Online Electrical Engineering
Design of Inductor in Switched Mode Power Supply Systems
Linear Variable Differential Transformer
Electrical Power Transformer | Definition and Types of Transformer
What is transformer? Definition and Working Principle of Transformer
Theory of Transformer on load and no load operation
EMF Equation of Transformer | Turns Voltage Transformation Ratio of Transformer
Resistance and Leakage Reactance or Impedance of Transformer
Equivalent Circuit of Transformer referred to Primary and Secondary
Hysteresis Eddy Current Iron or Core Losses and Copper Loss in Transformer
Open and Short Circuit Test on Transformer
Voltage Regulation of Transformer
Over Fluxing in Transformer
Parallel operation of Transformers
Transformer Accessories | Breather and Conservator Tank | Radiator
Transformer Insulating Oil and Types of Transformer Oil
Silica Gel Breather of Transformer
Conservator Tank of Transformer
Radiator of Transformer | Function of Radiator
Magnetic Oil Gauge or MOG | Magnetic Oil Level Indicator of Transformer
Oil Winding and Remote Temperature Indicator of Transformer
On Load and No Load Tap Changer of Transformer | OLTC and NLTC
Transformer Cooling System and Methods
Maintenance of Transformer
What is Auto Transformer ?
Buchholz Relay in transformer | Buchholz Relay operation and principle
Transformer Testing | Type Test and Routine Test of Transformer
Voltage and Turn Ratio Test of Transformer
Transformer Winding Resistance Measurement
Insulation Dielectric Test of Transformer
Transformer Oil and Winding Temperature Rise Test
Impulse Test of Transformer
Vector Group Test of Power Transformer
Sweep Frequency Response Analysis Test | SFRA Test
DGA or Dissolved Gas Analysis of Transformer Oil | Furfural or Furfuraldehyde Analysis
Distribution Transformer | All Day Efficiency of Distribution Transformer
Installation of Power Transformer
Commissioning of Power Transformer
Magnetizing Inrush Current in Power Transformer
Tertiary Winding of Transformer | Three Winding Transformer
Single Three Phase Transformer vs bank of three Single Phase Transformers
What is Earthing Transformer or Grounding Transformer
Air Core Transformer
High Voltage Transformer
Current Transformer CT class Ratio Error Phase Angle Error in Current Transformer
Voltage Transformer or Potential Transformer Theory
Accuracy Limit Factor and Instrument Security Factor of Current Transformer
Knee Point Voltage of Current Transformer PS Class
Differential Protection of Transformer | Differential Relays
Restricted Earth Fault Protection of Transformer | REF Protection
Core of Transformer and Design of Transformer Core
Design of High Frequency Pulse Transformer
Open and Short Circuit Test on Transformer
Under Electrical Transformer
These two tests are performed on a transformer to determine (i) equivalent circuit of transformer (ii) voltage regulation of transformer(iii) efficiency of transformer. The power required for these open circuit test and short circuit test on transformer is equal to the power loss occurring in the transformer.
Open Circuit Test on TransformerThe connection diagram for open circuit test on transformer is shown in the figure. A voltmeter, wattmeter, and an ammeter are connected in LV side of the transformer as shown. The voltage at rated frequency is applied to that LV side with the help of a variac of variable ratio auto transformer. The HV side of the transformer is kept open. Now with the help of variac, applied voltage gets slowly increased until the voltmeter gives reading equal to the rated voltage of the LV side. After reaching at rated LV side voltage, all three instruments reading (Voltmeter, Ammeter and Wattmeter readings) are recorded.
The ammeter reading gives the no load current Ie. As no load current Ie is quite small compared to rated current of the transformer, the voltage drops due to this current that can be taken as negligible.
Since, voltmeter reading V1 can be considered equal to secondary induced voltage of the transformer, the input power during test is indicated by watt-meter reading. As the transformer is open circuited, there is no output, hence the input power here consists of core losses in transformer and copper loss in transformer during no load condition. But as said earlier, the no load current in the transformer is quite small compared to full load current, so copper loss due to the small no load current can be neglected. Hence, the wattmeter reading can be taken as equal to core losses in transformer. Let us consider wattmeter reading is Po.
Where Rm is shunt branch resistance of transformer.
If, Zm is shunt branch impedance of transformer.
Therefore, if shunt branch reactance of transformer is Xm,
These values are referred to the LV side of transformer as because the test is conduced on LV side of transformer. These values could easily be referred to HV side by multiplying these values with square of transformation ratio.
Short Circuit Test on TransformerThe connection diagram for short circuit test on transformer is shown in the figure. A voltmeter, wattmeter, and an ammeter are connected in HV side of the transformer as shown. The voltage at rated frequency is applied to that HV side with the help of a variac of variable ratio auto transformer.
The LV side of the transformer is short circuited. Now with the help of variac applied voltage is slowly increased until the ammeter gives reading equal to the rated current of the HV side. After reaching at rated current of HV side, all three instruments reading (Voltmeter, Ammeter and Watt-meter readings) are recorded. The ammeter reading gives the primary equivalent of full load current IL. As the voltage applied for full load current in short circuit test on transformer is quite small compared to the rated primary voltage of the transformer, the core losses in transformer can be taken as negligible here.
Let’s say, voltmeter reading is Vsc. The input power during test is indicated by watt-meter reading. As the transformer is short circuited, there is no output; hence the input power here consists of copper losses in transformer. Since, the applied voltage Vsc is short circuit voltage in the transformer and hence it is quite small compared to rated voltage, so core loss due to the small applied voltage can be neglected. Hence the wattmeter reading can be taken as equal to copper losses in transformer. Let us consider wattmeter reading is Psc.
Where Re is equivalent resistance of transformer. If, Ze is equivalent impedance of transformer.
Therefore, if equivalent reactance of transformer is Xe
These values are referred to the HV side of transformer as because the test is conduced on HV side of transformer. These values could easily be referred to LV side by dividing these values with square of transformation ratio.