Voltage regulators connected wye 72

[JOE ROBB]

Voltage regulators connected wye 7200, the transformer wye is hooked to a grounding resistors 450 ohms. The voltage regulator source load or neutral bushing is connect to the transformer xo lead going to the resistor. The regulator tank is connected to the substation ground grid. First complaint voltage was at 170 volts from regulator for 70 hours. Then regulator failed has failed twice in 30 days 889 KVA. I don’t see how we have have to different grounds going to the regulators.

Thanks
In advance

 

[Mbrooke]

Get rid of the resistor- it will create neutral shift which will cause 1) hunting of all 3 voltage regulators as every increment of one will cause the others to be further be from their target voltage 2) over voltage on one phase with under voltage on the others from normal load imbalance.


Question- what was the reasoning behind the resistors?

 

[JOE ROBB]

Don’t know underground mines. Thank you.

 

[Mbrooke]

Is the load connected in delta?

 

[Mbrooke]

I am going to be honest- I know little if anything about mine power systems so it would not be wise for me to advise.


However, I know of an expert who works extensively in mine power systems on this forum:

http://forums.mikeholt.com/index.php

Just mention in your thread that this pertains of Mine work. I think you will get a lot of help on the subject.

 

[waross]

For the voltage regulators to work properly, the regulator wye point must be solidly connected to the transformer X0 or neutral bushing.
For high voltage work, the terms neutral and ground are often used interchangeably. What is actually a neutral connection is commonly called a ground connection.
This is one place where there is a difference and the difference does matter.
The transformer NEUTRAL is separated from the GROUND by a resistor of 450 Ohms.
Again, the regulator wye point must be connected to the transformer neutral, not the ground.
If that is the connection that you have, then check for breaks or corroded or heating connections in the conductor between the regulator wye point and the transformer XO bushing.
Possibly someone has inadvertently used a connection to ground instead of to the XO bushing.
Re-read Mbrooke's post. If the regulator is connected to ground instead of to the XO bushing that is what may happen. If there is an open or bad connection in the conductor from the regulator wye point to the XO bushing, similar things will happen, but possibly worse.
With a solidly grounded system, There is generally a neutral conductor run with the phase conductors. Although this is a neutral it is often grounded at regular intervals and is called a "ground" conductor. Someone used to these systems is ised to connecting the regulator wye point to the "ground" conductor.
When you use a resistor between XO and the ground grid to limit fault currents you may no longer ground the regulator wye point. It must be connected back to the transformer XO bushing.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

With the regulator connected to the wrong end of the grounding resistor, about 2.65 Amps of neutral current will produce a 170 Volt neutral shift.

Bill
--------------------
"Why not the best?"
Jimmy Carter