Repair and modernization of high frequency tube generators

Repair and modernization of high frequency tube generators

Tube generators

Tube generator (the lamp is a triode) are devices used for surface heat treatment with a working frequency from 100kHz to 4MHz. However, the most common devices in the industry work with a frequency of about 400kHz. By modernizing lamp generators, it is important to exchange essential components of the device. The replacement of these components is aimed at repairing or improving the functioning of the device in a technical sense as well as achieving better technological effects by these devices. Generators subject to modernization are usually devices designed and constructed by both domestic and foreign producers in the 50's, 60's, 70's and 80's of the last century. Tube generators are now often (due to the fact that high-speed semiconductor switches have appeared on the market) replaced by transistor generators (with IGBT or MOSFET type transistors).

The advantages of transistor generators

Transistor generators have the following advantages:

• Greater efficiency by approx. 20% (transistor converter: 90% -95%, triode: 70% -75%).
• Lower and safer work (transistor generator: approx. 0.5kV, tube generator: approx. 10kV).
• Cheaper transistor bridges at a relatively high cost of the generation lamp. The limited life span of the triode, although with proper operation, i.e. efficient protections and efficient water and air cooling systems, the work shall be guaranteed in a two-shift mode, even above 5 years.
• Very good operation (in terms of exploitation) in case of homogeneous heating in technological lines and in highly automated processes.

The advantages of tube generators

Tube generators have the following advantages:

• Generator lamp (triode) is resistant to all kinds of interferences and overloads (in semiconductor generators usually do damage transistor bridges, although their price is definitely lower than the price of triodes, but not without significance for operating costs though).
• Tube generator is a self-excited device, so that it is very versatile, i.e. it easily starts and works very well when overloaded and underloaded. In addition, it does not require any special adjustments when changing the inductors as well as changes in the workpieces. It is very easy to heat the details from the outside as well as from the inside, flat surfaces like the teeth of the gears.
• In semiconductor generators, when changing inductors, the interference in the connections (taps) as well as adjusting the settings in the control panel is needed.

The construction of tube generators

Tube generator consists essentially of two blocks:

• High voltage power supply with output voltage adjustment from 0.5kV to 10kV.
• The proper generator system that works most often in a self-excited system of the Meissner, Hartley or Colpitts type.

The process of modernisation of generators

Modernization of generator should be considered in several aspects:

1. In the high voltage power supplier.
   • Substitution of a thyratron regulator with a thyristor controller and diode bridge (diode stacks):
     
     
     • The safety of the device's operation is increased due to the operations at the level of the mains voltage, not the increased voltage.
     • The accuracy of the output power regulation is significantly improved and the possibility of connecting to modern control panels and coupling with the entire heat treatment process line.
     • After installing systems with increased sensitivity for overloading and other unfavorable working conditions, the durability and service life of components is improved.
   • Installing a modern thyristor controller.
     
     
     • The accuracy of the output control is significantly improved, and the ability to connect to modern control panels and interface with the entire heat treatment process line is achieved.
2. In the system of the generator itself.
   • Replacement of a generative lamp that is no longer produced, to the lamp that is easily available on the domestic market:
     
     
     • Triodes used so far - they were usually triodes of domestic production, placed in a special cooling jacket (or pot). Currently produced lamps have an integrated cooling system. It involves mechanical, hydraulic and electrical overbuilding. The advantage is the availability on the domestic market of a wide range of triodes with integrated cooling.
   • Modernization of the resonant circuit:
     
     
     • Rebuilding of the resonant circuit leads to an increase in electrical efficiency, reduction of thermal losses in the resonant circuit and increase in the output power of the device from a few to a dozen or so percent.

Conducting the modernization activities, means that tube generators produced several decades ago can still be very useful for applications even in technologically demanding heat treatment processes and with much smaller financial outlays than would be required by investments in modern transistor generators.

The DACPOL company offers a comprehensive selection of replacements for the non-manufactured LAMINA lamps: T-25W, T-25P, T26W/22, T26W/23, T-26P/22, T-26P/23, T-10P/22, T-12W/21, T-60W/12, T-60W/22, T-60V/12. We select the lamp, make a replacement and comprehensive service and start the generator.

The attached drawing shows the basic schematic diagram of the modernized GIS-10 generator; after modernization the generator was named GIS-10RT (RT - thyristor controller). Numerals (in a circle) 1, 3 indicate the high voltage power circuit of the high voltage power supply. The number 4 indicates the correct block of the induction generator. Figures 2 and 5 indicate the control, measuring, protecting and supplying cathodes of the triodes. GIS generators were produced in the 1960s and early 1970s at WAREL plants and after modernization they have been working successfully in small factories to this day. Prior to the modernization, the thyratron rectifier on the side of the 3TM1 high voltage transformer was used to regulate the power (3V1 diode rectifier is now in place). Modernization consisted in removing the thyratron controller and installing a 2U1 thyristor regulator with the 2U2 control panel and the diode rectifier (diode stacks) on the high voltage side 3V1. If necessary, the resonance system 4V1, 4T3, 4T4, 4T2 shall be modernized.

An example description of the modernisation

The modernization of the HFG / J40 generator was carried out in 2017 in FAMUR S.A. company that produce equipment for mining. Generator HFG/J40 was produced in 1962 in the austrian company ELIN. Its operating frequency: 400kHz, and power (guaranted by the manufacturer) on output terminal: 40kW. At the beginning of the 90s of the last century, the ELCAL company modernized the generator, which consisted of replacing the BBC triode, the triode of national production type T26W, and replacing the thyratron regulator with the thyristor regulator type: PRW 210/440 and rectifying diode stacks. Selected photos showing the device before modernization are presented below.

Modernization consisted of:

• Replacement of the lamp type T26W with the lamp type RD35ZM, available on the domestic market.
• Replacement of the lamp glow supply system.
• Replacement of the output transformer by an air transformer with a higher apparent power.
• Replacing the filter (replacement of high frequency choke and addition of low induction capacitors).
• Changing the old diode rectifier to a rectifier with a higher current load with a surge protector.
• Replacing the PRW 210/440 type regulator with a modern RP3 controller.
• Exchange overcurrent protectors.
• Use of water-cooled high current wires.

After modernization, the output power of the generator increased by approx. 20%.

Selected photos showing the device after modernization are presented below.