Ever wondered how electricians manage to install or fix electrical systems with high-voltage electricity? Besides following strict safety protocol, they carry specialized instruments that help them perform repairs and measurements safely. Among these instruments is the current transformer, which is designed to produce a current in a secondary winding that is proportional to, but with a much lower magnitude than, the current in the first winding.
Current transformers can be classified as bar-primary, wound, and ring-type. A bar-primary transformer consists of a toroidal core made with laminated strip wound steel, a feeder or bus-bar that forms one turn of the primary circuit, and an insulated wire that provides inter-turn insulation and secondary to core insulation The bus-bar serves as the primary conductor, providing connectors for the two ends of the circuit.
A wound CT, on the other hand, consists of both primary and secondary winding like a typical transformer, with the secondary winding having a smaller-magnitude current that is proportional to that of the primary. This transformer is used to measure currents from 1 amp to 100 amps and is insulated up to 600 volts.
Ring-type CTs, the most widely used and preferred by professionals, consist of a quadrilateral or circular core. The solid core CT is normally clamped around an electrical source, such as a live wire, while the split-core CT can be installed and attached to the source whenever necessary due to its opening. Among the three, split-core CTs are considered the safest and most convenient to use.
The Rogowski coil is a step up from current transformer technology. Its lightness, flexibility, and reduced number of parts make it one of the best in use today. Although it was named after German physicist Walter Rogowski, he didn't actually invent the coil. In fact, nobody really knows who pioneered it.
Why name something after someone who didn't come up with the idea? Rogowski is known throughout the scientific community for merging theoretical physics with electrical engineering, having worked all his life with fellow scientists to create inventions that typified this union. In a way, the Rogowski coil is putting Ampere's law into practice.
Under Ampere's law, the electromagnetic energy generated by a primary conductor around it can be considered the same as the current flowing along the conductor itself. This allows the apparatus to take precise current measurements without actually touching the wire. You could say Ampere himself lent a hand in making this system possible.
This current transformer type utilizes the actual cable of the main circuit as its primary winding, which is equal to a single turn. One major benefit of Bar-type CTs is that they are fully insulated from the high operating voltage of a system. They are typically bolted to the current-carrier.
Wound CTs
Wound CTs have primary winding that is physically connected with the conductor that delivers the measured current flowing in the circuit. The secondary current’s magnitude relies heavily upon the turns ration of the device.
Toroidal CTs
Unlike the aforementioned CT types, Toroidal CTs do not contain primary winding. What they have instead is a line that threads through a window or hole in the device; this line carries the current flowing in the network. Some toroidal CTs come with a split core, allowing them to be installed, closed, and opened without the need disconnect the circuit to which they are attached.
In film, flickering lights are usually associated with the supernatural. The truth is, this is a natural occurrence caused by low quality power. Yes, power or electricity also has quality just like any other product or utility you’re paying for regularly, and this quality varies depending on the connection and distribution.
When the waveform appears to be a simple, clean sine wave, the power produced and distributed by a particular electrical source is considered quality. On the other hand, when the waveform is distorted, meaning non-sinusoidal currents flow through the system, the power is of low quality. The main reason for low-quality power is the interruptions or impedance in the current flow due to nonlinear electrical system.
A technician can tell whether the power across an electrical system is of high quality by comparing voltage or current readings from a standard voltmeter or ammeter and a sophisticated one. The discrepancy (or existence of harmonics) indicates the quality of power.
In measuring the current flowing through a transmission line to determine the quality of power, a current transformer is necessary. This instrument protects the ammeter and the person doing the measurement from huge amounts of electricity.
Wherever you go, you’ll see business establishments reliant upon electricity for their daily operations. If you own a business, electricity no doubt takes up a huge chunk of your operating costs. Fortunately, there are ways to prevent costly misuse of electricity and accidents.
You are probably aware just how important power meters are, as they tell you how much current is consumed in the course of your daily operations. In effect, these devices let you know when your company must conserve energy to reduce your expenses. Without a set of functional current transformers to step-down or reduce high currents, these measuring instruments will fail and sustain damage.
When it comes to protecting equipment like air conditioning systems, therefore, current transformers can be a big help. For instance, they enable you to measure how much current is flowing through your electrical system and, by doing so, signal your fault circuit interruptor to break before high current enters your AC.
Indeed, current transformers can save you from wasteful energy consumption as well as fire hazards. That being said, it would be wise to purchase high-quality current transformers to maximize the economic benefits they offer.
Wound current transformers have their core directly connected to the current it is measuring. The magnitude of the secondary power produced depends on the tranformer’s turns ratio.
Window current transformers are the most common type, and have a hole through their core through which the conductor is passed through. In other words, window CTs are installed around the primary conducting cable. Nowadays, many window CTs have split cores, which enable their connection without disrupting the flow of current from the primary conductor.
Bar transformers work similarly to window type transformers; the main difference is that there is a central bar through the core through which current passes through. Cables are attached to both ends to carry the current.
Flexible current transformers make use of Rogowski coils, which are helical coils wrapped around a conductor to measure the current. Its non-magnetic core material makes it highly accurate and ideal for use in fast-changing currents.
Selecting current transformers will depend on your needs and purposes, as well as your budget.
Simpler versions of the transformer are made up of two coils of insulated wire: the primary and the secondary. The transformer uses its inherent mechanism to change electricity from high to low voltage (and vice versa) along with two properties of electricity itself, which are further explained below.
The first property is magnetism, which every electric circuit has. The second one involves a change in magnetic fields, which points out that when a magnetic field changes by virtue of moving or changing strength, a specific voltage is made. As these magnetic fields vary, so does the voltage inside the transformer.
The coils inside then do the work. There are two main coils, the primary and the secondary. The primary coil is connected to a power source, and the secondary is connected to another circuit. These coils rely on the number of their turns– for instance, if there is one turn in the primary and then ten turns in the secondary coil, the voltage in the secondary coil will be ten times greater than the other one. All transformers utilize the same principles in powering homes, commercial establishments, and even some toys today.
Rope CTs have several distinct advantages over their rigid counterparts. However, they also suffer from certain disadvantages, which must be taken into consideration when deciding whether to incorporate them into an electrical monitoring circuit or not. Take note of the following:
As with split core CTs, rope CTs may not be as accurate as their solid core counterparts. When high accuracy is important to the design, a solid core CT may be more appropriate.
Rope CTs are typically designed to monitor feeder lines with potentials of 600 volts or less. Higher voltage lines will require another (usually solid core) solution. Efforts are being taken, however, to design rope CTs suitable for high voltage use.
In order to obtain the current waveform, rope CTs need to be connected to an integrator. The integrator needs to be powered from an AC or DC source and this should be taken into account in the design.
Integrators of rope CTs can be lossy. This compromises noise immunity and can skew current measurements to a certain degree.
A glance at these disadvantages quickly reveals that there are surprisingly few major downsides to the use of rope CTs. If the additional energy to power the required integrator can easily be supplied, rope CTs are a practical alternative to other CT types in most situations.
