Different protection objects with different microcomputer protection device in relay protection. The very important main transformer in terms of the power stationand needs to configure a set of microcomputer protection to ensure the stable operation of the main transformer, commonly including the generator differential protection, main transformer high voltage back up protection, main transformer low voltage back-up protection and non electricity protection.The differential protection is the main protection of main transformer, when the the transformer is in normal operation,the differential current on both sides of the main transformer is almost 0, this protection device not trip. When the differential current value is greater than the rated value, the protection trip. General jumped the high and low pressure side of the switch of main transformer. When the transformer external fault, differential current value has little effect. Then the differential protection do not trip.
features of transformer differential protection：
1、A lot of magnetizing inrush current is generated in the transformer no-load closing or in the process of fault recovery, the magnetizing inrush current will influx the differential current loop, may will make the differential protection mistripped
2、 the main transformer easily lead to uneven current on both sides. This is mainly due to the selection of CT. And in terms of the transformer, the use of Y -] - 11 connection mode is universally used, in the microcomputer protection need to converse. Therefore need to pay attention to the connection coefficient and the coefficient of equilibrium. In terms of the differential protection
device also need to wiring according to the manufacturer's instructions, may be the wiring of 0 DEG or 180 DEG wiring
3、the 5A and 1A rated current protection for the present power plant needs to compared with current transformer ,and at the same time the differential protection device also need to match. Generally speaking, a station generally set 5A or 1A, all equipments or secondary equipment must be unified.
4,Doing the experiment, we need to add three phase currents in the two sides of the differential protection, simulated the differential current to do the experiment. In most cases, the microcomputer protection tester only provides three sets current, then can also do the single phase difference current experiment.
5 |transformer differential protection device generally has the protection function of the ratio differential protection differential current instantaneous trip protection .CT line-break blocking ratio differential protection, second harmonic blocking ratio differential. Differential protection is the main protection of transformer, when the transformer has internal fault, such as interphase short circuit, differential current will appear, when protection reaches a fixed value, transformer differential protection device tripping
For transformer protection in present electric power system, generally use differential protection, high and low voltage backup protection, non electricity protection then separate configuration. But according to the actual needs, sometimes is the integrated protection of differential protection and backup protection of various microcomputer protection. Such as 9671C comprehensive transformer protection
device it is used in the market thats composed the differential protection and backup protection of the low voltage side , thus can save a microcomputer protection device, reduce the cost of the equippment. With the development of power system, technologies continueimprove, in order to meet the market's actual need, microcomputer protection manufacturers also actively respond to it, I believe domestic market development of microcomputer protection is getting better and better