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LMZB3-20 CURRENT TRANSFORMER
1.current transformer2.rated voltage class:20kV3.Model:LMZB3-204.indoor,casting type,busbar type,with protective class,used in generator
1. General
Generator CT can be divided into epoxy resin casting type and bushing type based on insulation method. And it can be divided into open-vertically installed type, sealed-busbar installed type and generator bushing installed type based on installation type.
The large current CT, which is developed, manufactured by us and is used in generator, is with advanced technology and reliable quality. We adopt the special technology to eliminate the large current interference between the adjacent phases. We also make it realize the precision self-check function during the operation conditions.
Now we can make the largest current achieve 45000A and the large current CT can been applied to the 1000MW generator set.
2. Research of generator CT in our factory
The characteristics of generator CT are great current, limiting installation space and complex magnetic field.
These characteristics have a great impaction on generator bushing installed CT. So to this kind of product good shielding measurement is very important. These characteristics have less impaction on vertical installed type and sealed-busbar installed type CT. For these two types of product casting quality and winding processing is most important.
We provide more than 240,000 pieces epoxy resin casting type instrument transformers which occupy 25% of total Chinese market. We are the first option for National big project and Switchgear Company. With more than 30 years experience, we set up a complete quality-insurance program and pass the ISO9001:2000 AND ISO14001:1996 standard.
Our generator CT conforms to GB1208,GB16847 and IEC60044-1 Standard. We passed the type test report of QITC, authentication of CHINA ELECTRIC COMPANY UNION and got advanced technology in the electric APPLIANCE UNION.
We try to control temperature rise and insulation between winding turns from every step, e.g. structure designing, raw material, producing process, quality insurance system.
In recent years, we have done a lot of research in generator bushing installed type CT. The maximum primary current of this kind CT can even reach 30000A. Because of limitation of actual test condition, usually can only do error test, influence test between phases and temperature rise test on CT using equal Ampere-turns method, i.e. the multiplying result of actual primary current and turns is equal to the rated-ampere-turns of CT and winding the primary conductor evenly around the circle. But actually, influence between phases can really affect the error and temperature rise of CT on the service site. In order to simulate this affection, we distribute the primary conductor winding in a certain angle around the circle and then do error test and temperature rise test. We decide the angle by simulate the 3 phases operation condition. Please refer to the 3 phases test circuit below. With good design and strict testing, our products have good performance in resisting affection between 3 phases and temperature rise. So many running reports from customers can certify our products qualification.
T1----- Self voltage regulator 30KVAT2----- Large current transformer 30KVACT---- To be tested TPY, 10P or 0.2SBusbar row 100*12. Outlet busbar is parallet to the backing. The distance between them is 2m.Phase distance between busbar is 1.2m.CT is vertical to busbar, busbar passes through the center of CT.3. Special performance of our product.
1) The performance of measuring winding will not be affected by residual magnetism.
Normally,CT should be demagnetized before error test because of residual magnetism.All theory and test data certify :residual magnetism lower the accuracy class.Tested data in 500 kV grid net shows: 0.2 becaome 0.5 when in service.When large current especially short-circuit current and great DC component decaying time constant,there is greater residual magnetism. When in normal service, there is still residual magnetism. So the accrual accuracy class in service is much lower than the tested one. This leads to great loss and pollution in large capacity electric power plant.
If required by our customers. DYH charge magnetism to CT. And the accuracy class remains the same before and after charging magnetism. This certifies the good accuracy class in service.
2) Verify the error on service site by applying small secondary current
It is impossible to apply so large primary current on service.We can manufacture CTs being applied small secondary current to verify error on service site.
Please refer to the schematic diagram.When doing error test, we only apply maximum 6A current on secondary.It is not needed to connect primary conductor, increase primary current and using standard current transformer. So it is easier to test error on service site.
The two special performances above are achieved by using special CT and special shielding measurement .The cost is higher than normal but this method makes it easier to do error test periodically on service site.
20kV current transformer using in generator