Transformer Laboratorium Penelitian Konversi Energi Elektrik Institut Teknologi

Transformer Laboratorium Penelitian Konversi Energi Elektrik Institut Teknologi Bandung

Transformer A transformer is a device that convert ac electric energy at one voltage level at another voltage level.

1. Transformer are important to modern life • Thomas A. Edison (1882) Power Distribution System : New York-USA ; 120 Vdc Problems : Losses & Voltage Drop = inefficient Example :

High Voltage

Transformer are important to modern power system Low voltage High Voltage

Real Application on Power System 380 V/20 k. V/380 V

Transformer 1. Power Frequency , 50/60 Hz 2. Radio frequency, > 30 k. Hz 1. Power Transformer 2. Instrument Transformer

2. Type and Construction Of Transformer

3. The Ideal Transformer Turn ratio a

The Ideal Transformer Turn ratio a

The Ideal Transformer In term of phasor quantities

Power in ideal Transformer Power input ideal Turn ratio equation Power input

Power in ideal Transformer Active power reactive power Apparent power

Evaluasi • Untuk memahami konsep trafo ideal berikan ke mahasiswa, contoh sederhana misalnya : – Cara mendapatkan tegangan sekunder y volt jika tegangan primernya x volt. – Arus sekunder b ampere pada tegangan y volt, cari arus primer a ampere pada tegangan X volt. – Ambil nilai x dan y yang bedanya sangat besar – Soal pada sistem 1 fasa dulu saja.

Impedance Transformer Impedance = ratio of the phasor voltage across it ti the phasor current

Impedance Transformer if

Theory of operation of real singlephase transformers The basis transformer operation can be derived from Faraday’s law Flux linkage

EMF equation of a transformer Faraday law of electromagnetic induction RMS Value

Transformer Losses • Copper (I 2 R) losses • Eddy current losses • Hysteresis losses • Leakage flux

The equivalent circuit of a transformer the model of a real transformer

The equivalent circuit of a transformer

Phasor diagram corresponding – referred to primary

The equivalent circuit of a transformer

Test on transformers • Open-Circuit Test • Result : VOC IOC POC

Open-Circuit Test Result Conductance of the core-loss resistor Susceptance of the magnetizing inductor Admittance Magnitude admittance

Open-Circuit Test Result Power Factor angle Admittance

Test on transformers Short-Circuit Test Result : VSC , ISC , POC

Short-Circuit Test Result Series impedance Power Factor of the current Lagging - Current angle (-), Impedance angle (+) Therefore,

Short-Circuit Test Result Series impedance Admittance

2. 2 The equivalent circuit impedances of a 20 k. VA, 8000 / 240 V, 60 Hz transformer are to be determined. The open circuit test were performed on the primary side of the transformer, and the following data were taken : Open-circuit test (on primary) VOC = 8000 V Shots-circuit test (on primary) VOC = 489 V IOC = 0, 214 A IOC = 2, 5 A POC = 400 W POC = 240 W

The per-unit system of measurement In single-phase system :

Voltage Regulation & Efficiency Voltage Regulation Efficiency

Autotransformer Step-down autotransformer

Power rating -autotransformer SIO =Input and Output apparent powers SW = apparent power in the transformer windings For example, a 5000 k. VA autotransformer connecting a 110 k. V system to a 138 k. V system would have an NC/NSE turn of ratio of 110 : 28. Such an autotransformer would actually have windings rated at :

Three-phase transformer A three-phase transformer bank composed of independent transformer A three-phase transformer wound on a single three-legged core

Three-phase transformer connections • • Wye-wye (Yy) Wye-delta (Yd) Delta-wye (Dy) Delta-delta (Dd)

Wye-wye (Yy) Connection

Wye-delta (Yd) Connection

Delta-wye (Dy) Connection

Delta-delta (Dd) Connection

A 50 k. VA 13. 800 / 208 V, Dy distribution transformer has a resistance of 1 percent and reactance of 7 percent per unit. (a) What is the transformer’s phase impedance referred to the high-voltage side? (b) Calculate this transformer’s voltage regulation at full load and 0, 8 PF lagging, using the calculated highside impedance. (c) Calculate this transformer’s voltage regulation under the same conditions, using the per-unit system.

Instrument transformers • Potential transformer (PT) • Current transformers (CT)