Capacitor fuse overview — Capacitor fuse terminology An ideal fuse could be defined as a lossless smart switch that can thermally carry infinite continuous current, detect a preset change in the continuous current and open automatically (instantly) to interrupt infinite fault currents at infinite voltages without generating transients.
Are capacitor fuses capacitive limited?
Most capacitor fuses have a maximum power frequency fault current that they can interrupt. These currents may be different for inductive and capacitively limited faults. For ungrounded or multi-series group banks, the faults are capacitive limited.
What is a high voltage capacitor fuse?
For high voltage capacitor fuses, this is generally defined as 8.3, 15.5 or 23 kV, the distribution system maximum voltages. Other voltage ratings may be available for special applications. When a capacitor fails, the energy stored in its series group of capacitors is available to dump into the combination of the failed capacitor and fuse.
What is a capacitor fuse used for?
The fuse, by its design, avoids absorbing all of the available energy on the series group. This fuse is used for capacitor banks with a large number of parallel capacitors. It can be used on applications with essentially infinite parallel stored energy, as long as sufficient back voltage can be developed to force the current to extinguish.
What is a capacitor fusing factor?
The capacitor must be able to absorb this energy with a low probability of case rupture. Fuses are usually applied with some continuous current margin. The margin is typically in the range of 1.3 to 1.65 per unit. This margin is called the fusing factor.
How do I choose a capacitor bank energization fuse?
Inrush and outrush currents associated with capacitor bank energization. Based on the above information it is important that the design engineer select a fuse that is small enough (or sensitive enough) to prevent case rupture, yet large enough to prevent spurious or false fuse operation due to normal operating conditions.
What is the coefficient of capacitive current in fuses?
This rule applies equally to fuses, which, when combined with the derating required to take into account their installation, results in a coefficient of 1.7 to be applied to the capacitive current in order to determine the appropriate fuse link rating. Go back to contents ↑ 2. Inrush current peak