Voltage transformer fault handling - Solutions - Huaqiang Electronic Network

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1 When the secondary fuse of the voltage transformer is blown, when the secondary fuse of the transformer is blown, the following phenomenon will occur: there is a notice sound; the "voltage circuit broken" light plate will be bright; the voltmeter, active and reactive power meter The indication value will decrease or go to zero; the voltage of the insulation monitoring meter of the fault phase will decrease or go to zero; the "backup power disappears" light plate will be on; when the transformer and generator are severely overcurrent, the transformer fuse is blown, Low-voltage overcurrent protection may be malfunctioning.

Processing method: Firstly, according to the phenomenon, it is judged which device's transformer is faulty, and the protection device that may be malfunctioned is withdrawn. Such as low voltage protection, standby power supply self-injection device, generator forced excitation device, low-voltage over-current protection. Then it is judged which phase of the secondary fuse of the transformer is blown. At the upper and lower ends of the secondary fuse of the transformer, the multimeter is used to measure whether the secondary voltage between the two phases is 100V. If the upper end is 100 V and the lower end does not have 100 V, the secondary fuse is blown. It is determined by which the upper and lower ends of the two phases are crossed to determine which fuse is blown and replaced. If the voltage at the upper end of the fuse is not 100V, it may be that the auxiliary contact of the transformer isolating switch is poorly contacted or the fuse is blown. The mutual contact between the two phases of the auxiliary contact of the transformer isolating switch is determined by the transformer isolation switch. Poor contact in the contact or a fuse blown by the transformer. If the contact of the transformer isolation switch auxiliary contact is poor, adjust the adjustment. If the transformer is blown once, open the transformer disconnector and replace it.

2 Voltage transformer primary fuse blown

The fault phenomenon is the same as the secondary fuse blow, but it is possible to issue a "grounded" light plate. Because the transformer fuses one phase and the fuse is blown, the voltage at the opening triangle is 33V, and the voltage setting at the opening triangle is 30V, so the "grounding" optical word processing method is issued, which is the same as the secondary fuse blowing. Pay attention to whether the shrapnel is loose after the high-voltage fuse is installed in the primary fuse holder of the transformer.

3 Voltage transformer breakdown fuse blown

The secondary side neutral point of the transformer with grounding phase B has a breakdown fuse that breaks down the transformer. The main function of the fuse is: even when the secondary fuse of the B phase is blown, even if the high voltage is broken The low voltage still makes the breakdown fuse blown, so that the transformer has a protective ground twice, which protects the safety of the human body and the equipment. The breakdown fuse voltage is about 500V. The fault phenomenon is the same as the secondary fuse of the transformer. At this time, the B-phase secondary fuse is replaced, and a good fuse is blown when replaced with a good fuse. Do not blindly increase the fuse capacity, to find out the reason, whether the transformer breakdown fuse has been blown. Only after the breakdown fuse is replaced, the B-phase secondary fuse can be replaced. The primary and secondary fuses of the transformer are blown and the fuses are blown. The phenomenon is basically the same. When searching, the secondary fuses and auxiliary contacts are generally checked first, then the fuses are checked, and finally the fuses are broken and the mutual inductance is checked. Whether the internal fault of the device, if the generator is turned on, the primary transformer of the generator transformer is often blown and can not find the cause, it may be caused by the ferromagnetic resonance of the transformer.
4 voltage transformer smoke damage

When the voltage transformer smokes, the main body will emit smoke and have a strong odor; the voltage of the insulation monitoring meter may be lowered, and the indication of the voltmeter, active and reactive power meter may be lowered, and the generator transformer may be Smoke, there may be "stator grounding" light plate is bright, busbar transformers smoke, there may be "voltage loop disconnection", "backup power disappeared" and other light words.

Treatment method: If the fuse is never blown before the transformer smokes, and the secondary fuse is blown several times, and the smoke is not serious, there is no symbol of insulation damage. When the fuse is not blown, it should be blown. It is judged that the short circuit between the secondary windings of the transformer causes smoke. Before the secondary winding smokes without affecting the primary insulation damage, immediately withdraw the relevant protection and automatic device, remove the secondary fuse, open the isolation switch, and stop. Use a transformer.

For oil-filled transformers, if smoke is accompanied by a thick odor, there is abnormal noise inside the transformer; there is a spark discharge between the winding and the casing or between the lead and the casing; the fuse is blown before the smoke is blown When one of the phenomena is 2 to 3 times, it should be judged as smoke from the primary side insulation damage. If the generator transformer smokes, the method of de-energizing the generator should be used immediately. If the busbar transformer is used, the transformer is deactivated by stopping the busbar. At this point, the transformer must never be deactivated by pulling the isolation switch apart.
5 single phase ground fault

Phenomenon: The fault phase voltage is reduced or zero, and the other two phase voltages rise or rise to the line voltage. The grounding phase is determined by:

(1) If one phase voltage indicates zero and the other two phases are line voltages, the zero phase is the ground phase.

(2) If the phase voltage indication is lower and the other two phases are higher, the lower phase is the ground phase.

(3) If the voltage of one phase is close to the line voltage, the voltages of the other two phases are equal, and the voltages of the two phases are low, the principle of discrimination is “high voltage, bad phase”, that is, according to A, B, C phase sequence, which phase If the voltage is high, the lower phase may be grounded. For faults where the system is grounded but not broken, remembering the fault symbol can prevent the maintenance personnel from blindly checking the line.
6 Ferromagnetic resonance The so-called ferromagnetic resonance is a kind of transition process caused by the saturation of the core. The ferromagnetic resonance occurring in the system is divided into parallel ferromagnetic resonance and series ferromagnetic resonance [1, 2]. The case of exciting resonance is as follows: the power supply suddenly closes the empty bus with the transformer, and the single phase is grounded; when the switch is closed, the three phases of the switch are different. Therefore, the generation of resonance occurs when an operation or system failure occurs. In a neutral point ungrounded system, the nonlinear inductance of the transformer often forms a ferromagnetic resonance with the capacitance of the ground capacitance of the system, so that the neutral point displacement of the system generates a zero-sequence voltage, thereby causing a relative voltage of the transformer to generate an overvoltage. At this time, a ground signal is issued, and it is easy to misidentify the illusory grounding as single-phase grounding. Ferromagnetic resonance is also possible when the empty bus or the cut-away line or the single-phase ground fault disappears. At this point, the neutral point voltage (zero sequence voltage) may be the fundamental (50
Hz), or it can be divided (25 Hz) or high frequency (100~150 Hz). Frequently occurring are fundamental resonance and frequency division resonance. According to the operating experience, when the power supply suddenly closes to the empty busbar with only the transformer, the fundamental resonance is easy to occur; when single-phase grounding occurs, the two-phase voltage rises instantaneously, and the three-phase iron core is excited by different degrees to different degrees. Saturated, easy to generate crossover resonance.

From a technical point of view, in order to eliminate ferromagnetic resonance, the following measures can be taken: selecting a voltage transformer with good excitation characteristics or switching to a capacitive voltage transformer; in the same 10
In the kV power distribution system, the number of voltage transformers should be reduced as much as possible; in the neutral phase of the three-phase voltage transformer, the single-phase voltage transformer is connected in series or the damping resistor is connected to the secondary opening triangle of the voltage transformer; Connect a capacitor of a certain size, so that the ratio of capacitive reactance and inductive reactance is less than 001 to avoid resonance; the system neutral point is equipped with arc suppression coil; the ground compensation device adopts the automatic tuning principle, through overcompensation, full complement and Under-complementary operation to better solve such problems.