When calculating the transformer capacity, we multiply it by a 0A factor of 85 is calculated as a redundancy for capacity, which means that it is recommended that its average load factor does not exceed 85%, do you know why?
This is because, when using a transformer, the electrical load is not a constant value, but a power range that fluctuates at any time. In general,When the load factor reaches more than 90%, it is already close to full load operation。Some margins are also needed to cope with dynamic loads such as the start of high-power motors such as welding machines, cranes, and punches.
When these devices are started, a large starting current will be formed in a short period of time, which will inevitably cause the transformer to appear in a brief overload operation state. Although transformers can be overloaded for a short period of time, frequent overloads can also have irreversible effects on the transformer, reducing its lifespan. To sum up, the following situations arise:
1.The temperature of each component of the transformer rises, if the temperature rise value of the module is exceeded, the transformer will be damaged to a certain extent
2.The leakage flux density outside the core will increase, and the secondary leakage flux coupling will cause the eddy current effect of the metal parts to heat up
3.Other fittings placed in the transformer are also subject to high thermal stress, which can alter the structure
4.The combination of the main magnetic flux and the increased leakage flux limits the overexcitation capacity of the core.
Of course, if the load factor of the transformer is too small, it will cause unnecessary capacity waste, resulting in an increase in initial investment and an increase in operating costs. Therefore, it is a safer choice to choose 85% load factor.
StillDepending on the industry and the electricity consumption scenario, the load factor regulations are also differentSome of the national standards are as follows:
The long-term working load rate of the distribution transformer should not be greater than 85;When there are primary and secondary loads, it is advisable to install two or more transformers, and when one transformer is out of operation, the remaining transformer capacity should meet the power requirements of primary and secondary loads.
Electrical Design Standards for Civil Buildings
gb 51348-2019
The distribution transformer in the residential area should be set up as a group of two for the power supply unit, and the load rate should not exceed 65.
Code for power configuration of residential quarters" GB T36040-2018
Energy-saving transformers should be used in residential buildings. The junction line of the transformer should be D, YN11, and the load rate of the transformer should not be greater than 85.
Code for Electrical Design of Residential Buildings
jgj242-2011
The load rate of the transformer for financial facilities shall comply with the following provisions: the long-term workload rate shall not be higher than 75;
Code for Electrical Design of Financial Buildings
jgj284-2012
The load factor of the distribution transformer should be 70 85.
Scientific Research Building Design Standards
jgj91-2019
When the average load factor of the transformer is lower than 20 for a long time and the power load will not be increased in the future, it is advisable to transform the transformer.
Technical Code for Energy-saving Renovation of Public Buildings
jgj 176-2009
The load rate of the distribution transformer should not be greater than 85.
Code for Electrical Design of Educational Buildings
jgj310-2013
For large, important traffic buildings, the long-term working load rate of the transformer should be 60 75;For two transformers that are in backup with each other, when one is out of operation due to a fault, the other should be able to take it all.
Primary and secondary loads.
Code for Electrical Design of Transportation Buildings
jgj243-2011
When the extra-large exhibition building adopts the special transformer for the exhibition, the load rate of the special transformer should not be greater than 70.
Code for Electrical Design of Convention and Exhibition Buildings
jgj333-2014
Picture: Lei Lang Electric.
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