Electric transformers are static electrical machines that transform electric power from one circuit to the other without changing the frequency. An electrical transformer can increase or decrease the voltage with...
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This article will take an in-depth look at isolation transformers.
The article will look at topics such as:
This chapter will discuss the functioning, design, and customization of isolation transformers and considerations to make when choosing an isolation transformer.
An isolation transformer, just like typical transformers, is a non-moving device that transmits electrical energy from one circuit to another without requiring any physical contact. It works on the idea of magnetic induction, which uses a magnetic field to induce EMF in another circuit without affecting the frequency. Transformers are used in transmission and distribution networks to step up and down voltage levels. An isolation transformer is a type of transformer that provides electrical isolation between two circuits (primary and secondary) without modifying the secondary properties (voltage, current, and frequency levels).
The primary coil circuit and secondary coil circuit of the isolation transformer are electrically isolated. As a result, isolation transformers refer to all transformers used in transmission and distribution networks. An isolation transformer is a device that transfers electrical power from an alternating current source to some equipment or device. This happens while isolating the powered device from the power source, primarily for safety or to reduce transients and harmonics.
In general, secondary turns are bigger than primary turns in step-up transformers and vice versa in step-down transformers. On the other hand, the voltage and current levels are equal on the main and secondary sides of an isolation transformer. The number of turns on primary and secondary is the same. As a result, N1 = N2, V1 = V2, and I2 = I1 for an isolation transformer.
In terms of voltage, current, and turns ratio, an isolation transformer is also known as a 1:1 ratio transformer. AC systems using single-phase electricity experience simultaneous voltage fluctuations. Although single-phase AC is easy to install and operate, it is insufficient to power large motors and other industrial machinery. Three distinct signals, each with a separate peak time, are used in three-phase power. The oscillations present in a single-phase system are eliminated by using three distinct signals. Three-phase electricity results in less vibration and easier equipment design when utilized to power large motors.
An isolation transformer provides the physical and electrical separation between two circuits. It isolates and protects electronic circuits and people from mainline electrical shock. Magnetic coupling is used to transfer electrical energy from primary to secondary. Isolation transformers are only used with transformers with a ratio of 1:1.
An isolation transformer's main purpose is to reduce voltage spikes in the supply lines. Illumination, static electricity, or a quick voltage change can cause voltage spikes, transients, and surges in electrical power supply lines. A voltage spike is a rapid increase in voltage levels that lasts for a short time (3 nanoseconds or more).
The voltage spikes carry high voltages ranging from a few to several thousand volts. If such high voltage spikes reach the load, they might cause service interruptions or damage equipment. The voltage spikes can be reduced before they reach the load by connecting an isolation transformer between the power supply lines.
Assume a spike of high voltage and current with fast change occurs on the isolation transformer's primary side (i.e., on the supply side). When a voltage spike passes through the primary winding, it is called a voltage spike. While the inductor resists a sudden shift in current, the inductive primary winding allows for an exponential shift in current rather than an instantaneous change.
The flux rises as the current rises, causing the voltage to rise in the secondary. The spike is prevented from reproducing in the secondary due to the inductive nature of the primary and secondary. In addition, the resistance to the current is proportional to how fast it changes. Because a voltage spike involves rapidly changing voltage and current, the resistance generated will be larger. As a result, the secondary or load circuit spike is considerably decreased, avoiding negative impacts on load equipment.
Another essential feature of an isolation transformer is that it prevents load equipment or the secondary side from being grounded. As a result, an isolation transformer eliminates ground loop interference and noise effects on the load. An isolation transformer protects sensitive equipment in measurements, laboratories, medical equipment, and other applications from voltage spikes, ground loops, and other power line distortions.
An isolation transformer is built similarly to a standard core-type transformer. Electrostatic shields entirely isolate the secondary from the primary, suppressing noise. Due to the electrical connection between the two windings, an autotransformer with a common primary and secondary winding cannot be utilized as an isolation transformer.
An isolation transformer may be toroidal, or donut-shaped, in configuration. Toroid transformers provide several benefits, including their small size and light weight, which enable them to be used in various applications. A toroidal transformer's windings are spread uniformly across the whole thing since they pass through the center of the core. Silicon iron or a nickel-iron alloy can be used to make the core.
For higher frequency applications, amorphous alloys and iron powder are better alternatives for the core material. Additionally, toroidal transformers can reduce audible noise and stray field radiation. Toroidal isolation transformers can be fitted with a metal band to further limit stray magnetic fields. An isolation transformer may have extra insulation for equipment like patient monitoring systems that don't allow much room for interference.
The different types of isolation transformers include:
The ultra isolation transformer has a unique structure that eliminates all sorts of electrical noise, primarily common mode noise. Since it neutrally divides the ground on the secondary side and isolates the primary and secondary, it can be utilized to construct a separately derived source to counteract current loops. Transverse mode noise is reduced, and common mode noise is attenuated using high isolating materials and specialized shielding techniques.
Ultra isolation transformers are especially made for sensitive, important equipment like computers and peripherals, medical equipment, digital communication telemetry systems, CNC machines, and others. They prevent disruptions caused by noisy equipment loads injected into the power line. A high voltage between the windings, often in the 1000-volt to 4000-volt range, is tested, specified, and labeled for ultra isolation transformers, which are manufactured with specific insulation between the primary and secondary.
In particular, wireless stations and advanced medical equipment use this transformer. Low coupling capacitance is a feature. An ultra isolation transformer is a more sophisticated transformer supported by a good shielding technique and has a high noise attenuation level suitable for use as a power transformer. It is very efficient and has a long lifespan in various operating voltages.
A ferroresonant technology known as a constant voltage transformer (CVT) is a 1:1 transformer that is excitingly high on its saturation curves, delivering an output voltage that is not appreciably impacted by changes in input voltage. The constant voltage transformer, or CVT, converts a fluctuating input into a nearly constant average output using a tank circuit made up of a high-voltage resonant winding and a capacitor. Typically, the input winding operates at relatively low flux linkage values.
The output winding has built-in energy storage that works with the main capacitor to create a self-generated AC flux field that is subtly removed from the input winding. Due to the absence of relays, which might cause output voltage interruption for a brief period, CVT is chosen over conventional stabilizers. With a controlled output voltage, CVT completely protects against spikes.
Galvanic isolation in electrical equipment refers to the physical and electrical separation of the input power circuit from the output power circuit. An isolation transformer is used to achieve electrical isolation. The output power wiring is physically isolated from the input wiring if it does not touch or connect to it. Galvanic isolation between the input power and the computer logic is already present in every personal computer. International safety organizations have mandated this to reduce the risk of shock. Therefore, adding a second transformer is unnecessary.
Galvanic isolation is commonly thought to correct noise on ground (earth) wire. In actuality, all galvanic isolation transformers isolate only the power wires while allowing the ground wire to pass through unhindered. Some UPS systems offer galvanic isolation. Despite the widespread notion that they do, most online UPS systems do not offer galvanic isolation. For instance, the online versions Exide, Unison, and ON-LINE (Pheonixtec) do not offer galvanic isolation.
As a result, isolation is a feature that can be added to any UPS and is not dependent on the type of UPS. The actual advantage of installing an isolation transformer is the significant reduction in common mode noise fed to the computer. Noise filters, like those found in the APC Smart-UPS series, can also be used to lessen common mode noise. The filters can perform just as effectively as the isolation transformer, particularly at high frequencies where computers and networks operate. At very low (audio) frequencies, the isolation transformer performs well.
Audio frequency noise on the power line has no impact on computers or computer peripherals. Therefore, the isolation transformer has no advantage over filters in computer applications. The isolation transformer's drawback is the added heat, which reduces UPS battery life if the batteries are nearby. Another drawback is that using an isolation transformer significantly increases the weight of the UPS.
Drive isolation transformers provide power for both AC and DC variable frequency drives. These transformers provide a voltage shift to meet the necessary voltage for the SCR (Silicon Control Rectifier) Drive while magnetically isolating the incoming line from the motor drive. SCR-type drives call for robust mechanical and electrical design and testing due to the mechanical stresses, voltage distortions, and harmonics they produce. There are many different types of motor drives, but they all have one thing in common: the incoming power must be rectified to create a DC level.
The motor drive converts the power from AC-DC-AC to AC-DC using a three-phase rectifying bridge and an SCR. Electrical noise, or harmonics, is produced during the conversion from AC to DC. Harmonic currents (high-frequency currents) are especially dangerous for a transformer used as an isolation drive element because they create significant heating and mechanical stress at higher frequencies. Drive isolation transformers are especially made to handle the heating, voltage aberrations, and mechanical pressures brought on by motor drives. Motor bearing currents, line-to-ground voltage transients, and other system noise issues can be brought on by common-mode voltages.
Grounding the secondary side will stop the transfer of common-mode noise and greatly increase the system's reliability and safety. Delta-wye-linked drive isolation transformers can establish a ground reference on the secondary side. The current on the line is wave-distorted by the motor drive system; these high-frequency currents return from the drive to the transformer winding. These currents can significantly increase the eddy-current losses in the windings; when a new transformer is selected, the additional watts must be considered when calculating the temperature rise. For handling the high-frequency currents from the drive, Eaton's drive isolation transformers are built particularly. Drive isolation transformers have ThermoGuard protection built into coils to signal the presence of high temperatures since the winding's high temperatures can shorten the transformer's lifespan or cause a catastrophic failure. A set of “N.O.” dry contacts make up ThermoGuards.
This chapter will discuss the causes and effects of electrical noises in isolation transformers. It will also discuss the maintenance involved in isolation transformers.
The causes and effects of electrical noises in isolation transformers include:
A power transformer is the most expensive and crucial piece of equipment in an electrical substation. To maintain the transformer's high performance and long functional life, it is desirable to carry out various preventative maintenance tasks. Measurements and tests of the transformer's numerous properties are among the routine maintenance procedures needed for a power transformer.
Transformer maintenance can be divided into two categories. Perform the first group as part of preventative maintenance regularly and the second group when needed (i.e., as required). Other types of transformer maintenance, also referred to as emergency or breakdown transformer maintenance, are only carried out when necessary. However, properly doing routine maintenance greatly minimizes the likelihood of needing to carry out such emergency maintenance.
The term "condition maintenance" refers to the routine inspection and upkeep of transformers. So one can avoid emergency and breakdown maintenance by performing proper condition maintenance. Due to this, technical staff members should focus primarily on condition maintenance. Since all necessary maintenance is performed, there is no equipment breakdown.
Daily maintenance checks for the cleanliness of the transformer, the winding temperature, the oil temperature, and the transformer’s load hours. This ensures that the readings from the main tank and the conservator tank's MOG (Magnetic Oil Gauge) are monitored. The silica’s color in the breather can also be monitored. If the MOG's oil level is inadequate, the transformer must be filled with oil, and the tank housing the transformer must be examined for oil leaks. If an oil leak is discovered, take the necessary steps to stop it.
Every month, it is necessary to check the oil level in the oil cap beneath the silica gel breather. Transformer oil must be topped off if it is discovered that the level inside the cup has fallen below the required level. For appropriate breathing action, silica gel breather breathing holes should also be examined weekly and cleaned as needed. If the transformer has oil-filled bushings, it is necessary to manually check the oil level in each bushing using the oil gauge that is connected to them. This procedure must be followed on a monthly basis. If necessary, fill the bushing with oil to the proper level. Under a shutdown circumstance, oil filling will be performed.
The automatic, remote, and manual operation of the cooling system, which includes the oil pumps and air fans as well as their control circuit, must be examined annually. If there is a problem, look into the physical health of the pumps and fans as well as the control circuit. Every year, soft cotton cloths should be used to clean the transformer's bushings. The bushing should be examined for cracks while being cleaned.
On a yearly basis, the OLTC's oil condition should be checked. For that, an oil sample must be collected from the diverter tank's drain valve, and it must then undergo tests for dielectric strength (BDV) and moisture content (PPM). The oil inside the OLTC needs to be replaced or filtered if BDV is low and PPM for moisture is discovered to be higher than recommended levels.
Furthermore, all marshaling boxes must have their interiors thoroughly cleaned at least once a year. All lighting and space heaters must be checked yearly, including all of the terminal connections for the control and relay wire, which should be checked and tightened.
The relays, alarms, and control switches in the relay and control panel and remote tap changer control panel should all be cleaned with the proper cleaning agent. Each year, the proper operation of the Buchholz relay and pressure release device must be verified. To check whether the corresponding relays in the remote panel are functioning properly, trip contacts and alarm contacts of the aforementioned devices are briefly connected by a short piece of wire.
Transformer insulation resistance and polarization index must be tested using a battery-operated megger with a 5 KV range. Annual clamp-on earth resistance meter measurements of the earth connection are required. Dissolved Gas Analysis, or DGA, of transformer oil should be carried out every year for 132 KV transformers, once every two years for those below 132 KV, and twice every two years for those over 132 KV transformers.
This chapter will discuss the applications and benefits of isolation transformers. These include:
Different types of electrical gadgets are well-protected from power problems by isolation transformers. Voltage swings and abrupt shocks can harm crucial equipment parts, interfering with the equipment's typical operation. In order to avoid such threats, isolation transformers disconnect the equipment from the power source, extending its safety and quality of life.
Because medical facilities like hospitals use electronic equipment for diagnoses, treatments, and other purposes, medical staff, nurses, and patients are particularly vulnerable to sudden equipment damage. Using isolation transformers avoids such unwelcome problems caused by faulty equipment. They spare not only expensive appliances but also human lives.
Power-based appliances are severely damaged by power surges. Even while these voltage spikes only last a short time, the equipment can be seriously harmed. However, isolation transformers prevent such a catastrophe from happening. They prevent surges by galvanic isolation, which safeguards the machinery. There is typically no possibility of equipment damage from surges since isolation transformers isolate the DC power channels.
There are frequently noticeable noise disruptions when the signals from audio amplifiers reach the speakers' output circuit. Such audio issues are resolved with isolation transformers. As a result, they enable noise reduction and enhance the functionality of such electrical devices. Faraday shields, a specialized design element, are used in these transformers. These shields stop the electric field if there are any disruptions in the power flow. As a result, the equipment's electromagnetic noise will be minimized. Many industries can benefit from isolation transformers. In particular, dependable isolation transformers are essential for the efficient operation of telecommunication, CNC, remote controls, and other equipment.
Electronic motors are used in a variety of industrial machinery types, and they cause harmonic voltage distortions. The equipment breaks down as a result of these harmonic changes. The best options for harmonics correction are isolation transformers. As a result, they are great protectors of industrial electric and electronic machinery.
The ability to prevent earthing failures is a solid advantage of isolation transformers. There won't be a conductive connection between the ground and the secondary end of the transformer if these transformers are used. As previously stated, these transformers' Faraday shields increase efficiency.
Isolation transformers lessen the possibility of current leakage, raising the standard of the power delivered to the machinery. As a result, isolation transformers indirectly improve equipment durability.
An isolation transformer, just like typical transformers, is a non-moving device that transmits electrical energy from one circuit to another without requiring any physical contact. It works on the idea of magnetic induction, which uses a magnetic field to induce emf in another circuit without affecting the frequency. Transformers are used in transmission and distribution networks to step up and down voltage levels. An isolation transformer is a type of transformer that provides electrical isolation between two circuits (primary and secondary) without modifying the secondary properties (voltage, current, and frequency levels).
Therefore, it’s important to be mindful of the type, characteristics, applications, and advantages of an isolation transformer before selecting one.
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