Prof R T KennedyEMC & COMPLIANCE ENGINEERING 1 EET 422 EMC & COMPLIANCE ENGINEERING

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 2 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M EUT AC source X capacitors connected line – neutral for differential mode (symmetrical) interference Y capacitors connected line-ground neutral-ground for common mode (asymmetrical) interference

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 3 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M EUT AC source X capacitors NO restriction on value typical 0.1 μF → 1.0 μF

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 4 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M EUT AC source Y capacitors generally restricted to SMALL values typically 470 pF medical applications 4700 pF other applications

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 5 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M EUT AC source PROBLEM ? 50 Hz leakage current → ground medical applications: 50  A limit other applications: 0.5 mA limit

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 6 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M EUT AC source LEAKAGE CURRENT UNDESIRABLE for SAFETY REASONS ESSENTIAL for effective emi filtering

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 7 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M EUT AC source smaller CY capacitors reduce leakage current smaller CY capacitors reduce filter CM insertion loss

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 8 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M good earthing AC source

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 9 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M poor earthing AC source

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 10 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M insufficient earthing AC source

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 11 CX1 CX2 CY2 CY1 L N G L* N *N * G* L L M EUT AC source EMI suppression capacitors are connected directly to the line  are exposed to overvoltages and transients CAPACITOR DAMAGE FIRE or SHOCK

Prof R T KennedyEMC & COMPLIANCE ENGINEERING 12 A0.1μS/6kV atmospheric interference lightning B60μS/1.2kV network or equipment failure flashovers C200μS/800V On/off operation of motors air conditioning units D1000μS/400V Pulses from welders thyristor and triac switching

DEFINES 3classes of TYPE ‘X’ CAPACITORS 4 classes of TYPE ‘Y’ CAPACITORS equipment standards determine the required class X2 Y2 BUSINESS EQUIPMENT & COMPUTERS Prof R T KennedyEMC & COMPLIANCE ENGINEERING 13

X2 150 V -250 V rms ac MOST COMMON TYPE USED X2 capacitors ≤ 1.0 μF 2.5 kV impulse tested X2 capacitors > 1.0 μF impulse test voltage X TYPE applications in which failure of the capacitor will not lead to a dangerous electrical shock Prof R T KennedyEMC & COMPLIANCE ENGINEERING 14

Y2 POWER SUPPLIES MOST COMMON TYPE USED Y2 capacitors 5 kV impulse tested applications where capacitor failure could result in a dangerous electrical shock Y capacitors have limited capacitance and enhanced electrical and mechanical reliability Prof R T KennedyEMC & COMPLIANCE ENGINEERING 15

AC LINE CAPACITORS “self healing” impregnated metallised paper “self healing” metallised film Ceramic do not self heal and tend to be larger than the other types Prof R T KennedyEMC & COMPLIANCE ENGINEERING 16