Synchronization and reliable operation of triggered spark gap switches in 40 kJ, 20 kV EMM system

A 40kJ, 20kV Electromagnetic Manufacturing (EMM) system [1] has been developed for forming and welding of various metals. The EMM consists of four energy storage capacitor based sub-banks, constant current charging variable dc power supply, single type spark gaps (TSG) switches. Four switches are used, one for each sub-bank. A trigger generator [2, 3] provides four simultaneous trigger pulses for firing the spark-gaps when master trigger command is actuated through PLC. A HV dump switch is provided for conditioning of capacitor bank and also when pulse power is not required to be transferred to the load coil. This paper describes the synchronization of four TSG switches used in the 40 kJ EMM system using (i) Delay line (type 2297, 5.5 m) type co-axial cable (ii) operating TSG switches close to static breakdown voltage (SBV) without pre-fire or misfire. SBV of TSG switches (22 kV) have been set by electrical test using 70 kV, 5mA high voltage Megger and (iii) A gas purging system using PU tube, solenoid valve and N₂ gas (IOLAR grade) to ensure operation of TSG switches without pre-fire or misfire and (iv) optimization of trigger generator. Jitter measurement of trigger voltage for four TSG switches has been found to be within 22 ns.