ABB 15.04.2005 Instrument Transformer

ABB 15.04.2005 Instrument Transformer

Current transformer

Basic functions and principles

Function: Convert high current in power transmission and distribution systems into low current for use in low-voltage measurement and protection equipment. The secondary current is usually 1A or 5A, connected in series, and the secondary winding is mainly connected to an ammeter and protection relay.

Principle: Through electromagnetic induction, the secondary current is proportional to the primary current, and the conversion ratio K=I ₚᵣ/I ₛᵣ=N ₂/N ₁, where I ₚᵣ is the primary current, I ₛᵣ is the secondary current, N ₁ and N ₂ are the turns of the primary and secondary windings, respectively. The secondary current I ₛᵣ=I ₚᵣ × N ₁/N ₂. It can have one or more secondary windings, each with an independent magnetic circuit, used for different purposes such as metering or protection.

Key parameter

Rated primary current (I ₚₑ): The primary current value based on the performance of the transformer, which needs to be equal to or higher than the highest primary current of the system. The standard value is in accordance with IEC regulations, such as 10, 12.5, and their decimal multiples. It can also be produced in any proportion according to the protocol, usually with a 120% extended current range to avoid high temperature rise during installation.

Frequency: It can be set as 50Hz or 60Hz, or a combination of 50/60Hz, and 16 ⅔ Hz is also possible, depending on the network of each country.

Equipment maximum voltage (U ₘ): The insulation level should be set to be equal to or higher than the system maximum voltage U ₛᵧₛ (except for cable current transformers, whose insulation is provided by the application), with standardized values, such as 3.6kV corresponding to system voltage up to 3.3kV, etc.

Insulation level: Based on the U ₘ value, such as IEC insulation level 12/28/75kV, it represents the highest voltage, power frequency withstand voltage (effective value), and lightning impulse withstand voltage (peak value) of the equipment, respectively.

Accuracy level: divided into measurement class (0.2, 0.2S, 0.5, 0.5S, 1, 3) and protection class (5P, 10P, PX, TPX, TPY, TPZ), different levels are suitable for different purposes such as tariff measurement, laboratory measurement, protection, etc. The chart shows the current ratio error limit of commonly used measurement classes.

Secondary current and number of windings: The secondary current is 1A or 5A, and the number of windings depends on the size of the body. For example, the maximum 36kV TPU 7x.6x can have up to 8 iron cores.

System primary current (I ₛᵧₛ): The system current for installing transformers needs to be equal to I ₚᵣ, and different applications have different calculation methods. For example, the transformer feeder I ₛᵧₛ=S/(√ 3 × U ₛᵧₛ), the capacitor feeder I ₛᵧ=1.3 × Q/(√ 3 × U ₛᵧₛ), where S is the apparent power (kV). A), U ₛᵧₛ is the system voltage (kV), and Q is the reactive power of the capacitor (kVar).

Rated short-time thermal current (I ₜₕₙ): The maximum primary current that a transformer can withstand for a specified short period of time without causing harmful effects. The standard values are 2, 4kA, etc., and the duration standard is 1 second, or possibly 3 seconds. The rated dynamic current I dyn is 2.5 times I ₜₕ at 50Hz.

Extended current rating (EXT): The range of current increase that a current transformer can measure at an accuracy level, such as 120%.

Maximum continuous thermal current (I ₜₕ): The maximum continuous thermal current that the current transformer can still operate but is not at the accuracy level.

Accuracy Limiting Factor (ALF): Used for protection purposes, it defines the multiple of primary current that the error must meet. For example, 5P20 represents a composite error of ≤ 5%, and the error limit from 100% primary current to 20 times primary current must be met. ALF is related to the load, and unexpected increases in load can cause ALF to decrease. The actual load required for the secondary iron core, secondary circuit, and connecting equipment needs to be calculated. Different instrument loads vary, such as 0.5-4VA for ammeters, and cable losses need to be compensated.

Safety factor (FS): Used for measurement purposes, it protects all devices connected on the secondary side by setting iron core saturation to avoid secondary high current transmission during faults. For example, FS5 indicates an error of ≥ 10% under rated load at 5 times the rated primary current.

Environmental temperature and insulation level: Environmental temperature is divided into three categories according to IEC: -5/40 ° C, -25/40 ° C, and -40/40 ° C. The insulation level of ABB products corresponds to Class E, which means the maximum temperature rise of all active components is about 75K.

Other features

Capacitive voltage divider: integrated into the current transformer body, making voltage indication more convenient.

Reconnect: It can be achieved on the secondary or primary side. The left side features a dual core design with a secondary reconnection tap, while the right side has a primary reconnection that requires manual operation.

standard

Compliant with IEC 61869 standard, it can also be produced according to GOST, IEEE and other standards. Please consult the sales representative.

voltage transformer

Basic functions and principles

Function: Provide a secondary voltage proportional to the primary voltage for the secondary circuit, typically 100V, 110V, or 120V.

Principle: Through electromagnetic induction, the conversion ratio K=U ₚₑ/U ₛᵣ=N ₁/N ₂, where U ₚₑ is the primary voltage, U ₛᵣ is the secondary voltage, and N ₁ and N ₂ are the number of turns in the primary and secondary windings, respectively. The number of turns in the primary winding is greater than that in the secondary winding.

Key parameter

Rated primary voltage (U ₚₜ)

From the perspective of connection, it is divided into phase to phase voltage and phase to ground voltage, such as phase to phase voltage of 10000//100V, phase to ground voltage of 10000/√ 3///100/√ 3, 100/3V. The commonly used values specified by IEC include 3.3, 6.6kV, etc.

Rated secondary voltage: Any ratio can be produced, but the standard secondary voltage is preferred to be 100, 110, or 120V. When single-phase transformers are connected to ground, the rated secondary voltage for star connections needs to be divided by √ 3, and for open delta connections it needs to be divided by 3. Mixed ratio voltage transformers can also be produced.

Rated voltage factor: used to determine the maximum voltage that the transformer must meet the relevant thermal and accuracy requirements within a specified time. The ABB single pole voltage transformer is designed to be 1.9 × U ₚᵣ/8h, and the double pole is 1.2 × U/continuous. Different voltage factors can be discussed with the sales representative.

Number of windings and reconnection

Up to three secondary windings can be produced for measurement, protection, or ground fault indication, and can also be reconnected, such as a single pole insulated transformer with two secondary tap windings, one of which is the remaining winding.

Accuracy level: There are measurement categories of 0.2, 0.5, 1, and 3, and protection (a-n) and/or residual (da dn) categories of 3P and 6P. The measurement category is between 80% and 120% of the rated voltage at rated frequency, with voltage error not exceeding the IEC specified value. The protection category is within the range of 5% of the rated primary voltage to the rated voltage factor multiplied by the rated primary voltage (such as 190% when 1.9 times the rated primary voltage), with voltage ratio error not exceeding 3% (3P category) or 6% (6P category).

Fuse: In the supply of fuses for single pole voltage transformers, there are different specifications for the rated current, voltage, and whether the fuse has a firing pin.

Terminal markings

According to IEC standards, single pole primary winding A-N, secondary winding a-n (star), da dn (open triangle); Bipolar primary winding A-B, secondary winding a-b.

Thermal output: Under star connection and rated primary voltage U ₚᵣ, the maximum power that the transformer can achieve with a ratio error of ± 10%. Different voltage levels have different thermal output values, such as 12-17.5kV (TJC 4&TJC 5) and 400VA.

Other features

Parameters such as frequency, insulation level, ambient temperature, standard, cable loss, and load are the same as those of current transformers.

Example

Purchase order example: Current transformer TPU 40.13, 50//5/5 A, EXT 120%, 15/15 VA, 0.5FS5/5P10 grade, I ₜₕ=40kA/s, I dyn=100kA，12/28/75 kV，50Hz，IEC 61869 - 2， Environmental temperature 40 ° C, polarity P1-P2, with capacitive voltage divider.