Tap Changing (ULTC) Transformers and Reactive Power Control

In summary, ULTC (under load tap changer) and OLTC (on load tap changer) transformers can be used to regulate voltage and power flow through the transformer. This is done by changing the turns ratio, which affects the impedance seen by the network. The regulation is typically done through taps on the higher voltage winding, with small steps and a range of ±10%. However, in an EPS (electrical power system), reactive powers and voltages are closely related and are often regulated together using other means such as synchronous compensators or SVCs.
  • #1
powereng
1
0
So I am trying to understand how a ULTC operates in the Reactive Power Control mode (it adjusts taps to control the reactive power in a line). What equation is governing it's operation, and what variables does it adjust in order to increase/decrease reactive flow?
Is it just the simple reactive power flow equation between two buses:

[ tex ] Q_sending = V_sending V_receiving (\frac{V_sending}{V_receiving} - cos(\delta) [ /tex ]

?

And then the transformer just adjusts the sending (or receiving) end voltage, and this modulates the reactive power flow?
Thanks in advance for any help. I've tried looking up ULTC or OLTC reactive power control, but did not come up with much.
 
  • #3
Hi,

Voltage regulation and power flow through xfrmr can be infuenced by changing turns ratio of xfrmr; this changes impedance of xfrmr and impedance of load seen by network. If you are familiar with "T" and "π" schematic representations of an ideal xfmr, I believe you can derive equation of depedence of power flow exclusively on turns ratio n=N1:N2 (I don't know exact equation from memory). Number of turns of ULTC regulating xfrmrs are changed via taps on higher voltage winding due to smaller currents and better step discretization condition there. Steps are something like 1% and regulating ranges like ±10%. However, reactive powers and voltages in EPS are intimatelly related and we rather talk about Q-V regulation than about these things separately. This is especially important for HV grid where effects of reactive parameters of power transmission lines are unvoidable. Regulating transformers are not enough and reactive powers are regulated to significant extent by other means (synchrounous compensators, inductive shunt reactors, SVCs..)
 

1. What is a Tap Changing (ULTC) Transformer?

A Tap Changing (ULTC) Transformer is a type of transformer that allows for the adjustment of the transformer's turns ratio, which in turn controls the voltage output. This allows for precise control of the voltage levels in a power system.

2. How does a Tap Changing (ULTC) Transformer work?

A Tap Changing (ULTC) Transformer uses a mechanical or electronic device called a tap changer to adjust the transformer's turns ratio. This changes the amount of voltage induced in the secondary winding, thus controlling the output voltage.

3. What is the purpose of Tap Changing (ULTC) Transformers in power systems?

The main purpose of Tap Changing (ULTC) Transformers is to regulate the voltage levels in a power system. By adjusting the turns ratio, the transformer can compensate for changes in load and maintain a stable voltage throughout the system.

4. What is Reactive Power Control and how does it relate to Tap Changing (ULTC) Transformers?

Reactive Power Control is the ability to manage the reactive power (inductive or capacitive) in a power system. Tap Changing (ULTC) Transformers play a significant role in Reactive Power Control by adjusting the voltage levels to maintain a balance between reactive power and active power in the system.

5. How do Tap Changing (ULTC) Transformers impact the efficiency of a power system?

Tap Changing (ULTC) Transformers can greatly improve the efficiency of a power system by regulating voltage levels and minimizing losses due to over or under-voltage conditions. They also help to reduce the amount of reactive power in the system, which can improve overall efficiency.

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