Detailed explanation of transformer coupling groups
In the power system, the Transformer Connection Group is the key parameter that determines whether the equipment can operate safely, operate in parallel, and the quality of power. It defines the wiring method of high and low voltage windings and the phase relationship of line voltage, which directly affects the setting of relay protection, the design of grounding system and the harmonic suppression effect. This article will systematically analyze the core rules and selection strategies of the transformer coupling group based on the national standard GB/T 1094.1.
Key precautions for project selection and operation and maintenance
In the selection, installation, operation and maintenance of transformers, the following points should be focused on the connection group:
Parallel operation must be "three in the same"
When multiple transformers are connected in parallel, they must meet: the connection group is the same, the variable ratio is the same, and the short-circuit impedance is the same.
If the groups are inconsistent, even if the variable ratio is the same, a huge circulation will occur due to the phase difference, and the transformer may be directly burned down in severe cases.
The protection device needs to match the group
Different connection groups will affect the wiring methods and phase compensation logic of devices such as differential protection, backup power supply self-investment (backup self-investment), etc. When designing and debugging, it is necessary to ensure that the protection device settings are consistent with the actual group.
Reasonable selection according to the nature of the load
Suitable for civil and commercial power distribution: Dyn11 is preferred.
For occasions where harmonic pollution is heavy: try to avoid using Yy wiring.
When neutral ground or three-phase four-wire power supply is required: the group with the n logo should be selected.
Priority is given to standardized groups
Under the premise of meeting the system requirements, priority is given to selecting from commonly used groups such as Yyn0, Dyn11, Yd11, YNd11, and YNy0, which is not only conducive to later operation and maintenance, but also more conducive to the cooperation of spare parts and parameters.
On-site testing and judgment methods for connection groups
In the new installation, overhaul or handover acceptance stage, it is usually necessary to verify whether the transformer coupling group is consistent with the nameplate. Common methods include:
Variable ratio group tester
It is a commonly used equipment for factory testing and on-site acceptance. It can complete the coupling group, variable ratio and polarity testing at once, with fast speed and high accuracy, and is suitable for batch testing and engineering acceptance.
Double voltmeter method
When the field conditions are limited, a three-phase voltage can be applied to the low-voltage side, the high- and low-voltage side line voltages can be measured, and the phase difference can be calculated to determine the group. Suitable for quick troubleshooting and auxiliary verification.
DC polarity method
The battery and multimeter are used to test the terminal of the winding with the same name, and the phase relationship is determined by sensing the polarity. It is easy to operate and is mostly used for on-site troubleshooting and polarity verification
How to choose the transformer coupling group scientifically?
The choice of transformer coupling group is a system engineering that takes into account insulation cost, system grounding method, harmonic suppression and relay protection.In the actual project, you can refer to the following selection ideas:
Power distribution terminal
Dyn11 is preferred.
Traditional cost-sensitive scenarios
Yyn0 can be considered, but the neutral current needs to be strictly controlled.
uitable for high-voltage transmission and boost occasions
Choosing Yd11 or YNd11.
Suitable for parallel operation
Be sure to ensure that the group, variable ratio and short-circuit impedance are exactly the same.
Mastering the core principles and engineering applications of the coupling group will help to avoid electrical risks and improve system stability and power quality in the transformer selection stage.
