# Conclusion of transformer report

• Transformer Failure Analysis:Reasons and Methods
• Project Report On Maintenance Of Power Transformer
• A Complete Guide to Transformers
• Open Circuit and Short Circuit Test on Transformer
• Report shows transformer imports ‘a threat to US national security’
• ## Transformer Failure Analysis:Reasons and Methods

Conclusion Introduction It is possible to predict the performance of a transformer at various levels of load by knowing all the equivalent circuit parameters. Without actually loading the transformer, these two assessed tests give the test results, which are used to determine the equivalent circuit parameters. By these parameters, we can easily predetermine the efficiency and regulation of the transformer at any power factor condition as well as at any load condition.

This method of finding the parameters of a transformer is called as an Indirect Loading Method. This tutorial enumerates how to perform these tests, how determine the equivalent parameters from test data and significance HV or LV side in which the calculation to be performed.

Open Circuit or No Load Test on Transformer This test is performed to find out the shunt or no load branch parameters of equivalent circuit of a transformer. This test results the iron losses and no load current values, thereby we can determine the no load branch parameters with simple calculations. As the name itself indicates, secondary side load terminals of the transformer are kept open and the input voltage is applied on the primary side.

Since this test is carried out without placing any load, this test is also named as No Load Test. How to Perform Open Circuit Test? The open circuit OC test is carried out by connecting LV side as primary of the transformer to the AC supply through variac, ammeter, voltmeter and wattmeter instruments.

The secondary side or HV side terminals are left open and in some cases a voltmeter is connected across it to measure the secondary voltage. The primary side voltmeter reads the applied voltage to the transformer, ammeter reads the no load current, wattmeter gives the input power and the variac used to vary the voltage applied to transformer so that rated voltage is applied at rated frequency.

The OC test arrangement of a transformer is shown in below figure: When a single phase supply is given to the transformer, the rated value of the primary voltage is adjusted by varying the variac. At this rated voltage, the ammeter and wattmeter readings are to be taken. We know that, when the transformer is on no load, the no load current or primary current is very small, typically 3 to 5 percent of the rated current value.

Thus, the copper loss in the primary winding is negligible. In OC test, transformer is operated at rated voltage at rated frequency so the maximum loses will be the flux in the core.

Since the iron or core losses are at rated voltage, the power input is drawn to supply the iron losses by the transformer under no load. Thus, a low current will flow through the circuit during OC test. In order to be readable by the instruments, the measurements of voltage, current and power must be performed in the low voltage side.

And also, low range current coils and low range ammeter must be selected. The power factor of the transformer on no load is too low. So, in order work with this low value, a LPF watt meter is selected. The equivalent circuit obtained by the OC test is shown below: Short Circuit Test on Transformer This test is performed to find series branch parameters of an equivalent circuit such as equivalent impedance Zo1 or Zo2 , total winding resistance Ro1 or Ro2 and total leakage reactance Xo1 or Xo2.

Also, it is possible to determine copper losses at any desired load and total voltage drop of the transformer referred to primary or secondary. In this test, usually LV winding is shorted by a thick wire. And the test is conducted on the other side, i. HV side as primary. How to Perform Short Circuit Test? In Short Circuit SC test, the primary or HV winding is connected to the AC supply source through voltmeter, ammeter, wattmeter and a variac as shown in figure.

As the secondary winding is short circuited, at rated voltage, the transformer draws a very large current due to its very small winding resistance. Such high current can cause overheating and also burning of the transformer. Thus, to limit the high current, the primary winding must be energized with a low voltage, which is just enough to produce the rated current in the primary of the transformer. The SC test is conducted on HV side due to the two main reasons.

The first one is, the SC test conducted by applying rated current and the rated current of the HV side is much less than that of the LV side. Therefore, the rated current is easily achieved at HV side due to the low current value as compared to the LV side.

On the other hand, if we short the HV terminals by connecting measuring instrument on LV side, voltage in the secondary is zero. Therefore, the current flow through HV side is very high as VA rating is constant compared to the LV side and hence it will cause to burn the transformer. During this test, by varying the variac slowly, we apply a low voltage to the primary typically 5 to 10 percent of the rated voltage to cause a rated current to flow in both primary and secondary windings that we can observe on ammeter reading in some cases, the secondary is shorted through an ammeter.

At this rated current, we have to record the voltmeter Vsc , ammeter Isc and wattmeter Wsc readings. In other words, the voltage applied to the primary winding is very low, thereby the flux level in the core is very small. In turn there is negligible core loss. Therefore, the no load shunt branch is considered as absent in equivalent circuit of this test as core loss is negligible. As the iron or core losses are function of voltage, these losses are very small.

Therefore, the wattmeter reading shows the power loss or I2 R loss equal to the full load copper losses of the whole transformer.

It should be noted that, before calculation of parameters, you must be aware in which side primary or secondary the test reading being recorded. Suppose if the transformer is step-up transformer, then we carry out the SC test on secondary side HV side while primary or low voltage side is shorted.

In such case, we get the parameters referred to the secondary from calculations such as R02, X02 and Z If it is a step-down transformer, we get the parameter values as R01, X01 and Z01 because the meters are connected to the HV side of the primary. Therefore, for a meaningful equivalent circuit, all the parameters must be referred to the one particular side. The explanation regarding this transformation is explained in equivalent circuit of the transformer topic in our earlier articles.

Calculation of Efficiency from O. Tests As we have seen that, the practical transformer has two types of major losses namely copper and core losses. The temperature of the transformer rises due to these losses which are dissipated as heat. Due to these losses, input power drawn by the primary no longer equal to the output delivered at secondary. And the copper losses are depend on the square of the current. As the winding current varies from no load to full load, copper losses are also get varied.

Calculation of Regulation For a fixed voltage in the primary, the secondary terminal voltage will not be maintained constant from no load to full load. This is due to the voltage drop across leakage impedance which magnitude depends on both degree of loading and the power factor. So the regulation gives change in secondary voltage from no load to full load at a given power factor. It is defined as the change in the secondary voltage when the transformer is operating at full load of specified power factor supplied at rated voltage to no load with primary voltage held constant.

Hence, from the SC test data we can find out the regulation of a transformer. The positive sign is used for lagging power factor and negative sign is used for leading power factor. You learned how to perform Open Circuit and Short Circuit Test on Transformer, calculate the equivalent circuit parameters, calculate the efficiency and percent of regulation.

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## Project Report On Maintenance Of Power Transformer

A practical transformer is given here with all the parts and their protective devices. The typical test results are also available. The transformer is a device that enables the transmission of electrical energy from one circuit to another circuit without any change in frequency. It is coupled electrically and magnetically separated.

Actually, the transformer is an electromagnetic energy conversion device, because the energy is converted from the primary first magnetic energy is absorbed and then converted into usable electrical energy. Power transformer is one of the step-up or step down the voltage level on demand without changing the frequency. At every step, whether the voltage level should have to be increased or decreased we need a transformer.

If there is any fault or damage in the transformer then there will be heavy loss to the distribution system. So, periodical maintenance and testing is very important for a power transformer. The report also explains the details of protection of transformer, principles, safety devices, Pressure relief valve, maintenance of transformer etc. The transformer mainly works on the principle of electromagnetic induction between two circuits linked by a common magnetic flux. Project Report On Maintenance Of Power Transformer Conclusion: Power transformer is very important in the transmission and it must be monitored closely followed by their state during operation.

In order to take remedial measure at appropriate times to avoid errors and increase reliability of service of the transformer.

## A Complete Guide to Transformers

The report also explains the details of protection of transformer, principles, safety devices, Pressure relief valve, maintenance of transformer etc. The transformer mainly works on the principle of electromagnetic induction between two circuits linked by a common magnetic flux. Project Report On Maintenance Of Power Transformer Conclusion: Power transformer is very important in the transmission and it must be monitored closely followed by their state during operation.

In order to take remedial measure at appropriate times to avoid errors and increase reliability of service of the transformer. If no visible damage is found externally, then next step is to conduct diagnostic testing of transformer. Diagnostic Testing When there is no visible damage is found in external examination of transformer. Then diagnostic tests are conducted to find out fault and to give indication of repair. Test data should be recorded carefully and several tests may be interpreted together to diagnose a problem.

## Open Circuit and Short Circuit Test on Transformer

Samples of insulating oil for testing must be taken prior to opening the transformer for inspection. Following tests can be conducted on transformer. Insulation Resistance: Winding to winding, winding to ground, core to ground, dielectric absorption Polarization Index.

Other tests: Transformer Turn ratio; Winding DC Resistance; Oil dielectric breakdown; Excitation low voltage Before performing field tests, safety precautions should be taken to ensure that the transformer is disconnected from all power and auxiliary sources and has been properly earthed. Internal Inspection When the results of diagnosis test indicate the failure of transformer, an internal inspection is performed on site to determine the location of fault and extent of damage.

Transformer oil is removed for inspection, the exposure time must be kept to a minimum to reduce moisture entrance into the tank. Internal abnormalities may include. The odor of burnt insulation, burnt oil, color of oil, indication of moisture and its location and free water in tank and amount. Evidence of burns, discoloration, or deposits due to arc or stray flux overheating on tank walls, bushing terminals, copper connectors.

Evidence of loose connection or splices to bushings, collar, spacers etc. Displacement of winding and leads.

Condition of core and evidence of core damage. Tear down Inspection If the internal inspection of do not provide any cause of failure of transformer, then it is necessary to perform de tank the transformer to identify the cause of failure. The core is bring out of tank for inspection which can provide following evidences of failure Damage to core breakdown of core insulation. Evidence of tracking results from dielectric breakdown.

Evidence of radial and axial failure. Evidence of mechanical failure. Evidence of thermal failure. The energy from the power system can cause both to occur. So care must be taken while reporting cause and effects.

Analysis of Mechanical Failure of Windings To thoroughly analyze distribution transformer failure, an understanding of the axial and radial forces causing mechanical deformation to winding is required.

This method of finding the parameters of a transformer is called as an Indirect Loading Method. This tutorial enumerates how to perform these tests, how determine the equivalent parameters from test data and significance HV or LV side in which the calculation to be performed. Open Circuit or No Load Test on Transformer This test is performed to find out the shunt or no load branch parameters of equivalent circuit of a transformer.

This test results the iron losses and no load current values, thereby we can determine the no load branch parameters with simple calculations. As the name itself indicates, secondary side load terminals of the transformer are kept open and the input voltage is applied on the primary side.

Since this test is carried out without placing any load, this test is also named as No Load Test. How to Perform Open Circuit Test? The open circuit OC test is carried out by connecting LV side as primary of the transformer to the AC supply through variac, ammeter, voltmeter and wattmeter instruments.

### Report shows transformer imports ‘a threat to US national security’

The secondary side or HV side terminals are left open and in some cases a voltmeter is connected across it to measure the secondary voltage. The primary side voltmeter reads the applied voltage to the transformer, ammeter reads the no load current, wattmeter gives the input power and the variac used to vary the voltage applied to transformer so that rated voltage is applied at rated frequency.

The OC test arrangement of a transformer is shown in below figure: When a single phase supply is given to the transformer, the rated value of the primary voltage is adjusted by varying the variac. At this rated voltage, the ammeter and wattmeter readings are to be taken. We know that, when the transformer is on no load, the no load current or primary current is very small, typically 3 to 5 percent of the rated current value.

Thus, the copper loss in the primary winding is negligible. In OC test, transformer is operated at rated voltage at rated frequency so the maximum loses will be the flux in the core. Since the iron or core losses are at rated voltage, the power input is drawn to supply the iron losses by the transformer under no load.

Thus, a low current will flow through the circuit during OC test. In order to be readable by the instruments, the measurements of voltage, current and power must be performed in the low voltage side.

And also, low range current coils and low range ammeter must be selected. The power factor of the transformer on no load is too low. So, in order work with this low value, a LPF watt meter is selected. The equivalent circuit obtained by the OC test is shown below: Short Circuit Test on Transformer This test is performed to find series branch parameters of an equivalent circuit such as equivalent impedance Zo1 or Zo2total winding resistance Ro1 or Ro2 and total leakage reactance Xo1 or Xo2.

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