Ground fault monitoring of the main circuit of the diesel locomotive to prevent protection against short circuit accidents caused by grounding. The so-called "ground" is the car body, the frame and various conductive objects connected to them. Since the car body and the frame are directly connected to the earth through the wheel pair and the rail, they have the same potential as the earth, called "ground potential". ". On the locomotive, for safety reasons, all motor and electrical appliances and other electrical equipment without power, casings, shelves, etc. are grounded.
When the locomotive is in operation, if the cable or wire of the main electrical appliance is damaged by insulation, or the traction motor is ring-fired, the electrical contacts are arcing, etc., the grounding will be formed. If a little grounding occurs, it does not constitute a current path, so it does not immediately cause electrical damage, but it is a hidden danger; if grounding occurs at two points of different potentials, it will cause a major accident. Therefore, it must be detected immediately when only a little grounding occurs in the main circuit, and protection should be carried out in time to prevent it from happening.
The existing grounding Baohua circuit is provided with an artificial grounding point, and a grounding electrical electromagnetic coil is connected between the grounding point and a potential point (referred to as a comparison point) selected and connected in the main circuit. When a ground fault occurs in the main circuit, if the potential difference between the ground fault point and the comparison point is sufficiently large, the generated short-circuit current will flow through the electromagnetic coil of the grounding relay to cause the grounding relay to operate and protect. Due to the randomness of the ground fault, when the potential of the fault ground point is equal to or close to the potential of the comparison point, the current flowing through the coil of the grounding relay DJ is small, which is insufficient for the grounding relay to operate, which causes the grounding protection to appear. The "dead zone".
In order to eliminate the "dead zone" and expand the grounding protection range for the live circuit, it is very important to select the main circuit comparison point reasonably. In the diesel locomotive with AC-DC transmission, the main circuit comparison point is usually selected at the midpoint N of the armature group of the three-phase synchronous traction generator star connection method, and the grounding switch DK and the grounding relay DJ are connected to the artificial grounding point. In this way, regardless of the contact between the positive terminal or the negative terminal of the main electrical device, a certain current flows through the DJ coil to cause the grounding relay to operate, and the "dead zone" of the grounding protection is eliminated to some extent. In order to make the grounding protection of the AC side of the main circuit, a bridge rectifier circuit 4ZL is added to the grounding relay circuit, so that the grounding relay can be operated and protected regardless of the grounding of the DC or the AC main circuit.
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