Limiting Current Loads
A capacitor can act as an AC resistor, coupling AC voltage and AC current between two points. Every AC current flow through a capacitor generates heat inside the capacitor body. These dissipation power loss is caused by and is the squared value of the effective (RMS) current
The same power loss can be written with the dissipation factor as
The internal generated heat has to be distributed to the ambient. The temperature of the capacitor, which is established on the balance between heat produced and distributed, shall not exceed the capacitors maximum specified temperature. Hence, the ESR or dissipation factor is a mark for the maximum power (AC load, ripple current, pulse load, etc.) a capacitor is specified for.
AC currents may be a:
- ripple current—an effective (RMS) AC current, coming from an AC voltage superimposed of an DC bias, a
- pulse current—an AC peak current, coming from an voltage peak, or an
- AC current—an effective (RMS) sinusoidal current
Ripple and AC currents mainly warms the capacitor body. By this currents internal generated temperature influences the breakdown voltage of the dielectric. Higher temperature lower the voltage proof of all capacitors. In wet electrolytic capacitors higher temperatures force the evaporation of electrolytes, shortening the life time of the capacitors. In film capacitors higher temperatures may shrink the plastic film changing the capacitor's properties.
Pulse currents, especially in metallized film capacitors, heat the contact areas between end spray (schoopage) and metallized electrodes. This may reduce the contact to the electrodes, heightening the dissipation factor.
For safe operation, the maximal temperature generated by any AC current flow through the capacitor is a limiting factor, which in turn limits AC load, ripple current, pulse load, etc.
Other articles related to "limiting current loads, load, current":
... An AC load only can be applied to a non-polarized capacitor ... The rated AC load for an AC capacitor is the maximum sinusoidal effective AC current (rms) which may be applied continuously to a capacitor within the specified temperature range ... In the datasheets the AC load may be expressed as rated AC voltage at low frequencies, rated reactive power at intermediate frequencies, reduced AC voltage or rated ...
Famous quotes containing the words loads, limiting and/or current:
“Every increased possession loads us with a new weariness.”
—John Ruskin (18191900)
“O wily painter, limiting the scene
From a cacophony of dusty forms
To the one convulsion,”
—Thom Gunn (b. 1929)
“We all participate in weaving the social fabric; we should therefore all participate in patching the fabric when it develops holesmismatches between old expectations and current realities.”
—Anne C. Weisberg (20th century)