The primary winding of the transformer is connected to the high voltage or. The different types of transformer are step up and step down transformer, power transformer, distribution transformer, instrument transformer comprising current and potential transformer, single phase and three phase transformer, auto transformer, etc. Basics, maintenance, and diagnostics vii contents continued page 4. The main difference between a potential transformer and a power transformer is that the load current of the potential transformer depends purely on the exciting current and its secondary impedance. Cts current transformers pts potential transformers. The secondary voltage is substantially proportional to the primary voltage and differs from it in phase by an angle that is approximately zero. Definition the potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. Jun 01, 2015 types of voltage or potential transformers. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. There are three primary types of potential transformers pt. Transformer types instrument transformers instrument transformers comprise a large category of current and potential transformers for various voltage, frequency and physical size ranges. Current transformer basics and the current transformer. According to the design, transformers can be classified into two. A bartype current transformer which has 1 turn on its primary and 160 turns on its secondary is to be used with a standard range of ammeters that have an internal resistance of 0.
Instrument transformers are of two types current transformer c. The types of transformers differ in the manner in which the primary and secondary coils are provided around the laminated steel core. Current transformers ct are a series connected type of instrument transformer. Potential transformer accuracy voltage disturbance. Secondary ratings of 5a, 1a, and 100ma are all common in splitcore current transformers. Introduction generally a transformer is an electrical device or machine which inductively transfers the electrical power operating at a particular current and voltage of one circuit to the other circuit which is operating at different current and voltage level.
Here we discuss different types of transformers are the step up and step down transformer, distribution transformer, potential transformer, power transformer, 1. Basics, maintenance, and diagnostics ix contents continued page 6. Current transformer, ct is used in the measurement of very large current. Voltage transformer or potential transformer voltage transformers vt, also called potential transformers pt, are a parallel connected type of instrument transformer, used for metering and protection in highvoltage circuits or phasor phase shift isolation. Aug 28, 2014 the main difference between a potential transformer and a power transformer is that the load current of the potential transformer depends purely on the exciting current and its secondary impedance. Above 33kv single phase outdoor potential transformers can be two types electromagnetic type and capacitive voltage transformer cvt. Potential transformer is also known as voltage transformer.
Circuit globe all about electrical and electronics. The former is provided with a stainless steel screwclamp band securing the two core halves. Figure 1 small transformer infeed protection scheme. By using a pt, voltage is reduced that can be safely handled by meter or relay circuits. Lets say, for instance, that you have a 100kv grid and want to know how much powerenergy you. Working of potential transformer the electrical portal. The secondary impedance of the potential transformer will be resistive in nature. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering. These are the most commonly used transformer types for all the applications. There are three basic styles used to transformer system voltages to control voltages. This section is complemented with photographs and describes the specific classes and uses for.
Voltage transformer or potential transformer theory. Actually they are protective type voltage transformer. Instrument transformer basic technical information and. There are several transformer types used in the electrical power system for different purposes, like in power generation, distribution and transmission and utilization of electrical power. Voltage and potential transformers selection guide. On the secondary side, all the measuring tools and instruments such as meters are connected to measure and analyse the voltage level. May 22, 2017 such specially constructed transformer with accurate turns ratio are called as instrument transformer. A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple circuits. Such specially constructed transformer with accurate turns ratio are called as instrument transformer. What are a potential transformer and a current transformer. Voltage and potential transformers that are designed for monitoring singlephase. Most of the transformers are manufactured such that their characteristics must match for special application requirements. Due to the covid19 outbreak, people in ohio have been ordered to shelter in place until april 6, 2020.
Matching transformers as used with traditional relays are therefore no longer applicable. They are small dimension ferrule type fuses and mount in standard clips. Instrument transformer theory and testing steve hudson, pe. Types of instrument transformer instrument transformer has two type 1 current transformer 2potential transformer 5 6. In coretype transformer, the windings are given to a considerable part of the core. Voltage transformers vt, also called potential transformers pt, are a. Jan 31, 2015 types of instrument transformer instrument transformer has two type 1 current transformer 2 potential transformer 5 6.
A varying current in any one coil of the transformer produces a varying magnetic flux in the transformers core, which induces a varying electromotive force across any other coils wound around the same core. Majorly these are classified into outdoor and indoor potential transformers. Potential transformers pt or voltage transformers vt can be defined as devices used to step down voltage from high voltage typically used in transmission and distribution to a low voltage typically between 50150v. Lvqb220 sf6 gas insulated type current transformer, outdoor used, is intended for power and current measurement and relay protection in power system. Potential transformers pts are necessary to a power system for metering and protective relaying to convert higher system voltages to lower control voltages that are more practical from an equipment, operation, and safety perspective. Most indoor current transformers are supplied with an enclosed secondary terminal block.
Cts current transformers pts potential transformers 5 potential transformers pts pts step down high voltages to the voltage needed by the meter usually 120v occasionally 67v. Voltage and potential transformers are used to measure voltage potential. It can be designed to step up or step down voltages and works on the magnetic induction principle. Potential transformer voltage transformer is used for protection and measurement. Equivalent current transformer circuit x 1 primary leakage reactance r 1 primary winding resistance x 2 secondary leakage reactance z 0 magnetizing impedance r 2 secondary winding resistance z b secondary load note. A transformer has no moving parts and is a completely. Instrument transformer in power system, the currents and voltages are very large therefore, their direct measurements are not possible. The primary windings of the potential transformer are directly connected to the power circuit whose voltage is to be measured. Instrument transformers comprise a large category of current and potential transformers for various voltage.
Current transformer is used to step down the current of power system to a lower level to make it feasible to be measured by small rating ammeter i. The potential transformers shall be electromagnetic, outdoor type, single phase, oil filled, self cooled, having shaded porcelain bushing insulator as per is. The electromagnetic potential transformer is a wirewound transformer. Voltage transformers is also called as potential transformers this is a parallel connected type of instrument transformer.
Construction features the layer wound and shielded high voltage winding is designed to withstand continuous operation at 1. Commercially available relays and meters used for protection and metering, are designed for low voltage. Potential transformers are used in high voltage voltmeters while current transformers are used in place of the ordinary ammeter. Potential transformer testing ptvt valence electrical. Types voy20 and voy20g outdoor voltage transformers.
Ferrule mounting for standard clips and interchangeability with other brands of fuses. Voltage transformers vt, also called potential transformers pt, are a parallel connected type of. Potential transformer or voltage transformer gets used in electrical power system for stepping down the system voltage to a safe value which can be fed to low ratings meters and relays. Types of electrical transformers and their applications. Types of transformer different types of transformer. These can be single or three phase voltage transformers available for different range of operating voltages that are used for outdoor relaying and metering applications. This is step up transformer because when we step up, the voltage increases and current decrease. A potential transformer or voltage transformer is a special kind of transformer used to measure voltages higher than you would want to measure directly.
Instrument transformers are high accuracy class electrical devices used to isolate or transform. Current transformers ct are a series connected type of instrument. Electromagnetic or wound type conventional potential transformer. A general overview of abbs current and voltage transformers.
Normally the leakage fluxes x 1 and x 2 can be neglected. It might appear that the extension of range could be conveniently done by the use of shunts for currents and multiplier for voltage measurement, as in dc. Types voy20 and voy20g outdoor voltage transformers are designed for solidstate relaying and electronic metering where the burden of the device is negligible. They are designed to present negligible load to the supply being measured and have an accurate voltage ratio and phase relat. Instrument transformers, dry and compoundfilled types geh230 t ary connections while primary current is flow ing, the secondary terminals must be shortcir cuited while the change is being made. Voltage transformer is necessary for directional, voltage, distance protection. To do so, the primary winding of the transformer is connected across the high voltage lines.
We have broken them up into several different groupings. The transformers are classified based on voltage levels, core medium used, winding arrangements, use and installation place, etc. Diagrammatic plan of connections for potential transformer testing. Relay 7ut612 provides numerical ratio and vector group adaptation. This is a common method used in portable current measuring instruments but permanent installations use more economical types of current transformer. The potential transformer is mainly classified into two types, i. Potential transformer testing ptvt i cowrote an article for the neta world magazine in 20042005 that covers several different manual techniques for potential transformer testing that explains several lowtech solutions for potential transformer testing. Mar 11, 2017 a potential transformer or voltage transformer is a special kind of transformer used to measure voltages higher than you would want to measure directly. Difference between a potential transformer and current transformer. Different types of transformers and their applications. A potential transformer is a conventional transformer having primary and secondary windings. Two types of voltage transformer are used for protectiverelaying purposes, as follows.
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