Single Phase Transformers
Single phase transformers are
designed to supply electric power to single-phase systems. These electrical
devices transfer energy from one circuit to another via electromagnetic
induction. Single phase power usually includes one hot lead and a grounded return
line or neutral. Single phase electrical distribution is used mainly in
residential and commercial applications, typically for lighting and heating.
Single phase transformers carry many product specifications, including
transformer type, winding turns, cooling method, core type, output voltage, and
mounting or form factor. Performance specifications, approvals, and features
are also important parameters to consider.
There are many types of single phase
transformers. Products include audio, balun, buck-boost, constant voltage
(CVT), constant current, distribution, fly back (FBT), generator step-up (GSU),
harmonic mitigating, high frequency, high voltage, impedance matching, and
industrial control transformers. Categories of single phase transformers also
include interface, inverter, isolation, leakage, lighting, medical,
multi- ratio, neutral grounding, power, rectifier, resonant, solar power, and
substation transformers. Auto transformers and variac or variable
auto transformers are also available from single phase transformer
suppliers.
Like other types of transformers, single
phase transformers may be used to increase or decrease the voltage from one
side of the transformer to the other. The turn ratio or number of windings on
the primary and secondary sides of the device determines the change in voltage.
Step-up transformers produce a secondary voltage that is larger than the
primary voltage. Step-down transformers have a secondary voltage that is
smaller than the primary voltage. Variable single phase transformers are
devices with a setting for changing the turn ratio as needed. One-to-one
transformers are single phase transformers with a turn ratio of 1:1 or near
1:1.
Cooling method, core type, output
voltage, and mounting or form factor are additional product specifications to
consider when selecting single phase transformers. There are four choices for
cooling method: dry-type or air cooled, oil filled, water cooled, and other.
Core types are listed as laminated, split, toroidal, and other. The output
voltage is either alternating current (AC) or direct current (DC). There are
many mounting or form factor styles for single phase transformers. Choices
include chassis mount, chip transformer, dish or disk, H-frame, modular jack,
pad mounted, printed circuit board (PCB), and pole mounted.
Selecting single phase transformers requires an
analysis of performance specifications (including the single-phase primary
configuration) as well as compliance with regulatory standards. Performance
specifications include operating frequency range, maximum primary voltage
rating, maximum secondary voltage rating, maximum secondary current rating,
power rating and operating temperature. The single-phase primary configuration
is listed as single, dual, quad (2+2) 5-lead, ladder, or other. In terms of
regulatory standards, single phase transformers that are sold in Europe must be
Ro HS and WEEE compliant.
Transformers parallel circuit
Transformers
are placed in parallel by electric utilities when they want to provide a
‘stronger’ voltage source and will result in higher available fault current
that can be delivered downstream. Usually the utility transformer can
serve its own load but two are put together to achieve with a ties primary and
secondary bus to ‘stiffen’ the voltage to ride through system load changes.
Because here we have more transformers connected in parallel. So even if, one
of the transformers gets into a fault or is taken out for maintenance or
repair, the load can continued to be serviced. Therefore by this we can reduce
the spare capacity also.
Before two
or more transformers connected in parallel and to share a common load
satisfactorily, there are some conditions to be satisfied. Those are the
voltage ratio (turns ratio) and the per unit impedance of each machine on its
own base must be the same. When two transformers are
connected in parallel, the impedances of the transformers must match (within
10%) to divide the load approximately equally between the two transformers or
to divide the load according to the rating of each transformer. If the
transformers to be connected in parallel are equipped with load tap changing
windings, then the impedances for each of the tap changer positions must match.
If these conditions are not met, then one of the transformers could conceivably
carry a continuous overload, resulting in overheating.
Also the
polarity must be the same, so that there is no circulating current between the
transformers. The polarity of connection in the case of single phase
transformers can be either same or opposite. Inside the loop formed by the two
secondary the resulting voltage must be zero. If wrong polarity is chosen the
two voltages get added and short circuit results.
The phase sequence must be the same and no phase difference
must exist between the voltages of the two transformers. When these
requirements are satisfying we can have a good parallel operation of
transformers which is very useful and favourable in practice.
1)
Reducing the
total capacity of electrical transformers (as
compared to separate their work). The decrease of total installed capacity is
reached:
· less
required backup in case of electrical transformer failure
2) Reduction of electricity losses in electrical transformers due to a
possible disconnection of unloaded transformers
3) Improving the power quality due to the stable level of short
circuit current throughout the network
4) Increasing the reliability of operation of protective devices in the
case of phase-to-earth short circuits in the network.
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