Power Fluctuations in our AC Mains Power Generation Facility

In summary, the power plant is injecting a capacitive current into the system in order to maintain a steady 5 kV on the connection point.
  • #1
sponeill3031
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I am currently at a power plant here in Texas and the 480VAC system swings from 480 while equipment is on line and as high as 536VAC when equipment is off line. They tell me that this is prefectly normal but I have never seen swings like this at any power plant. So, is this normal???
 
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  • #2
Welcome to PF.

What kind of power plant? Are you supplying power to the grid somehow, or just to a local facility? What are the output specs for voltage when it is online and supplying power to whatever?
 
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  • #3
It's a steam power plant and we generate power for the grid. Our line voltage is 19K that steps down to 4160 for some of our plant use and then steps down to 480 for plant use. While the plant is on line the voltage is 480 due to plant load but when the plant is off line (No plant load) the voltage goes up to 525 or 535. The issue we are having is when the voltage goes that high it causes significant issues when running things like bolt heaters, cranes and other portable equipment that contractors bring in to work on equipment during outages.
 
  • #5
Sounds like the 19KV:4160 and/or the 4160:480 Transformer has relativly high impedance and the load is at or over the KVA rating. The Trans is tapped to be correct when the load is on.

Do you have a way to monitor the 4160V

A tapchanger for the 19KV:4160 may work, but tap changers on 4160 to 480 are rare.
 
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  • #6
sponeill3031 said:
They tell me that this is prefectly normal but I have never seen swings like this at any power plant.
I would want to identify why such a change occurred. Maybe begin by identifying the reactive neutralisation and checking how it is connected, or partitioned, when the plant goes off-line.
 
  • #7
In my opinion, the power plant [5-10 MVA at 20kV] injects a "capacitive" current in the System order to maintain 5 kV on System connection point.

So, when the plant works the voltage drop is negative and 4.16 is the voltage on the point of connection 4.16/0.48 kV transformer.

If the plant is disconnected then this transformer is supplied from the System and instead of 4.16, we get here 4.6 kV
Voltage up.jpg
 
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