Analysis and troubleshooting of motor control circuit breaks, short circuits and grounding faults

Control Circuit Maintenance - Insulation Monitoring - Marine Electrical Practices

I. Motor control circuit somewhere broken fault analysis and troubleshooting

Any break in the motor control circuit will result in one or all of the motor's functions not being realized. When troubleshooting such faults, be sure to narrow down the scope of the investigation according to the fault phenomenon, so as to get twice the result with half the effort. Most wiring diagrams for real boats will have indicator lights to assist in analyzing the problem.

Failure phenomenon a: forward / reverse rotation are no response
Focus on troubleshooting the common parts: fuse FU₂, normally closed auxiliary contact FR (1-2) of the thermal relay, stop button SB₁, and the common cable.

Failure phenomenon two: only one-way operation
If only forward rotation is possible, check the reverse rotation branch (3→6→7→0); if only reverse rotation is possible, check the forward rotation branch (3→4→5→0).

Failure phenomenon III: can only click (not self-locking)
Troubleshoot the self-locking contacts for forward or reverse rotation, i.e., the normally open contacts of KM₁ or KM₂.

Failure phenomenon four: after ignition once can not start again
Consider thermal relay overload. Motors that have not been running for a long time should be “coiled” before starting. Loose wiring is common.

Second, motor control circuit somewhere short circuit fault analysis and troubleshooting

1. Failure phenomenon I: normal operation but can not be stopped
Generally, it is caused by SB₁ normally closed contacts, self-protection contacts sticking or bad insulation.

2. Trouble phenomenon 2: Fuse FU₂ blows after pressing SB₂/SB₃.
Control circuit short circuit, such as contactor coil short circuit (normal resistance should be tens to hundreds of ohms).

3. Trouble phenomenon III: Press SB₂/SB₃ and then the circuit breaker trips.
Severe phase-to-phase short circuits in the main or control circuits, and the fuses do not act as prior protection.

Insulation Measurement and Grounding Exclusion Method:

Current marine control circuits are often electrically isolated by transformers. If a ground is found, it is necessary to disconnect the electronic components and measure them in sections with a megohmmeter:

(1) Segment-by-segment measurements:Connect one end to a megohmmeter and the other end to ground. Normal resistance should > 0.5 MΩ。
(2) Check the components:After locating the faulty section, check the status of contactors, relays, cables and terminals.
(3) Repair validation:Repair the specific point of failure (broken cable, etc.) and then re-run the full test.

⚠️ High hair parts alert: sensors, space heaters, kitchen electric heating equipment, cold storage frost melting electric heaters.

Third, motor control circuit somewhere ground fault analysis and troubleshooting

Circuit grounding is the direct contact of the guide body with the earth or grounding conductor. It can cause protective device action, voltage drop causing start-up failure, unstable operation (speed fluctuation), abnormal instrument display and increased electromagnetic interference.

Overheating and malfunction:
Grounding leads to overheating caused by abnormal currents; interference with control signals leads to relay malfunction or refusal to operate, threatening personal safety.

No risk of isolated loops:
If the control circuit is not isolated through the transformer, the ground fault will be directly reflected in a drop in the 380V insulation level of the grid and must be investigated immediately.

Troubleshooting a single grounding point is relatively straightforward and simple, however, as the number of grounding points increases, the difficulty of troubleshooting increases significantly.