Oil-filled transformers undergo prolonged drying processes to ensure that the transformer is completely free of water vapor before the cooling oil is introduced.

Oil-filled transformers may fail, rupture, and burn, causing power outages and losses.

Oil-filled equipment allowed arc energy to be contained and safely controlled.

This may be obtained using one or more dual tuned IF transformers, or a multipole ceramic crystal filter.

In the case of step-up transformers, this may sometimes be stated as the reciprocal, N < sub > s </ sub >/ N < sub > p </ sub >.

Leaky transformers may be used to supply loads that exhibit negative resistance, such as electric arcs, mercury vapor lamps, and neon signs or for safely handling loads that become periodically short-circuited such as electric arc welders.

For example, transformers may need to be equipped with " volts per hertz " over-excitation relays to protect the transformer from overvoltage at higher than rated frequency.

Losses in transformers ( excluding associated circuitry ) vary with load current, and may be expressed as " no-load " or " full-load " loss.

Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and secondary windings.

Larger power transformers operating at high voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks of pressboard.

For signal transformers, the windings may be arranged in a way to minimize leakage inductance and stray capacitance to improve high-frequency response.

Before 1977, even transformers that were nominally filled only with mineral oils may also have been contaminated with polychlorinated biphenyls at 10-20 ppm.

Larger transformers may have heavy bolted terminals, bus bars or high-voltage insulated bushings made of polymers or porcelain.

Alternating current is normally preferred as its voltage may be easily stepped up by a transformer in order to minimize resistive loss in the conductors used to transmit power over great distances ; another set of transformers is required to step it back down to safer or more usable voltage levels at destination.

Advantages of the UK setup are that the transformers may be fewer, larger and more efficient, and due to diversity there need be less spare capacity in the transformers, reducing power wastage.

In very dense city areas, a secondary network may be formed with many transformers feeding into a common bus at the utilization voltage.

A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages.

A transmission station may have transformers to convert between two transmission voltages, voltage control / power factor correction devices such as capacitors, reactors or static VAr compensators and equipment such as phase shifting transformers to control power flow between two adjacent power systems.

Switches, circuit breakers, transformers and other apparatus may be interconnected by air-insulated bare conductors strung on support structures.

Once having established buses for the various voltage levels, transformers may be connected between the voltage levels.

The SWER line is a single conductor that may stretch for tens or even hundreds of kilometres, with a number of distribution transformers along its length.

A large SWER line may feed as many as 80 distribution transformers.

The storage may be in either magnetic field storage components ( inductors, transformers ) or electric field storage components ( capacitors ).

Electric motors, field coils, transformers and capacitors may also be assembled with ultrasonic welding.

* Firewalls can be used to separate high value transformers at an electrical substation in the event of a mineral oil tank rupture and ignition.

The size of the core can be decreased at higher frequencies and, for this reason, aircraft use 400 hertz alternating current rather than the usual 50 or 60 hertz, allowing a great saving in weight from the use of smaller transformers.

This signal can be distributed by standard audio wiring, connectors, distribution amplifiers, and patchbays, and can be ground-isolated with audio transformers.

As trains began to be powered by transformers and rectifiers more sophisticated throttles appeared, and soon trains powered by AC contained mechanisms to change direction or go into neutral gear when the operator cycled the power.

Unlike DC, AC could be stepped up to very high voltages with transformers, sent over thinner and cheaper wires, and stepped down again at the destination for distribution to users.

Their patents included two other major interrelated innovations: one concerning the use of parallel connected, instead of series connected, utilization loads, the other concerning the ability to have high turns ratio transformers such that the supply network voltage could be much higher ( initially 1, 400 to 2, 000 V ) than the voltage of utilization loads ( 100 V initially preferred ).

It can be shown that if the " per-unit " inductance of two transformers is the same ( a typical value is 5 %), they will automatically split power " correctly " ( e. g. 500 kVA unit in parallel with 1, 000 kVA unit, the larger one will carry twice the current ).

By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve the same impedance.

Eddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other, rather than a solid block ; all transformers operating at low frequencies use laminated or similar cores.

It is common in transformer schematic symbols for there to be a dot at the end of each coil within a transformer, particularly for transformers with multiple primary and secondary windings.

As first mentioned in regard to earliest ZBD closed-core transformers, transformers are generally considered to be either core form or shell form in design depending on the type of magnetic circuit used in winding construction ( see image ).

At higher voltage and power ratings, shell form transformers tend to be more prevalent.

Shell form design tends to be preferred for extra high voltage and higher MVA applications because, though more labor intensive to manufacture, shell form transformers are characterized as having inherently better kVA-to-weight ratio, better short-circuit strength characteristics and higher immunity to transit damage.

Indoor liquid-filled transformers are required by building regulations in many jurisdictions to either use a non-flammable liquid or to be located in fire-resistant rooms.

Air-cooled dry transformers are preferred for indoor applications even at capacity ratings where oil-cooled construction would be more economical, because their cost is offset by the reduced building construction cost.

Tube instrument amplifiers are often equipped with lower-grade transformers and simpler power regulation circuits than those of hi-fi amplifiers.

Early series street lights were equipped with isolation transformers.

As with two-winding transformers, autotransformers may be equipped with many taps and automatic switchgear to allow them to act as automatic voltage regulators, to maintain a steady voltage at the customers ' service during a wide range of load conditions.

In the field of electric power distribution and transmission, a Buchholz relay is a safety device mounted on some oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a conservator.