power transients 3

[v6racer]

Hi, to start my degree is in micro electronics so power distribution isn't my strong suit despite working through college as a journeyman. The journeyman stuff was why I have been asked to look into this.

Anyway, on the 480 volt power to some of our crystal furnaces we have some regularly occurring transients that our process guys insist are affecting yield. These are +- 1% which is well within the spec for incoming power. I have confirmed that it is most likely incoming power as I have seen the pattern on two different substations. Supposedly we do not have automatic power factor correction or on load tap changers and can't say those would match the data. Any idea what would cause the changes shown in the pic below?

Since the process engineers insist it affect their yield I will have to mitigate these changes. I am thinking either a rotatory or battery UPS. Can you suggest anything else I might want to look into?

 

[crshears]

Perhaps then some tuning/tweaking of the P&I settings similar to what Bill described is needful...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

The heaters have a time constant. This is the time for a block change in input to cause a 63% change in the temperature.
The oven and contents will have a time constant, however the oven and contents will not see a block change in input, they will see the rising change in the output of heat from the heaters.
I can't solve this over the internet.
You need a controls guru who can suggest the proper settings.
ps: Do you have a chart correlating temperature deviations with voltage steps?
Can you show us an expanded trace where we can see if there is a time lag between the voltage change and the temperature change and the SCR output change?
I suspect that the voltage rises, then the melt temp rises, then the SCR output is cut back, too late.

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

 

[waross]

Stepping back and taking another look at the problem and possible solutions.
I believe that the cheapest solution will be a control solution.
On the other hand we have the choice between what can be done and what can WE do.
The control solution may require bringing in someone from outside to set it up.
Then in the event of any future problems. you will have to call and wait for the expert.
On the other hand, you can probably handle voltage stabilization in house.
If a control guru who can walk you through the settings drops in, great.
In the end it is your choice.
Keep us posted.

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