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Excitation, Rotors & Stators

Newton Derby has produced exciters for a variety of applications, including oil, gas, and hydro power. We have designed and manufactured for some of the largest blue-chip companies in the world. Newton Derby can manufacture exciters either to print, based on customer drawings, or we can design and manufacture from scratch based on a given specification.

We manufacture brushless exciters, supplied with a rotating rectifier, eliminating the maintenance usually required with sliprings and brushes. We can design exciters either to a new specification, or to replace an existing excitation system, in which case we will endeavour to replicate the characteristics of the existing exciter as closely as possible. If a complete excitation system is required, then we can also supply a PMG pilot exciter to go with the main exciter.

When carrying out the design of the exciters ourselves, we can work to a required field current and voltage, forcing ratio, and speed rating. The field will be designed to cope with the excitation available from the supply the customer wishes to use. Class F insulation is used in all our exciters as standard, which can withstand a temperature of 155°C, with higher temperature insulation available if necessary. Mountings available for our exciters include flange, skirt, or foot.

All our exciters undergo dynamic balancing and static tests including surge and flash testing, as well as insulation and winding resistance measurements. For dynamic tests, we can carry out open and short circuit measurements, overspeed, as well as on load tests up to a power of 100kW. Type tests are available upon request.

Excitation Machines

Newton Derby prides itself on the quality of its design and development skills, enabling the company to offer special equipment for the most demanding applications, in addition to its established product range. Exciters are usually provided as Stator/Rotor units for mounting within the enclosure of the main generator/motor.

  • The Exciter Rotor has an internal bore suitable for fitting to the shaft of a large synchronous machine, usually by means of a shrink fit and key.
  • Stator housings and mounting arrangements are designed for individual applications. These can incorporate Foot or Flange Mounting as required, or can be supplied entirely without housing.
  • A Vacuum and Pressure Impregnation Process for the rotors, combined with a High Integrity Class F insulation system ensures excellent reliability and long insulation life in the most hostile industrial, marine and military environments.

All rotors are designed to withstand 20% over-speed for a period of 2 minutes.

Newton Derby offer a full design service and produce bespoke designs for most customers.  However in some cases, Newton Derby offer a build-to-print service manufacturing to the customer’s design and drawing package.

Permanent Magnet Pilot Excitors

A PMG can be incorporated into the Exciter Machine if required by the customer.

  • PMG’s can be supplied as Stator/ Rotor units, or as fully enclosed auxiliary machines.
  • PMG’s are designed incorporating either Alnico or Rare Earth type magnets depending on the application and specifications.

Rotating Rectifiers

The rotating rectifier with surge protection is one of many available options. Rotating rectifiers are produced with ceiling ratings in excess of 2000 amps DC. The rectifier bridge is also protected against overvoltage spikes by a Voltage Dependent resistor and suppressor assembly.

All diodes are mounted and clamped to withstand the rotational forces and are rated for the continuous and ceiling output power required by the main generator field system. Balancing slots are an optional feature of rotating rectifier units.

Newton Derby’s sales and design team are ready and able to assist with your specific requirements for quality assured products in accordance with Newton Derby’s ISO 9001 Quality approval.

Optional Equipment

In their simplest form, exciters are produced as basic stator/rotor units but a wide range of optional extras are available. Some of our customers opt for a fully comprehensive service where the Exciter Machine is supplied as a self-contained machine, incorporating a variety of optional equipment and features including:

  • Earth Fault Detection Sliprings & Brushgear
  • Brush Lifting Actuator
  • Shaft Seals
  • PMG Pilot Exciter
  • Anti-condensation Heaters
  • Rotating Rectifier Assembly
  • Self Contained Air Cooling System with Internal Fan and Ducting
  • Split Stators to ease maintenance


  • Power Generation
  • Oil & Gas
  • Renewable Energy


Newton Derby manufacture a large range of sizes of Excitation Machines, and is capable of creating a bespoke design to suit most requirements.

Technical Specifications

  • Power Output: Capable of carrying out on-load testing on exciters up to 100kW, higher output exciters can be manufactured by Newton Derby depending on other parameters
  • Maximum Speed: 1800rpm

Contact Us

Tel: 0113 255 5666
Fax: 0113 257 2206
Email: sales@newtonderby.co.uk