E3 Plus Ground Fault

[Berna 0]

We have an Allen Bradley MCC and we have E3 Plus Overload Relays. So I'm in the phase of configuration and I'm not pretty sure how bad a Ground Fault can affect. Can someone explain to me in plain English how a Ground Fault could affect the motor, and how necessary it is to have that protection. Thanks in advance.

[Shiner 2]

Depending on the size of the motor and the application, detecting ground fault early can save much in maintenance costs. I am not sure what you have, but say you have a large costly motor. The mechanic on night shift has nothing to do so he overlubricates the bearings. The grease leaks out all over the windings till they are saturated. Eventually depending on the type of grease and type of wire used in the coils, the insulation can break down or leak some current to ground. If the sensor trips out first by detecting the low levels of fault, now you can simply send the motor to a repair shop to be cleaned and possibly redipped (another coat of insulation applied). This is much more cost effective than letting the fault grow till a short occurs, making a full rewind or replacement necessary. There is a manual available for these http://samplecode.rockwellautomation.com/idc/groups/literature/documents/um/193-um002_-en-p.pdf and if you read it you can see that there are many available monitoring features that help protect the motor such as phase loss, current imbalance and things like that. Some can be simply for monitoring purposes only, but being a solid state device it should protect faster than old fashioned overloads (heaters) that are based on heat and time. Remember that the heat that trips those is also being applied to the windings of your motor.

[Berna 0]

Yeah I got the manual, just didn't understand 100 % how far a ground fault can go. Anyways great explanation Shiner, now i figure out more or less how to configure this relays. There are 12 5HP Motors and 4 15 HP I mean they are not that big , but they need to keep working as long as possible, and having this preventive maintenance would be great. Thanks

[Shiner 2]

There are many who tend to assume that ground fault is all about total failure when in fact, many motors and transformers are in some state of ground fault. I cannot count how many times in my career as a motor repair tech that a customer brought us a running motor for preventative maintenance and it failed insulation tests due to dirt, grease, moisture or some contaminent. These motors would not be 'blown', just near failure and with a good wash and bakeout they would run for many years to come. It used to be you had a plant electrician who would megger test all the critical motors in a process and log the results. A difference in readings over time indicated the need for attention. Now in today's economy, the maintenance personnel either does not have the knowledge, tools, or more often ability to take the piece of equipment offline to perform the test. That is if there is a maintenance department at all. Having a control system designed to monitor these conditions automatically is becoming more commonplace as companies try to find ways to keep running with minimal overhead.

[Berna 0]

Shiner, do you know if an E3 Plus can provide protection for motors that have Variable Frequency Drives? Thanks for response.

[Shiner 2]

I suppose it could do some protections, depending on how you are using the drive. If you use one of the aux contacts on the drive and set it up so that the contact closes when the drive is outputting full rpm of the motor, but I don't see it as an advantage. Most of todays drives have multiple types of protection built in, making the need for using the E3 for protection redundant and an added headache to set up. If it were me, I would use the drive for all the protections and the E3 just as a monitoring tool.

[Berna 0]

I guess it can do fairwell as a monitoring tool, but can it protect from Ground Fault?