{"id":15866,"date":"2026-01-07T11:45:39","date_gmt":"2026-01-07T03:45:39","guid":{"rendered":"http:\/\/www.erun-tech.com\/?post_type=dt_portfolio&p=15866"},"modified":"2026-01-07T11:45:39","modified_gmt":"2026-01-07T03:45:39","slug":"diandongjizhuhuiluduanluyuquexiangguzhangfenxiyupaichu","status":"publish","type":"dt_portfolio","link":"http:\/\/www.erun-tech.com\/en\/project\/diandongjizhuhuiluduanluyuquexiangguzhangfenxiyupaichu","title":{"rendered":"Analysis and Troubleshooting of Short Circuit and Phase Loss in Main Circuit of Electric Motors"},"content":{"rendered":"
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Analysis and Troubleshooting of Short Circuit and Phase Loss in Main Circuit of Electric Motors<\/h1>\n
Forward and Reverse Circuit Safety - Troubleshooting - Marine Electrical Maintenance<\/div>\n<\/div>\n
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Forward and reverse circuits are critical in marine applications that include, but are not limited to, winchers, cargo lifters, anchors, gangways, and various auxiliary machinery such as pumps and fans. To prevent safety incidents caused by short circuits or other electrical faults, all forward and reverse circuits should be designed with interlocking mechanisms, including but not limited to mechanical interlocks as well as electrical interlocks, to ensure that contactors in both directions do not close at the same time.<\/p>\n<\/section>\n

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I. Motor main circuit short circuit fault analysis and elimination<\/h2>\n
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A short circuit is a fault condition in an electrical circuit in which current does not pass through the intended load (such as a resistor, light bulb, or other electrical device), but instead passes through a low impedance path and returns directly to the power source. Ideally, the current in a circuit should flow through all designed components, including the various electrical appliances and protective devices. However, in the case of a short circuit, the current will bypass these components and find a path of lower resistance, which usually means that the current will flow directly from one pole of the power supply to the other without passing through any or very few loads.<\/p>\n

1. Types of short circuits<\/h3>\n
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(1) Phase-to-phase short circuit<\/strong>
\nIn a three-phase power system, non-normal connections occur between different phases. It can occur both on the power-using equipment and on the lines.<\/span><\/div>\n
(2) Short circuit to ground<\/strong>
\nUnusual contact between a phase or phases of energized conductors and the ground (or a grounded metal part).<\/span><\/div>\n<\/div>\n

2. Causes of short-circuit faults in the main circuit<\/h3>\n

Figure 21-1 shows a motor forward and reverse circuit. In order to prevent mechanical shocks or electrical overloads caused by the inertia of the motor not stopping completely when switching between forward and reverse rotation, some forward and reverse circuits are equipped with time relays. In the diagram, it can be assumed that the KM\u2081 contactor is the forward contactor, the KM\u2082 is the reverse contactor, the SB\u2082 is the forward start push button, the SB\u2083 is the reverse start push button, and the SB\u2081 is the general stop push button.<\/p>\n

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\"36c8146010c34b27136f663aa4975ed6\"Figure 21-1 Motor Forward and Reverse Circuitry<\/p>\n<\/div>\n

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(1) Main circuit phase-to-phase short circuit:<\/strong>It may occur in any part of the main circuit. u\u2081, v\u2081, w\u2081 Any two cables can occur without direct contact with the power-using equipment. Specific causes include:<\/p>\n

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  • \u25cf Contactor main contacts sticking:<\/strong>KM\u2081 or KM\u2082 main contacts are welded or mechanically jammed. If the reverse start button is pressed at this time, it will lead to a short circuit in both phases of the power supply. It can be judged by measuring whether the upper and lower ends of the contactor are disconnected with a multimeter.<\/li>\n
  • \u25cf Interlock failure:<\/strong>The normally closed contact of KM\u2082 in the control circuit is sticking. Pressing the reversing button SB\u2083 while the motor is rotating forward may cause a short circuit in the main circuit.<\/li>\n
  • \u25cf Physical factors:<\/strong>Loose junction box wiring, broken insulation due to vibration and friction, extremely humid environment (water in the junction box), and so on.<\/li>\n<\/ul>\n

    (2) Motor turn-to-turn short circuit:<\/strong>Refers to a short circuit between neighboring coils (turns) in the same winding due to insulation damage. It can cause current imbalance, overheating and mechanical damage. It can be initially determined by measuring the resistance of the three-phase windings with a multimeter to see if they are roughly equal.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

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    Second, the motor main circuit phase fault analysis and troubleshooting<\/h2>\n
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    Physical characterization of the missing phase:<\/strong>Motor vibration increases, temperature rises, speed decreases, current increases, and there is a \u201cbuzzing\u201d sound. If the protection components do not act, the motor can continue to run but it is very easy to burn; after stopping and starting again, the noise is very loud and cannot be successfully started.<\/div>\n

    Troubleshooting Logic<\/h3>\n
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    \u25cf Power side with fuse:<\/strong>
    \nMeasure the voltage between L\u2081-L\u2082, L\u2082-L\u2083, and L\u2081-L\u2083. If the fuse (FU\u2081) is burnt out, confirm it by the power-off troubleshooting method (measuring the on-off) or the power-on troubleshooting method (measuring the upper and lower voltages).<\/span><\/div>\n
    \u25cf Control appliances and wiring:<\/strong>
    \nCheck for loose or broken wiring; observe contactor contacts for severe wear. A thermal relay (FR) that has a single-phase action instead of a three-phase linkage means that the thermal relay itself is faulty.<\/span><\/div>\n
    \u25cf Motor windings:<\/strong>
    \nThe internal winding is disconnected. To measure, disconnect the star-delta connector and measure the resistance between U\u2081-U\u2082, V\u2081-V\u2082, and W\u2081-W\u2082.<\/span><\/div>\n<\/div>\n
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    Comprehensive Maintenance Summary<\/h4>\n

    Whether it is a blown fuse, a faulty contactor or a faulty thermal relay, it means that there is an abnormality in the circuit. When replacing parts, in addition to paying attention to consistent specifications, theIt is important to verify that the motor and the entire circuit are in good condition<\/strong>. The initial period of energized operation is focused on:
    \n1. Motor current value;
    \n2. Operating sounds (bearings and loads);
    \n3. Motor temperature (focus on bearing end temperatures at both ends).<\/p>\n<\/div>\n<\/div>\n<\/section>\n