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The following is a glossary of the technical terms related to power transformers. It is intended to provide an understanding of the basics of transformer design, needed when discussing your requirements with us. 230VAC This simply means 230 volts, AC (alternating current) See AC-DC. 2- phase see single phase The term 2-phase is sometimes used to indicate the use of 2 of the 3 output lines of a 3-phase supply. In the diagram below this would be "400 volt, 2-phase" 3-phase transformers see also Single phase-3phase TSL can build 3- phase transformers up to 150,000 VA (150 kVA) The 3 windings can be connected in Star configuration, or in Delta configuration, as per the diagram below. One transformer can have the primary connected in Delta, and the secondary windings in Star, or vice versa, or any other combination. Which is best for your requirements is the job of our designers. If the end user requires access to the star point, then the secondary must of course be connected in Star  AC-DC Abbreviation for Alternating Current and Direct Current. Most power is distributed in the form of AC. Basically, the power company generators produce electricity by rotating (3) coils or windings through a magnetic field within the generator .The magnetic flux through the coil increases and decreases while a coil comes in line with the magnetic field, and then rotates to a right angle position, continues on to in line and then to right angle again, but this time pointing in the opposite direction. The result is a voltage that constantly changes polarity. In a 230v circuit one moment the brown line is + and the blue is -, then a moment later the situation is reversed. When the load is connected the current will flow one way first, the other way next, and so on. This is called Alternating Current (AC).  This process is repeated in NZ 50 times per second, (the frequency is 50 Hz). In the US the frequency is 60 Hz. Most power equipment in the home or in industry runs on AC. To charge a battery however, and to run most electronic equipment, DC power is required. DC means that one terminal is always +, the other always -. It is possible to convert AC to DC by using a diode. (a set of 4 diodes is often referred to as a rectifier bridge). A diode is a device that allows current to flow one way, but not the other. If a diode is wired into an AC circuit current would flow for a short while, but then would stop for a moment, start again, etc. The result looks like this:  This is obviously not a good way to go, since half of the energy is unused. We also do not recommend using it because of DC magnetisation of the transformer core. If we use a rectifier bridge, the current that was otherwise unused is now put to good use:  A voltage like this is often referred to as “DC RAW”. It is suitable for most charging and some other applications. However often the “bumps” need to be flattened out, which can be achieved with further components. (see DC Power supply) Another way to obtain DC is by the use of an electronic circuit called a “Switchmode Power supply”, which tends to be much smaller than a transformer with rectifier, but is not suitable for all applications. Our specialists at TSL can help you to determine which is the correct device for your application. DC powersupply terminology: DC RAW: rectified, but not flattened DC Linear: fully flattened DC regulated: electronics ensure that the DC output voltage does not change when the load changes. ASNZS 61558 This is a NZ standard for the manufacture and testing of transformers. It specifies such things as the quality of the insulation, how it should be labelled, what tolerances are required, etc. It is a legal requirement that a transformer used, for instance, in an approved switchboard, is built to this standard. Autotransformer (or Auto-Wound transformer)  An Autotransformer only has one winding. The start of this winding is called “Common”, or “0”. There are one or more taps along the length of the winding, and it’s finish is also connected. In our drawing, if a voltage of 220volt is applied between 0 and 220v, a voltage of 440v can be obtained from the finish of the winding. Equally when 440v is applied to 0 and the finish of the winding, 220v *) can be obtained from the tap. By varying the size of the transformer core and the diameter of the wire of the coils, transformers can be made for very large currents. For small currents an Autotransformer is not practical. An “ordinary” isolating transformer provides a physical separation between primary and secondary windings, but an auto transformer offers no such protection. It is therefore essential when ordering an auto transformer to make sure that it is safe and legal to be used for the intended application. *) These values can vary slightly. See Transformer losses. Battery chargers See also AC-DC Essentially a DC powersupply, they range in complexity from a simple transformer with a rectifier, to a sophisticated electronic device that monitors the charge level of the battery and supplies current to it accordingly. A battery charger needs to be chosen carefully, since overcharging will damage the battery, while too low a capacity may not be enough to keep up with demand. A fully exhausted Lead- Acid battery can draw a very large current, which can easily damage the charger or the battery if it has not been designed to avoid this. Caravans and recreational vehicles imported from overseas TSL can supply transformers to convert 230vAC to 100, 110, 115 or 120 volt AC. However New Zealand has some specific mandatory requirements for the construction of electrical appliances and fittings that deviate (extend) from the relevant international Standards. Equipment designed to operate at 100, 110, 115 or 120 volts, 60 Hz in the North American, Japanese and other markets, is not likely to meet with these requirements and, unless it does so, its use is unsafe and its sale in NZ constitutes an offence. To be acceptable as a safe installation, any Recreational Vehicle or Caravan must be demonstrably able to meet all of the mandatory requirements of the Electricity Regulations, AS/NZS 3000 and AS/NZS 3001. All appliances that form part of that connectable installation, or are supplied with it, must comply with AS/NZS 3820 and the Declared Article and Supplier Declaration Regulations. Choke A choke is a single winding on a core. The core has a gap, interrupting the magnetic field. A choke is not intended to change the voltage, but is a device with other electrical properties, often used for instance for DC “smoothing” (See AC-DC). TSL designs and builds chokes for many purposes. Class 1, Class II IEC Protection Classes apply to all electrical appliances connected to the mains. Class I is an appliance that requires a separate earth pin in the mains plug. The earth pin must be connected in an appropriate manner to the chassis of the appliance. Class II is an appliance that does not need an earth pin in the mains plug, because there are no exposed metal parts on the appliance. 2 Layers of insulation are in place between the live conductors and any other metal components. This is also called “Double Insulated”. The appliance carries the Class II symbol:  Class 0 and Class III also exist, but are not relevant to our product line. Coil The coils on the transformer are wound from copper wire around plastic bobbins. If a transformer is called an “Isolating Transformer” it has both one or more primary windings, which are connected to the power source, and secondary windings, which are connected to the load. The ratio of the number of windings between primary and secondary coils is directly proportional to the ratio of the primary voltage and the secondary voltage. The number of windings on the primary side is dependent on the size of the core, the maximum allowable strength of the magnetic field, and the AC frequency. An alternative type of transformer is called “Auto transformer”. See description under auto transformer. The maximum current that the transformer is designed for determines the diameter of the wire used. The wire diameter for primary and secondary coils is usually different. For single phase TSL uses two types of designs: smaller transformers, up to around 250VA, usually have only one bobbin, with the secondary winding on top of or next to the primary winding. Over 250 VA we tend to use a double bobbin design. Here both coils still have a primary and secondary winding, but by choosing to connect the windings in parallel or series we can design the most efficient transformer for the task. We hold the NZ patent for the double bobbin “LL core” design.  The copper wires are coated with an insulating layer of enamel, which has to be removed from the end of a wire by scraping for proper electrical contact to be made. Further layers of special insulation separate the primary and secondary windings from each other. Some transformer designs have more than one secondary winding, so you can have what is in fact two (or 3, or 4, etc) transformers in one. It is also possible to have more than one input or output voltage by taking a “tap” from the winding.  Core (see also Transformer ) The Core of the transformer is the laminated iron part around which the transformer windings are placed. It functions as the “path” of the magnetic field through the coils that transports the energy from primary coil to secondary coil. The larger it is, the more power the transformer can handle. TSL uses many standardised core sizes, most of which we produce ourselves in our own engineering workshop. The laminated steel is specially produced for transformer production. The laminations are insulated from each other by allowing the steel to oxidise during manufacture. This is to reduce the amount of stray currents (called Eddie currents) which would otherwise reduce the efficiency of the transformer. DC-DC converter Although a transformer is only able to convert AC to AC, TSL can also supply electronic devices that do the same for DC voltages. They are available in a wide range of voltages and currents. Please contact our experts for advice. DC-AC inverter Useful for powering normal mains operated equipment, like laptops or faxes, from the car battery. It has also become a useful means for people who would like to generate their own power for the home via wind or solar power, and store their energy in batteries. Available in a range of input DC and output AC voltages and currents. Contact TSL for details. DC power supply (See also AC-DC) TSL can supply DC power supplies of several types. “DC RAW” implies a transformer to supply the AC, and a rectifier bridge to turn it into DC. The DC however is not very “flat” and the voltage can vary with the load applied. Adding a capacitor or choke to the circuit will “flatten” the DC, but it is still unregulated. This is called an “Unregulated Power Supply”. A regulated DC power supply has a circuit that controls the output voltage. As long as the load does not exceed the design value, the voltage will always be the same, + or - a few %. The output voltage can usually be set by means of a potentiometer, within certain limits. To produce higher DC currents often requires bulky and expensive components. In a “Switchmode” power supply the 50Hz frequency is first increased to usually about 100 kHz. This allows a very much smaller transformer to be used to go from 230 volt to, for instance, 12 volt. The 12volt can now be rectified, resulting in a very small power supply for the Amps. TSL can supply a number of Switchmode power supplies, often in the form of a plugpack, or in-line power supply. Switchmode are not very suitable for some applications, for instance for DC motors, or solenoid valves. DIN series transformers Our DIN series consists of a range of plastic encapsulated transformers with integrated DIN rail clip. Links can be placed to select 230 or 400 volt input, and output of 115 and 230 volt, or 12 and 24 volt. Terminals are integral to the housing. If an open transformer needs to be DIN rail mounted, TSL can at small cost modify one of the smaller EW, PX or TX ranges. EN series transformers The EN series from TSL is identical to the EW series, but have the added feature of an enclosure. They are smaller general purpose isolating transformers in the range of 30 to 300VA, in 230 or 400 volt primary, and 230, 115, 24 and 12v secondary. The EN series are enclosed in an ABS plastic, waterproof (to IP67) enclosure, and have a glass fuse fitted inside the case. Encapsulated transformer A transformer in a non-ventilated enclosure is usually encapsulated. This means that, after the transformer is fitted to the case, the case is filled with resin to just above the transformer, leaving the terminals exposed. Encapsulation is primarily done to conduct heat from the transformer to the environment, and for mechanical protection. Encapsulating does not make the transformer waterproof. In fact, an encapsulated transformer exposed to water will eventually fail! Enclosed Transformer This simply means the transformer is fitted inside some sort of case, which can be ventilated or not ventilated, and has an IP rating (see IP 40) EW series transformers The EW series are smaller general purpose isolating transformers in the range of 5 to 300VA, in 230 or 400 volt primary, and 230, 115, 24 and 12v secondary. They are open transformers (not enclosed) with flying input and output leads. High voltage transformers TSL designs and builds transformers to 15000 volt (15 kv). These transformers are built with special insulation and to special high voltage design specifications. Hz (Herz) The number of times the AC current changes polarity in one second. See AC-DC Inrush Current When a transformer is energised, the initial surge of current will be very much greater than would be expected (up to 25x) from the design parameters. This surge will last for only a fraction of a second, but can in some cases be enough to trip the fuse in the mains supply. IP40, IP65, IP67 See also Enclosed Transformer, Potted Transformer Our enclosures are mostly rated IP 40 (safe to touch, protected against solid objects over 1mm in size) IP 65 (totally protected against dust, and against sprayed water) or IP 67 (protected against temporary immersion). For complete details of IP rating see the relevant literature, or contact TSL ISA range The ISA range of stock transformers is a “ready to go” range, enclosed, and complete with input mains cable and plug, and output leads (12/24v) or sockets. ISA Transformers are available as isolating transformers for use of mains operated equipment in wet areas, with output of 230 or 115 volt. We also have in-line type and plugpack type 12vac and 24vac. ISD range The ISD range includes our stock range of DC plugpacks (12vDC and 24vDC). A more extensive range of regulated, unregulated, raw and linear dc powersupplies is available as a special on 2-3 days delivery. Isolating transformer A Transformer is normally wound with the primary and secondary windings completely isolated from each other, and from the iron core. There is no electrical contact possible. This is tested to 4000 volt as part of our standard testing procedure. Sometimes a transformer, which is specifically designed to be used as a safety measure for instance to run a mains operated power tool in a wet area, is referred to as an isolating transformer. (see our ISA range in the catalogue). However all transformers which have separate primary and secondary windings are officially designated as “Isolating Transformers”.  ISA 2301725 Isolating transformer kVA see VA Kilowat(kW) see Watt Leads (Colour) All transformer leads are coded according to a fixed protocol:
Exceptions are possible with multitap transformers, to enable us to identify the various taps or windings If a shield (see Shield) is built into the transformer this will have a Green/Yellow lead since it is always connected to Earth. Yellow leads are no longer legal. Marine Applications Transformers for Marine Applications are used to provide power to the vessel while at berth, as a temporary replacement of the on-board generator, or to provide power to equipment on board that requires a different input voltage from that supplied by the generator. For ships sailing internationally TSL can produce a range of single-phase and 3-phase transformers with multiple input voltages to suit the voltage supplied from shore. For private yachts a single-phase transformer is often required to power fridges, radios and lights while at berth. The transformer offers galvanic protection, and is often built with a shield to provide additional safety. Open transformer This is the term used for a transformer that is supplied without an enclosure, usually to be built in to an existing cabinet or enclosure. Overload Protection ASNZS 61558 specifies that transformers must be protected against overload and short circuit conditions during normal operation. A transformer can be supplied with or without overload protection. This is usually provided for in the form of a fuse or circuit breaker. Some TSL transformers have a self-resetting thermal trip built into the primary winding. If the design temperature is exceeded the trip will automatically interrupt the primary. It will reset itself after cooling down. The transformer label will always list either the recommended fuse value, or the value of a fuse already fitted. Either the primary or secondary side, or both can be protected. PN series transformers These are identical to the PX series (see below), but are enclosed. The enclosure is vented, and has an IP40 rating. Potted transformer (Resin Encapsulated) All “Special” transformers can be ordered fitted to a case and encapsulated in Resin. Only the terminals are exposed under the lid of the enclosure. The purpose for doing this is to offer maximum mechanical and dust protection to the transformer. The resin conducts the heat produced within the transformer to the outside. Resin encapsulation in itself does not make the transformer waterproof. Our Portable Isolating Transformers for 230 or 115 volts in the ISA range are Resin Encapsulated. See also IP67 PX series transformers TSL’s PX series (see catalogue) are open transformers built with two secondary windings. Both have the same voltage and VA rating. A connector block for secondary connection is provided on the transformer, with a label showing how, by inserting link wires, the transformer can be used for either the highest voltage (series connection), or the highest current (parallel connection). Re-useable link wires are inserted at the factory, usually set to the highest current. PX series are available with primaries of 230 and 400 volt, and secondaries of 12/24volt, or 115/230 volt. A large range of VA’s is available, making them also an excellent option if the required VA rating is not available in the EW range. Reversing a transformer see also Transformer losses. Because some losses are unavoidable in any transformer, the ratio of primary to secondary windings is calculated to provide a secondary voltage that is slightly higher than the nominal voltage. For instance a transformer designed for 230 volt primary to 12 volt secondary, would have a turns ratio to give it a slightly higher secondary voltage of about 14v, depending on the VA rating of the transformer. When the load is applied this will drop to 12 volt. If this transformer was connected with it’s secondary side to a 12 volt supply, the ratio’s will not be totally correct to deliver the 230 volt on the other side. Instead, the voltage will be lower. The variations vary with the size of the transformer. Safety Isolating Transformer This term is used for transformers with an output of less than 50v. The transformer label can indicate this class with the diagram below:  If the transformer is also Short Circuit Proof, (fitted with an overload/short circuit protective device that can not be removed, ie a thermal trip), the diagram looks like this:  Or, if the protective devise can be replaced (like a self resetting trip, fuse or circuit breaker):  If the transformer is designed for a secondary voltage of more than 50v, it cannot be called a “Safety Isolating Transformer” in this case the label will carry this diagram:  And if it is fitted with a fuse or thermal trip:  Short circuit Proof< See Overload Protection Single phase – 3-phase (see also 3-phase) Most power is distributed in the form of three-phase AC. Basically, the power company generators produce electricity by rotating (3) coils or windings through a magnetic field within the generator. These coils or windings are spaced 120 degrees apart. As they rotate through the magnetic field they generate power which is then sent out on 3 lines as 3-phase power. The end user usually receives this as 400 volt AC between each of the 3 lines. 3 phase transformers must have 3 coils or windings connected in the proper sequence in order to match the incoming power and therefore transform the power company voltage to the level of voltage we need, and maintain the proper phasing or polarity. If the 3- phase step down transformer is constructed with one side of each transformer winding connected to one side of each of the 2 others this is called a Star configuration. The common point is called the star point. We can obtain 230 volts AC in single phase between the starpoint (connected to earth to form the neutral) and one 400v leg of the transformer. 230 volts single phase is supplied to the domestic home in New Zealand, and is available from every wall socket.  Specials TSL carries a range of stock transformers. Any transformers outside the stock range can be manufactured in-house as a special. This includes outputs in both AC and DC, and special transformers for for instance marine applications. All 3-phase transformers are made as specials. Manufacturing times are normally several days, but if required we can often manufacture in 24 hours. Our expert design service will be happy to assist with out of the way enquires. We also have an extensive range of DC power supplies, Variacs, etc available as specials. Shield A single sheet of copper foil placed between the primary and secondary windings, and connected to earth is known as a (Faraday or Electrostatic) shield. It almost completely eliminates irregular voltages being transmitted through the transformer. A shield is fitted to our TX series as standard. Stock transformers TSL carry a range of stock transformers. Primaries are 400 or 230 volt, secondaries 230v, 115v, 24v and 12v. In addition the TX range offers 22, 24 and 26 volt output. See also EW, EN, PX, PN, TX, ISA, ISD, DIN range. Tap A tap is an output or input lead attached to one of the windings of a transformer partly along the winding. This way a transformer can be built with more than one input or output voltage. Our TX 100 for instance has a secondary of 26 volts, with taps at 22 and 24 volts.See also coil Termination Termination of the transformer windings is the way the primary and secondary windings connect to the supply and the load. The simplest form, as in our EW range, is flying leads. Smaller transformers can have a terminal strip, larger ones a DIN rail with screw-terminals or screw studs. When ordering a Special the termination needs to be specified. Thermal trip TSL can on request fit a thermal cutout device inside the windings of the transformer. The device will interrupt the primary winding if the internal temperature is too high. A resettable trip will reset itself once the winding has had a chance to cool down. See also Overload Protection. Testing All transformers produced by TSL are tested in accordance with ASNZS 61558. The primary is connected to a calibrated power supply, and the secondary no-load voltage is measured, together with the magnetising current (the current in the primary when no load is connected). These values are checked against the design parameters. A flash test is performed, whereby 4000 volts are placed across the insulation between primary and core, secondary and core, and primary and secondary. The resistance is measured and must exceed 50 Megohm. All transformers are tested twice: once directly after the initial assembly, and once when it is ready to be packed prior to warehousing or shipping. On request TSL can perform a load test, where secondary voltage and temperature rise are checked while the transformer is working under load. Transformer types See 3- phase - single phase and auto transformer Transformer losses A transformer uses a small amount of energy, referred to as a loss, when in operation. This loss is very minimal, well designed transformers will have losses of less than 5% TX series multiple output transformers The TX series are 230 volt input and have outputs of 24 volt (TX 10), 24 and 26 volts (TX 30) or 22, 24 and 26 volts (TX 50, 70, 100, 150, 250 and 500). They are fitted with a Faraday Shield and are intended for use with industrial controls, power electronics, etc. US and Japanese appliances TSL can supply transformers to convert 230vAC to 100v, 110v, 115v or 120v AC. However you should be aware that New Zealand has some specific mandatory requirements for the construction of installations that deviate from the relevant North American and Japanese Standards. Equipment designed to operate at 100, 110, 115 or 120 volts, 60 Hz in the North American, Japanese and other markets, is not likely to meet with these requirements and, unless it does so, its use is unsafe and its sale in NZ constitutes an offence. To be acceptable as a safe installation, any Recreational Vehicle or Caravan must be demonstrably able to meet all of the mandatory requirements of the Electricity Regulations, AS/NZS 3000 and AS/NZS 3001. All the appliances that form part of that connectable installation, or are supplied with it, must comply with AS/NZS 3820 and the Declared Article and Supplier Declaration Regulations. VA The power handling capacity of a transformer is referred to as “VA” or ”kVA”, since the formula for it is VA = U (Volts) x I (Amps). The physical size of the transformer is almost totally determined by the power that it is designed to handle. (see also Core) A transformer designed with a primary input of 400 volt, a secondary output of 24 volt and a secondary max current of 10A will have a capacity of 24 x 10 = 240 VA. Since the capacity is always the same for primary and secondary the primary current will be 240/400 = 0.6 Amps. If the transformer is used to carry a heavier load than for which it is designed, it will run at a higher internal temperature. This can cause failure of the insulation, or of the windings. A lighter load is never a problem, except that the transformer is bigger than it has to be. Variable Voltage Auto transformer The Watt (1000 Watt = 1 kW) is a unit of power. It is used for all sorts of power, including engines, heaters, etc. The relationship between the power (P) of an electrical device, the voltage (U) at the terminals and the current (I) flowing through it is: P= U x I x pf (power factor) The powerfactor depends on the type of load and can vary from 0.65 for reactive loads, to 1.0 for resistive loads. For highly reactive loads such as induction motors the Watt rating can be up to 35% less than the VA. Transformers for reactive loads must be based on the higher value. In resistive loads the (k)W and (k)VA are the same, since the power factor is 1. Paul van Beusekom Transformer Specialties Ltd | |||||||||||||||||||||||||||||||||||||||||||
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