Question about transformers and on-load tap changers (OLTCs)

[meyra]

Hi,


I have a network with hundreds of busbars (ranging from 33kV to 6.6kV). I have some electrical loads connected at the far end of the network via 2-winding transformers and I am analysing the voltage drops at the point of load connections.

Some of these busbars experience around 10% voltage drops (0.90 pu) therefore I want to add tap changers on my transformers (I am using IPSA simulation tool). There are some settings I need to change as follows:

Basic tap data:
Setting (%) = Current tap position
Minimum (%) = Minimum tap position
Maximum (%) = Maximum tap position
Step (%) = Tap change increment

Which of these should I vary to improve voltage profiles? Also what are the ideal values I should set for the above data?

Thanks.

 

[Darkwood]

Is this for coursework/homework ?

 

[meyra]

Is this for coursework/homework ?

No. It is a project I am working myself.

 

[Darkwood]

That's fine then we just approach Q&A for coursework in a different way. Your question is set around voltage range that is not a common subject on the forum but hopefully we have a few members that can help you out.
PS - Welcome to the forum

 

[Lucien Nunes]

Those are mainly defining the limitations of real-world transformers (i.e. they don't have an infinite number of taps) rather than part of the control loop. The step percentage will define the granularity although not necessarily the accuracy of the secondary voltage, but if the drops are reasonable you won't hit the limits so they will have no influence. Try setting the steps rather smaller than the tolerance at the next sub.

 

[Andy-1960]

Most mv transformers have 5 step tap changers on the primary winding and although these are off load devices the principal is the same.
Tap1 +5%
Tap2 +2.5%
Tap3 0%
Tap4 -2.5%
Tap5 -5%

The plus percentages add windings so therefore reduce the voltage, the minus percentages therefore take windings out and therefore increase the voltage.

 

[Carl S]

Bear in mind that at low load you will have an over voltage at the remote end of the line.

 

[meyra]

Most mv transformers have 5 step tap changers on the primary winding and although these are off load devices the principal is the same.
Tap1 +5%
Tap2 +2.5%
Tap3 0%
Tap4 -2.5%
Tap5 -5%

The plus percentages add windings so therefore reduce the voltage, the minus percentages therefore take windings out and therefore increase the voltage.

So in IPSA, there is a basic tap data parameter called Setting (%) which means "current tap position", I am assuming this is where I have to set -2.5 right? Because there is also parameters called Minimum (%- minimum tap position), Maximum (%- maximum tap position), and Step (%- tap change increment). What are the features of these?

 

[rapparee]

Bear in mind that at low load you will have an over voltage at the remote end of the line.

Yes, I've come up against this recently

We've changed our layout

At the end of our factory we do electrical tests before they are packaged

Unfortunately the voltage fluctuates depending on the time of day. These fluctuations can put our tests outside the acceptable parameters for our QC department

For example a 2kw heater is pulling 2.3kw

I'm looking at getting a load of variacs and digital volt meters.

 

[Richard Burns]

So in IPSA, there is a basic tap data parameter called Setting (%) which means "current tap position", I am assuming this is where I have to set -2.5 right? Because there is also parameters called Minimum (%- minimum tap position), Maximum (%- maximum tap position), and Step (%- tap change increment). What are the features of these?

Presumably if you are working to the same basic standards as given by Andy-1960 then you would have current tap position at 0%, minimum tap position at -5%, maximum tap position at +5% and step change increment at 2.5%.

 

[Carl S]

The problem is you can’t change a tap setting on load.

Well you can, but you will have an early appointment at Gabriel’s gates.

 

[Andy-1960]

The problem is you can’t change a tap setting on load.

Well you can, but you will have an early appointment at Gabriel’s gates.

Actually you can get on load tap changers, I have only ever seen them on induction furnace transformers where blips in the supply are not too important, so not too sure about distribution transformers for general loads.. think it would be potentially cause a lot of issues.
But I also believe there are transformers that feature solid state switching on the secondary which can be seamless.

 

[Bobster]

Tap changers are a solution, but you're system is clearly not designed for the load/vd It's experiencing.