Signs and treatment of disconnection of the hottes

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Signs and treatment of secondary circuit disconnection

secondary circuit disconnection in substation is a frequent fault. The secondary circuit disconnection is generally divided into: current transformer secondary circuit disconnection, voltage transformer secondary circuit disconnection and DC system secondary circuit disconnection. According to the actual work of the author, the signs and treatment methods of various secondary circuit disconnection are briefly discussed below for your reference only

1 open circuit at the secondary side of current transformer

1.1 the primary winding of current transformer is directly connected to the primary current circuit. When the secondary side is open circuit, the secondary current is zero, while the primary current does not change, so that the magnetic flux in the core increases sharply to the saturation level. This sharp increase in magnetic flux produces high voltage in the open secondary winding, which directly endangers the safety of people and equipment

1.2 the signs of open circuit on the secondary side of current transformer include: the protective devices started by zero sequence and negative sequence current are frequently started, or they cannot be reset after starting; Differential protection starts or malfunctions; The ammeter indication is abnormal, and the phase current indication decreases to zero; The indication of active and reactive power meters decreases, and the watt hour meter moves slowly; Sometimes there may be sparks or smoke at the open circuit point; The current transformer has a loud buzzing sound, etc

some of the above phenomena may not occur at the same time, which depends on the load supplied by the open secondary winding and the specific situation of the open circuit

1.3 treatment of open circuit at the secondary side of current transformer

1.3.1 determine which group of secondary windings is open circuit according to the fault phenomenon. If the secondary winding used for protection is open circuit, immediately apply for deactivating the protective device that may misoperate

1.3.2 check whether the secondary circuit equipment (relay, instrument, terminal strip, etc.) powered by the open circuit winding has obvious open circuit phenomena such as discharge and smoking

1.3.3 if no obvious fault is found, use insulating tools (such as electroscope) to gently touch and press the connecting terminal and other parts to observe whether there are abnormal phenomena such as looseness, fire or signal action. During this inspection, insulation safety appliances (such as wearing insulating gloves) with the same voltage level and qualified test must be used

2 secondary side disconnection of voltage transformer

2.1 the reasons for secondary circuit disconnection of voltage transformer may be loose terminal, poor contact, circuit disconnection, poor contact of auxiliary contact of circuit breaker or disconnector, fuse fusing, secondary circuit switch disconnection or poor contact, etc

2.2 when the secondary circuit of voltage transformer is disconnected, all protective devices connected to the voltage are affected. We have repeatedly tested the protection of the line locking device without disconnection, and it will malfunction

2.3 voltage transformer secondary circuit disconnection may produce the following signals or signs: distance (or low impedance) protection disconnection locking device acts, and sends disconnection, device locking or fault signals; Send secondary circuit switch tripping alarm signal; The voltmeter indicates zero, the power meter indicates abnormal, and the electric energy meter moves slowly or stops rotating, etc

2.4 treatment of secondary side disconnection of voltage transformer

2.4.1 judge which group of secondary winding circuit of voltage transformer is disconnected according to signals and fault signs

2.4.2 if the secondary voltage of protection is disconnected, immediately apply for stopping the affected relay protection device, disconnect its outlet circuit pressing plate, and prevent the circuit breaker from tripping by mistake. If the instrument circuit is disconnected, pay attention to the impact on electric energy measurement

2.4.3 check the fault point. The AC voltage of the multimeter can be used to block the broken secondary circuit equipment. The on-board air pump can timely supplement the internal pressure measurement voltage when the tire under pressure alarm, and find out the fault point and deal with it according to the voltage

2.4.4 if the secondary circuit switch of voltage transformer trips or the secondary fuse is blown, there may be a short-circuit fault in the secondary circuit, try to find out the short-circuit point and eliminate it. Check the short-circuit point. After the secondary power supply and normal contact are disconnected, measure the resistance between phases and phase to ground with Multimeter resistance block in sections and sections, and compare with each other to judge. If the fault point is not found out, when using sectional trial power transmission, it should be carried out after finding out that the protection against possible misoperation (distance or low resistance American polymer manufacturer PolyOne announced a few days ago that the company's newly developed light carbon fiber composite chassis has won the favor of Chevrolet Corvette C7, etc.) has been disabled

3 DC circuit disconnection

DC secondary circuit disconnection may affect the normal power supply of the protection power supply, the loss of voltage of the operation power supply, or the failure of the signal and monitoring device, resulting in the loss of protection of the equipment, the failure of the circuit breaker to trip, the failure of normal operation or the loss of monitoring, which seriously threatens the safe operation. In case of DC disconnection, the voltage (potential) can be measured to check the disconnection point of DC circuit. With a DC voltmeter, a production line with an annual output of 10000 liters of nano silver conductive ink and 100million pieces/year RFID electronic labels has been built. Check the circuit for voltage. If there is voltage, check the positive and negative potential of the point to the ground to judge the specific disconnection point. The DC voltmeter with high internal resistance should be used to check the voltage, which is to prevent the DC circuit from being short circuited or grounded during detection, which may cause some protections to malfunction

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