# Power Factor Correction (open leg on a floating wye)

• RBloomer
In summary, the conversation revolved around a switch failure on the A phase of a floating wye connected capacitor bank. The C phase fuse was found to be bad and replaced, but then the B phase fuse blew. The bad switch was replaced and the system operated normally. The contractor stated that the open phase caused overcurrent on the other two phases, but the speaker expected the current on the remaining circuit to reduce to 86.6% of normal. However, this was not the case due to the nature of the load and the floating wye connection. The system operates at 13.8 kV and is used for power factor correction in an industrial setting. Overall, the speaker was not missing anything and their conclusion was correct.
RBloomer
We had a switch fail to close on the A phase of a floating wye connected capacitor bank. The C phase fuse was found to be bad and was replaced, however the B phase fuse then blew. The bad switch was then found and replaced. After that the system operated normally. The contractor said the open phase caused the overcurrent on the other two phases. I would have thought that the current on the remaining circuit would reduce to 86.6% of normal. What am I missing?

RBloomer said:
We had a switch fail to close on the A phase of a floating wye connected capacitor bank. The C phase fuse was found to be bad and was replaced, however the B phase fuse then blew. The bad switch was then found and replaced. After that the system operated normally. The contractor said the open phase caused the overcurrent on the other two phases. I would have thought that the current on the remaining circuit would reduce to 86.6% of normal. What am I missing?
Welcome to the PF.

Others will be able to give you a better answer than I can, particularly @anorlunda but it would help to know more about the situation. What is the nature of the load? If the load is mostly a constant-power type of load (like switching power supplies), then the current will go up in the other phases to try to supply the same power.

The capacitor bank consists of 6 400 Kvar capacitors, 2 in parallel per phase, connected in a floating wye. Each leg has a series 11.5 mH inductor. It operates at 13.8 kV. It is doing power factor correction for typical industrial loads i.e. many motors, ac inverter drives etc.

With a floating wye connection, each phase of the capacitor bank sees 13.8/sqrt(3) kV or 57.7% of the phase to phase voltage under normal conditions.

If you energize the same capacitor bank with A phase open (i.e., switch fails to close on this phase), you still have phase to phase voltage across the other two phases. Under this condition, these two phases would be seeing 13.8/2 kV or 50% of the phase to phase voltage.

So my conclusion is that you are not missing anything at all. 50/57.7 is the 86.6% that you expected if you are dealing with the current to the capacitor bank and not the line current.

## What is Power Factor Correction (open leg on a floating wye)?

Power Factor Correction (open leg on a floating wye) is a technique used to improve the power factor of a three-phase electrical system. It involves connecting a capacitor between the open leg of a three-phase wye transformer and the neutral point.

## Why is Power Factor Correction important?

Power Factor Correction is important because it helps to reduce energy waste and improve the efficiency of an electrical system. A low power factor can result in higher energy bills and equipment overheating, while a high power factor can save energy and increase the lifespan of equipment.

## How does Power Factor Correction (open leg on a floating wye) work?

Power Factor Correction works by adding reactive power to the electrical system, which helps to balance out the reactive power already present. This reduces the overall reactive power and improves the power factor.

## What are the benefits of Power Factor Correction?

The benefits of Power Factor Correction include reduced energy costs, improved efficiency of equipment, and increased capacity of the electrical system. It also helps to reduce voltage drops and line losses, which can improve the overall reliability of the system.

## What are the potential risks of Power Factor Correction?

The potential risks of Power Factor Correction include overcorrection, which can lead to overvoltage and damage to equipment. It is important to carefully calculate and monitor the power factor to avoid these risks. Additionally, improper installation or maintenance of the correction equipment can also pose a safety hazard.

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