Applications
Electrostatically (faraday) sheilded transformers
are designed to protect sensitive electrical and electronic devices
and systems from high frequency voltages (electrical noise) or transients
that occur due to switching and loading on distribution lines.
Electrical noise and transients are classified
two ways:
- Normal Mode - noise which appears
between the hot & neutral current carrying conductors.
- Common Mode - noise which appears
between between the ground wire and hot and neutral current carrying
conductors. Common mode noise is more prevalent and should be
the key criterion for any noise suppression device.
Typical Applications
- Hospital operating rooms & X-ray equipment
- Computer installations
- Data processing
- Programmable controllers
- Instrumentation
Features
- Shielded transformers are available with copper
or aluminum windings
- Knock outs provided for simplified wiring
- Class 220 insulation us used throughout entire
range
- General purpose ventilated steel enclosure,
suitable for indoor locations finished in ASA 61 power epoxy paint.
- Transformers rated up to 75 KVA may be readily
hung on H columns, walls, shelves or floor mounted to suit each
installation. All units come complete with provisions for lifting.
- Internal ground lugs
- CSA certified, file no. LR 34493
- UL listed, file no. E1088255
Electrostatic
Shielding
The shielded transformer suppresses common
mode noise by introducing a grounded shield (copper or aluminum)
between its primary and secondary windings. The grounded shield
provides a low resistance path to ground by the effect of capacitive
coupling which prevents high frequency signals presnt in the source
voltage from reaching the secondary of the transformer and subsequently
the connected load.
The electrostatic shield will not perform any
function with regard to harmonic current or voltage distrotion of
waveforms. By redirecting unwanted commom mode electrical noise
and transients generated on the source side of the transformer to
ground the shield is extremely valuable in protecting sensitive
equipment connected to the transformer output.
Several types of electrostatically shielded
transformers are available providing the option of various degrees
of common mode noise attenuation.
The ratio of the common mode noise attenuation
on the input to that of the output is expressed in Decibels (dB).
Isolation transformers with electrostatic shields
installed can have unput noise to output noise ratios within the
range of 10:1 to 1,000,000 or higher.
Effects of Electrostatic
Shielding
| 3 Phase Isolation Transformer
Common Mode |
Attenuation
Ratio Range |
Noise
Attenuation |
Transformer
with no shield: |
Minimum attenuation 12 dB
Range: 12 dB - 20 dB |
10:1 |
Single Shield: |
Minimum attenuation 50 dB
Range: 50 dB - 65 dB |
1000:1 |
Double Shield: |
Minimum attenuation 65 dB
Range: 65 dB - 90 dB |
10,000:1 |
Triple Shield: |
Minimum attenuation 90dB
Range: 90dB - 120dB |
100,000:1 |
Ultra Isolating: |
Minimum attenuation 120 dB
Range: 120 dB - 150 dB |
1,000,000:1 |
* Information
subject to change without prior notice.
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