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GB/T 1094 consists of the following parts under the general title of Power Transformers:
——Part 1: General;
——Part 2: Temperature rise for liquid-immersed transformers;
——Part 3: Insulation levels, dielectric tests and external clearances in air;
——Part 4: Guide to the lightning impulse and switching impulse testing—Power transformers and reactors;
——Part 5: Ability to withstand short circuit;
——Part 6: Reactors;
——Part 7: Loading guide for oil-immersed power transformers;
——Part 10: Determination of sound levels;
——Part 10.1: Determination of sound levels—Application guide;
——Part 11: Dry-type transformers;
——Part 12: Loading guide for dry-type power transformers;
——Part 14: Design and application of liquid-immersed transformers using high-temperature insulation material;
——Part 15: Gas-filled power transformers;
——Part 16: Transformers for wind turbine applications;
——Part 18: Measurement of frequency response;
——Part 23: DC magnetic bias suppression devices.
This part is Part 15 of GB/T 1094.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part has been redrafted and modified in relation to IEC 60076-15:2015 Power transformers—Part 15: Gas-filled power transformers.
The main technical differences with respect to IEC 60076-15: 2015 are as follows:
——As for the normative references, adjustments of technical differences are made to this part to keep them in line with the technical conditions in China. The adjustments are embodied in a concentrated way in Clause 2 "Normative references", specifically as follows:
? IEC 60076-1:2011 is replaced by GB/T 1094.1-2013, which is modified in relation to the international standard;
? IEC 60076-2:2011 is replaced by GB/T 1094.2-2013, which is modified in relation to the international standard;
? IEC 60076-3 is replaced by GB/T 1094.3-2017, which is modified in relation to the international standard;
? IEC 60076-5 is replaced by GB/T 1094.5, which is modified in relation to the international standard;
? IEC 60076-10 is replaced by GB/T 1094.10, which is modified in relation to the international standard;
? IEC 60137 is replaced by GB/T 4109, which is modified in relation to the international standard;
? IEC 60480 is replaced by GB/T 8905, which is modified in relation to the international standard;
? IEC 62271-1 is replaced by GB/T 11022, which is modified in relation to the international standard;
? The reference of GB/T 12022 and GB/T 13499-2002 is added;
? The reference of IEC 60376 is deleted;
——In order to adapt to China's national conditions, the content "In case capacitive bushing is adopted, a dry bushing shall be used, and on-load tap changer shall be gas-filled switch” is added in 5.10;
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——In order to adapt to China's national conditions, the "product model" is added in rating plates of 8.2; and the contents “Maximum system short-circuit power or current used to determine the transformer withstand capability if not infinite" in 8.2 of IEC 60076-15:2015 is adjusted to 8.3 of this standard;
——In order to adapt to China's national conditions, the ambient temperature during the test is changed from "10°C-+40°C" to "5°C -+40°C” in 11.1.1;
——In order to adapt to China's national conditions, "insulating gas test" is added in 11.1.2.2;
——In order to adapt to China's national conditions, the content “Measurement of DC insulation resistance of windings-to-earth and between windings" in 11.1.2.3 and 11.1.4 is adjusted to 11.1.2.2.
The following editorial changes have also been made in this part:
——The last paragraph of Clause 1 of IEC 60076-15:2015 is adjusted to the content of Note 1 of this part, and the “Note” of IEC 60076-15:2015 to “Note 2” of this part;
——The “Note” in 3.3 of IEC 60076-15:2015 is adjusted to 3.1 of this part;
——The title of 3.5 of IEC 60076-15:2015 is deleted, and 3.5.1, 3.5.2 and 3.5.3 are adjusted to 3.5, 3.6 and 3.7 of this part;
——The contents of “Note 2” in 5.11.1 of IEC 60076-15:2015 is adjusted to the contents of official text;
——The number 5.5 cited in item 1) of 8.2 in IEC 60076-15:2015 is adjusted to 6.5;
——The text of the penultimate paragraph in 11.1.4 of IEC 60076-15:2015 is deleted;
——The contents of “Note” in 11.2 of IEC 60076-15:2015 is adjusted to the contents of official text;
——The "compound gauge" in "Recommended components for gas-filled power transformers" in Table C.1 of IEC 60076-15:2015 is deleted;
——Annex A and Annex B in IEC 60076-15:2015 are adjusted to Annex B and Annex A of this part.
——The bibliography is adjusted.
This standard was proposed by the China Electrical Equipment Industry Association.
This part is under the jurisdiction of SAC/TC 44 National Technical Committee on Transformers of Standardization Administration of China.
Power transformers
Part 15: Gas-filled power transformers
1 Scope
This part of GB/T 1094 specifies the terms and definitions, service conditions, rating and general requirements, requirements for transformers having a tapped winding, connection phase displacement symbols, rating plates, safety, environmental and other requirements, tolerances, tests, electromagnetic compatibility (EMC), high frequency switching transients, earthing terminal, information required with enquiry and order of gas-filled power transformers.
This part applies to three-phase and single-phase gas-filled power transformers (including auto-transformers) with the exception of certain categories of small and special transformers such as:
——single-phase transformers with rated power less than 1kVA and three-phase transformers less than 5kVA;
——transformers, which have no windings with rated voltage higher than 1,000V;
——instrument transformers;
——traction transformers mounted on rolling stock;
——starting transformers;
——testing transformers;
——welding transformers.
When standards do not exist for such categories of transformers (in particular transformer having no winding exceeding 1,000V for industrial applications), this part may still be applicable either as a whole or in part. This part does not address the requirements that would make a transformer suitable for mounting in a position accessible to the general public. For those categories of power transformers and reactors which have their own standards, this part is applicable only to the extent in which it is specifically called up by cross-reference in the other standard. Such standards exist for:
——reactors in general (GB/T 1094.6);
——self-protected transformers (IEC 60076-13);
——transformers for wind turbine applications (GB/T 1094.16);
——traction transformers and traction reactors (GB/T 25120);
——converter transformers for industrial applications (GB/T 18494.1);
——converter transformers for HVDC applications (GB/T 18494.2).
Note 1: At several places in this part, it is specified or recommended that an 'agreement' shall be reached concerning alternative or additional technical solutions or procedures. Such agreement is made between the manufacturer and the purchaser. The matters should preferably be raised at an early stage and the agreements included in the contract specification.
Note 2: This part can be applicable to the gas parts of a transformer in which an insulating gas is used with an insulating liquid.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated reference, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 1094.1-2013 Power transformers—Part 1: General (IEC 60076-1:2011, MOD)
GB/T 1094.2-2013 Power transformers—Part 2: Temperature rise for liquid-immersed transformers (IEC 60076-2:2011, MOD)
GB/T 1094.3-2017 Power transformers—Part 3: Insulation levels, dielectric tests and external clearances in air (IEC 60076-3:2013, MOD)
GB/T 1094.5 Power transformers—Part 5: Ability to withstand short circuit (GB/T 1094.5-2008, IEC 60076-5:2006, MOD)
GB/T 1094.10 Power transformers—Part 10: Determination of sound levels (GB/T 1094.10-2003, IEC 60076-10:2001, MOD)
GB/T 4109 Insulated bushings for alternating voltages above 1,000V (GB/T 4109-2008, IEC 60137:2008)
GB/T 8905 The guide for management and measuring SF6 gas in electrical equipment (GB/T 8905-2012, IEC 60480:2004, MOD)
GB/T 11022 Common specifications for high-voltage alternating-current switchgear and control gear standards (GB/T 11022-2011, IEC 62271-1:2007, MOD)
GB/T 12022 Industrial sulfur hexafluoride
GB/T 13499-2002 Power transformers—Application guide (IEC 60076-8:1997, IDT)
IEC 62271-4:2002 High-voltage switchgear and controlgear—Part 4: Handling procedures for sulphur hexafluoride (SF6) and its mixtures
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
Note: See GB/T 1094.1, GB/T 1094.2, GB/T 1094.3, GB/T 1094.5, GB/T 1094.10 or GB/T 2900.95 for other terms.
3.1
gas-filled power transformer
transformer of which the magnetic circuit and windings are placed in an enclosure filled with an insulating gas
Note 1: Generally, sulfur hexafluoride (SF6) gas is used, and sometimes this transformer is called a gas-insulated transformer.
Note 2: The transformer whose magnetic circuit and winding are placed in a closed box filled with insulating liquid (such as perfluorocarbon, natural ester, synthetic ester, silicone oil, etc.) shall be regarded as liquid-immersed transformer.
3.2
rated gas pressure
gas pressure (gauge pressure) at 20°C designed for use in a gas-filled power transformer
3.3
guaranteed minimum gas pressure
minimum gas pressure (gauge pressure) at 20 °C, which is able to guarantee the insulation of a gas-filled power transformer
3.4
design pressure of tanks
relative pressure used to determine the design of the tanks
Note: It is at least equal to the maximum pressure in the tank at the highest temperature that the gas can reach under specified maximum service condition.
3.5
absolute leakage rate
F
amount of gas escaped by time unit at rated filling pressure (or density)
Note: It is expressed in Pa·m3/s.
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3.6
permissible leakage rate
Fp
maximum permissible absolute leakage rate of gas at rated filling pressure (or density) specified by the manufacturer
Note: It is expressed in Pa·m3/s.
3.7
relative leakage rate
Frel
absolute leakage rate related to the total amount of gas in the transformer at rated filling pressure (or density)
Note: It is expressed in %/y or %/d.
4 Service conditions
Service conditions in GB/T 1094.1 apply. As far as cooling conditions are concerned, see GB/T 1094.2.
5 Rating and general requirements
5.1 Rated power
5.1.1 General
The rated power for each winding shall either be specified by the purchaser or the purchaser shall provide sufficient information to the manufacturer to determine the rated power at the enquiry stage.
The transformer shall have an assigned rated power for each winding which shall be marked on the rating plate. The rated power refers to continuous loading. This is a reference value for guarantees and tests concerning load losses and temperature rises, and also a guarantee value of the manufacturer.
If different values of apparent power are assigned under different circumstances, for example, with different methods of cooling, the highest of these values is the rated power.
A two-winding transformer has only one value of rated power, identical for both windings.
For multi-winding transformers, the purchaser shall specify the required power-loading combinations, stating, when necessary, the active and reactive outputs separately.
When the transformer has rated voltage applied to a primary winding, and rated current flows through the terminals of a secondary winding, the transformer receives the relevant rated power for that pair of windings.
The transformer shall be capable of carrying, in continuous service, the rated power (for a multi-winding transformer: the specified combination(s) of winding rated power(s) under conditions listed in Clause 4 of GB/T 1094.1-2013 and without exceeding the temperature-rise limitations specified in 5.3.
Note 1: The interpretation of rated power according to this subclause implies that it is a value of apparent power input to the transformer – including its own absorption of active and reactive power. The apparent power that the transformer delivers to the circuit connected to the terminals of the secondary winding under rated loading differs from the rated power. The voltage across the secondary terminals differs from rated voltage by the voltage drop (or rise) in the transformer. Allowance for voltage drop, with regard to load power factor, is made in the specification of the rated voltage and the tapping range (see Clause 7 of GB/T 13499-2002).
Note 2: For a multi-winding transformer, half the arithmetic sum of the rated power values of all windings (separate windings, not auto-connected) gives a rough estimate of its physical size as compared with a two winding transformer.
5.1.2 Preferred values of rated power
Preferred values of rated power in GB/T 1094.1 apply.
5.1.3 Minimum power under alternative cooling modes
Where the purchaser has a particular requirement for a minimum power under a particular cooling mode other than the cooling mode for rated power, this shall be stated and subjected to agreement between the supplier and the purchaser in the tender stage.
The transformer shall be capable of carrying, in continuous service, the specified minimum power (for a multi-winding transformer: the specified combination(s) of winding rated power(s) under conditions listed in Clause 4 of GB/T 1094.1-2013, and under the specified cooling mode, without exceeding the temperature-rise limitations specified in 5.3.
Note: An example of this is where the transformer is required to operate at a particular minimum percentage of rated power with the forced cooling out of service (GNAN) to allow for the loss of auxiliary supply and large GNAN rating will be pushed up the transformer cost. A minimum percentage of rated power is determined with consideration of the cost-effectiveness.
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5.1.4 Loading beyond rated power
Temporary loading beyond rating capability is subjected to agreement between the supplier and the purchaser in the tender stage.
Note 1: The concept of GB/T 1094.7 may be applicable to the consideration of the loading beyond rated power of gas-filled power transformers, but constants and/or factors may not be applicable.
Any specific requirements for loading beyond rated power, operation at higher external cooling medium temperatures or reduced temperature rise limits shall be specified by the purchaser in the enquiry and the contract. Any additional tests or calculations required to verify compliance with these specific requirements shall also be specified.
Note 2: This option is intended to be used in particular to give a basis for design and guarantees concerning temporary emergency loading of power transformers.
The bushings, tap-changers, current transformers and other auxiliary equipment shall be selected so as not to restrict the loading capability of the transformer.
Note 3: The relevant component standards GB/T 4109 for bushings and GB/T 10230.1 for tap-changers are consulted for the loading capability of those components.
Note 4: These requirements do not apply to transformers for special applications, which do not need a loading capability beyond rated power. For these transformers, if such a capability is required, it is specified.
5.2 Cooling mode
5.2.1 General
The purchaser shall specify the cooling medium (air or water). If the purchaser has particular requirements for the cooling method(s) or cooling equipment, this shall be stated in the enquiry and the contract.
5.2.2 Identification symbols
Transformers shall be identified according to the cooling method employed. For gas-filled power transformers, this identification is expressed by a four-letter code as described below.
First letter (Internal cooling medium):
——G: insulating gas.
Second letter (Circulation mechanism for internal cooling medium):
——N: natural/thermosiphon flow through cooling equipment and in windings;
——F: forced circulation through cooling equipment (e.g., gas blower), thermosiphon flow in windings;
——D: forced circulation through cooling equipment, directed from the cooling equipment into at least the main windings.
Third letter (External cooling medium):
——A: air;
——W: water.
Fourth letter (Circulation mechanism for external cooling medium):
——N: natural convection;
——F: forced circulation (fans, air blowers, water pumps).
5.2.3 Transformers with alternative cooling methods
A transformer may be specified with alternative cooling methods. In this case, the specification and the rating plate shall then carry information about the power values at which the transformer fulfills the temperature rise limitations when these alternatives apply.
The power value for the alternative with the highest cooling capacity is the rated power of the transformer (or of an individual winding of a multi-winding transformer, as shown in GB/T 1094.1). The alternatives are conventionally listed in rising order of cooling capacity.
Example:
GNAN/GDAF: The transformer has cooling equipment with blowers and fans but is also specified with a reduced power-carrying under natural cooling.
Note: The percentage of natural cooling capacity to forced cooling capacity of gas-filled transformers is smaller than that of oil-immersed transformers. It is not difficult generally in oil-immersed transformers to achieve ONAN capacity as 50 % of the OFAF or ODAF capacity. But in gas-filled transformers, it is sometimes difficult and not economical to achieve GNAN capacity as 50 % of the GDAF capacity. The purchaser consults with the manufacturer about natural cooling capacity to forced cooling capacity.
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5.3 Temperature-rise limits
5.3.1 Classification and insulation system temperature
Transformers are classified by the insulation systems shown in Table 1.
An approximate value for practical purposes of hot-spot temperature can be calculated by using the concept of Annex B.
The application of insulating materials with different thermal classes leads to unconventional insulation systems (see the examples of unconventional insulation systems as described in GB/Z 1094.14).
Table 1 Classification and insulation system temperature
Letter designation a Thermal class
(insulation system temperature °C)
A 105
E 120
B 130
F 155
H 180
N 200
R 220
a Temperature classifications are given in GB/T 11021.
5.3.2 Normal temperature-rise limits
The temperature rise of each winding of the transformer, designed for operation at normal service conditions, shall not exceed the corresponding limit specified in Table 2 when tested in accordance with 11.5.
The temperature of the core, metallic parts and adjacent materials shall not reach a value that will cause damage to any part of the transformer.
In most of the gases, the temperature-rise limit of gas is higher than the temperature-rise limit of winding, so that the temperature-rise limit of gas is not necessary to be specified. If necessary, it is subjected to agreement between the supplier and the purchaser.
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Table 2 Winding temperature-rise limits
Thermal class
(insulation system temperature °C) Average winding temperature-rise limits a
K
105 60
120 75
130 80
155 100
180 125
200 135
220 150
a Temperature-rise measured in accordance with 11.5.
5.3.3 Reduced temperature-rises for transformers designed for high cooling air temperatures or special air cooling conditions
Reduced temperature-rises for transformers designed for high cooling air temperatures or special air cooling conditions in GB/T 1094.2 apply.
5.3.4 High altitude temperature-rise correction
Unless otherwise agreed between the supplier and the purchaser, for transformers designed for operation at an altitude greater than 1,000 m but tested at normal altitudes, the limits of temperature-rise given in Table 2 shall be reduced by the following amounts for each 500 m by which the intended working altitude exceeds 1,000 m:
——natural-air-cooled transformers: 2 %;
——forced-air-cooled transformers: 3 %.
A corresponding reverse correction may be applied in cases where the altitude of the factory is above 1,000 m and the altitude of the installation site is below 1,000 m.
Any temperature-rise correction in dependence on altitude shall be rounded to the nearest whole number of Kelvin.
The influence of differing ambient temperature or altitude on the air cooling of the tank is disregarded for the water-cooled transformers.
5.3.5 Reduced temperature-rise for transformers designed for high cooling water
temperatures
Reduced temperature-rise for transformers designed for high cooling water temperatures in GB/T 1094.2 apply.
5.3.6 Temperature rise during specified load cycle
By agreement between manufacturer and purchaser, temperature rise limits can be guaranteed and/or a special test regarding load cycle operation specified (see GB/T 1094.7).
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Service conditions
5 Rating and general requirements
6 Requirements for transformers having a tapped winding
7 Connection and connection symbols
8 Rating plates
9 Safety, environmental and other requirements
10 Tolerances
11 Tests
12 Electromagnetic compatibility (EMC)
13 High frequency switching transients
14 Earthing terminal
15 Information required with enquiry and order
Annex A (Informative) Transient loading – Mathematical model
Annex B (Informative) Technical requirements to be provided with enquiry and order
Annex C (Informative) Gauges, indicators and relays for gas-filled power transformers
Bibliography
Figure A.1 Temperature distribution model
Table 1 Classification and insulation system temperature
Table 2 Winding temperature-rise limits
Table 3 Exponents for the corrections of temperature-rise test results
Table C.1 Comparison of gauges, indicators and relays between gas-filled power transformers and oil-immersed power transformers
