***The Design of this Trainer Uses EXTREMELY DANGEROUS Voltages and should only be used under QUALIFIED supervision***
The electrical trainee can learn to recognize some of the more common symptoms and their causes encountered during operation of an industrial motor that incorporates controllers with contactors. I adapted an existing controller from an obsolete and removed system to enable junior electricians to experience the same symptoms they would in their job but in a more controlled environment. Most of the environments where these type of controllers are found are in an industrial and/or marine setting, so the noise level, temperature and space considerations are not conducive to directed training. With this setup, the junior technicians are able to have quiet troubleshooting while being directed in a safe manner.
This controller was from a system that utilized a remote signal to operate the contactor in an engineering space. This required a modification to the front panel to add a 'Stop' and a 'Start' button with associated labeling to enable the trainee to conduct trials beside the supervisor.
The learning objective of this instructible is to make you aware of a few common symptoms of a few motor controller faults, and how they can be simulated in a training environment. An individual can re-purpose familiar equipment, thus reinforcing training and save on spending on expensive off the shelf trainers.
The Inside of the controller does not look markedly different after the modifications, which is really the point as I did not want the trainees to be able to spot obvious defects to aid in their troubleshooting. The only obvious differences would be the cabling that leads off the left side of the photo which goes to the new 'Start' and 'Stop' buttons on the door of the controller.
The terminal strip on the bottom of the photo was the original termination point for the remote signal cables that controlled a rotary relay to activate the contactor. The rotary relay was also removed as redundant, as the trainer was going to be used locally under supervision.
The addition of switches on the side of the controller is an obvious understanding that they are there to make the controller a 'trainer' yet provides no physical clue as to the fault introduced for troubleshooting.
In this series of photos, the only thing missing is the 3 wires leading to the external motor (not shown). The connection points are noted on the photo as T1, T2 and T3. The power for the controller comes in through the top of the cabinet box via a 3 core cable that is connected to a shipboard test panel that supplies the 450 volts AC.
This is a schematic of the circuit as the trainee sees it.
A very basic 3-phase, single direction, single speed controller.
It utilized the same voltage for control.
This is the schematic that the supervisor sees. With all switches in the 'Normal' position, the schematic is identical to the trainee's for expected meter readings.
Here is a description of what each switch will do to the circuit.
Switch 1 will simulate a tripped overload so that there is no control voltage path for the contactor coil. This was accomplished by removing the inner circuit of the overload switch and putting switch 1 in parallel.(symptom: The motor will not start at all)
Switch 2 will simulate a failed 'holding on' contact. accomplished by putting in series with the holding-on contact. (symptom: The motor will start when the button is pressed but stop when the button is released)
Switch 3 will simulate a 'frozen' (dirty/ rusted) stop button. switch 3 was placed in parallel with the stop button (The motor will start but not stop)
Switch 4 will simulate a line break in the control circuit . Switch 4 in series with the control circuit.(The motor will not start)
Switch 5 will simulate the loss of one phase. The motor will run ragged if already running, but not start if stopped. Called single-phasing . Switch 5 in series with the 'T2' lead. (did not have time to complete before submitting instructible)
An additional switch could be put in parallel with the control fuse to simulate a blown fuse. The actual fuse would have to be an already blown fuse or no difference would be measured in voltages.