Why doesn't Cos Phi use 100kVAR steps?

---

In the manufacturing world today, there are many sensitive loads and measurement devices that are susceptible to poor power quality, especially transients from switching large loads. There is also a problem with ring-waves on systems with transformers smaller than 2500kVA.

In order to address transients and ring-waves, we have limited ourselves to 60kVAR as a maximum step size on 600V systems, with the exception of 2-leg thyristor switched steps. Switching 100kVAR steps is possible, but a cascade of smaller steps, such as a 60/40 split is necessary.

On 480V systems, we use 50kVAR as the maximum step size. On 208V, we use 20kVAR steps.

Excerpt from an Electronicon catalog: A typical power factor correction system would incorporate a number of capacitor sections determined by the characteristics and the reactive power requirements of the installation under consideration. Sections of 12.5kVAR, 25kVAR, and 50kVAR are usually employed. Larger stages (e.g. 100kVAR and above) are achieved by cascading a number of smaller sections. This has the beneficial effect of reducing fluctuations in the mains caused by the inrush currents to the capacitors and minimizes supply disturbances. Where harmonic distortion is a concern, appropriate systems are supplied incorporating de-tuning reactors.

Certainly a 100kVAR step is less expensive in the manufacturing process than a cascaded split step, but is the risk of damage to your equipment, resulting in possible production downtime, really worth it in the long run?

We believe it is design considerations such as this that separate the specialists from everyone else.

---