1. Introduction As a important part of the power system, DC power supply provides uninterrupted power supply for some important conventional loads, relay protection and automatic devices, and telecontrol devices, and provides accident lighting power. If the DC system is grounded at one point and no short-circuit current is generated, it can continue to operate. However, it is necessary to find the grounding point in time and eliminate the grounding fault as soon as possible. Otherwise, when another point is grounded, it may cause malfunction or rejection of the signal device, relay protection and automatic device, circuit breaker, and may cause short-circuit of the DC power supply. Causes the fuse to blow, or the quick-disconnect power switch is disconnected, causing the device to lose operating power, causing serious power system failure and even accidents. Therefore, the DC system is not allowed to run for a long time under one grounding condition. It is necessary to strengthen online monitoring, quickly find and eliminate ground faults, and prevent power system faults caused by DC system grounding.
2. Several reasons for causing the substation DC system to be grounded (1) During the thunderstorm season, the wet water in the outdoor terminal box or the mechanism box causes the insulation resistance of the positive or negative power supply in the DC secondary circuit to drop to the ground, and the serious may reach zero. Form a ground.
(2) The connection plug or socket of the movable part and the fixed part of some models of the handcart switch lacks reliable insulation isolation measures. The handrail moves back and forth to cause the wire to be damaged, so that the DC link is in contact with the metal part of the switch, resulting in grounding. .
(3) Some DC systems have been in operation for many years, and the secondary equipment is aging and damaged, which is prone to grounding.
(4) Due to the imperfect construction process, bare wires appear in the DC circuit, the wire ends touch the cabinet, etc., causing grounding.
3. Basic principles and methods for finding ground faults (1) General treatment principle: According to the field operation mode, operation situation and climate influence, the location that may be grounded is determined. According to the outdoor outdoor and indoor, the first control is closed, and the total power supply to the branch The principle of power supply, gradually narrowing the scope, and adopting the method of finding and processing the road. It should be noted that the time for cutting off each dedicated DC link should not be too long (generally no more than 3 seconds), regardless of whether the loop is grounded or not.
(2) Specific treatment method: Firstly, understand the composition of the on-site DC power supply system. It is judged whether the DC positive pole grounding or the negative pole grounding is determined by the DC system insulation monitoring device or the grounding test button (the following assumption is that the insulation monitoring is reliable and assumes that it is grounded). Then, all the closing power switches are instantaneously cut off, for example, the grounding signal disappears, indicating that the grounding point is in the closing circuit, and the same method may be used to pull the load switch or release the positive power terminal in the same way in the station to perform the branch check and judgment; If the device is still reported to be grounded, the grounding point is in the loop of control, signal, etc., and the protection screen, control panel, signal screen and its control loop in the DC screen, battery cabinet and station should be further checked in the same way. After finding out which output power circuit the grounding point belongs to, you should quickly pull the DC power switch of the grounding circuit or the positive power supply insurance in the plugging circuit, and judge the grounding point before or after the switch (insurance) according to the alarm condition of the insulation monitoring device. . After judging clearly, according to the detected range, quickly cancel the positive terminal of the relevant equipment in the range, observe the alarm signal, and judge whether the grounding point is in this part of the equipment. Then continue to follow the above principles and methods, gradually narrow the search range until you find the grounding point.
4. Summarize the factors that cause the grounding of the substation DC system. In order to solve this problem better, different measures should be taken in the daily operation and maintenance according to the specific situation:
(1) Strict secondary equipment construction process, exerting subjective initiative and reducing the probability of occurrence of ground faults. For example, strengthen the outdoor terminal box, mechanism box, etc., add moisture-proof dehumidification equipment or materials; take measures to improve the insulation performance of the active parts of the opponent's switch, such as wrapping the thread part with insulation material, etc., to avoid the activity caused by the bicycle. Grounding; for insulation aging, control cables that cannot meet the requirements for grounding insulation resistance and related secondary equipments are replaced in time.
(2) Strengthen the operation and maintenance management of primary equipment such as circuit breakers, disconnectors and handcarts. Strict circuit breakers, disconnectors, etc. have operating procedures for mechanical transmission parts to avoid grounding faults due to unreasonable operation.
(3) When dealing with the grounding fault, strictly abide by the relevant electrical equipment maintenance and operation regulations, and combine with the actual conditions on site. It is forbidden to work alone, and it is forbidden to stop the DC power supply for a long time (especially if the weather conditions are not allowed). The time for removing and restoring each terminal and each switch should be as short as possible.
KNLE1-63 Residual Current Circuit Breaker With Over Load Protection
KNLE1-63 TWO FUNCTION : MCB AND RCCB FUNCTIONS
leakage breaker is suitable for the leakage protection of the line of AC 50/60Hz, rated voltage single phase 240V, rated current up to 63A. When there is human electricity shock or if the leakage current of the line exceeds the prescribed value, it will automatically cut off the power within 0.1s to protect human safety and prevent the accident due to the current leakage.
leakage breaker can protect against overload and short-circuit. It can be used to protect the line from being overloaded and short-circuited as wellas infrequent changeover of the line in normal situation. It complies with standard of IEC/EN61009-1 and GB16917.1.
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