Isolation
Transformer is a special type of transformer, wherein the primary and secondary
windings are physically separated through a so-called double insulation. Also,
an isolation transformer with electrostatic shields is commonly employed as
power supplies for sensitive devices like computers, laboratory measurement
instruments and medical equipment.
The
leakage inductance of isolation transformers is the primary feature that electrically
isolates people and equipment from the hazards of power quality problems such
as transients and high-frequency noise. Subsequently, they have a lower leakage
current than those that use a shield. In addition, isolation transformers can
prevent transfer of DC signals from one circuit to the other, as well as block
interference due to ground loops. However, they permit AC power or signals to
pass.
Isolation Transformer |
Applications
and Benefits
Basically,
isolation transformers are used to protect people against the hazards of
electric shocks, and isolate electrical equipment from the negative effects of
transients and high-frequency noise. Some of the applications are discussed
below.
Medical
Transformers
Medical
transformers are basically isolation transformers, which are designed to
isolate hospital patients and operators from electric shock, and to protect the
equipment from power surges or faulty components. They are used to offer a
safer environment by minimizing the potential hazards caused by touch voltages
and by avoiding loss of power even under single fault conditions.
Electronics
Isolation
transformers are used as a safety precaution in electronics troubleshooting and
testing. Grounded things near the device under test (lamp, oscilloscope ground
lead, etc.) may have a dangerously high potential difference relative
to that device, since the neutral wire of an outlet is directly connected to
ground. With the use of an isolation transformer, the bonding is removed and
the shock hazard is contained within the device.
Ships
Metal
ships are subject to corrosion due to use of grounded power from
shore when anchored. This is because galvanic currents flow through the water
between shore ground and the hull. To avoid this problem, an isolation
transformer with the primary and case connected to shore ground, and the secondary
floating should be employed.
In
addition, a metal safety screen between the primary and secondary of the
transformer is connected to shore ground. Consequently, when a short circuit
occurs in the primary, it will cause the fault current to trip a shore-based
circuit breaker rather than making the hull live.
Separately
Derived System
An
isolation transformer is used to establish a new neutral point (ground
reference) or a separately derived system. For example, when installing
electrical equipment in a grid without a neutral point, the solution is to
install an isolating transformer. Also, several applications require the
neutral point for controlling purposes.
Furthermore,
other benefits and uses of isolation transformers are the following:
- Capacitor-switching and lightning transients can be
attenuated, thus preventing nuisance tripping of adjustable-speed drives
and other equipment.
- Improve power quality by reducing high-frequency
noise currents.
- Complete isolation from the input AC line.
- Combined with surge protective devices, it offers
continuous filtering of power line noise in all modes.
- Active transformer filtering provides common-mode
noise rejection with no wearable parts, exceptionally reducing surges in
the worst of power environments to harmless levels.
- Limit voltage notching due to power electronic
switching.
- Eliminate neutral-to-ground voltage and noise, which
cause reliability problems for microprocessor-based electronics.
Construction
and Design
Isolation
transformers are normally designed with consideration to capacitive coupling
between the transformer windings. This is because excessive capacitance could couple
AC current from the primary to the secondary. Therefore, a double isolation is
required to solve such problem.
There
are two methods to set up double isolation:
1.
Placing
grounded metallic safety or Faraday shields between the primary and secondary
windings.
The
electricity simply flows to ground if the isolation breaks, providing the
required safety. The shield will attenuate transients and will reduce the
coupling of common-mode noise by decreasing the capacitive coupling.
2.
Reinforced
insulation
This
is made up of multiple layers, which pass the tests required by established
standards. If one layer gets damaged, the next layer gives the required safety.
Reference:
De Potter,
P. (2011). Isolation Transformers
No comments:
Post a Comment