MSE of Canada
Ltd.
MSE of Canada
Ltd.
The following are answers to some of the questions you may have.
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1. What causes motor insulation deterioration?
In motors in intermittent operation, the heating and cooling of the windings promotes cracking of the insulation, allowing moisture and environmental contaminants access.
2. What are the real benefits of monitoring motor insulation resistance?
The benefit is seen on the bottom line.
- With early warning, production downtime cost from motor insulation failures is eliminated,
- spare motor inventory costs can be minimized and
- preventative maintenance can be scheduled and its costs controlled.
3. Can I use the monitors on AC and DC motors?
Yes.
4. Can I use the monitors on grounded or ungrounded power systems?
Yes. The type of system is not relevant, as the motor(s) must be isolated from the system when being monitored.
5. Is there any deterioration of motor insulation or equipment as a result of continuously testing?
No, the unit uses a non-destructive, very low current for monitoring system.
6. Is 24 volts sufficient voltage to monitor insulation resistance?
The purpose of the MotoSafe Insulation Monitor is to alert the operator to a low insulation condition which may lead to failure on starting. For this purpose, 24 volts is more than adequate, as the insulation has effectively lost its dielectric strength when it has reached this condition.
7. I think 24 volts is too low - can you offer monitors with higher monitoring voltages?
Yes. We have the Type MHV-H and the Type LM602IND, which monitor with 400 volts DC.
8. Can I do 500V Megger Test with the monitor installed?
Disconnect the control power to the monitor to isolate it from the motor.
9. How does it works?
Electric motors are wound with copper wire, which is insulated to resist the leakage of current from the winding to the motor frame. MotoSafe Insulation Monitors compare the resistance of the insulation to a standart resistance in the unit, to monitor the insulation resistance.
When the motor is idle, the standart resistance joins to the winding isolation resistance and the monitor uses a fixed DC voltage to pass the same electric current through them both, so by comparing the voltage across the two resistarnces it determines whether the insulation resistance is greater than, equal to or smaller than the standart resistance. If it is equal or smaller than the standart resistance, the MotoSafe unit goes into alarm. The value of the standart resistance can be selected by selecting the alarm level with the switch on the MotoSafe faceplate.
10. How does the MotoSafe unit connect itself and disconnect itself?
The isolation circuit senses whether or not the motor is energized. If it is not, it closes the isolation relay in the MotoSafe unit to begin monitoring. When the motor is energized, the isolation circuit responds by opening the isolation relay contacts, disconnecting the MotoSafe unit from the motor.
11. Where is monitor normaly located in typical installation?
It is mounted in the starter enclosure or control center.
12. How is the MotoSafe unit connected to the motor?
Details of the connections for all common types of motors are given in the Installation Instructions supplied with each unit. They give the procedure to follow for the installation, which is simple and easily done.
13. When the MotoSafe unit goes into alarm, do I have to have the motor rewound?
The purpose of monitoring the insulation resistance with the MotoSafe unit is to receive early warning of insulation problems, so that preventative maintenance can be carried out before it is necessary to rewind - or replace - the motor. Generally, all that is required is that the windings be cleaned, dried and revarnished before the motor is returned to service. Following this procedure the original motor efficiency level is retained, whereas when a motor is rewound the efficiency can be expected to be reduced somewhat.
14. Will your units handle remote alarm system?
The alarm relay in monitors is rated for 250 volts 5 amps AC and 30 volts 8 amps DC. If your DC control voltage exceeds 30 volts, an external relay will be required.
15. I want to supply the MotoSafe unit from a 24 volt battery. Is this possible?
Yes.
16. Can I have a meter indication of the actual insulation resistance?
For motors and generators to 600 volts we offer such a unit - our Type IM600IND. It has a single alarm level of 2 Megohms and has an external, i.e.. separately mounted, meter showing the insulation resistance.
17. Can I perform trend analysis using the MotoSafe units?
Yes, because the low voltage units have three selectable alarm levels, so the analysis can be done by switching the alarm level to its highest setting, recording the date, then when an alarm occurs, switching it to the next lower level and monitoring the time until the next alarm occurs. With the Indicating MotoSafe Type IM600IND, it is only necessary to record the meter indication at suitable intervals.
18. How can I be sure that the unit is working?
When the green light is on, the MotoSafe unit is receiving power. Then its operation can be checked by pushing the “TEST’ button and holding it for 10 seconds. During that time the red “ALARM” light will light, showing that the unit is in good working order. Note however that this procedure does NOT check the external connections to the motor. Those connections can be checked when the motor is NOT energized by grounding one of the motor terminals with the Test Resistor supplied with the unit.
19. Can I connect the MotoSafe unit to monitor all of my motors at once?
The MotoSafe Insulation Monitor is designed to monitor insulation resistance of motors when they are not energized, so it will only monitor several motors at the same time if they are all controlled by the same disconnect. The results will be difficult to interpret, as the insulation resistances will all be in parallel, i.e.. two identical motors will produce an indication equal to one-half of that of a single motor, and the motor with the lowest insulation resistance will dominate the indication. Because of the difficulty of interpreting the results we do not recommend such an installation.
For such cases we recommend our Type MCM603INDE which can monitor up to eight electrical motors individually in a single industrial application.
20. Are the Insulation Monitors compensated for the variations of insulation temperature?
No. Temperature compensation is unnecessary at the insulation resistance alarm levels used and would complicate the units without conferring any benefits.
21. If I connect the units for start prevention, can I bypass that feature in an emergency?
Yes. If the selected alarm level is one of the higher levels, switching to a lower level and resetting the unit will bypass the start prevention connection. If the MotoSafe unit is set to the lowest alarm level, the start prevention may be by-passed by pushing the “Reset” button and starting the motor immediately, i.e.. within 8 seconds.