Specifications For Electrolytic Motor Start Capacitors
1 A power capacitor which provides a leading current to an auxiliary winding of a motor and which is switched out of circuit once the motor is running.
ARISTO range of aluminium Electrolytic Motor Start Capacitors specifically designs for a.c. operation, which help to start the motor by providing a leading current to the auxiliary winding. The capacitor is not permanently connected to the winding of the motor and is switched off after starting, usually automatically. Capacitors for this application are designed for intermittent duty only, and must be capable of withstanding a.c. voltage applied to the motor during starting.
The current shall be calculated as follows :
I = 2 * 3.147 * fv * C / 106 = C * V / 3180
C = Capacitance in microfarad,
I = rms value of current in amperes,
f = frequency in hertz,
V = rms value of test voltage in volts.
Operation in which periods with the capacitor energized are followed by intervals during which the capacitor is unexercised.
A special type of intermittent operation in which the capacitor is energized for only a very short period while the motor is accelerating to rated speed.
Rated Duty Cycle
A rated value indicating the type of intermittent or starting duty for which a capacitor is suitable. It is specified by the duty cycle duration, in minutes, and the percentage of the time during which the capacitor is energized.
Duty Cycle Duration
Total time of one energized and one unenergized interval during the intermittent operation.
Quality Requirements And Tests
Unless otherwise specified for a particular test or measurement, the temperature of the capacitor dielectric shall be in the range +15° C to 35° C range and shall be recorded.
Type tests are carried out by the manufacturer under the supervision of a proper authority, which will issue a certified record and/or type approval. ARISTO follows the European
Standard EN 60252-2 for type test.
Routine tests shall be carried out by the ARISTO on every capacitor before delivery. The norms of European standard EN 60252 will be followed.
The preferred minimum and maximum permissible capacitor operating temperature shall be as follows:
Minimum : – 30° C, -25° C, -10° C, – 0° C
Maximum : +55° C, +70° C, +85° C, +100° C
Operating temperatures may be adopted on agreement from purchaser. Normal production shall be with temperature limits -25° C or -30° C and +70° C.
Damp Heat Severity
Capacitor is retained without application of voltage and no measurement shall be taken during the test. The severity shall be 21 days. After the test keeping capacitor under standard atmospheric condition for minimum one hour (not more than two hrs.), the capacitance and tan delta is observed. Capacitance should not differ by +/- 10% and tan delta should not exceed more than 0.20.
Capacitor shall be visually examined and checked for finish and marking.
Capacitor shall be subject to an ac voltage test. The test shall be carried out with stabilized voltage at a frequency as near as possible to the rated frequency. Voltage application between terminals should not be more than 2 seconds. The test voltage may be increased by 10%.
Capacitance shall be determined by measuring the current through the capacitor at rated voltage and rated frequency of the capacitor. The rated voltage should not be applied for more than 3 seconds. Test should be carried out at room temperature. (Range from 18° C to 30° C).
Tangent Of Loss Angle
The measurement of tangent of the loss angle should be in the temperature range from 18° C to 28° C. Tan delta should not exceed 0.15 after endurance and damp heat test; a limit of 0.20 shall be applied.
Dimensions of container, terminals, cable and the clearances between creep age distances shall be checked.
Capacitance should be positioned most likely to reveal leakage at a temperature +5° C higher than the maximum permissible capacitor operating temperature for minimum 4 hours and cooling time 4 hours. The temperature should be increased uniformly. No leakage should be observed after 8 hours cycle mentioned above.
The capacitor should be mounted in a chamber in which heated air is circulated in such a way that capacitors shall have uniform heat. No heating shall take place through radiation. The temperature of the capacitor should reach the stated temperature with a tolerance +/-2°C. The test time is computed from the moment of exercitation. The maximum permitted variation of capacitance compared to the value measured before the test, and the maximum permitted individual values of tangent of the loss angle should not exceed 0.20, and the capacitance variation up to 15%.
2.4.0 Creep Age Distance & Clearances
Distance between the different polarities should be 6 mm up to 250 VAC, and 12 mm for higher voltage.
Voltage Test To Case
Voltage of 2000 VAC is applied between capacitor leads and the outer casing.
The insulation resistance shall be measured between terminals connected together and the outer casing.
Capacitor can be stored for one year without damage. The capacitor shall be recharged by applying rated voltage for 2 – 3 seconds. This may be repeated 2 – 3 times.
Capacitor is directly applied with its rated voltage continuously and the bursting time shall be noted. The mode of bursting and formed gas passing is observed. At the time of bursting the formed gases should be passed through the vent hole of the capacitor.