When carrying out the relay protection device test, the opening amount of the relay protection tester is closely related to the operation of the protection device and the operation time. In the field test, the relay protection often jumps, but the relay tester does not receive the action contact, and the inspection of the opening wiring and protection action are good, and the opening and opening amount of the individual short circuit is also displayed normally. In order to solve such problems, we can start with the principle of opening volume.
Figure 1 Schematic diagram of the infeed terminal
Fig.2 Potentioless contact Fig.3 Fig.1 of the potentiometric contact takes open A as an example, and the other channels have the same principle as open A, and share the power supply and COM end. The voltage source voltage in the diagram is U1, and the o1 in Figure 1 is the optocoupler, and the negative side of the optocoupler is connected to the main board of the test device. The working principle of this circuit: O1 minimum on-current is imin, maximum working current is imax, loop current is i, when i imin, o1 is on, i imin, o1 is not on, when i imax, the circuit burns out. In the following sections, we will use two cases: an uncharged contact (Fig. 2) and a live contact (Fig. 3).
1. Non-potentiometric contacts:
Tripping terminal wiring directly from the protection device, no DC power circuit is introduced. There are two possible ways to connect during the test:
1. Take the amount of com, a of the two-point access test device, because there is no potential, the two-point wiring can be exchanged at will. At this time, if the switch is divided, the circuit is open, i=0, and the optocoupler is not connected. When the protection device gives a trip signal, the switch in the figure will be divided into closes
The values of U1, R1, and R2 are fixed) and the test device records the action. This method of testing is usually not abnormal.
2. When accessed from two points, one more resistor r is serial in the loop
The magnitude of the current i depends on R, the larger the R, the smaller the I, when R is large enough to cause the i imin, the optocoupling is not working, and the tester cannot detect the action. But in fact, there is no fault in the tester and no fault in the protection device, but the contact point is not right. 2. Potential contact.
When the protection device has been connected to the system and the DC system of the system is electrified, it is assumed that the voltage between +km and -km is U2, and the direction is positive and negative. At this time, the com of the test device must be connected to the positive potential electricity, if it is reversed, no matter how it is wired, the optocoupler is always in the conduction state, and it has nothing to do with whether the protection trips or not, so it must be excluded. There may be a variety of connections under the normal wiring line, and the following is analyzed with 3 examples: 1. COM contact 1, A contact 2, in this case, the current is not closed when the switch is not closed
Among them, U2 is the system voltage, 110V or 220V, and U1 is the internal voltage of the test device, which is generally 24V, and the current I is 0, and the optical coupling is not connected. When the protection trips, when the switch is closed, the voltage at both ends of the switch is 0V, and the current is at this time
Optocoupler is turned on, and the test device records the action. 2. COM contact 1, A contact 3, in this case, the current when the switch is not closed
Optocoupler is not working. When the protection is tripped, the switch is closed, and the voltage at both ends of the switch is 0V, and the current is at this time
The optocoupler is still not working, and the test device cannot record the action, so this connection method is wrong.
3. COM contact 2, A contact 3, in this case, when the switch is not closed, the current
If R is small and can make i imin, then the optocoupler is turned on, and when the protection is tripped and the switch is closed, the voltage on the resistor R is ur=U2, and the current is current
Optocoupler is not working. In this way, the optocoupler changes from on to not, the state changes, and the test device can record the operation time normally. If R is large, the current is generated when the switch is not closed.
In this case, regardless of whether the switch is closed or not, the optocoupler is not connected, and the test device cannot record the protection action normally. Therefore, this connection method is the same as the second connection method without potential, and whether it can be tested normally depends on the size of r, and it is generally not recommended. In addition, there are other wiring methods and tests of pure potential, the principle of which is similar to the basic ones listed above, and will not be repeated.
To sum up, during the field test, whether it is a non-potentiometric contact or a potentiometric contact, the wiring should be used as much as possible in the first of the two cases, and there will usually be no abnormality. When the normal recording can not be recorded, you can throw off the protection wiring, and use the short wire to short the A and Com directly when the test device is running, if the test device can record the action normally, you can eliminate the fault of the relay tester.