Five points for attention in AC test of microcomputer relay

The problems that electric power workers need to pay attention to when using the microprocessor relay protection tester for AC test are summarized as follows:
 
1. In general detection of relay protectors, one of the steps is to set the “switch positioning confirmation time”. Here we need to pay attention to setting it larger, such as about 20 ms. If there is a big error in the return value of the test, maybe because of the greater jitter of the relay contacts, the test can be continued in the “manual” mode at this time. In order to ensure the reliable action of relay protection, when detecting the action time of relay, it is necessary to ensure that the output of the tester is larger than the starting value of the protection.
 
2. The conventional way to detect multi-stage over-current protection is to test separately in one section and then gradually increase the current until the protection action. However, the action time detected by this conventional method is generally inaccurate. At this time, when detecting the action time, pay attention to output 1.2 times or more of the positive action value directly from the tester. At this time, the low-voltage protection becomes 0.8 times or less, which ensures the start-up action of the protection, so the action time measured is more accurate.
 
3. The detection of distance protection needs to pay attention to the fact that the conventional setting value is 0.95 times to carry out the test. In this case, the short-circuit impedance is smaller than the setting value, so as to ensure the reliable exit of the protection. It is also necessary to pay attention to the correct setting of zero-sequence compensation coefficient when simulating the grounding distance fault.
 
4. When checking the zero-sequence current, it is necessary to distinguish whether the fixed value given in the value sheet is 3I0 or I0. If the customization is 10, the lower left corner of the detection module will be displayed; if the customization is 310, the value of the lower left corner will be multiplied by 3. See if it is consistent with the value.
 
5. For the detection of low-cycle protection, the selection frequency can be changed. The step size of frequency change is better in “automatic mode” than in manual mode, which is not well controlled, because of the lock-in value of df/dt in low cycle. The step size of frequency variation is set according to the accuracy requirement. Frequency decreases from 50 to protective action. It should be noted here that the interval time is longer than the protective action time.
 
These are the five points that should be paid attention to when the microprocessor relay protection tester carries out AC test.