Factors Contributing To The Safe Usage of Capacitors

一、Rated Voltage & Working Voltage

(1)   Normally, the working voltage shall not exceed the rated voltage; otherwise there will be breakdown and damage. For self-healing metallized film capacitor, short-circuit may not happen immediately when it is applied with over-voltage, but the insulation resistance will decrease gradually, making the leak current increase gradually, and finally the capacitor will break down, even causing possible fire or smoking.

(2)   In case the capacitor used for DC circuit is adopted in AC circuit, the maximum working voltage will drop due to heat and discharge. The conversion depends on different models. Please contact us for more details.

二、Rated Voltage, Working Temperature & Working Frequency

When operating under high frequency, the film dielectric will be aged by generated heat, resulting possible breakdown. For safe purpose, the rated voltage under high frequency shall be decreased properly. The temperature rise shall be also taken into account. When used in those circuits with high effective voltage or high peak-peak voltage, make sure that the total rise in temperature (self-temperature-rise + ambient temperature rise) will not exceed the allowable temperature limit (Table1, Table2).

Table 1. Rated Temp, workable Temp and Voltage Drop under Workable Temperature (For Reference Only)                        

*Note：Rated Temperature：the fault-free upper temperature limit under rated DC voltage.

Workable Temperature：the fault-free upper temperature limit by decreasing rated DC voltage.

Table 2. The Self-Temperature-Rise

Table 3. Effective Value Calculation for Different Wave Form

三、Allowable Current & Working Current

(1)     Compared to other capacitors, the film capacitor has a smaller internal resistance, leading to a larger charging & discharging current. When the current exceeds the allowable range, the internal dielectric may be deteriorated and broken down. The allowable current can be categorized into impulsive current (peak value) and continuous current (effective current) depending on different breakdowns. Make sure that working current does not exceed the allowable value.

(2)      Generally, the allowable pulse current is a product of change of voltage (dv/dt)and the capacitance, and varies with different dielectric, working frequency and capacitance, for film capacitor, dv/dt(v/μs)is decided by its mandrel structure, for metallized capacitor, the internal electrodes and the leading-out slabs are linked by metal contacts, so the upper limit of dv/dt is relatively low,  which shall be considered. Please contact us for more details.

Typical maximum dv/dt of the metallized film capacitor(for reference oniy) unit：v/μs