Analysis of common external faults in residual current action protection devices - Programmer Share

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

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At present, the low-voltage residual current protectors commonly used in China are classified into different types according to the characteristics of the electrical signals causing their actions, and can be classified into a voltage action type, a current action type, and an AC pulse type. Below we take the AC pulse type protector commonly used as a primary protection switchboard as an example to analyze its common external faults.
1 Ask, smell, see, test the "four diagnosis" method to diagnose the fault
1.1 Ask. That is, ask the cause, process and status of the electrician's fault, and determine the scope or device of the fault.
1.2 smell. Just smell the inside of the protector, the contactor coil, etc., if there is any smell of overheating.
1.3 Look. That is to see if the protector is installed correctly, the wiring is correct, the device is obviously damaged, and the neutral point of the distribution transformer is in good contact.
1.4 Measurement. That is, use a multimeter to measure whether the input and output voltage of the protector is normal, whether the zero-sequence transformer is disconnected, and measure the magnitude of the neutral point grounding resistance.
2 External failure analysis
2.1 Determine whether the external fault is analyzed according to the “four diagnoses” of asking, smelling, watching and measuring. Firstly, it is judged whether the protector is faulty or external (including human fault, line or power equipment fault). The method of judging is: all the lines and the electrical equipment after the protector are completely taken out of operation, and the protector is tested separately. After power transmission, press the test button on the protector several times to see if the indicator light is correct. Can you hear the sound and release sound of the sensitive relays “咔嗒” and “咔嗒”. If the indicator light is correct, the sound of the relay can be heard and released, indicating that the protector itself is functioning properly and can be judged as an external fault.
2.2 Installation and wiring errors and other human external faults and treatment methods
2.2.1 Protector wiring installed on the three-phase load power line The correct wiring shall be the zero-sequence current transformer coil of the three-phase phase line and the neutral line all passing through the protector. Wrong wiring can be roughly divided into the following types.
1 The neutral point of the distribution transformer is not grounded or the grounding is poor. When the test button is pressed repeatedly, the protector works normally, but when there is electric shock or simulated electric shock test, the protector cannot operate. This is because the neutral point of the distribution transformer is not grounded or the grounding is poor. The contact and leakage currents are not returned to the neutral point of the distribution transformer. The protector cannot be operated. Therefore, the neutral point of the distribution transformer using the current type protector. Must be grounded and grounded must be good. 2 The phase line is passed through the protector, and the neutral line is mistaken for zero voltage and zero current without passing through at the same time. Although the neutral line voltage in operation is very low, there is often a single line on the neutral line. The phase load current has a three-phase unbalanced current, so the neutral line does not pass through the protector, which will cause the three-phase current synthesis phasor to be non-zero, causing the protector to malfunction. Therefore, both the phase and neutral lines should be routed through the zero-sequence current transformer coil of the protector. 3 The line protected by the protector is mixed with the unprotected line, so that the protector cannot be put into operation. 4 Distribution transformer neutral point grounding wire is taken after the protector, the protector is bypassed and does not work. The protector is too close to the electromagnetic interference source such as the AC contactor. At this time, the secondary side of the zero-sequence current transformer may output an incorrect signal, causing the protector to malfunction.
2.2.2 Installer on the neutral grounding wire The correct wiring is the zero-sequence current transformer of the neutral wire passing through the protector. The advantage is that the wiring is simple and not limited by capacity. The disadvantage is that each distribution transformer only A protector can be installed, which is characterized by poor insulation or failure of the neutral when the neutral cable is poorly insulated or grounded. 1 The load neutral line passes through the protector alone, which will result in the protector not being put into operation. Because the three-phase load is impossible to balance in the rural low-voltage power grid, the zero-sequence current transformer detects the three-phase load unbalanced current, and the current is far greater than the rated operating current of the protector, so the protector cannot be put into operation. . 2 When the neutral line has repeated grounding, the protector will be rejected or mis-operated. If the three-phase load is completely symmetrical, the neutral line current of the low-voltage grid is equal to zero, and the protector can be put into operation; if someone is in an electric shock, part of the electric shock current is repeatedly grounded back to the neutral point of the power supply, so that the electric current is significantly reduced due to the shunting. The sensitivity of the protector; if the three-phase load of the low-voltage line is asymmetrical, there is an unbalanced current in the neutral line. Since the neutral line has two grounding points, it is divided into two paths to return to the neutral point of the power supply, and the grounding impedance Much larger, so most of the current goes back to the neutral point of the power supply through the neutral line. A part of the current returns to the neutral point of the power supply after repeated grounding and zero-sequence current transformer. This current is much larger than the rated operating current of the protector. The protector cannot be put into operation.
3 Line and electrical equipment troubleshooting methods
3.1 Line and electrical equipment failure
3.1.1 The insulation of the line and the electrical equipment is poor, and the leakage current is large, which makes the protector malfunction or difficult to put into operation.
3.1.2 The relative insulation imbalance is unbalanced, causing the leakage current of each phase to be unbalanced. The so-called sensitive phase and the insensitive phase appear. If the electric shock occurs on the insensitive phase or the simulated electric shock test is performed, the protector may refuse to move.
3.1.3 Neutral insulation is poor or grounded, which forms a shunt with the neutral point grounding wire of the distribution transformer, resulting in a decrease in the sensitivity of the protector or refusal.
3.2 Treatment method Use a 500 V megger to measure the low-voltage line. If the insulation to the ground is low or even zero, the following rectification must be carried out: take the branch, segment or household measures to find the line insulation. Weak points and grounding points are treated; the old lines, lighting lines and buried lines with large leakage are evenly distributed to the three phases, and the leakage is balanced as much as possible to reduce the zero-sequence current; the branches close to the line are regularly trimmed to make the wires The distance complies with the regulations.