Sub:- Testing of capacitors.

         

          Proper testing of capacitor is essential for ensuring reliable performance of capacitors.

 EC1 & EC 2 capacitors in the stabilisation circuit are critical and if not replaced regularly, may lead to loco failure.

          Whenever, panels need schedule inspection, following steps would lead to better performance of capacitors.

a.      Measurement of parameters by a calibrated instrument.

b.      Confirming critical parameters as per technical specification.

c.      Replacing capacitors in regular intervals.

d.      Life of the capacitor: Normally, life of capacitors is between 3-4 years. It has been observed the Capacitors are not changed in regular intervals of time.

e.      Critical Parameters: Quality of the capacitor can’t be ascertained by simply measuring Capacitance. Other important parameters to be checked are the measurement of Power Factor, ESR(equivalent series resistance), Leakage current and Voltage Buildup.

f.       Instruments to be used for measurement are

I     Capacitance meter

II    Leakage current tester

g.      Technical specification and Test procedure for electrolytic capacitors are mentioned at Annexure-A. Procedure as laid down should also be referred in addition to BHEL maintenance practice.

h.     It is requested to organize technical audit of Capacitor testing and checking procedure in Diesel shed in consultation with OEM.

Technical specification for electrolytic capacitors with casing of heavy duty moulded phenolic with integral safety valve and temperature range of -25 o C to + 85 o C:

Type of  capacitors	Capacitance ©	Working voltage	Tolerance	Leakage current	Power factor	Surge
100 ufd/250 VDC(non polar)	100 ufd	250 VDC	-10% to +25%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	400 volts
500 ufd/125(non polar)	500 ufd	125 VDC	-10% to +25%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	200 volts
1000 ufd     ( polar)	1000 ufd	150/200 VDC	-10% to +50%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	200/300 volts
1300 ufd/100VDC    ( polar)	1300 ufd	100/150 VDC	-10% to +50%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	160 volts
1500 ufd  ( polar)	1500 ufd	100/150 VDC	-10% to +50%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	160/200 volts

Note

Surge voltage as per IS standards is 115 times rated voltage. However, considering the application is critical and to improve reliability, the surge voltage is specified in higher side.