GB 1094.5-1985 Power transformers Part 5 Capacity to withstand short circuits GB1094.5-1985 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Power transformers
Part 5: Ability to withstand short circuit
Power transformers
Part 5: Ability to withstand short circuitThis standard refers to and adopts the international standard IEC76-5 (1976) "Power transformer 1 Requirements for short circuit resistance
1.1 Overview
Part 5
UDC621.314.222
GB1094.5-85
Replaces 1094-79
Ability to withstand short circuit".
The transformer should be able to withstand the thermal and dynamic stability effects of external short circuit without damage under the conditions specified in Article 1.2 of this standard. External short circuit includes three-phase short circuit, phase-to-phase short circuit, two-phase grounding and phase-to-ground fault. The current caused by these faults in the winding is called "overcurrent" in this standard.
1.2 Overcurrent conditions
1.2.1 Transformers with two independent windings 1.2.1.1 The rated capacity of three-phase or three-phase group transformers is divided into three categories: Category I: less than 3150kVA;
Category II: 3150~40000kVA;
Category III: 40000kVA and above.
1.2.1.2 Symmetrical short-circuit current (effective value see Section 2.1.2 of this standard) For transformers of capacity of Category II and Category III, the short-circuit impedance of the transformer plus the impedance of the system should be used for calculation. For transformers of capacity of Category I, if the short-circuit impedance of the system is greater than 5% of the short-circuit impedance of the transformer, the short-circuit current calculation is the same as above, otherwise the short-circuit impedance of the system is ignored. The peak value of the short-circuit current should be calculated in accordance with Section 2.2.3 of this standard.
1.2.1.3 The typical values ​​of the short-circuit impedance of the transformer, expressed as the impedance voltage at the rated current (main tap), are given in Table 1. If a lower impedance voltage value is required, the ability of the transformer to withstand short circuits shall be determined by negotiation between the manufacturer and the user. Table 1:
Typical impedance voltage values ​​for transformers with two independent windings Rated capacity, kVA
630 and below
631~1250
1251~3150
3151~6300
6301~12500www.bzxz.net
12501~25000
25001~200000
Note: ① The typical impedance voltage of transformers with a rated capacity greater than 200MVA shall be determined by negotiation separately. ②When the three-phase group is composed of several single-phase transformers, the value of the rated capacity applies to the three-phase group. ③For specific impedance voltage values ​​of different rated capacities and voltage levels, see the provisions of the corresponding national standards. Approved by the National Bureau of Standards on November 22, 1985
Impedance voltage, %
Implementation on July 1, 1986
GB1094.5-85
1.2.1.4In order to obtain the symmetrical short-circuit current required for design and testing, the user department shall propose the system's apparent short-circuit capacity. If not proposed, it shall be selected according to Table 2.
Table 2 System short-circuit apparent capacity
Voltage level, kV
System maximum voltage, kV
System short-circuit apparent capacity, MVA
1.2.2 The overcurrent in the windings (including the stabilizing winding and the auxiliary winding) of multi-winding transformers, transformers with stabilizing windings and autotransformers with tertiary windings shall be determined according to the impedance of the transformer and the system. The possible feedback from rotating machines or other transformers and different types of system faults should be considered. These system faults can occur during operation, such as phase-to-ground and phase-to-phase faults, which are related to the grounding conditions of the system and transformer. The characteristics of each system (at least the range of short-circuit level and the ratio of zero-sequence impedance to positive-sequence impedance) shall be technically required by the user department when inquiring and ordering. When the overcurrent caused by the combined impedance of the transformer and the system exceeds the value calculated according to the data in Tables 1 and 2, the manufacturer shall inform the user department of the maximum overcurrent that the transformer can withstand. At this time, the user department shall take measures to limit the short-circuit current to the overcurrent value specified by the manufacturer.
The stabilizing winding of a three-phase transformer shall be able to withstand overcurrents caused by different types of system faults, which may occur during operation and are related to the grounding conditions of the relevant system. For auxiliary windings in multi-winding transformers, it may be uneconomical to design them to withstand short circuits at the terminals. In this case, appropriate methods (such as series reactors or fuses) must be used to limit the effects of overcurrents. Care should also be taken to prevent faults in the line between the transformer and its protective device. In the case of a three-phase group composed of single-phase transformers, the stabilizing winding shall be able to withstand short-circuit currents at its terminals unless the user has determined that special protection measures will be taken to avoid phase-to-phase short circuits. 1.2.3 Step-up transformer
The impedance value of the step-up transformer can be very low, so the overcurrent in the winding is mainly determined by the system characteristics at the location where the transformer is installed. These characteristics should be proposed by the user when inquiring and ordering. When the overcurrent caused by the combined impedance of the transformer and the system exceeds the value calculated according to the data in Tables 1 and 2, the manufacturer shall inform the user of the maximum overcurrent that the transformer can withstand. At this time, the user should take measures to limit the short-circuit current to the overcurrent value specified by the manufacturer.
1.2.4 Transformers directly connected to other electrical appliances When the transformer is directly connected to other electrical appliances, the impedance of these appliances will also limit the short-circuit current. The sum of the impedances of the transformer, the system and the electrical appliances directly connected to the transformer can be considered, which must be determined by the manufacturer and the user. If the connection between the generator and the transformer makes the possibility of phase-to-phase or two-phase grounding faults negligible within this range, the above description also applies to generator transformers. Note: If the generator and transformer are connected as above and a star-delta connected generator transformer with a grounded neutral point is used, the most serious short-circuit situation may occur when a line-to-ground fault occurs in the system connected to the star-connected winding. 1.2.5 Special transformers
The ability of the transformer to withstand frequent overcurrents caused by operating mode or special use occasions (such as electric furnace transformers and traction transformers) should be determined by the manufacturer and the user. GB1094.5—85
1.2.6 Tap-changing device
When the transformer has tap-changing, the tap-changing device should be able to carry the same overcurrent caused by short circuit as the winding. 1.2.7 Neutral point terminal
The neutral point terminal of the star connection or zigzag connection should be designed according to the maximum overcurrent that may flow through this terminal. 2 Verification of the ability to withstand short circuit
2.1 Thermal resistance to withstand short circuit
2.1.1 Overview
The thermal resistance of the transformer to withstand short circuit should be verified based on calculation. 2.1.2 Symmetrical short-circuit current 1 value of two-winding transformer The effective value of the symmetrical short-circuit current of a three-phase transformer is calculated as follows: U
J3 (Z. +Z.)
Where:
--symmetrical short-circuit current, kA;
--system impedance, ohms per phase;
system rated voltage;
system short-circuit apparent capacity, MVA.
U and Z. are as follows:
For the main tapping
U is the rated voltage Un of the winding under consideration, expressed in kV. Z: is the short-circuit impedance of the transformer converted to the winding under consideration, calculated as follows: UzUn?
100·SN
Where: Z.-
short-circuit impedance, ohms per phase;
impedance voltage at rated current converted to reference temperature, expressed as a fraction; SN
rated capacity of the transformer, MVA.
b. Other taps except the main tap
U is the tap voltage (kV) of the winding under consideration at the corresponding tap. Z: is the short-circuit impedance converted to the winding under consideration at the corresponding tap, expressed in ohms per phase. For transformers of Class 1 capacity, if the short-circuit impedance of the system is equal to or less than 5% of the short-circuit impedance of the transformer, it shall be ignored in the calculation.
2.1.3 Duration of symmetrical short-circuit current 1 When the user department does not make other requirements, the duration of the current used to calculate the short-circuit heat resistance capacity is 2s. Note: For autotransformers and transformers with short-circuit current exceeding 25 times the rated current, the duration of the short-circuit current may be less than 25 after consultation between the manufacturer and the user department.
2.1.4 The maximum permissible value of the highest half-average temperature 9, is based on the initial temperature of the coil. Its value is the sum of the maximum permissible ambient temperature and the coil temperature rise measured by the resistance method under rated conditions (if this temperature rise value is not available, the temperature rise corresponding to the insulation heat resistance grade of the coil may also be used). When the current value calculated in 2.1.2 and the duration of 2.1.3 are carried, the highest average temperature 9, of any tap of the coil shall not exceed the value 2 specified in Table 3. 81
Transformer type
Oil immersed
2.1.5 Calculation of temperature 6,
GB1094.5-85
Table 3 Maximum permissible value of the average temperature 2 of the coil after short circuit 92
Insulation heat grade
250℃
After short circuit, the highest average temperature ?, reached by the coil is calculated by the following formula: 9,=9. [email protected]?.t.10-3
Maximum average temperature, ℃;
200 ℃
Starting temperature of the coil (℃), which is the sum of the maximum temperature of the cooling medium and the temperature rise limit of the coil. For example, for air-cooled oil-immersed transformers 0. is 105℃, and for water-cooled oil-immersed transformers it is 95℃ Short-circuit current density, A/mm2;
Duration, s;
0—1/2 (92+9.) function, see Table 4. Table 4 corresponds to the value of a of the 1/2 (92+6) function
(2+),℃
Copper wire coil
Aluminum coil
2.1.6 Symmetrical short-circuit current 1 value overcurrent of multi-winding transformers, transformers with stabilizing windings, and autotransformers with third windings shall be calculated in accordance with the provisions of 1.2.2. The maximum average temperature of each coil is calculated according to 2.1.3, 2.1.4 and 2.1.5, and its value should not exceed the maximum allowable value listed in Table 3.
2.2 Dynamic stability ability to withstand short circuit
2.2.1 Overview
The dynamic stability ability of the transformer to withstand short circuit is verified by test or reference to the test of similar transformers. The short-circuit test is a special test and is carried out in accordance with the following clauses. Transformers with a capacity of Class III cannot generally be tested in accordance with this standard. The test conditions for multi-winding transformers and autotransformers are usually determined by consultation between the manufacturer and the user department. 2.2.2 Conditions of the transformer before the short-circuit test
2.2.2.1 Unless otherwise specified, the test should be carried out on a new transformer that can be put into operation. During the short-circuit test, accessories that do not affect the performance of the transformer (such as removable coolers) may not be installed. 2 Short-circuit test should be carried out after the factory test specified in GB1094.1-85 "Power Transformer Part 2.2.2.2
General Principles". If the winding has taps, the reactance must be measured at the tap position where the short-circuit test is performed, and the resistance should also be measured when necessary. The repeatability of all reactance measurements should be within ±0.2%. The test report includes the results of the factory test and should be prepared before the short-circuit test begins. 2.2.2.3 At the beginning of the short-circuit test, the average temperature of the coil should be between 0 and 40°C. 2.2.3 Short-circuit current peak value of double-winding transformer 1 The first peak value of the asymmetrical test current is calculated as follows: Full = IK2
Where: Symmetrical short-circuit current| is determined according to Items 1.2.1.2 and 2.1.2 of this standard. The coefficient K√2 is determined by the ratio of X/R.
Where: X is the sum of the reactance of the transformer and the reactance of the system (X: +X,), expressed as 2. R is the sum of the resistance of the transformer and the resistance of the system (Rt+Rs), expressed as 2. Unless otherwise specified, the coefficient K2 is limited to 1.8V2=2.55. Table 5 specifies the values ​​of KV2 for different values ​​of X/R. Table 5 Values ​​of coefficient K√2
Note; Other values ​​of X/R between 1 and 14 can be determined by linear interpolation. 2.09
For transformers of class I capacity and Zs<0.05Zt (see 1.2.1.2 and 2.1.2), X and R are only related to the transformer (Xt and R). When Zs>0.05Zt, X and R are related to the transformer and the system (Xt+X, and Rt+Rs). Note: When Zs<0.05Zt, U and U can be used instead of Xt and R (for main tapping). Where: U, is the impedance voltage of the transformer at the reference temperature, expressed in percentage; U is the reactive component of Uz, expressed in percentage; U, is the active component of Uz at the reference temperature, expressed in percentage. 2.2.4 Value and duration of short-circuit test current for two-winding transformers The first peak value of the asymmetrical current (if the duration of the short-circuit test current is long enough) will change to the symmetrical current". The peak current obtained in the test shall not deviate from the specified value by more than 5%, and the symmetrical short-circuit current shall not deviate from the specified value by more than 10%. The duration of the short-circuit test current shall be in accordance with the provisions of Item 2.2.5.4 of this standard. 2.2.5 Short-circuit test method for two-winding transformers 2.2.5.1 In order to obtain the test current as required by 2.2.4, the no-load voltage of the power supply may be higher than the rated voltage of the voltage-applied winding. The short circuit of the winding can be carried out after the voltage is applied to the other winding of the transformer or before the voltage is applied (pre-short circuit). The voltage of the former should not exceed 1.15 times the rated voltage of the winding.
When the transformer with a single concentric coil is pre-shorted, in order to avoid saturation of the core, the voltage should be applied to a winding far away from the core, and the winding close to the core should be short-circuited. Otherwise, excessive magnetizing current will be generated in the first few cycles of the test and superimposed on the short-circuit current.
For transformers with overlapping coils or double concentric coils, the pre-short circuit method can only be used after consultation between the manufacturer and the user department.
2.2.5.2 In order to obtain the initial peak value of the short-circuit current in the phase coil under test, the synchronous switch should be used for adjustment when closing. In order to verify the test current↑ and I value, these currents should be recorded using an oscilloscope. In order to obtain the maximum asymmetric current in one of the three phase coils, the circuit breaker should be closed when the voltage of the phase coil passes through zero. Note: ① For star-connected windings, the maximum asymmetric value can be obtained when the phase voltage passes through zero and the switch is closed. The system K of the peak current can be determined based on the oscillogram of the line current. For three-phase tests of delta-connected windings, this condition can be obtained by closing the switch when the line voltage passes through zero. During the pre-adjustment 83
GB1094.5-85
test, closing the switch when the maximum debugged line voltage passes through zero is a method to determine the coefficient K. At this time, the coefficient K can be found from the oscillogram of the line current. Another method to determine the phase current of the delta-connected winding is to appropriately connect the secondary windings of the various transformers that measure the line current to each other. The phase current values ​​can be recorded using the oscillogram. ② For constant flux voltage regulating transformers with star-zigzag connection belonging to Class 1 capacity, when Ux/Ur<3 (see Clause 2.2.3), the three phases can be closed simultaneously without using a synchronous switch. For other star-zigzag connected transformers, the closing method must be determined by the manufacturer in consultation with the user department.
2.2.5.3 For three-phase transformers, a three-phase power supply should be used during the test, as long as the requirements of Clause 2.2.4 of this standard are met. If the situation is different, the following single-phase power supply can be used. For triangle-connected windings, a single-phase power supply should be applied to the two corners of the triangle, and the voltage of the single-phase power supply during the test should be equal to the phase-to-phase voltage during the three-phase test. For star-connected windings, a single-phase power supply is applied to one line end connected to the other two line ends. During the test, the single-phase voltage must be equal to √3/2 times the phase-to-phase voltage during the three-phase test. Note: ① Single-phase power supply is mainly used for short-circuit tests of Class II and Class III capacity transformers, and is rarely used Short-circuit test for transformers of Class I capacity. ② For star-connected transformers with graded insulation, it is necessary to check whether the neutral point insulation can meet the requirements of single-phase test. ③ For star-connected windings, if the above-mentioned single-phase test is adopted, when the power supply capacity is insufficient and the neutral point is available, the single-phase test can be carried out between the line end and the neutral point after consultation between the manufacturer and the user department. In the absence of specific technical specifications, three tests should be carried out for single-phase transformers, one of which is 100% of the maximum 2.2.5.4
asymmetric current, and the other two tests should not be less than 75% of the maximum asymmetric current value; for three-phase transformers, the number of tests for each phase is three, one of which should be 100% of the maximum asymmetric current. Pre-adjustment tests with less than 70% of the specified current are not included. This test is used to verify the inherent characteristics of the test equipment, such as settling time, current adjustment, attenuation and duration. For transformers of Class I capacity, the duration of each test is 0.5s, with an allowable deviation of ±10%. Single-phase transformers, unless otherwise specified, should be subjected to three short-circuit tests at different tapping positions, i.e., one at the maximum voltage ratio tapping, one at the main tapping, and one at the minimum voltage ratio tapping.
For three-phase transformers, when single-phase power is used, nine short-circuit tests should be conducted, three times on each core leg. Unless otherwise specified, short-circuit tests of transformers with tapping should be conducted at different tapping positions for each core leg. That is, on a side core leg, conduct three times with the tapping position of the highest voltage ratio, on the middle core leg, conduct three times with the main tapping position; on another side core leg, conduct three times with the tapping position of the lowest voltage ratio. When a three-phase power supply is used, three short-circuit tests should be conducted, and they should be conducted at different tapping positions of the three core legs.
For transformers of class II and class III capacity, the number of tests, the duration of each test and the tapping position of the test shall be determined by the manufacturer and the user department. 2.2.6 Fault detection and judgment of short-circuit test results 2.2.6.1 Before the short-circuit test, measurements and tests shall be carried out in accordance with the requirements of clause 2.2.2 of this standard, and the gas relay (if any) shall also be observed. These measurements and tests are used as a reference for finding faults. 2.2.6.2 During each test (including preliminary tests), the following items shall be recorded oscillographically: applied voltage (between line ends)
Current (see note to item 2.2.5.2).
In addition, the transformer under test shall be visually inspected. Note: Supplementary methods of fault finding can be used, for example, oscillographic recording of radiated stray flux obtained by additional line diagrams, information obtained from noise. Also, in particular, the method of recording the current between the oil tank (insulating the oil tank) and the ground. After each test, the oscillogram records and gas relays obtained during the test should be observed, and the short-circuit reactance should be measured. 2.2.6.3
Note: ① Supplementary methods for finding faults can be used, such as measuring resistance, comparing the pulse voltage oscillogram with the oscillogram obtained in the initial stage (repeated pulse oscillogram method), and measurements of no-load tests (for finding inter-turn short-circuit faults). ② The difference between the measurement results before and after the test can be used as a basis for determining possible defects. During the continuous test, special attention should be paid to observing the changes in the measured reactance after each test. This reactance value may be increasing or tend to reach a stable value. After the test is completed, the transformer and gas relay (if any) should be checked, and the short-circuit reactance measurement results and the oscillograms taken at different stages of the test should be analyzed to find out abnormal phenomena during the test, especially the changes shown in the short-circuit reactance. 84
GB1094.5—85
At this stage, the following different methods should be used for Class I and Class II or Class III transformers. a. For Class I transformers, repeat all the "out" tests.
Unless a higher voltage value is agreed upon by the manufacturer and the user department, out! "The insulation test voltage shall be 85% of the original test voltage value.
The transformer shall then be tested and inspected to detect possible surface defects. If the lead position changes, although this change does not prevent the transformer from passing the test, it may endanger the safe operation of the transformer. The transformer is considered to have passed the short-circuit test if the following three requirements are met: (a) All repeated factory tests are qualified;
(b) The results of the short-circuit test, the recording and hanging inspection during the short-circuit test did not find any defects (such as obvious displacement, deformation or discharge marks of the coil, connecting wire and supporting structure); (c) The difference between the reactance value measured after the test is completed and the original measured value: for transformers with concentric coils, it is not more than 2%, but in the case of low-voltage coils made of metal For transformers with foil winding and for transformers with impedance voltage of 3% or more, a value not exceeding 4% may be taken. For transformers with non-circular concentric coils, the impedance voltage of 3% or more shall not exceed 7.5%. The value of 7.5% may be reduced after consultation between the manufacturer and the user department, but shall not be less than 4%. Note: For transformers with non-circular concentric coils with impedance voltage less than 3%, the maximum range of reactance variation cannot be specified by ordinary methods. Experience with certain structures has shown that a variation of up to (22.5~5U,)% is acceptable for such transformers, where U is the impedance voltage expressed as a percentage.
If the three requirements for the short-circuit test are met, the transformer is restored to its initial state. At the same time, in order to prove that the transformer is suitable for operation, Any further factory tests shall be repeated before the product leaves the factory. If any of these three requirements fails, the transformer shall be disassembled to determine the cause of the change in the above conditions, depending on the circumstances. b. Repeated factory tests for Class II and Class III transformers
are usually carried out after the short-circuit test, but it can be postponed until the inspection is completed based on the agreement between the manufacturer and the user department. Unless a higher voltage value is stipulated by consultation between the manufacturer and the user department, the voltage value of the repeated factory insulation test shall be 85% of the original test voltage value. Note: If the transformer is initially subjected to the insulation test selected in accordance with Method 2 of GB1094.3-85 "Power Transformers Part 3 Insulation Levels and Insulation Tests", the voltage applied for the induction withstand test shall be determined by the manufacturer and the user department. The user department shall determine the determination. The transformer shall be suspended and the body shall be inspected. If the following two requirements are met, the transformer is considered to have passed the short-circuit test. First, the measurement during the short-circuit test, the measurement of short-circuit reactance, and no surface defects (such as displacement, deformation or discharge marks of coil connections and supporting structures, etc.) are found during the suspension inspection; second, the repeated factory test is qualified. The judgment of any difference in the reactance measurement values ​​shall be determined by consultation between the manufacturer and the user department.
If any of the above two requirements for proving the qualification of the short-circuit test is unqualified, the transformer shall be inspected in more detail. If necessary, the transformer shall be partially or completely disassembled.
Additional Notes:
This standard was proposed by the Ministry of Machinery Industry and the Ministry of Water Resources and Electric Power of the People's Republic of China. This standard was drafted by the Shenyang Transformer Research Institute and the Electric Power Science Research Institute of the Ministry of Water Resources and Electric Power. The main drafters of this standard are Wang Zhaoping and Ling Han. From the date of implementation of this standard, the relevant contents of the original GB1094-79 "Power Transformer" shall be invalid. 855—85
At this stage, the following different methods should be used for class I and class II or III transformers. a. Class I transformers
Repeat all the "out" tests.
Unless a higher voltage value is agreed between the manufacturer and the user department, out! "The insulation test voltage shall be 85% of the original test voltage value.
The transformer shall then be tested and inspected to detect possible surface defects. If the lead position changes, although this change does not prevent the transformer from passing the test, it may endanger the safe operation of the transformer. The transformer is considered to have passed the short-circuit test if the following three requirements are met: (a) All repeated factory tests are qualified;
(b) The results of the short-circuit test, the recording and hanging inspection during the short-circuit test did not find any defects (such as obvious displacement, deformation or discharge marks of the coil, connecting wire and supporting structure); (c) The difference between the reactance value measured after the test is completed and the original measured value: for transformers with concentric coils, it is not more than 2%, but in the case of low-voltage coils made of metal For transformers with foil winding and for transformers with impedance voltage of 3% or more, a value not exceeding 4% may be taken. For transformers with non-circular concentric coils, the impedance voltage of 3% or more shall not exceed 7.5%. The value of 7.5% may be reduced after consultation between the manufacturer and the user department, but shall not be less than 4%. Note: For transformers with non-circular concentric coils with impedance voltage less than 3%, the maximum range of reactance variation cannot be specified by ordinary methods. Experience with certain structures has shown that a variation of up to (22.5~5U,)% is acceptable for such transformers, where U is the impedance voltage expressed as a percentage.
If the three requirements for the short-circuit test are met, the transformer is restored to its initial state. At the same time, in order to prove that the transformer is suitable for operation, Any further factory tests shall be repeated before the product leaves the factory. If any of these three requirements fails, the transformer shall be disassembled to determine the cause of the change in the above conditions, depending on the circumstances. b. Repeated factory tests for Class II and Class III transformers
are usually carried out after the short-circuit test, but it can be postponed until the inspection is completed based on the agreement between the manufacturer and the user department. Unless a higher voltage value is stipulated by consultation between the manufacturer and the user department, the voltage value of the repeated factory insulation test shall be 85% of the original test voltage value. Note: If the transformer is initially subjected to the insulation test selected in accordance with Method 2 of GB1094.3-85 "Power Transformers Part 3 Insulation Levels and Insulation Tests", the voltage applied for the induction withstand test shall be determined by the manufacturer and the user department. The user department shall determine the determination. The transformer shall be suspended and the body shall be inspected. If the following two requirements are met, the transformer is considered to have passed the short-circuit test. First, the measurement during the short-circuit test, the measurement of short-circuit reactance, and no surface defects (such as displacement, deformation or discharge marks of coil connections and supporting structures, etc.) are found during the suspension inspection; second, the repeated factory test is qualified. The judgment of any difference in the reactance measurement values ​​shall be determined by consultation between the manufacturer and the user department.
If any of the above two requirements for proving the qualification of the short-circuit test is unqualified, the transformer shall be inspected in more detail. If necessary, the transformer shall be partially or completely disassembled.
Additional Notes:
This standard was proposed by the Ministry of Machinery Industry and the Ministry of Water Resources and Electric Power of the People's Republic of China. This standard was drafted by the Shenyang Transformer Research Institute and the Electric Power Science Research Institute of the Ministry of Water Resources and Electric Power. The main drafters of this standard are Wang Zhaoping and Ling Han. From the date of implementation of this standard, the relevant contents of the original GB1094-79 "Power Transformer" shall be invalid. 855—85
At this stage, the following different methods should be used for class I and class II or III transformers. a. Class I transformers
Repeat all the "out" tests.
Unless a higher voltage value is agreed between the manufacturer and the user department, out! "The insulation test voltage shall be 85% of the original test voltage value.
The transformer shall then be tested and inspected to detect possible surface defects. If the lead position changes, although this change does not prevent the transformer from passing the test, it may endanger the safe operation of the transformer. The transformer is considered to have passed the short-circuit test if the following three requirements are met: (a) All repeated factory tests are qualified;
(b) The results of the short-circuit test, the recording and hanging inspection during the short-circuit test did not find any defects (such as obvious displacement, deformation or discharge marks of the coil, connecting wire and supporting structure); (c) The difference between the reactance value measured after the test is completed and the original measured value: for transformers with concentric coils, it is not more than 2%, but in the case of low-voltage coils made of metal For transformers with foil winding and for transformers with impedance voltage of 3% or more, a value not exceeding 4% may be taken. For transformers with non-circular concentric coils, the impedance voltage of 3% or more shall not exceed 7.5%. The value of 7.5% may be reduced after consultation between the manufacturer and the user department, but shall not be less than 4%. Note: For transformers with non-circular concentric coils with impedance voltage less than 3%, the maximum range of reactance variation cannot be specified by ordinary methods. Experience with certain structures has shown that a variation of up to (22.5~5U,)% is acceptable for such transformers, where U is the impedance voltage expressed as a percentage.
If the three requirements for the short-circuit test are met, the transformer is restored to its initial state. At the same time, in order to prove that the transformer is suitable for operation, Any further factory tests shall be repeated before the product leaves the factory. If any of these three requirements fails, the transformer shall be disassembled to determine the cause of the change in the above conditions, depending on the circumstances. b. Repeated factory tests for Class II and Class III transformers
are usually carried out after the short-circuit test, but it can be postponed until the inspection is completed based on the agreement between the manufacturer and the user department. Unless a higher voltage value is stipulated by consultation between the manufacturer and the user department, the voltage value of the repeated factory insulation test shall be 85% of the original test voltage value. Note: If the transformer is initially subjected to the insulation test selected in accordance with Method 2 of GB1094.3-85 "Power Transformers Part 3 Insulation Levels and Insulation Tests", the voltage applied for the induction withstand test shall be determined by the manufacturer and the user department. The user department shall determine the determination. The transformer shall be suspended and the body shall be inspected. If the following two requirements are met, the transformer is considered to have passed the short-circuit test. First, the measurement during the short-circuit test, the measurement of short-circuit reactance, and no surface defects (such as displacement, deformation or discharge marks of coil connections and supporting structures, etc.) are found during the suspension inspection; second, the repeated factory test is qualified. The judgment of any difference in the reactance measurement values ​​shall be determined by consultation between the manufacturer and the user department.
If any of the above two requirements for proving the qualification of the short-circuit test is unqualified, the transformer shall be inspected in more detail. If necessary, the transformer shall be partially or completely disassembled.
Additional Notes:
This standard was proposed by the Ministry of Machinery Industry and the Ministry of Water Resources and Electric Power of the People's Republic of China. This standard was drafted by the Shenyang Transformer Research Institute and the Electric Power Science Research Institute of the Ministry of Water Resources and Electric Power. The main drafters of this standard are Wang Zhaoping and Ling Han. From the date of implementation of this standard, the relevant contents of the original GB1094-79 "Power Transformer" shall be invalid. 85
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