Cause of Malfunction in AC machine and Practical solution
Overheating of the stator winding of a synchronous machine
Cause of the malfunction:
Generator current overload
Turn-to-turn connection, short circuit between phases or grounding in two places of the stator winding (phase-to-phase voltages are not the same)
Measures taken:
Check the load, avoid overloading
Rewind the faulty coil or replace it with a new one. When connecting all coils of one phase in series and connecting the phases with a “star”, it is possible to temporarily turn off the damaged coil by cutting and insulating it. In this case, the number of turns should not exceed 10% of the total number of turns of one phase. When connecting coils in parallel or when switching phases with a “delta”, it is necessary to turn off the corresponding number of coils in other phases or parallel groups
Overheating of the excitation winding (rotor)
Cause of failure:
Excessive excitation current
Reduced speed of the prime mover
Low load power factor
Turn-to-turn connection or short to ground in two places of the excitation winding, which is sometimes accompanied by vibration
Measures to be taken:
Reduce the excitation current
Check and increase the speed
Reduce the reactive load. Take measures to improve the power factor
Find and eliminate the turn-to-turn connection or connection to the case
The generator does not give voltage
Cause of the malfunction:
Open or poor contact in the excitation regulator
Malfunction of the automatic excitation regulator
Open or poor contact in interpole connections
Breakage of the output ends of one or more pole coils
Breakage or poor contact in the conductors between the winding and slip rings
Breakage or poor contact of the connecting wires between the exciter and slip rings eliminate the malfunction
Check the condition of the interpole connections of the coils. Restore electrical circuits
Eliminate the break. If it is impossible to fix the coils, replace them with new ones.
Measure the rotor resistance. In case of a strong increase in resistance against a nominal or complete break in the rotor, open the current supply and eliminate the malfunction.
Check the integrity and condition of the wires. If the wires are broken, eliminate it.
The generator at idle gives voltage only between two phases
Cause of the malfunction:
Break in one phase of the stator when connected with a “star” or break in two phases when connected with a “delta”
Measures to be taken:
Determine the location of the break. If the break is in outer connections, reconnect; if the break is inside the coil, then replace it with a new one.
The generator gives a voltage less than the nominal
Cause of the malfunction:
Reduced speed
The exciter is faulty
Measures to be taken:
Check the rotational speed of the generator, bring it to the nominal
See malfunctions of DC machines 6.
Fluctuation in the voltage or power of the generator Cause of the malfunction: Measures: a) Check exciter circuit and troubleshoot b) Check RPM, troubleshoot prime mover speed controller
Uneven distribution or “swing” of the load of parallel generators
Cause of malfunction:
Malfunction of the speed controller of the primary engine
Measures to be taken:
Eliminate the malfunction of the speed controller of the primary engine
Measures to be taken:
Adjust the excitation
Eliminate the fault
Asynchronous motor does not work at start-up
Cause of failure:
Fuses in the main or control circuits are blown. Power is not applied to the electric drive
Break in the stator or rotor phase
Starting device is damaged
Overheating of the stator winding of an asynchronous electric motor, the electric motor hums, runs at a reduced speed
Cause of malfunction:
The electric motor is overloaded or its ventilation is broken
The mains voltage is lower than the nominal
The stator winding is connected by a “triangle” instead of a “star” connection
Short circuit on the case of the winding of one phase in two places
Interphase connection in the stator winding
Turning connection in the stator winding
Poor contact or open circuit in the rotor circuit
Starting device circuits are broken
Measures to be taken:
Check the load and the cleanliness of the ventilation ducts
Raise the mains voltage to the nominal value or reduce the load of the electric motor
Check the connection of the windings according to the factory scheme
Check the stator winding and eliminate the short circuit
Check the stator winding circuit and eliminate the interphase connection
Find the coil connection and eliminate it
Check the circuit rotor windings
Eliminate the malfunction
When turned on, the electric motor does not start, it hums, the contactors turn on
Cause of the malfunction:
The fuse in one phase of the power circuit burned out
The heating element of the thermal relay burned out
Incorrect connection of the beginnings and ends of the phase windings
Measures to be taken:
Check and replace the blown fuse
Notice the defective element of the thermal relay
Check and switch the ends contacts, jammed or faulty springs
The electric motor turns off when the “Start” button is released
Cause faults:
The circuit of the auxiliary contacts of the line contactor shunting the start button is broken
Measures to be taken:
Check the circuit shunting the start button, eliminate the malfunction
The electric motor does not stop when the Stop button is pressed
Cause of the malfunction:
line contactor contacts jammed Measures to be taken: a) Eliminate the malfunction b) Inspect the contactor, check the condition of the contacts and springs , eliminate malfunctions
Measures to be taken
Replace the blown fuse
Eliminate the cause of the overload.