in 10.5. For water-cooled transformers, the ambient temperature is the inlet water temperature, which varies less with time than the air.
If the peak load time exceeds several hours, the change in ambient temperature must be considered. The user can choose one of the following methods.
a. Weighted ambient temperature is used for thermal aging calculation. The average value of the maximum ambient temperature per month is used to calculate the maximum hot spot temperature (see 10.1 and 10.2).
b The actual temperature distribution diagram (10.3) can be used directly. The changing ambient temperature can be approximated by a double sine function (10.4). 10.1 Weighted ambient temperature for thermal aging calculation (e) If the ambient temperature changes significantly during the load cycle, a weighted value should be used in the thermal aging calculation because the weighted ambient temperature is higher than the arithmetic mean ambient temperature. The weighted ambient temperature is an assumed constant ambient temperature, and the insulation aging caused by it in a certain period of time is equivalent to the insulation aging caused by the actual changing ambient temperature in the same period (which can be a few days, a few months or even a year). For every 6K increase in temperature, the aging rate doubles, and the ambient temperature is considered to change according to a sinusoidal curve. The weighted ambient temperature is equal to:
= + 0.01(4)1 5
Where: Average ambient temperature
A is the temperature range during which the temperature values are read (the average value of the maximum value minus the average value of the minimum value). The correction factor for the average ambient temperature can be obtained from Figure 2. It is a graphical form of formula (9). ..com (9)
GB/T 15164—94
Figure 2 Calibration between weighted ambient temperature and average ambient temperature 10.2 Ambient temperature for hot spot temperature calculation 6m Weighted ambient temperature can be used for thermal aging calculation, but it cannot be used to verify the highest hot spot temperature reached during peak load. It is recommended to use the average value of the monthly maximum temperature. In view of the low probability of the occurrence of the absolute maximum value and the effect of the oil time constant, the absolute maximum temperature value is not used. 10.3 Continuously changing ambient temperature
When the calculation of thermal aging and hot spot temperature is limited to a few loads exceeding the nameplate rating, it may be more appropriate to use the actual ambient temperature change curve during the predetermined period. The ambient temperature change curve must represent a set of discrete values corresponding to the selected time interval of the load change.
10.4 Sinusoidal variation of temperature
When calculations are made over periods of many days or months, it is convenient to regard the ambient temperature variation as following two sinusoidal variations, the first representing the temperature variation over the whole year and the second representing the temperature variation at each stage. (T-TX)
= d + Acos
(D - DX) +(R or B.)cos
Annual average ambient temperature, S;
Annual variation amplitude of daily average ambient temperature, K: daily temperature variation amplitude used to calculate aging rate, K, daily temperature variation amplitude used to calculate maximum hot spot temperature, K; -The hottest day number in the year, D represents the number of a certain day in a year, such as February 1st is 32 days;.(10)
: The time sequence number of the hottest hour in the day, T represents the time sequence number of a certain hour in a day, such as 1:15 pm is 13.25 h.
To calculate these parameters, it is necessary to compile a computer program (as shown in Appendix D) and input the four temperature characteristics of each month of the year into the computer.
10.5 Ambient temperature correction when the transformer is running in an enclosure When the transformer is running in an enclosure, its temperature rise will increase by an additional value, which is about half of the temperature rise of the air in the enclosure. Tests show that the law of change of the additional temperature rise of the top layer oil with the load current is roughly similar to the law of change of the top layer oil temperature rise. Therefore, for transformers installed in an enclosure (such as a metal shell or a concrete room), △ in formula (1) should be replaced by the following. A - 4. + A(40..)
(11)℃.
GB/T 1516494
Life duration-e
Note: The Münsinger thermal aging rule is a simplified form of the Ahrens chemical thermal aging law. Within the temperature range specified in this guideline, the Münsinger rule still has sufficient accuracy and gives conservative thermal aging estimates. However, there is no simple and unique end-of-life criterion that can be used to accurately describe the remaining life of transformer insulation. However, it is practical to express the aging rate as the inverse of the Münsinger aging life formula. Aging rate-co&st · ers
The constant const in the above formula is related to many factors, such as the intrinsic quality of fiber products (composition of raw materials and chemical additives> and environmental parameters (water and free oxygen in the insulation system, etc.). However, the overflow variation coefficient P is independent of these factors and can be taken as a constant in the actual temperature range of 80-140°C. Its relationship with temperature is that the aging rate increases by 1 times for every 6K increase in temperature. This variation relationship is the basis of this guideline. The aging rate is related to the hot spot temperature of the winding. For transformers designed according to GB1094, the commonly used reference value of the hot spot temperature is 98°C at rated load and normal ambient temperature. This guideline stipulates that the relative aging rate at this temperature is equal to 1. At present, the insulation system of many transformers uses high-quality heat-resistant insulation materials. GB1094.2 does not consider this insulation level for oil-immersed transformers. The thermal characteristics and temperature rise limits can be considered according to the agreement between the manufacturer and the operating department. After the transformer uses high heat-resistant grade insulation, its expected normal life is based on a hot spot temperature of 110°C. 9.2 Relative thermal aging rate
For transformers designed according to GB1094, the relative thermal aging rate is 1 at a hot spot temperature of 98°C. This hot spot temperature corresponds to "operating at an ambient temperature of 20°C and a hot spot temperature rise of 78K". The definition of relative thermal aging rate is: V
Thermal aging rate under product
Thermal aging rate at 98°C
—20-98)6
This function represents the law of relative aging rate changing with hot spot temperature. Its change rate is as shown in the following table. 80
Relative aging rate
9.3 Calculation of life loss
GB/T15164—94
The life loss caused by running for several months, several days or several hours at a hot spot temperature of 98 is expressed in normal months, normal days or normal hours respectively.
If the load and ambient temperature remain unchanged during the operation period, the relative loss of life is equal to Vt (t represents the operating time). This also applies to constant operating conditions and changing ambient temperature (if weighted ambient temperature is used, see Chapter 10). In short, when both operating conditions and ambient temperature are changing, the relative aging rate changes with time. The relative aging value (or relative loss of life) in a certain load period is equal to: or
Where: n—the ordinal number of each time period (or time interval); N—the total number of time periods (or time intervals). 10 Ambient temperature
For outdoor air-cooled transformers, the actual air temperature shall be used as the ambient temperature. For indoor distribution transformers, the correction value for the ambient temperature is given in 10.5. For water-cooled transformers, the ambient temperature is the inlet water temperature, which varies less with time than the air.
If the peak load time exceeds several hours, the change in ambient temperature must be considered. The user can choose one of the following methods.
a. Weighted ambient temperature is used for thermal aging calculation. The average value of the maximum ambient temperature per month is used to calculate the maximum hot spot temperature (see 10.1 and 10.2).
b The actual temperature distribution diagram (10.3) can be used directly. The changing ambient temperature can be approximated by a double sine function (10.4). 10.1 Weighted ambient temperature for thermal aging calculation (e) If the ambient temperature changes significantly during the load cycle, a weighted value should be used in the thermal aging calculation because the weighted ambient temperature is higher than the arithmetic mean ambient temperature. The weighted ambient temperature is an assumed constant ambient temperature, and the insulation aging caused by it in a certain period of time is equivalent to the insulation aging caused by the actual changing ambient temperature in the same period (which can be a few days, a few months or even a year). For every 6K increase in temperature, the aging rate doubles, and the ambient temperature is considered to change according to a sinusoidal curve. The weighted ambient temperature is equal to:
= + 0.01(4)1 5
Where: Average ambient temperature
A is the temperature range during which the temperature values are read (the average value of the maximum value minus the average value of the minimum value). The correction factor for the average ambient temperature can be obtained from Figure 2. It is a graphical form of formula (9). ..com (9)
GB/T 15164—94
Figure 2 Calibration between weighted ambient temperature and average ambient temperature 10.2 Ambient temperature for hot spot temperature calculation 6m Weighted ambient temperature can be used for thermal aging calculation, but it cannot be used to verify the highest hot spot temperature reached during peak load. It is recommended to use the average value of the monthly maximum temperature. In view of the low probability of the occurrence of the absolute maximum value and the effect of the oil time constant, the absolute maximum temperature value is not used. 10.3 Continuously changing ambient temperature
When the calculation of thermal aging and hot spot temperature is limited to a few loads exceeding the nameplate rating, it may be more appropriate to use the actual ambient temperature change curve during the predetermined period. The ambient temperature change curve must represent a set of discrete values corresponding to the selected time interval of the load change.
10.4 Sinusoidal variation of temperature
When calculations are made over periods of many days or months, it is convenient to regard the ambient temperature variation as following two sinusoidal variations, the first representing the temperature variation over the whole year and the second representing the temperature variation at each stage. (T-TX)
= d + Acos
(D - DX) +(R or B.)cos
Annual average ambient temperature, S;
Annual variation amplitude of daily average ambient temperature, K: daily temperature variation amplitude used to calculate aging rate, K, daily temperature variation amplitude used to calculate maximum hot spot temperature, K; -The hottest day number in the year, D represents the number of a certain day in a year, such as February 1st is 32 days;.(10)
: The time sequence number of the hottest hour in the day, T represents the time sequence number of a certain hour in a day, such as 1:15 pm is 13.25 h.
To calculate these parameters, it is necessary to compile a computer program (as shown in Appendix D) and input the four temperature characteristics of each month of the year into the computer.
10.5 Ambient temperature correction when the transformer is running in an enclosure When the transformer is running in an enclosure, its temperature rise will increase by an additional value, which is about half of the temperature rise of the air in the enclosure. Tests show that the law of change of the additional temperature rise of the top layer oil with the load current is roughly similar to the law of change of the top layer oil temperature rise. Therefore, for transformers installed in an enclosure (such as a metal shell or a concrete room), △ in formula (1) should be replaced by the following. A - 4. + A(40..)
(11)2 Relative thermal aging rate
For transformers designed according to GB1094, the relative thermal aging rate is 1 at a hot spot temperature of 98°C. This hot spot temperature corresponds to "operating at an ambient temperature of 20°C and a hot spot temperature rise of 78K". The definition of relative thermal aging rate is: V
Thermal aging rate under product
Thermal aging rate at 98°C
—20-98)6
This function represents the law of relative aging rate changing with hot spot temperature. Its change rate is shown in the following table. 80
Relative aging rate
9.3 Life loss calculation
GB/T15164—94
The life loss caused by operating for several months, several days or several hours at a hot spot temperature of 98 is expressed in normal months, normal days or normal hours respectively.
If the load and ambient temperature remain constant during the operation, the relative loss of life is equal to Vt (t represents the operating time). The same applies to constant operating conditions and changing ambient temperature (if weighted ambient temperature is used, see Chapter 10). In short, when both operating conditions and ambient temperature are changing, the relative aging rate changes with time. The relative aging value (or relative loss of life) during a certain load period is equal to: or
Where: n is the ordinal number of each time period (or time interval); N is the total number of time periods (or time intervals). 10 Ambient temperature
For outdoor air-cooled transformers, the actual air temperature should be used as the ambient temperature. For indoor distribution transformers, the correction value for the ambient temperature is given in Article 10.5; for water-cooled transformers, the ambient temperature is the inlet water temperature, which varies less with time than the air.
If the peak load time exceeds several hours, the change in ambient temperature must be taken into account. The user can choose one of the following methods.
a. Thermal aging calculation uses weighted ambient temperature. The maximum hot spot temperature is calculated by taking the average value of the maximum ambient temperature per month (see 10.1 and 10.2). The actual temperature distribution diagram (10.3) can be used directly. The changing ambient temperature can be approximated by the double sine function (10.4). 10.1 Weighted ambient temperature for thermal aging calculation (e) If the ambient temperature changes significantly during the load cycle, a weighted value should be used in the thermal aging calculation because the weighted ambient temperature is higher than the arithmetic mean ambient temperature. The weighted ambient temperature is an assumed constant ambient temperature. The insulation aging caused by it in a certain period of time is equivalent to the insulation aging caused by the actual changing ambient temperature in the same period (which can be several days, several months or even years). For every 6K increase in temperature, the aging rate doubles, and the ambient temperature is considered to vary according to a sinusoidal curve, the weighted ambient temperature is equal to:
die = + 0.01(4)1 5
where: Average ambient temperature
A is the temperature range during which the temperature values are read (the average of the maximum values minus the average of the minimum values). The correction factor for the average ambient temperature can be obtained from Figure 2. It is a graphical form of formula (9). ..com (9)
GB/T 15164—94
Figure 2 Correction factor between weighted ambient temperature and average ambient temperature 10.2 Ambient temperature for hot spot temperature calculation 6m The weighted ambient temperature can be used for thermal aging calculations, but it cannot be used to verify the highest hot spot temperature reached during peak load. It is recommended to use the average value of the monthly maximum temperature. Considering the low probability of the occurrence of the absolute maximum value and the effect of the oil time constant, the absolute maximum temperature value is not used. 10.3 Continuously Changing Ambient Temperature
When the calculations of thermal aging and hot spot temperatures are limited to a few hours of operation above the nameplate rating, it may be more appropriate to use a curve of the actual ambient temperature variation over a predetermined period of time. The ambient temperature variation curve must represent a set of discrete values corresponding to selected time intervals of load variation.
10.4 Sinusoidal Pattern of Variation of Temperature
When calculations are made over periods of many days or months, it is convenient to consider the ambient temperature variation as varying according to two sinusoidal patterns, the first sinusoid representing the temperature variation over the entire year and the second sinusoid representing the temperature variation at each stage. (T-TX)
= d + Acos
(D - DX) +(R or B.)cos
Annual average ambient temperature, S;
Annual variation amplitude of daily average ambient temperature, K: daily temperature variation amplitude used to calculate aging rate, K, daily temperature variation amplitude used to calculate maximum hot spot temperature, K; -The hottest day number in the year, D represents the number of a certain day in a year, such as February 1st is 32 days;.(10)
: The time sequence number of the hottest hour in the day, T represents the time sequence number of a certain hour in a day, such as 1:15 pm is 13.25 h.
To calculate these parameters, it is necessary to compile a computer program (as shown in Appendix D) and input the four temperature characteristics of each month of the year into the computer.
10.5 Ambient temperature correction when the transformer is running in an enclosure When the transformer is running in an enclosure, its temperature rise will increase by an additional value, which is about half of the temperature rise of the air in the enclosure. Tests show that the law of change of the additional temperature rise of the top layer oil with the load current is roughly similar to the law of change of the top layer oil temperature rise. Therefore, for transformers installed in an enclosure (such as a metal shell or a concrete room), △ in formula (1) should be replaced by the following. A - 4. + A(40..)
(11)2 Relative thermal aging rate
For transformers designed according to GB1094, the relative thermal aging rate is 1 at a hot spot temperature of 98°C. This hot spot temperature corresponds to "operating at an ambient temperature of 20°C and a hot spot temperature rise of 78K". The definition of relative thermal aging rate is: V
Thermal aging rate under product
Thermal aging rate at 98°C
—20-98)6
This function represents the law of relative aging rate changing with hot spot temperature. Its change rate is shown in the following table. 80
Relative aging rate
9.3 Life loss calculation
GB/T15164—94
The life loss caused by operating for several months, several days or several hours at a hot spot temperature of 98 is expressed in normal months, normal days or normal hours respectively.
If the load and ambient temperature remain constant during the operation, the relative loss of life is equal to Vt (t represents the operating time). The same applies to constant operating conditions and changing ambient temperature (if weighted ambient temperature is used, see Chapter 10). In short, when both operating conditions and ambient temperature are changing, the relative aging rate changes with time. The relative aging value (or relative loss of life) during a certain load period is equal to: or
Where: n is the ordinal number of each time period (or time interval); N is the total number of time periods (or time intervals). 10 Ambient temperature
For outdoor air-cooled transformers, the actual air temperature should be used as the ambient temperature. For indoor distribution transformers, the correction value for the ambient temperature is given in Article 10.5; for water-cooled transformers, the ambient temperature is the inlet water temperature, which varies less with time than the air.
If the peak load time exceeds several hours, the change in ambient temperature must be taken into account. The user can choose one of the following methods.
a. Thermal aging calculation uses weighted ambient temperature. The maximum hot spot temperature is calculated by taking the average value of the maximum ambient temperature per month (see 10.1 and 10.2). The actual temperature distribution diagram (10.3) can be used directly. The changing ambient temperature can be approximated by the double sine function (10.4). 10.1 Weighted ambient temperature for thermal aging calculation (e) If the ambient temperature changes significantly during the load cycle, a weighted value should be used in the thermal aging calculation because the weighted ambient temperature is higher than the arithmetic mean ambient temperature. The weighted ambient temperature is an assumed constant ambient temperature. The insulation aging caused by it in a certain period of time is equivalent to the insulation aging caused by the actual changing ambient temperature in the same period (which can be several days, several months or even years). For every 6K increase in temperature, the aging rate doubles, and the ambient temperature is considered to vary according to a sinusoidal curve, the weighted ambient temperature is equal to:
die = + 0.01(4)1 5
where: Average ambient temperature
A is the temperature range during which the temperature values are read (the average of the maximum values minus the average of the
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