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Energy Efficient 80oC and 115oC Rise Transformer
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| These types of ventilated transformers incorporate the same features as general purpose transformers with the exception that they handle temperature differently . Specifically, energy efficient transformers utilize a 220 oC insulation system and are designed for normal operation at a reduced temperature rise either 80 oC or 115 oC, instead of the normal 150 oC rise. This is accomplished by increasing the size of the coil conductors result in a lower operating cost (energy savings) and an improved life expectancy since the 220 oC insulating is subjected to lower operating temperatures. These units will also have a continuos overload capacity of15% for 115 oC rise units and 30% for 80 oC rise units when operate at 150 oC rise. Again, since the insulation system is rated 220 ( C, this overload operation will not reduce the normal life expectancy of the transformers. Since operating in an overload condition results in higher temperatures and higher losses, the efficiency will decrease under these conditions. |
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These types of ventilated transformers also incorporate the same features an general purpose transformers. However , electrostatic shielded transformers can attenuate (reduce) undesirable high-frequency signals.High -frequency signals can be thought of as static in a radio. These signals (noise) are commonly produced by certain types of lighting, switching surges, motors and SCR’s which feed this static back into the power lines. The power lines transmit this static to all loads and especially to certain loads that operate sensitive electrical equipment (which can cause some equipment to malfunction). An electrostatic shielded transformer incorporates a single turn of foil placed between the primary and secondary windings with one side grounded. The shield will then attenuate (reduce) the noise, thus suppressing its effect upon sensitive loads. (Refer to FPT catalog, page 35)
Typical use of shielded isolation transformers include:
Suppression to transients or noise when traveling from its source
to the sensitive load equipment.
Suppression of noise and transients at the point or transients
originate, thus preventing them from back feeding from the source to the
feeders.
Transforming one voltage level to another.
Isolating one circuit from another. |
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Dry Type Transformers and Non-Linear Loads
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| In general, a transformer’s performance is not affected by the type of loads they serve. However, in recent years, advances in the design of power supplies for various types of office equipment (particularly the personal computer) and SCR drives has presented some unusual problems. Specifically, overheating in standard dry-type transformers, even when ampere measurements indicate the current is within rating. Very basically, the problem appears when the transformer load distorts the sinusoidal current waveform. These distorted (non-linear) current waveforms are said to contain”harmonic distortion. (See Note) As transformer’s ability to handle these non-linear/harmonic loads is determined by its K-factor rating. K-factor is a simple numerical rating that can be used to specify transformers for non-linear/harmonic loads. Normally, the customer or consulting engineer will specify K-factor ratings, if necessary, for certain transformers within a distribution system. (Refer to FPT catalog, page 32). Note: Harmonics are multiples of the fundamental frequency (normally 60 hertz). Therefore, the 3rd harmonic equals 60 X 7 or 420 hertz, and so on. |
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Type FH Motor Drive Isolation Transformers
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| Type FH motor drive isolation transformers are designed to meet the requirements of SCR controlled variable speed motor drives. They are specifically constructed to withstand the mechanical forces associated with SCR drive duty cycles and to insolate the line from most SCR generated voltage spikes and transient feedback . Similarly, the two winding construction also aids in reducing some types of line transients that can cause misfiring of the SCRs. The units are UL Listed and incorporate all the features of the FH transformer line. The transformer can also be supplied core and coil units with UL components recognition. Delta-wye designs are available for all commonly use primary and secondary voltages. All units include primary and secondary voltages. All units include primary taps consisting of one 5% FCAN and one 5% FCBN. (Refer to FPT catalog, page 30) |
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| The type FB Insulating and Buck-Boost Transformer has four separate windings, two windings in the primary and two windings in the secondary. The unit is designed for use as an isolating transformer or as auto-transformer. As an auto transformer, the unit can be connected to buck (decrease) or Boost (increase) a supply voltage. When connected in either the Buck or Boost mode, the unit is no longer an isolating transformer but is an autotransformer. Autotransformers are more economical and physically smaller than equivalent two-winding transformers designed t carry the same load. They will perform the same function as two-winding transformers with the exception of insulating or isolating two circuits . Since autotransformers may transmit line disturbances directly , they may be prohibited in some areas by local building codes. Before applying them, care should be taken to assure that they are acceptable according to local code. Note: Autotransformers are not used in close Delta connections as they introduce a phase shift into the circuit. As isolating transformers, these units can accommodate a high voltage of 120 x 240 volts (SB12N and SB16N series) or 240 x 480 volts (SB24N series). For the units with two 12 volt secondaries, the low voltage output can be 12 volts, 24 volts, or 3- wire 12/24 volts. Volts. For the units with two 16 volt secondaries, these output voltages can be 16 volts, 32 volts, or 3-wire 16/32 volts. For the units with two 24 volt secondaries, these output voltages can be 24 volts, 48 volts, or 3 wire 24/28 volts. The unit is capacity rated (KVA) as any conventional transformer. |
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| Electrical and electronic equipment is designed to operate on a standard supply voltage. When the supply voltage is constantly too high or too low, (usually greater than (5%), the equipment fails to operate at maximum efficiency. Buck-Boost transformer is a simple and economical, means of correcting this off-standard voltage up to (20%. A Buck-Boost transformer will NOT, however, stabilize a fluctuating voltage. Buck Boost transformers are suitable for use in a three-phase autotransformer bank in either direction to supply 3-wire loads. They are not suitable for use in a three-phase autotransformer bank to supply a 4-wire unbalanced load when the source is a 3-wire circuit. |
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Operation
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To select the proper transformer for Buck-Boost applications, determine:
A Input Line Voltage-the voltage that you want to buck (decrease) or boost (increase). This can be found by measuring the supply line voltage with a voltmeter.
B Load Voltage - the voltage at which your equipment is designed to operate. This is listed on the nameplate of the load equipment
C Load KVA or Load Amps- you do not need to know both. One or the other is sufficient for selection purposes. This information usually can be found on the nameplate of the equipment you want to operate.
D Number of Phases- single or three-phase line and load should mach because a transformer is not capable of converting single-phase to three-phase. It is however, a common application to make a single -phase transformer connection from a three-phase supply by use of one leg of the three-phase supply . This particularly true in a Buck-Boost application because the supply must provide the load KVA, not just the nameplate rating of the Buck-Boost transformer
E Frequency- the supply line frequency must be the same as the frequency of the equipment to be operated; either 50 or 60 cycles
Six Step Selection |
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A Choose the selection table with the correct number of phases. Tables I, III, and V for single-phase applications and Table II, IV, and VI for three-phase applications. Tables I and II are for 120x 240-12/24 volts: Tables III, IV are for 120 x 240-16/32 volts; and Tables V and VI are for 240 x 480-24/48 volts. (Refer to FPT catalog pages 13, 14, 15)
B Line/Load voltage combinations are listed across the top of the selection table. Select a line/load voltage combination which comes closest to matching your application.
C Follow the selected column down until you find either the load KVA or load amps of your application. If you do not find the exact value, go on to the next highest rating.
D Follow across the table to the far left-hand side to find the rated KVA of the transformer you need.
E Follow the column of your line/load voltage to the bottom to find the connection diagram for this application. Note: Connection diagrams show low voltage and high voltage connection terminals. Either can be input or output depending upon Buck or Boost application.
F In the case of three-phase loads either two or three single-phase transformers are required as indicated in the “quantity required “ line at the bottom of Table II, IV or VI Select depending on whether a Wye connected bank of three transformers with a neutral is required or weather an open Delta connected bank of two transformers for a Delta connected load will be suitable. |
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| For line/load voltages not listed on the table, use the pair listed on the table that is slightly above your application for reference. Then apply the first formula at the bottom of Table II, IV, or VI to determine “New” output voltage. The new KVA rating can be found using the second formula. |
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