Capacitors require a resistor to discharge because they store electrical energy in the form of an electric field between two conductive plates separated by a dielectric material.
Can a capacitor charge and discharge fast without a resistor?
However, the value of this resistance is quite low, so without any external resistor added in series, a capacitor can charge and discharge pretty fast. In addition, all capacitors also possess some inductance due to magnetic flux created by currents flowing in or out of the cathode and anode plates.
How does a capacitor discharge?
Easiest and most reliable way to ensure capacitor discharge is to permanently connect resistors across the capacitor terminals. As soon as power source is turned off, capacitor starts to discharge through the resistor. Discharge resistor can be externally connected or mounted inside the capacitor can.
For three phase capacitors, ideally three resistors are required to discharge. For capacitor cans connected in delta, 'V connection' is commonly used which only requires two resistors as shown in figure 4 (c). Note that effective capacitance across each resistance in this case is not C but 1.5C due to delta connected capacitors.
Resistors are the preferred discharge device for capacitors though reactors and voltage transformers can also be used if faster discharge is necessary. By using resistor, the rate of discharge, resistor power dissipation can be controlled to a high degree by the designer.
Can a power capacitor be discharged?
For most power system switching applications, once the voltage is decayed below 10% it is typically safe for reclosing, switching etc. The most common method of power capacitor discharge is to permanently connect resistors across the terminals.
Are capacitors resistors?
Capacitors are not resistors; they don't inherently resist the flow of current. So, what's the deal with “capacitor resistance”? While capacitors don't exhibit a static resistance like resistors, they do influence the behavior of circuits in ways that can be interpreted as resistance-like behavior. This is particularly evident at high frequencies.