High Frequency

High Frequency Generators

Kato Engineering offers a complete line of high frequency (400 Hz) generators. These units provide economical power for grounded aircraft's navigational equipment, ground power and military support products.

Voltage range: 115/200, 120/208, 240/416

Phase: 3

Power factor: 0.8


Pole RPM kVA
26 1846 up to 312.5
24 2000 up to 156
20 2400 up to 156
Other ratings are available upon request.

Exciter: Brushless rotating type

Enclosure: Open dripproof

Bearings: Double shielded re-greaseable ball type

Driver adaptation: All units are available in a two-bearing design. Typically, units rated 100 kW and lower with 26 or fewer poles can be supplied in a single-bearing design for direct connection to the SAE engine drive arrangements.

Rotor and stator insulation: Class F or Class H with resin vacuum-pressure impregnated (VPI)

Efficiency: 82% to 94% depending upon kW rating

To find out more on our high frequency generators, please contact us at:

KatoEngineering@mail.nidec.com or 507-625-4011


  • Standards & Certifications
    Kato Engineering designs power generation systems that can comply with numerous international standards (ISO, IEEE, MIL-STD, NEMA…) and meet/exceed industry standards for performance, reliability, maintainability and compactness. With each proposal, we quote specific requirements for your application needs.
  • Design Features

    Temperature rise: For continuous duty applications, generators are typically 80° C, 105° C or 125° C rise by resistance per NEMA MG-1. Standby ratings are either 105° C, 130° C or 150° C rise per NEMA MG-1. Rise is based on an ambient temperature of 40° C.

    Overload: Typical allowable overloads are 50% for 5 minutes and 10% for 2 hours during 6 hours of operation. Short-circuit capability is at least 15 seconds at 300%.

    Waveform: Generators are specifically designed to minimize harmonic distortion. Typical waveform characteristics are as follows:

    • Deviation factor: less than 5%
    • Crest factor: 1.3 - 1.5.
    • Harmonic content: any single harmonic is less than 3% and the total harmonic is less than 4%
    • Telephone influence factor (TIF): meets or exceeds NEMA MG-1- 22.43 standards
    • Telephone harmonic factor (THF): meets or exceeds IEC 60034-1 requirements


    Power factor: 0.8 standard (other PFs available upon request)

    Phase: 3

    Voltage regulation: The voltage regulation can be from plus or minus 1/4% to plus or minus 2% depending on regulator choice. Kato manufactures a complete line of voltage regulators and accessories in accord with varying application requirements.

    Voltage balance: With balanced loads, the voltage is held within 1.0% between phases.

    Field excitation: Fast voltage response time to generator load changes with short time constant is provided with the Kato brushless excitation systems. This allows the voltage regulator to react to changes in field excitation requirements. Three-phase high-frequency revolving armature excitation current is full-wave rectified through six silicon-type rectifiers mounted in heat sinks and positioned in the air stream for maximum heat dissipation. Diode PIV rating is at least twice the peak operating voltage normally required.

    Permanent magnet supplemental generator: A separate permanent magnet rotating generator (PMG) can be supplied, in addition to the brushless exciter, as an option.

    A Kato Engineering PMG has the following advantages:

    • Provides an economical and simple means of reliable, responsive and stable input power to the voltage regulator
    • Supplies continuous power to the exciter through the voltage regulator to maintain up to 300% short-circuit current from the alternator during a fault condition
    • Provides full exciter power, regardless of alternator voltage, for motor starting and is a separate voltage source for use external to the generator set, such as a tachometer and relay options
    • Reduces the effects of both conducted and radiated electromagnetic interference (EMI). With an EMI filter, the PMG and a Kato voltage regulator will meet the emissions requirements of Mil-Std. 461C, Part 9, Class C2
    • Enhances manual voltage control regulation as the PMG provides a more stable power source to the manual control


    Bearings: Bearings for machines up to 2000 kW are re- greaseable radial ball bearings. For 2000 kW and over, grease lubricated split roller bearings and pressure or ring-oil lubricated sleeve bearings are available for all sizes. Spherical roller bearings or cylindrical roller bearings are used when there are special thrust, shock or radial load requirements.


      Ball bearing: The most popular and universally used bearing. Equipped with grease fittings, it is suitable for low, medium or high speeds and single or two-bearing generators. The ball bearing is lowest in cost.
      Cylindrical roller bearing: Excellent for heavy radial loads and radial shock, such as railway generators. The cylindrical bearing is also suitable for low and medium speeds. It is used on two-bearing machines only. 
      Spherical roller bearing: Capable of withstanding heavy thrust and radial loads, it has the additional feature of being self aligning. It is suitable for single and two-bearing machines.
      Split roller bearing: Used on large generators of low and medium speed up to 1800 RPM. It is self aligning and can be replaced without moving the generators endbracket or shaft, a feature desirable when the generator is driven by an engine on each end. Because it is self aligning, this bearing is suitable for single or two-bearing machines.
      Sleeve bearing: Has a long life and the ability to run at higher speeds and loads. It is also capable of high radial shock. Because it is split, it can be easily removed without disturbing the shaft and endbracket. It is self aligning and can be used on single or two-bearing generators. It may be self lubricated or pressure lubricated depending upon the application. 


    Prime mover connections: Units with single-bearing designs may have either SAE flexible disk type couplings or forged flanged shafts for direct connection to engine flywheels. Generators with two-bearing designs have shaft extensions that are suitable for direct coupling to prime movers. Close-coupled SAE housing adapters are also available with both single and two-bearing designs.

    Controls: When requested, KATO™ voltage regulators and other controls will be supplied to provide complete system compatibility.

    Parallel Operation: All Kato Engineering designed generators can operate in parallel with any generator when proper system coordination is made. We will assist the customer by providing all generator parameters needed for a system study. We offer consultation for the design of the generator requirements.

  • Construction Features

    Stator Construction

    Stators: From the lamination steel to the frame material to the windings, Kato Engineering's stators are precisely designed and constructed to ensure peak generator performance and operating life. 

    Frames: Sophisticated design software and over 75 years of experience ensure that the generator frame is made with strength and support where needed instead of just adding useless size and weight. Stator frames are welded with heavy rings and bar steel. The frame is reinforced with welding plates between bars or with a heavy wrapper. Heavy gauge steel is formed and fasted to the frame to provide an ample airflow path. The endrings are precisely machined to support the bearing brackets.

    Form-wound windings: Because of the high voltages they incur and their importance to generator performance and life, the stator coils are the heart of a generator. Kato Engineering uses modern and precise equipment to make these coils. Insulating tapes are precisely layered to ensure maximum insulation properties and optimum fit in the coil slot, eliminating discharges that would shorten the generator's operating life.

    In the stator, coil end windings are supported with surge ropes and blocking material to withstand short-circuit fault conditions. Entire stator assemblies are immersed into liquid epoxy resin and vacuum-pressure impregnated. The vacuum exhausts air and moisture from the windings and permits complete penetration of the epoxy resin during the pressure cycle, filling voids and creating a rigid mass with optimum dielectric strength.

    Random-wound windings: Random windings are used for selected applications under 1000 volts and for high frequency generators. The windings are made with the highest quality round copper wire, which has a heavy film coating rated at 200° C. The windings are fully impregnated with resin.  

    Rotor Construction

    Rotors: For long, smooth operation Kato Engineering rotors are precisely made with the highest quality components. State-of-the art equipment ensures the most stringent manufacturing requirements are met.

    Rotor pole shape is designed to withstand mechanical stresses caused by rotational forces and prime mover pulsations. The pole contour is optimized to minimize harmonics in the voltage waveform.

    Field coils are machine wound on the poles with high temperature rated insulated copper wires. The coil end and interpolar region are blocked to prevent coil movement and distortion. Depending upon the application, damper bars are inserted into the pole face and brazed or welded at each end to complete the damper/amortisseur winding. The purpose of the damper windings is to reduce the generator harmonics and absorb torque pulsations caused by the prime mover or an unbalanced load distribution. The damper windings also reduce system oscillations caused during parallel operation. The rotor is either vacuum-pressure impregnated or wet wound.

    The shaft is precision machined to meet the stringent tolerance requirements for runout and concentricity of the shaft bearing surfaces. The rotor is dynamically balanced to meet specifications.

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