Impulse Voltage Generator (Pneumatic)

 

Application

GTN type impulse generators suitable for indoor use in Research lab and Industries. This Generator is a modular design & cover a range from 1200kV to 3600kV, with energy from 120kJ to 360kJ. For lower voltages, we supply High voltage construction kit and GTU type generators.

Function

For the production of impulse voltages, a number of parallel-connected impulse capacitors is charged with constant current. Owing to this direct parallel connection, no charging resistors are required. This also ensures the uniform charging of all generator stages. Another advantage of charging the generator with constant current lies in that no regulating transformer with moving parts is required and that the desired charging current can be pre-set step-less and with better accuracy. After the generator is charged, the charged impulse capacitors are automatically connected in series by means of a pneumatically operated mechanism. For discharging, all spark gaps are triggered simultaneously by means of trigger pulses. The spark gaps are encapsulated and filled with pressurised air. The desired trigger voltage is pre-selected on the control desk. The gap setting is adjusted roughly by varying the gap distance, and more accurately by varying the air pressure within the encapsulation. Encapsulation of the spark gaps makes low-noise triggering of the generator possible and eliminates the effects of the outside phenomena, for instance a variation in the atmospheric pressure, on the accuracy of the impulse test.

After triggering of the spark gaps, the energy stored in the impulse capacitors is discharged on the test object. The impulse shape depends on the wave-front and wave-tail resistors, Test object impedance and Divider/MCG impedances.

Design

All elements, with the exception of the control desk and charging unit, are arranged on a welded steel frame. For ease of generator transport in the laboratory, the steel frame is moved using air-cushion pallets.

The DC charging unit are mounted on a separate steel base frame. By rotating the rectifier (remote control from desk), positive or negative impulse voltage can be produced. The DC charging unit is oil-insulated and housed in an FRP-cylinder and it also comprises measuring resistor to measure the DC Charging voltage, protective resistor and an earthing switch.

The produced DC voltage are connected to the parallel-connected impulse capacitors. The impulse capacitors are arranged in pairs per stage. Various sizes of impulse capacitors for different energy per stage are available (5kJ, 7.5kJ, 10kJ, 15kJ, 20kJ). The capacitors are housed in sheet-steel tanks and insulated for 200kV. They are built-up from capacitor coils and oil-paper insulation and have low inductance. To attain an almost unlimited life of the generator, special emphasis has been give to the mechanical and electrical withstand capabilities of the internal connections. The FRP-encapsulated, pressurized air filed spark gaps are also arranged in pairs per stage. The resistors are especially wound from nickel-chromium wire for particularly low inductance. On request, other resistors can be installed either in addition to the resistors for lighting and switching impulse or as an alternative to serve special test purposes.

Controls

The generator is operated from the control desk, which is to be placed in the control room. The desk consists of several sheet-steel sections with modular plug-ins incorporating all essential equipment for automatic remote control of the generator. After switching-on of the main switch, the desired number of shots and the impulse voltage level can be set. According to the impulse voltage level, automatically values of the charging voltage, gap distance, air pressure, charging time etc. are selected from the built-in memory.

After switching-on of the high voltage, the generator is automatically charged. When the charging voltage is attained, the generator fires the pre-set number of shots. The interval between the shots can be pre-set stepless. Also appropriate trigger command is given to the digitizer and Multiple chopping gap with the desired time delay. The impulse generator is automatically earthed when the pre-set number of shots has been fired.