Transformer Instruments are high-accuracy class electrical devices used to isolate or change voltage or current levels. The most common instrument transformer use is to operate the instrument or the meterization of a high voltage or high current circuit, securely isolating the secondary control circuit from high voltage or current. The main winding of the transformer is connected to a high voltage or high current circuit, and a meter or relay connected to a secondary circuit.
The instrument transformer can also be used as an isolation transformer so that the secondary quantity can be used in phase shift without affecting other main connected devices.
Video Instrument transformer
Transformer now
The current transformer (CT) is a type of series connected instrument transformer. They are designed to present a negligible load on the measured inventory and have an accurate phase-to-phase and phase relationship to allow accurate secondary metering connections.
Current transformers are often made by passing a single primary loop (either isolated cable or uninsulated bus bus) through an isolated toroidal core wrapped with multiple winding wires. This provides an easy implementation of high-voltage bus transformer networks and other devices by installing a secondary rotary core inside a high-voltage bushing insulator and using pass-through conductors as a single main rotation.
The flow clamp uses a current transformer with a separate core which can easily coil the conductor in the circuit. This is a common method used in portable current measuring devices but a permanent installation using a more economical type of current transformer. Special constructed wideband CTs are also used, usually with an oscilloscope, to measure high-frequency waveforms or pulsed currents in a pulsed power system. One type provides an output IR voltage that is proportional to the measured current; another, called the Rogowski coil, requires an external integrator to provide a proportional output.
Ratio
CT is usually described by the ratio of the current from primary to secondary. A 1000: 5 CT will give an output current of 5 amperes when 1000 amperes flow through the primary winding. The current standard secondary rating is 5 amperes or 1 ampere, compatible with standard gauges. This is used to reduce the flow for measuring purposes for equipment and operator safety.
Load and accuracy
Loads and accuracy are usually expressed as joint parameters because they depend on each other.
- Metering style CTs are designed with smaller cores and VA capacities. This causes the CT meter to saturate at a lower secondary voltage saving a sensitive connecting metering device from damaging major fault currents in case of major power failure. CT with a rating of 0.3B0.6 will show up to 0.6 ohms secondary secondary current load will be within 0.3 percent errorogram in the accuracy diagram that combines both phase angles and error ratios.
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- Conveying the CT used for the protective circuitry is designed with larger cores and higher VA capacities to ensure secondary measurement devices have the correct representation with large grid fault currents on the primary circuit. A CT rated of 2.5L400 will indicate it can generate a secondary voltage of up to 400 volts with a secondary current of 100 amperes (20 times the 5 ampere rating) and still within the correct 2.5 amperes of accuracy.
It should be noted that the secondary winding of the CT is unbroken from its low impedance load while the current flows in the primer, as this may produce dangerous high voltage in the open secondary (especially in relay type CT) and may permanently affect the transformer's accuracy.
multi-ratio CT
Secondary windings can be either a single ratio or have multiple tap points to provide various ratios.
Maps Instrument transformer
Voltage transformer or potential transformer
The transformer voltage (VT), also called the potential transformer (PT), is a type of parallel-connected instrument transformer. They are designed to present a negligible load on the measured inventory and have an accurate phase-to-phase and phase link to allow accurate secondary metering connections.
Ratio
PT is usually explained by its voltage ratio from primary to secondary. A 600: 120 PT will provide a 120 volt output voltage when 600 volts impressed on the primary winding. The standard secondary voltage rating is 120 volts and 70 volts, which is compatible with standard gauges.
Load and accuracy
Loads and accuracy are usually expressed as joint parameters because they depend on each other.
- PTs style metering is designed with smaller cores and VA capacities than power transformers. This causes the measurement of PTs to saturate at lower secondary voltage outputs that store sensitive connecting metering devices from the damage of large voltage spikes found in grid disturbances. Small PT (see name plate in photo) with 0.3W rating, 0.6X will show with load up to W (12.5 watt) Secondary current secondary load will be in parallel error 0.3 percent on accuracy diagram combining both phase of fault angle and ratio. The same technique applies to the load X (25 watts) except in the 0.6% accuracy of the parallelogram.
Alerts
Some main cables of the main transformer (usually high voltage) have many types. can be labeled as H 1 (sometimes H 0 if designed internally for ground) and X 1 , X 2 and sometimes tap X 3 may exist. Sometimes the second isolated winding (Y 1 , Y 2 , Y 3 ) (and third (Z 1 , Z 2 , Z 3 ) may also be available on the same voltage transformer.The main phase can be connected to ground or phase to phase The secondary part is usually earthed at one terminal to avoid capacitive induction from destructive low-voltage equipment and to human safety.
Type PTs
There are three main types of potential transformers (PT): electromagnetic, capacitor, and optical. The electromagnetic potential transformer is a wire-wound transformer. Voltage voltage transformer (CVT) uses a potential divider capacitance and is used at higher voltages due to lower cost than electromagnetic PT. Optical voltage transformers exploit the Faraday effect, rotating polarized light, in optical materials.
src: en.el-insta.cz
References
Source of the article : Wikipedia
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