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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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