What is an Ultra-Isolation Transformer

Advance ultra-Isolation Transformer (AIT) and Medical Isolation Transformer (MIT) series


The Advance series of AIT power conditioners was introduced some years ago to provide a highly effective noise filter for modern ICT equipment. The technical differences between the AIT and our traditional ferroresonant power conditioners are covered in sg026. However we are routinely asked for type test results relating to their performance. Perhaps the best test is the high integrity of all the thousands of installations world-wide in telecomm and EPoS applications.


The technical results show that the electrical performance of this type of conditioner is second to none for noise spike attenuation. Common mode noise is virtually eliminated and transverse mode noise is reduced well below any CBEAMA threshold. In addition the unit provides galvanic isolation between the input and output. These conditioners have conservatively rated magnetics to accommodate the large surges and high crest factor loads found in modern SMPS. The AIT is ideally suited to office applications where small size and low audible noise are of paramount importance.


Protected ICT systems will not be damaged by the high energy spikes associated with lightning striking overhead distribution wires. Other electrical mains-borne noise will either be reduced to an acceptable level or completely eliminated. The AIT reduces warranty and power supply maintenance costs of ICT equipment to a minimum.


The results shown are typical for a range of type tests designed to stress the unit as far as possible without destroying it.

Electrical safety

AITs comply with Class 1 to EN 60950, BS 1362:1973, BS 1363:1984 sect 12 + 13, BS 2754:1977. Units were tested with BS standard finger and pin and found compliant.

Breaking capacity

Fuses comply with BS 1362. Units with Circuit Breaker fitted to BS3871 breaking capacity 6kA minimum.


Materials found to be compliant with UL 94VO.

Insulation resistance

Between any two terminals the insulation resistance is approx 2MOhms measured at 500Vac. (Mains neon and protection elements removed).

Voltage regulation (<5%)

A step change from 10 to 90% in applied load was made in less than 1mS. The output voltage decreased by less than 5%. The RMS output voltage tracks the input typically within +/-4% of nominal for any unity power factor load from zero to full load.

Frequency (47-63Hz)

Output Frequency will be the same as input.

Power Factor

Suitable for power factor loads from +0.6 to -0.6.

Efficiency ( approx 94%)

Typical efficiency at full unity PF load and nominal input voltage is between 94 and 98% depending on model

Waveform distortion(<0.5%)

The Ouput waveform is normally identical to the input waveform, the exception is where high dv/dt changes are reduced by the saturation response of the iron core. Any additional distortion of nominal input sinewave will be less than 0.5%.

Critical phase angle

The AIT is insensitive to the effects of phase angle.

Load side surge protection

An impulse generator capable of producing a combination waveshape of 2.4kV open circuit and 200A short circuit was used for this test. No electrical or mechanical damage occurred.

Transient Noise Attenuation

Transverse Noise attenuation (Series Mode Noise attenuation) (55dB)

Transverse Mode noise appearing between live an neutral, attenuation approx 55dB @ 100kHz

Common mode noise attenuation (140dB)

Common Mode noise appearing between either live or neutral and ground attenuation approx 140dB from 10Hz to 1MHz

Test Electrical fast transient

The surge generator used is capable of producing a 5nS/50nS waveshape of 2kV open circuit voltage and a 2.5kHz repetition frequency. The test waveform is applied for 15mS every 300mS for 10 minutes. The waveform is described in IEC 801-4 1988. For both polarities the peak voltage appearing on the output terminals was <250V.

Ring Wave test 0.5µS 100kHz

Positive and negative polarity tests were made LN/LE/NE. Output voltages were <10V symmetric and <0.5V asymmetric for 0.5µs 100kHz waveshape @ 6kV with 500Amp capacity.

Impulse discharge limiting voltage

A generator capable of a current of 5kA peak 8 x 20uS waveshape into a short circuit was used to apply 30 tests incorporating both polarities and all terminals. Output voltage peaks were all < 250V.

Transient Failure modes

The 5kA, 8 x 20µS waveshape blew the input fuse as required on all tested samples.

Overcurrent performance

The units were tested with slowly increased loads until the overload protection operated. Units must run for approx 2 hours at a load just below the point at which protection operates. Case temperatures remained below 46 deg C

Mode transfer

The 5kA 8 x 20uS waveshape was applied between LE and measured between LN + NE. The 5kA 8 x 20uS waveshape was applied between NE and measured between LN + LE. At no time did the peak impulse output voltage exceed 200V.

Insertion loss

The symmetric and asymmetric insertion losses were measured using both methods described in BS 6299 section 4.1 Appendix A. Insertion loss was <65db over the range 10kHZ to 30MHz. Negligible noise is transferred between modes. Waveforms relating to these tests can be viewed at the factory.


Suitable for ambients 0-40degC, relative humdity up to 95% Altitude <10,000 feet.