What are the most common power problems?
Research conducted by both IBM and Bell indicates that most line disturbances to sensitive equipment are line noise and voltage fluctuations.
How does Dirty Power affect my electronic equipment?
Your computer operates by reading electronic impulses. Dirty power contains a great number of random pulses riding on the normally smooth surface of a power wave. As these random pulses enter the circuits, your computer 'reads' them as data. This can cause a whole range of problems. You may suddenly get garbled numbers or letters in a readout or printout. You could loose files, skip program steps, have trouble loading programs or have connection problems while on the Internet.
How bad can the Dirty Power problem get?
One form of dirty power usually called a surge can burn out computer, audio, video or nay other electronic circuitry in seconds. A surge is a high voltage pulse riding the normal power wave. Surges will commonly measure 600 to 2500 volts. Even though they occur for only mille-seconds, this is enough time to melt down circuits.
It is the transformer electrical losses, which include no-load losses (core losses) and load losses (winding losses).
Normal, routine production tests include:
- (1) core loss;
- (2) load loss - winding or copper loss;
- (3) Impedance;
- (4) hi-pot - high voltage between windings and ground;
- (5) induced - double induced two times voltage.
Optional special tests include:
- (a) heat run - temperature testing;
- (b) Noise tests - sound level measurement;
- (c) impulse tests - BIL tests:
- (d) partial discharge.
When you calculate the VA requirement of a Transformer, do you use the Primary or the Secondary Voltage?
When selecting the VA requirement, you use the Secondary Voltage.
Yes, a control transformer can be connected in reverse. However, keep in mind the output voltage will be less than it's rating, due to the compensation factor of the windings.
Can a Control Transformer regulate the output voltage?
A control transformer will not regulate the voltage. Output voltage is a function of the coil's turn ratio only, times the input voltage.
Insulating Materials, what are they made of and what is their purpose?
PTI high quality insulating materials. Insulation is used to electrically insulate turn-to-turn windings, layer-to-layer windings, primary to secondary windings and ground.
How does a buck-boost transformer differ from an isolating transformer?
A Buck-Boost transformer is manufactured as an isolating transformer, with separable primary and secondary, and is shipped from the factory in that configuration. When the end user at site connects it, the primary is connected to the secondary changing the transformer's electrical characteristics to those of an autotransformer. This provides the smaller voltage correction that is typical of Buck-Boost. The primary and secondary windings are no longer isolated as they are connected together.
What is the difference between a buck-boost transformer and an autotransformer?
As noted above, when the primary and secondary are connected together to buck or boost voltage, the transformer becomes an autotransformer. If the connection between the primary and secondary winding is not made, then the unit remains as an isolation transformer.
A Buck-Boost transformer is a simple and effective way of correcting off-standard voltages. Electrical and electronic equipment is designed to operate within a standard tolerance of nominal supply voltages. When the supply voltage is consistently too high or low - typically more than 10%, the equipment will operate below peak efficiency.
Can Buck-Boost transformers be used to power low voltage circuits?
Installed as two-winding, isolation transformers, these units can be used to power low voltage circuits including control, lighting circuits, or other low voltage applications that require 12, 16, 24, 32 or 48 volts output, consistent with the secondary of these designs. The unit is connected as an isolating transformer and the nameplate kVA rating is the transformer's capacity.
Why do Buck-Boost transformers have 4 windings?
A four winding buck-boost transformer with 2 primary and 2 secondary windings can be connected eight different ways to provide a multitude of voltages and kVA's. This provides the flexibility necessary for the broad variety of applications. A two-winding transformer can only be connected in two different ways.
Will a Buck-Boost transformer stabilize voltage?
Autotransformers will not stabilize supply line voltage. The output voltage of an autotransformer is a function of the input voltage. If the input voltage varies, then the output voltage will also vary by the same percentage.
Are there any restrictions on the type of load that can be operated from a Buck-Boost transformer?
There are no restrictions as to application for Buck-Boost, including single or three-phase motor loads.
As an Autotransformer, how can a Buck-Boost transformer supply kVA power?
This is a function of adding voltage - a small amount of voltage is added and a small amount of corresponding power capacity is added as well. For example, if the transformer is connected in such a way that 22 volts is added to a 208 volt primary, a 230-volt output will result.
Using this example, the calculation for autotransformer kVA is as follows:
KVA = (Output Volts x Secondary Amps)/1000
KVA = (230V x 41.67 Amps)/1000 = 9.58 KVA
How are single phase and three phase load amps and load kVA calculated?
Single phase Amps = (kVA x 1000)/Volts
Three phase Amps = (kVA x 1000)/Volts x 1.73
Single phase KVA = (Volts x Amps)/1000
Three phase KVA = (Volts x Amps x 1.73)/1000
Can Buck-Boost transformers be used on 3 phase systems?
Interconnecting two or three single-phase units will readily accommodate three phase systems - refer to the corresponding three-phase section in this catalog. The number of units to be used in a 3-phase installation depends on the number of wires in the supply line. If the 3-phase supply is 4-wire Wye, then three Buck-Boost transformers are required. If the 3-phase supply is 3-wire Wye (neutral not available), two Buck-Boost transformers are needed.
Should Buck-Boost transformers be used to develop 3-phase 4 wire Wye circuits from 3-phase 3 wire Delta circuits?
No - a three-phase "Wye" buck-boost transformer connection should be used only on a 4-wire source of supply. A delta to Wye connection does not provide adequate current capacity to accommodate unbalanced currents fl owing in the neutral wire of the 4-wire circuit.
Why isn't a 'closed Delta' Buck-Boost connection recommended?
This connection requires more kVA power than a "Wye" or open delta connection, and phase shifting occurs on the output. The closed delta connection is more expensive and electrically inferior to other three-phase connections.
How do you know how to connect a Buck-Boost transformer?
A connection chart is provided with each unit that shows how to make the corresponding connections. These same charts are also shown in this section.
Can 60-Hertz Buck-Boost transformers be operated on 50-Hertz?
Due to 'saturation' of the core, 60-Hertz Buck-Boost transformers should only be operated at 60 Hertz, and not 50 Hertz. Units manufactured as 50-Hertz units will however, operate at 60 Hertz.
Why are Buck-Boost transformers shipped from the factory connected as isolating transformers, and not pre-connected autotransformers?
The same 4-winding Buck-Boost transformer can be connected eight different ways to provide a multitude of voltage combinations. The user when assessing the supply voltage at site can best determine the correct connection.
Why is the isolation transformer kVA rating shown on the nameplate instead of the autotransformer kVA rating?
Shipped as an isolating transformer, the nameplate is required to show the performance characteristics accordingly. Additionally, as an autotransformer, the eight different combinations of voltages and kava's would be impractical to list on the nameplate. A connection chart, listing the various connections, is included with each unit.
Do Buck-Boost transformers present a safety hazard compared to conventional autotransformers?
Buck-Boost transformers only change voltage by a small amount, such as 208 to 240 volts. This small increase does not represent a safety hazard. Conventional autotransformers, manufactured as single winding transformers, change much higher magnitudes of voltage, e.g. 480 to 240 volts. In a system where the line is grounded, it is possible to have 480 volts to ground when the expectations are that 240 volts is at the output. For this reason, qualified personnel only should maintain conventional autotransformers.
How does the sound level differ between Buck-Boost and isolation transformers?
Buck-Boost transformers, connected as autotransformers, will be quieter than an equivalent isolation transformer capable of handling the same load. The isolation transformer would have to be physically larger than the buck-boost transformer, and smaller transformers are quieter than larger ones. For example, a 10kVA is 35dB and a 75kVA is 50dB.
How do the costs compare between a Buck-Boost transformer and an Isolation transformer handling the same load?
For most Buck-Boost applications, the savings are about 75% compared to the use of an isolation transformer for the same application.
What is the life expectancy of a Buck-Boost transformer?
Buck-Boost transformers have exactly the same life expectancy as other dry type transformers. Buck-Boost transformers are almost always installed as autotransformers.
Does the National Electrical Code (NEC) permit the use of autotransformers?
Autotransformers are very common and recognized by all the safety and standard authorities. You can refer to N.E.C. Article 450-4, "Autotransformers 600 Volts, Nominal, or Less", as a reference publication. Item (a) details over-current protection for an autotransformer, and Item (b) covers an isolation transformer being field connected as an autotransformer for a Buck-Boost application.
What is Nuisance Tripping and how can a Line Reactor eliminate it?
Transients due to switching on the utility line and harmonics from the drive system can cause intermittent tripping of circuit breakers. Furthermore, modern switchgear, equipped with solid-state trip sensing devices, is designed to react to peak current rather than RMS current. As switching transients can peak over 1000 volts, the resulting over-voltage will cause undesirable interruptions. A reactor added to your circuit restricts the surge current by utilizing its inductive characteristics, and therefore eliminates nuisance tripping.
How does a Line Reactor extend the life of switching components?
Due to the attenuation of line disturbances, the life of your solid state devices are extended when protected by the use of a line reactor.
What are Industrial Control Transformers?
A control transformer is an isolation transformer designed to provide a high degree of secondary voltage stability (regulation) during a brief period of overload condition (also referred to as "Inrush Current"). Control transformers are usually rated for 600 volts or less.
What are General Purpose Distribution Transformers and where are they used?
General Purpose distribution transformers are rated for 600 volts and below. They are generally used for supplying appliance, lighting, motorized machine and power loads from electrical distribution systems. They are either ventilated or totally enclosed, and are available in standard ratings from 250VA up to 750kVA.
What are Shielded Distribution Transformers and where are they used?
Shielded distribution transformers provide a copper electrostatic shield between the primary and secondary windings. The shield is grounded and thus shunts most noise and transients to the ground path rather than passing them through to the secondary. Applications for shielded transformers are similar to those above, and they are ideal for commercial or electrical installations where electronic circuitry operating at low voltage DC is present and is very sensitive to 'noise'.
What are K-Factor Transformers and where are they used?
K-factor transformers are used as a general-purpose transformer but are designed to withstand the variety of harmonics created in today's office and industrial environments. The expanding use of devices with switch-mode power supplies and rectifier circuits with the subsequent wave distortion requires transformers to withstand the higher harmonics in the neutral conductor in the distribution system.
What are Autotransformers?
Autotransformers are similar to Buck-Boost transformers in that they are also an economical means of adjusting an output voltage. Autotransformers are designed to adjust the supply voltage when isolation from the line is not necessary and where local electrical codes permit. Units are designed in either a step-up or step-down application and to meet motor inrush currents.
What are Motor Starting Autotransformers?
Motors have a large inrush current component that requires a special design. Motor starting transformers are designed to withstand an inrush of upward of 25 times normal current. They typically are tapped on larger sizes to soft-start the motor until it is up to full RPM.
What are Energy Efficient (TP1) Transformers?
There is a growing movement in the electrical industry towards energy efficient products in all sectors including dry type transformers. In addition to the benefits to the environment, energy efficient transformers also can realize substantial savings in operating costs thereby having a direct impact on the initial investment evaluated over a period of time.
The specifications covering energy efficiency in transformers, is the NEMA Standards Publication, TP-1-1996, "Guide for Determining Energy Efficiency for Distribution Transformers". This specification has carefully considered the total owning cost unique for industrial or commercial installations where the load factor is an integral part of the efficiency rating.
All transformers have operating losses, and heat is the product of these losses. Low temperature rise transformers are designed with reduced 115°C or 80°C full load operating temperature rises. These units decrease total operating losses by 20% and 35% respectively, compared with the standard 150°C rise operating system. Low temperature rise transformers provide greater efficiency under normal operating conditions, and overload capability without harm to their service life or reliability.
What are Encapsulated Transformers and where are they used?
These units are encapsulated and completely enclosed. The encapsulated design is especially suited for installations in harsh environments where dust, lint, moisture and corrosive contaminants are present. Typical applications include: pulp and paper plants; steel mills; food processing plants; breweries; mines; marine and shipboard installations.
What are Medium Voltage Transformers and where are they used?
Medium voltage transformers are really 5kV class dry type distribution transformers. They are designed primarily for use in stepping down medium voltage power to a lower operating voltage for commercial, institutional or industrial applications.
What are Drive Isolation Transformers and where are they used?
Drive isolation transformers are designed to supply power to AC and DC variable speed drives. The harmonics created by SCR type drives requires careful designing to match the rated hp of each drive system. The duty cycle included is approximately one start every 2 hours. The windings are designed for an over-current of 150% for 60 seconds, or 200% for 30 seconds.
What are Clean Power Products?
Computer regulators and hard-wired line voltage conditioners protect equipment from both noise and voltage fluctuations while super isolation transformers are all designed to provide protection against frequency variation or noise related disturbances.
When is Sound Level an issue in the design?
Sound needs to be considered when transformers are located in close proximity to occupied areas. All energized transformers emanate sound due to the alternating flux in the core. This normal sound emitted by the transformer can be a source of annoyance unless it is kept below acceptable levels. There are ways of minimizing sound emission to meet the latest ANSI, CSA and UL standards.
When can you Reverse Connect a transformer?
In general, distribution transformers can be reverse connected without de-rating the nameplate KVA capacity. However some precautions need to be taken for reverse connection of some smaller transformers. On transformers under 6kVA three phase and 3kVA single phase, there is a "turns ratio compensation" on the low voltage winding.
When the input voltage, equal to the nameplate rated voltage, is connected to the low voltage winding, the output voltage will be slightly lower than the nameplate rating.
When a three-phase transformer is reverse connected thus resulting in a Wye-Delta configuration, the neutral terminal must be isolated. Further, the reverse connected transformer may draw a higher inrush current during energization. Hence the sizing of the line fusing or circuit breaker may be affected.
Under what circumstance does need D.C. Resistance Measurement?
Current from a D.C. resistance bridge is applied to the transformers windings to determine the D.C. resistance voltage of the coils. This test is important for the calculation of I2R for use in the winding temperature test, and as base data for future assessment in the field.
What is a Polarity and Phase-Relation test for?
Polarity and phase-relation tests are made to determine angular displacement and relative phase sequence to facilitate connections in a transformer. Determining polarity is also essential when paralleling or banking two or more transformers.
What is the "Efficiency" of a transformer?
The percentage of power transferred from the input of equipment to the output of equipment in Watts. (power out/power in x 100).
No-load losses (excitation losses) are the core losses of a transformer that are "excited" at rated voltage and frequency, but which do not supply load. No-load losses include core loss, dielectric loss, and losses in the windings due to exciting current. The transformer is excited at rated voltage with all other windings open circuited. The exciting current and no load loss is then measured.
(Note: This is a standard test only on units over 500kVA. It will only be carried out on lower kVA units when specifically requested.)
The voltage required to circulate the rated current under short-circuit conditions when connected on the rated voltage tap, is the impedance voltage. Rated current is circulated through the windings with the secondary short-circuited. The impedance voltage and load loss is measured. They are corrected to rise +20°C reference temperature. (Note: This is a standard test only on units over 500kVA. It will only be carried out on lower kVA units when specifically requested.)
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