Harmonics-induced problems in theatrical-lighting installation: Real-case measurements and proposed solutions

Professional light-dimming equipment used in theaters, usually employees triacs to control the rms value of voltage on the light bulbs. This paper presents a real-case problem where, voltage harmonic distortion, induced by the high harmonic currents of the light-dimming equipment, led to dimming-control malfunction. It is shown that control systems based on the detection of voltage zero-crossing may not function properly when high triplen (3rd, 9th, 15th, 21st, etc) current harmonics -such as those produced by triac operation- flow in a circuit. Measurements of current and voltage harmonic distortion at the Royal Theatre of Thessaloniki, Greece are presented. Computer simulation shows that the arrangement of the cable feeding the triacs, plays a significant role on the harmonic voltage distortion, whereas the cable cross-section has a smaller effect.