Comissioning of Electrical Systems
Commissioning is the process of ensuring that the systems and components of a building or industrial unit are designed, installed, tested, operated and maintained according to the owner’s requirements, operational needs and maintenance specifications. Commissioning can be applied to new projects as well as existing units and systems undergoing expansion, modernization or adjustment.
The primary objective of commissioning is to ensure the orderly and safe transfer of a civil or industrial unit from the constructor to the owner, guaranteeing its operability in terms of performance, reliability and traceability of information. Additionally, when executed in a planned, structured and effective manner, commissioning tends to become a key element in meeting the project’s deadlines, costs, safety and quality requirements.
Testing Instruments
Proper diagnostics of substation conditions are essential in maintenance. Electrical tests show the equipment’s condition, evaluate its current state and help identify anomalies that might cause equipment unavailability. The main testing instruments used in substation maintenance are described below:
Megohmmeter
The megohmmeter is an instrument used to measure insulation resistance, allowing the detection and diagnosis of faults in electrical equipment. Its operation is based on applying a DC voltage to an insulating material, which produces a current composed of three distinct components:
. Capacitive charging current, natural to the tested material
. Dielectric absorption current, which flows through the material’s body
. Leakage current, with components that flow both through the surface and the material itself
Based on these components, the megohmmeter provides accurate readings of dielectric resistance. It has three terminals with corresponding colored cables:
. Red terminal (LINE): Sends the voltage to the tested equipment
. Black terminal (EARTH): Serves as the return path for leakage current readings
. Green terminal (GUARD): Eliminates parasitic or inductive currents that could affect the measurement
For substations operating at 15 kV, tests can be conducted using the 5 kV or 10 kV ranges of the megohmmeter. Special care must be taken when testing the low-voltage winding of a transformer, typically using a 500 V setting.
After testing, one must wait for the voltage indicator light to turn off before handling the cables, which may take a few seconds.
Hipot (High-Potential) Tester
The Hipot tester is used to assess electrical insulation in devices and equipment. The name “Hipot” stands for High Potential. This test uses high voltage.
Under normal conditions, any electrical device will exhibit minimal leakage current depending on the voltage class and dielectric strength of its materials. However, issues such as moisture absorption or dirt accumulation can lead to excessive leakage, potentially causing equipment failure or even electric shock.
Test procedure:
A high voltage is applied to the equipment for one minute. The insulation must withstand the voltage without breakdown. If the insulation fails, the Hipot should detect the leakage and shut down. If it doesn’t, the equipment could be damaged.
The Hipot is commonly used for testing high-voltage cables and includes a voltage cable and a return cable. The test setup is simple: the Hipot is connected to the tested cable and its shielding (if present). The equipment then sends a voltage pulse and analyzes the cable’s behavior to determine its suitability for installation.
Key safety measures include ensuring the Hipot panel remains grounded, keeping a safe distance from energized parts, ensuring the tested cable does not touch any conductive or grounded surfaces.
Several warnings are given regarding potential accidents and damage to the equipment. Since it operates with high voltage levels and stored energy (which is the very purpose of the equipment), the Hipot requires careful operation, with heightened attention to all possible safety aspects.
During the use of the equipment, the operator must be attentive to the necessary precautions for their protection.
It is emphasized that the operator must always maintain the greatest possible distance from energized components of the system during the test (such as cables, connectors, and the Hipot device itself). Additionally, it is recommended that the cables being tested be arranged so they are suspended freely in the air, without contact with any other point that could carry voltage or grounding.
The main safety feature observed by the team in the analyzed equipment was the system that ensures the equipment’s panel is always at zero electrical potential (i.e., grounded). This measure is essential to prevent accidental human contact with energized parts of the Hipot, which could result in an electric shock.
Another critical point in the operation of the Hipot equipment is the applied voltage level. Due to the various types of reference values commonly used (for example, phase-to-phase voltage, phase-to-neutral, etc.), it is common for discrepancies to occur between the intended value and the actual value applied during the test. Therefore, it is important to routinely verify the electrical parameters in use, in order to avoid unwanted incidents or even measurement errors by the equipment or misreadings by the operator.
According to technical specifications, a cable with insulation failure, when subjected to a Hipot test, will show an increasing leakage current. This increase is only stopped when the current reaches the cut-off value of the equipment (a value that, in some cases, is preset by the operator). Hence, it is crucial to properly set all the variables involved in the procedure before performing the test.
Main Applications of the Equipment
The main users of the Hipot equipment are cable and wire manufacturers, electric utility companies, telecommunications companies and professionals working in field engineering.
Procedures Prior to Testing:
Grounding and Safety
For a successful test without unforeseen events or accidents, it is essential that all safety standards and procedures are fully followed. Therefore, a qualified and responsible operator must be selected to handle the test equipment (Hipot), as well as the cables, connection wires, and other materials involved in the testing process.
Additionally, proper grounding of the system is crucial to prevent any accidents involving unwanted voltages that may arise in the testing environment. Thus, the first step after verifying the safety of the equipment and the operator is to perform and check the grounding of the equipment, including its casing. It is necessary to ensure a proper connection to a reliable grounding point for the safety and reliability of the subsequent tests.
Power Supply Connections in the System
Next, the Hipot power supply connection must be made, once again checking the system’s grounding. Then, the power source and the high-voltage cable are connected to the appropriate terminals. These latter connections must also be properly grounded using suitable cables.
At this point, the guard terminal becomes relevant, as its main function is to protect the Hipot equipment’s casing, internal circuits, and the established connections. The terminal must be solidly grounded to ensure zero potential at the necessary points.
Making the connections in the correct order and arrangement is essential to ensure complete protection during the test, as well as to obtain reliable readings of leakage current, insulation resistance of the tested material, among other parameters. For this reason, the operator must always follow the instructions provided by the manufacturer of the Hipot equipment and the cable being tested, ensuring that no physical limits are being exceeded.
Connection of the Cables Under Test
The connections for the cable to be tested are explained in the manual according to the type of cable used (with reference to the presence of shielding and the type of construction, single-phase or three-phase).
Finally, the equipment’s potentiometer must be adjusted to an appropriate shutdown current value. The manufacturer initially recommends a maximum value of 5 mA.
Test Adjustments and Procedures
Voltage Level Adjustment
When turning on the equipment, it is necessary to check whether the voltage settings are appropriate (with the adjustment dial turned to the “start” position). Once any discrepancies in settings and references are corrected, the high-voltage (HV) indicator lamp should light up, indicating that the equipment is ready and enabled to supply voltage for conducting the test.
Next, the voltage level should be adjusted to the desired value (according to current standards and the specifications provided by the party requesting the test). It is important to always remember that, because these are high-voltage tests, all adjustments must be made slowly to prevent excessively abrupt electrical variations, which could otherwise trigger equipment shutdowns or improper activation of safety protections.
At this point, the operator should be able to read the leakage current present in the cable or material under test. From there, it is the responsibility of the engineer or test operator to take measures to verify whether the leakage current is within acceptable limits. If it is not, appropriate action must be taken regarding the tested material.
Choosing the Appropriate Voltage Level
The Hipot equipment manufacturer provides a list of average voltage level values based on various international standards, including: VDE (Verband der Elektrotechnik, Elektronik Und Informationstechnik – Association for Electrical, Electronic & Information Technologies), IEC (International Electrotechnical Comission), IPCEA (Insulated Power Cable Engineers Association) and AEIC (Association of Edison Illuminating Companies)
Test Measurements and Results
Once the initial test parameters are defined and the equipment has been properly adjusted, the actual test can proceed. Again, all electrical connections for the tested cable and the equipment terminals must be checked. If anything is not in accordance with the manufacturer’s manual and applicable standards, the necessary adjustments must be made before continuing the test.
The measurements taken during the test must be analyzed carefully to avoid errors due to incorrect reading or misinterpretation of results. The test must be performed correctly, as it is not advisable to repeat the applied voltage test multiple times on the same cable. Even though this is not considered a destructive test, it can compromise the cable’s service life due to the voltage level applied being higher than that used during normal operation.
By following all the procedures described in this section, the test should yield reliable and useful measurements for determining the lifespan of cables, validating installations and other applications.
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Micro-ohmmeter
A micro-ohmmeter is an instrument used to accurately measure low resistance values, typically those of contact resistance in circuit breakers and disconnect switches. It can also be used to measure the ohmic resistance of transformer windings.
Usually, the test current ranges from 1 mA to 100 A. During the test, an electric current is applied which, when passing through the equipment under test, causes a voltage drop. According to Ohm’s First Law, dividing the measured voltage by the applied current yields the electrical resistance.
Turns Ratio Tester (TRT)
A TRT (Turns Ratio Tester) is an instrument used to accurately measure the turn ratio in a transformer. Since a transformer is a magnetic device that operates based on the proportion between windings, measuring the turn ratio allows us to evaluate the condition of the windings, both in terms of the transformation ratio and continuity.
The instrument measures the turn ratio, phase displacement and polarity in power transformers, potential transformers (PTs) and current transformers (CTs).
It comes with four cables: two commonly labeled H1 and H2, used to excite the higher-voltage winding and two labeled X1 and X2, used to measure the current in the lower-voltage winding of the transformer.
During testing, it is important to know the type of primary and secondary connection of the transformer under test, as well as its operating voltage on both sides.
The turns ratio tester may be Digital (electronic TRT), or Analog (manual crank-type TRT).