ground indicator lights
- Thread starter clayton
- Start date
- Status
charlie
Senior Member
- Location
- Indianapolis
Re: ground indicator lights
I am assuming this is an ungrounded or resistance grounded system.
There are three large value resisters (around 20 k ohms if my memory serves me correctly) that are connected in a wye configuration and the center point is grounded to the grounding system. Lamps are tapped part way down on each resister and the other side is grounded to the same point.
When the system is operating, a little current will flow through the resisters and a little will be tapped off and go through each lamp. Under normal operating conditions, all three lamps will be lit. Under a ground fault, the phase that is grounded will no longer be at a different potential over one of the lamps and that one will go out. The other two will remain on.
I am assuming this is an ungrounded or resistance grounded system.
There are three large value resisters (around 20 k ohms if my memory serves me correctly) that are connected in a wye configuration and the center point is grounded to the grounding system. Lamps are tapped part way down on each resister and the other side is grounded to the same point.
When the system is operating, a little current will flow through the resisters and a little will be tapped off and go through each lamp. Under normal operating conditions, all three lamps will be lit. Under a ground fault, the phase that is grounded will no longer be at a different potential over one of the lamps and that one will go out. The other two will remain on.
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: ground indicator lights
I believe that I have put this incident in a thread some time ago. I feel that it is important enough to discuss it again.
This incident happen in 1965, when I became a 1st Line Electrical Supervisor for the Dupont Company.
We have on the plant a 2300 volt, 3-phase, ungrounded system, with the three lights at the sub-station. The primary voltage is 11000 volts, and the secondary 2300 volts.
I received a call from our Power department and they informed me that one of my lights was out.
Now, it was my job to go with an electrician and find the ground, before we get another ground in a different phase, then you will have a problem.
Our procedure was to go and shut down 2300 volt motors, and open up the 2300 volt disconnects.
Almost 100 percent of the time, we would find the ground in a motor.
Well, we proceeded to do this, when we came to a building and told the operations that we needed to shut down their 2300 volt motor, and they informed me that they needed to start up another motor before they could shut down the motor that I asked for.
Well, unbeknown to us, the motor that the operator started up, had a ground in another phase, and we had a big electrical explosion out at the sub-station.
This is a lesson that I will never forget, and I took a lot of ribbing from my fellow electricians of how not to check for a 2300 volt ground.
I know that this was lengthy message, but I felt that I wanted to pass it along.
I believe that I have put this incident in a thread some time ago. I feel that it is important enough to discuss it again.
This incident happen in 1965, when I became a 1st Line Electrical Supervisor for the Dupont Company.
We have on the plant a 2300 volt, 3-phase, ungrounded system, with the three lights at the sub-station. The primary voltage is 11000 volts, and the secondary 2300 volts.
I received a call from our Power department and they informed me that one of my lights was out.
Now, it was my job to go with an electrician and find the ground, before we get another ground in a different phase, then you will have a problem.
Our procedure was to go and shut down 2300 volt motors, and open up the 2300 volt disconnects.
Almost 100 percent of the time, we would find the ground in a motor.
Well, we proceeded to do this, when we came to a building and told the operations that we needed to shut down their 2300 volt motor, and they informed me that they needed to start up another motor before they could shut down the motor that I asked for.
Well, unbeknown to us, the motor that the operator started up, had a ground in another phase, and we had a big electrical explosion out at the sub-station.
This is a lesson that I will never forget, and I took a lot of ribbing from my fellow electricians of how not to check for a 2300 volt ground.
I know that this was lengthy message, but I felt that I wanted to pass it along.
- Status