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EM/EMS Stabilisers

EM/EMS Stablilisers

Electronic Servo AC Voltage Stabilisers & Power Conditioners

The EM and EMS range offers the most cost effective and efficient way to ensure a stable, undistorted mains supply for the vast majority of applications.

Based on the proven electronic servo design, a double wound transformer has its secondary winding connected between the incoming AC supply and the load, with the primary winding voltage controlled by a motor-driven variable auto transformer. A solid-state servo amplifier continuously monitors the output voltage of the stabiliser, and any error voltage is amplified to operate the servomotor of the variable transformer, driving its brush-gear to a point where it is injecting a voltage that will correct the supply voltage by adding or subtracting from it.

Over six thousand models span ratings from 1kVA to 8,000kVA , single or three phase, incorporating full transient spike and noise suppression if required. Available with a wide selection of input voltage ranges from ± 7.5% to ± 40%

Output voltage accuracy: ± 0.5% accuracy maintained over the full range of input voltage variations from zero to full load irrespective of power factor, frequency variations and ambient temperature changes from -5 Deg C to +45 Deg C. Three phase stabilisers will also maintain the accuracy of each phase, both line to line and line to neutral, even if the input voltage. Load and power factor are totally unbalanced.

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Key Features

  • Fast response


  • Low internal impedance capable of sustaining high surge currents


  • Efficiency better than 98% with up to 99.5% on higher models


  • Waveform distortion negligible with any type of load


  • Frequency 47 to 65Hz


  • Soft-Start ensures low output voltage at the moment of switching on


  • Soft-Stop dampens the force of impact when the variable transformer brush gear reaches the end stop.


  • Full Transverse and Common Mode spike / interference suppression when required.


  • Oil Immersed versions for outdoor use or for use in hostile environments.


  • Stabilised Output Voltage Can be preset to any value within these ranges

    • H Models L models
    200 to 254 V single phase 100 to 127 V single phase
    346 to 440 V three phase 173 to 220 V three phase

  • Power Factor has no effect on the performance


  • Surge rating ten times the rated current up to 2 seconds. Three times up to 1 minute. Twice up to 5 minutes


  • Environment the quoted current ratings apply to ambient temperatures from -5 Deg C to +45 Deg C. Derate by 2% per each additional degree C up to 70 Deg C. Temperature stability better than 0.03% per degree C. Maximum altitude 1000m. Derate by 2.5% for each additional 500m, EM stabilisers are suitable for indoor tropical use.


  • EMT/EMST stabilisers incorporate the advanced Rotavolt technology and additional cooling resulting in a considerable cost and weight reduction per kVA


  • Audible noise level less than 40dB at 1m distance EM & EMS models 50dB for EMT & EMST models


  • Spike Suppression. Metal oxide transient voltage suppression is fitted as standard. Additional protection can be provided to attenuate spikes and noise down to harmless levels


  • Lightning Arrestors. Can be provided to protect the stabiliser and the load from the harmful effects of induced lightning strikes to the incoming supply distribution network.


  • Construction, the larger stabilisers are enclosed in robust floor standing cubicles, with door access for easy installation and servicing. The smaller single phase models are suitable for floor or bench mounting, Enclosures to IP20 BS60529


  • CE Conformity Conforms to the requirements of council directive 89/336/EEC EMC (Valid to Oct 2009) & 2004/108 EEC emissions / immunity and directive 2006/95/EC , (Formally 73.23.EEC) Low voltage directive.


  • Speed of response Defined as the time taken to restore a 10% voltage variation to within 2%, these will vary 0.15 secs on smaller units to 1 sec for larger models.


  • Three Phase models are normally supplied for "star" connection and require an incoming neutral. If no neutral available a static balancer can be fitted to provide an artificial neutral.


  • Quality Management System. Assessed and approved to ISO 9001:2000


  • Environmental Management Policy. Assessed and approved to ISO 14001:2004



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