How to Test a Shunt Reactor: A Comprehensive Guide

A shunt reactor is defined as a device that absorbs reactive power from a power system and helps regulate the voltage level. Shunt reactors are typically used in high-voltage transmission lines and substations to compensate for the capacitive effect of long cables and overhead lines. Shunt reactors can be either fixed or variable, depending on the degree of voltage regulation required.

Shunt reactors are essential for maintaining the stability and efficiency of power systems, especially in long-distance transmission and renewable energy integration. Therefore, they need to be tested regularly to ensure their performance and reliability. Testing shunt reactors involves measuring various electrical parameters, such as resistance, reactance, losses, insulation, dielectric strength, temperature rise, and acoustic noise level. Testing shunt reactors also helps detect any defects or faults that may affect their operation or safety.

There are different standards and procedures for testing shunt reactors, depending on the type, rating, application, and manufacturer of the device. However, one of the most widely used standards is IS 5553, which specifies the tests to be performed on extra-high-voltage (EHV) or ultra-high-voltage (UHV) shunt reactors. According to this standard, the tests can be categorized into three groups:

• Type tests

• Routine tests

• Special tests

In this article, we will explain each of these tests in detail and provide some tips and best practices for conducting them effectively.

Type Tests of Shunt Reactor

Type tests are performed on a shunt reactor to verify its design and construction features and to demonstrate its compliance with the specified requirements. Type tests are usually done once for each type or model of shunt reactor before it is put into service. The following tests are essentially performed on a shunt reactor as type tests:

Measurement of Winding Resistance

This test measures the resistance of each winding of the shunt reactor using a low-voltage direct current (DC) source and an ohmmeter. The test is done at ambient temperature and after disconnecting all external connections. The purpose of this test is to check the continuity and integrity of the windings and to calculate the copper losses.

The measured resistance values should be corrected for temperature using the following formula:

where Rt is the resistance at temperature t (°C), R20 is the resistance at 20°C, and α is the temperature coefficient of resistance (0.004 for copper).

The corrected resistance values should be compared with the manufacturer’s data or previous test results to detect any abnormality or deviation.

Measurement of Insulation Resistance

This test measures the resistance of the insulation between the windings and between the windings and the earthed parts of the shunt reactor using a high-voltage DC source (usually 500 V or 1000 V) and a megohmmeter. The test is done at ambient temperature and after disconnecting all external connections. The purpose of this test is to check the quality and condition of the insulation and to detect any moisture, dirt, or damage.

The measured insulation resistance values should be corrected for temperature using the following formula:

where Rt is the insulation resistance at temperature t (°C), R20 is the insulation resistance at 20°C, and k is a constant that depends on the type of insulation (usually between 1 and 2).

The corrected insulation resistance values should be compared with the manufacturer’s data or previous test results to detect any abnormality or deviation.

Measurement of Reactance

This test measures the reactance of each winding of the shunt reactor using a low-voltage alternating current (AC) source (usually 10% of rated voltage) and a wattmeter or a power analyzer. The test is done at ambient temperature and after disconnecting all external connections. The purpose of this test is to check the inductance and impedance of the windings and to calculate the reactive power consumption.

The measured reactance values should be corrected for voltage using the following formula:

where Xt is the reactance at voltage Vt, and X10 is the reactance at 10% rated voltage (V10).

The corrected reactance values should be compared with the manufacturer’s data or previous test results to detect any abnormality or deviation.

Measurement of Losses

This test measures the losses of each winding of the shunt reactor using a low-voltage AC source (usually 10% of rated voltage) and a wattmeter or a power analyzer. The test is done at ambient temperature and after disconnecting all external connections. The purpose of this test is to check the efficiency and power factor of the windings and to calculate the total losses.

The measured losses consist of two components:

• Copper losses: These are due to the Joule heating effect in the windings and can be calculated by multiplying the measured winding resistance by the square of the rated current.

• Iron losses: These are due to hysteresis and eddy currents in the core and can be calculated by subtracting the copper losses from the total losses.

The measured loss values should be corrected for voltage using the following formula:

where Pt is the loss at voltage Vt, and P10 is the loss at 10% rated voltage (V10).

The corrected loss values should be compared with the manufacturer’s data or previous test results to detect any abnormality or deviation.

Dielectric Withstand Tests

These tests measure the ability of the insulation system of the shunt reactor to withstand high-voltage AC or DC stresses without breakdown or damage. There are two types of dielectric withstand tests:

• Power frequency withstands test: This test applies a high-voltage AC source (usually 1.5 times rated voltage) between the windings and between the windings and earthed parts for one minute. The purpose of this test is to check the integrity and strength of the insulation under normal operating conditions.

• Lightning impulse withstands test: This test applies a high-voltage DC impulse source (usually 1.2/50 μs wave shape) between the windings and between the windings and earthed parts for three impulses, each polarity. The purpose of this test is to check the integrity and strength of the insulation under lightning surge conditions.

The dielectric withstand tests should be performed according to IS 2071 or IEC 60076-3 standards. The applied voltages should not cause any flashover, puncture, sparking, or deterioration in the insulation system.

Temperature Rise Test

This test measures the temperature rise in the windings and oil of the shunt reactor under rated load conditions using thermocouples or thermometers. The test is done after running the shunt reactor for several hours until thermal equilibrium is reached. The purpose of this test is to check the cooling system and heat dissipation capacity of the shunt reactor.

The measured temperature rise values should not exceed the limits specified by IS 5553 or IEC 60076-6 standards. The maximum allowable temperature rise depends on the type, rating, cooling method, ambient temperature, altitude, soil quality, etc., but generally ranges from 40°C to 65°C for oil-immersed shunt reactors.

Routine Tests of Shunt Reactor

Routine tests are performed on every shunt reactor before dispatch from the factory or installation at the site to ensure its quality control and conformity with specifications. Routine tests are similar to type tests but less extensive and less stringent. The following tests are essentially performed on a shunt reactor as routine tests:

• Measurement of winding resistance.

• Measurement of insulation resistance.

• Measurement of reactance.

• Measurement of losses.

• Dielectric withstand tests.

The procedure, purpose, correction factors, comparison criteria, and standards for these tests are the same as those described for type tests.

Special Tests of Shunt Reactor

Special tests are performed on a shunt reactor upon request by the customer or manufacturer to obtain additional information or data that may not be covered by type or routine tests. Special tests are usually done for research, development, or design purposes. The following tests are essentially performed on a shunt reactor as special tests:

Measurement of Zero Sequence Reactance

This test measures the zero sequence reactance (or impedance) of each winding of the shunt reactor using a low-voltage AC source (usually 10% rated voltage) applied between one phase terminal connected to the neutral terminal while other two-phase terminals shorted together and an ammeter or a power analyzer. The purpose of this test is to check how much reactive power will flow through neutral point during single line-to-ground fault condition.

The measured zero sequence reactance values should be corrected for voltage using the same formula as that used for the measurement of reactance in type tests.

The measured zero sequence reactance values should be compared with the manufacturer’s data or previous test results to detect any abnormality or deviation.

The zero sequence reactance of a shunt reactor is important for predicting the current flow during single-line-to-ground faults and for designing the neutral grounding system1.

Measurement of Mutual Reactance

This test measures the mutual reactance (or impedance) between two windings of the shunt reactor using a low-voltage AC source (usually 10% rated voltage) applied between one phase terminal of one winding and one phase terminal of another winding while shorting the other terminals of both windings and an ammeter or a power analyzer. The purpose of this test is to check the coupling and leakage flux between the windings and to calculate the mutual inductance.

The measured mutual reactance values should be corrected for voltage using the same formula as that used for the measurement of reactance in type tests.

The measured mutual reactance values should be compared with the manufacturer’s data or previous test results to detect any abnormality or deviation.

The mutual reactance of a shunt reactor is important for calculating the equivalent circuit parameters and for analyzing the transient behavior of the device.

Measurement of Acoustic Sound Level

This test measures the acoustic sound level emitted by the shunt reactor under rated load conditions using a sound level meter and a microphone. The test is done after running the shunt reactor for several hours until thermal equilibrium is reached. The purpose of this test is to check the noise level and vibration of the shunt reactor and to ensure its compliance with the environmental standards.

The measured acoustic sound level values should be corrected for background noise and frequency range using the methods described in IEC 60076-10 or IEC 60076-62 standards. The sound pressure level and sound power level should be calculated and reported.

The measured acoustic sound level values should not exceed the limits specified by IS 55533 or IEC 60076-6 standards. The maximum allowable sound level depends on the type, rating, cooling method, location, etc., but generally ranges from 40 dB(A) to 65 dB(A) for oil-immersed shunt reactors.

Measurement of Vibration and Stress on Tank

This test measures the vibration and stress on the tank of the shunt reactor under rated load conditions using accelerometers, strain gauges, or other sensors. The test is done after running the shunt reactor for several hours until thermal equilibrium is reached. The purpose of this test is to check the mechanical strength and integrity of the tank and to detect any cracks, leaks, or deformations.

The measured vibration and stress values should be corrected for temperature, frequency, and loading using appropriate formulas or methods. The vibration amplitude, frequency spectrum, stress distribution, and fatigue life should be calculated and reported.

The measured vibration and stress values should not exceed the limits specified by IS 55533 or IEC 60076-6 standards. The maximum allowable vibration and stress depend on the type, rating, cooling method, material, etc., but generally follow the guidelines given in IEC 60068-2 or IEC 60076-6 standards.

Measurement of Magnetizing Characteristics

This test measures the magnetizing characteristics of the shunt reactor core using a low-voltage AC source (usually 10% rated voltage) applied between one phase terminal connected to a neutral terminal while other two-phase terminals shorted together, and a wattmeter or a power analyzer. The purpose of this test is to check the magnetic saturation and hysteresis of the core and to calculate the magnetizing current and losses.

The measured magnetizing characteristics consist of two components:

• Magnetizing current: This is the current required to establish the magnetic flux in the core and can be calculated by dividing the applied voltage by the zero sequence reactance.

• Magnetizing losses: These are due to hysteresis and eddy currents in the core and can be calculated by multiplying the magnetizing current by the applied voltage.

The measured magnetizing characteristics should be plotted as a curve of magnetizing current versus applied voltage or magnetic flux density versus magnetic field intensity. The curve should show the linear and nonlinear regions of the core operation.

The measured magnetizing characteristics should be compared with the manufacturer’s data or previous test results to detect any abnormality or deviation.

The magnetizing characteristics of a shunt reactor are important for determining the reactive power consumption and losses at different voltage levels and for designing the protection system.

Measurement of the tan delta of winding

This test measures the tan delta (or dissipation factor) of each winding of the shunt reactor using a high-voltage AC source (usually 10% rated voltage) applied between one phase terminal connected to the neutral terminal while other two-phase terminals shorted together, and a bridge circuit or a power analyzer. The purpose of this test is to check the dielectric losses and quality factor of the winding insulation and to detect any moisture, aging, or deterioration.

The measured tan delta values should be corrected for temperature using appropriate formulas or methods. The tan delta values should also be corrected for stray capacitances using appropriate methods.

The measured tan delta values should be compared with the manufacturer’s data or previous test results to detect any abnormality or deviation.

The tan delta of a shunt reactor winding is important for estimating the dielectric losses and heating effect at different voltage levels and frequencies.

Dissolved Gas Analysis of Insulating Oil

This test analyzes the dissolved gases in the insulating oil of an oil-immersed shunt reactor using a gas chromatograph or other instruments. The test is done after sampling the oil from different locations in the tank according to IS 10593 or IEC 60567 standards. The purpose of this test is to check the condition and quality of the oil and to detect any faults or defects in the shunt reactor.

The analyzed dissolved gases consist of various components, such as hydrogen, methane, ethane, ethylene, acetylene, carbon monoxide, carbon dioxide, nitrogen, oxygen, etc. The concentration and ratio of these gases indicate different types of faults or degradation processes in the shunt reactor.

The analyzed dissolved gases should be interpreted using various methods, such as gas ratios, the Duval triangle, the Rogers ratio, etc. The interpretation should indicate the type, location, severity, and evolution of the fault or degradation process in the shunt reactor.

The dissolved gas analysis of insulating oil is important for monitoring the condition and health of the shunt reactor and for planning preventive or corrective maintenance actions.

Conclusion

Testing shunt reactors is a vital task for ensuring their performance and reliability in power systems. Testing shunt reactors involves measuring various electrical parameters and analyzing them according to different standards and procedures. Testing shunt reactors also helps detect any faults or defects that may affect their operation or safety.

In this article, we have explained the three categories of tests for shunt reactors: type tests, routine tests, and special tests. We have also described each test in detail and provided some tips and best practices for conducting them effectively. We hope this article has been informative and useful for anyone who is interested in or involved in testing shunt reactors.

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