Thermography is a non-destructive test method that may be used to detect poor connections, unbalanced loads, deteriorated insulation, or other potential problems in energized
electrical components. These problems may lead to excess power use, increased maintenance costs, or catastrophic equipment failure resulting in unscheduled service interruptions, equipment damage, or other problems.
Thermography, also called infrared inspection, is based upon the sensing of heat emitted from the surface of an object in the form of infrared radiation. Test instruments are used to detect and convert the infrared radiation into either a temperature value or a thermal image, which can be used to assess the thermal condition of the object at the time of measurement. An infrared camera is one common type of an infrared thermal imaging device. Energized electrical systems generate heat because of electrical resistance. The amount of heat generated is related to the amount of current flowing through the system and the resistance of the individual system components and connections within the system. As components deteriorate, their resistance increases, causing a localized increase in heat. Similarly, a poorly made connection will have higher resistance than a well-made connection, along with a higher temperature profile. Thermography may be used to detect these temperature differences.
Thermography is a non-destructive test method that may be used to detect poor connections, unbalanced loads, deteriorated insulation, or other potential problems in energized electrical components. These problems may lead to excess power use, increased maintenance costs, or catastrophic equipment failure resulting in unscheduled service interruptions, equipment damage, or other problems. Thermography, also called infrared inspection, is based upon the sensing of heat emitted from the surface of an object in the form of infrared radiation. Test instruments are used to detect and convert the infrared radiation into either a temperature value or a thermal image, which can be used to assess the thermal condition of the object at the time of measurement. An infrared camera is one common type of an infrared thermal imaging device. Energized electrical systems generate heat because of electrical resistance. The amount of heat generated is related to the amount of current flowing through the system and the resistance of the individual system components and connections within the system. As components deteriorate, their resistance increases, causing a localized increase in heat. Similarly, a poorly made connection will have higher resistance than a well-made connection, along with a higher temperature profile. Thermography may be used to detect these temperature differences.
Cable Insulation can be nicked or scraped from individual conductors when pulled through raceways. Insulation can also be damaged when exposed to moisture, excessive heat, or certain chemicals. To verify that insulation has not been damaged during the installation process, an insulation resistance test must be performed after installation.
A cable insulation resistance test is a test that is performed by applying 500 V or more between the conductor and ground and measuring the resulting leakage current. An insulation resistance tester is a test instrument that measures current that leaks through the insulation into ground. Insulation resistance tests can be performed with insulation multi- meters (IMMs) or megohmmeters. Insulation resistance testers are calibrated to display megohms (MΩ) of resistance. A satisfactory insulation resistance measurement should be in millions of ohms. Conductors with damaged insulation must be replaced.
When cable and conductor installations are tested, they should be disconnected from panels and machinery to keep them isolated. The conductors should be tested against each other and against ground. See Figure 2. Minimum resistance readings and specific test methods are determined by acceptance testing specifications for the project.
Cables and conductors should be tested and maintained on a three-year cycle at minimum. Insulation resistance tests should be performed more frequently for systems that show deterioration of insulation material. When performing insulation tests on conductors and cable, apply the following procedure:
- Inspect exposed sections of cables and conductors for physical damage. Replace or repair sections that exhibit damage.
- Inspect cables and conductors for proper grounding, cable support, and termination. Terminate sections that are not properly terminated.
- If cables and conductors are properly terminated, verify that neutrals and grounds are properly terminated for operation of protective devices.
- Perform an insulation resistance test on each conductor in the cable. Apply 1000 VDC for 1 min (one-minute insulation resistance test) to low-voltage cables (1 kV or less) and use a clamp-on ammeter, DMM, megohmmeter, or IMM to measure the insulation resistance.
Thermography is a non-destructive test method that may be used to detect poor connections, unbalanced loads, deteriorated insulation, or other potential problems in energized electrical components. These problems may lead to excess power use, increased maintenance costs, or catastrophic equipment failure resulting in unscheduled service interruptions, equipment damage, or other problems. Thermography, also called infrared inspection, is based upon the sensing of heat emitted from the surface of an object in the form of infrared radiation. Test instruments are used to detect and convert the infrared radiation into either a temperature value or a thermal image, which can be used to assess the thermal condition of the object at the time of measurement. An infrared camera is one common type of an infrared thermal imaging device. Energized electrical systems generate heat because of electrical resistance. The amount of heat generated is related to the amount of current flowing through the system and the resistance of the individual system components and connections within the system. As components deteriorate, their resistance increases, causing a localized increase in heat. Similarly, a poorly made connection will have higher resistance than a well-made connection, along with a higher temperature profile. Thermography may be used to detect these temperature differences.
An RCD is a protective device used to automatically disconnect the electrical supply when an imbalance is detected between live conductors in a Three Phase Circuit. In the case of a Single Phase circuit, the device monitors the difference in currents between the line and neutral conductors.
RCD and ELCB Testing is done by simulating an appropriate fault condition – by injecting a low magnitude fault current say 30 to 200 mA to test whether the device/breaker will trip. This Electrical test is recommended since any test facility or test button, incorporated into the device can check only the mechanical operation of the breaker.
Protective relays, also called protection relays, prevent unnecessary trips, isolate faults, protect transformers, breakers & motors and provide electrical system information.
With usage, the connections of relay get deteriorated or contaminated with carbon particles, etc. Since these are critical protection equipment, it is the interest of the end user to check the healthiness and behavior of relays periodically through a secondary current injection method.
An RCD is a protective device used to automatically disconnect the electrical supply when an imbalance is detected between live conductors in a Three Phase Circuit. In the case of a Single Phase circuit, the device monitors the difference in currents between the line and neutral conductors.
RCD and ELCB Testing is done by simulating an appropriate fault condition – by injecting a low magnitude fault current say 30 to 200 mA to test whether the device/breaker will trip. This Electrical test is recommended since any test facility or test button, incorporated into the device can check only the mechanical operation of the breaker.
Protective relays, also called protection relays, prevent unnecessary trips, isolate faults, protect transformers, breakers & motors and provide electrical system information.
With usage, the connections of relay get deteriorated or contaminated with carbon particles, etc. Since these are critical protection equipment, it is the interest of the end user to check the healthiness and behavior of relays periodically through a secondary current injection method.
Every circuit must be tested to make sure that the actual loop impedance does not exceed that specified for the protective device concerned. Because of the severity of coming into contact with an electrical fault, having your electrical installations and power points tested for earth fault loop impedance is crucial. Your systems are valuable and circuitry needs to be maintained for the durability and functionality of your business. In most homes, basic shock protection is done by organizing an earthing circuit with automatic switches in the indoor wiring circuits. This quickly cuts off supply to an earthing circuit where a fault occurs and touch voltage exceeds an acceptable limit.
According to the current national safety standards, you are required to conduct a loop impedance test on your premises to ensure the safety of all guests and employees. The electrical earth of all your electrical installations and power points has to be tested to discover any faults within your electric circuit. Having a functional earth return circuit will allow the detection of circuit faults and facilitate a reaction from your MCB (miniature circuit breaker). PWA technician will detect the resistance level in your earth return circuit and notify you if it is at the wrong level – it needs to be low enough to allow the circuit breaker to function correctly. PWA will inspect and test your electrical wiring and by asking us to test you are protecting both your employees and your liability. It is important to adhere to national legislation to avoid harsh penalties.
The required values of impedance and time will change dependent upon the type of installation (TN/TT etc.) and the type of protection, whether it be a miniature circuit breaker (MCB), cartridge fuse, or rewireable fuse for example. The fault current can either be in the Line-Neutral or Line-Earth circuit, so there is a need to confirm the loop impedance of each.
It is generally accepted that, where the measured earth fault loop impedance of a circuit is not greater than 80% of the relevant limit specified in BS 7671, the impedance can be expected to be sufficiently low under earth fault conditions to meet the relevant limit specified in BS 7671, and for the protective device to automatically disconnect within the time specified.
Proper protection against electric shock hazards is given when the TT wiring system complies with:
Ra x Ia <50,
Where “Ra” is the sum of the resistances of earth bars and protective conductors and “Ia” is the maximum current of the protection system. Ra multiplied by Ia should not be more than 50 V, i.e. the maximum voltage one can touch will not exceed 50 V in the event of an earth fault.
A fault loop impedance test is done between the active conductor and the earth. To test the loop impedance our technician will use an earth loop impedance tester which is plugged into the power socket (GPO) to take a reading.
Our highly-trained staff are fully mobile and offer earth loop impedance test services across the nation
The purpose of this test is to establish that the resistance of the soil surrounding an earth electrode is suitable and that the electrode makes contact with the soil
An earth electrode and earth electrode resistance are defined in BS 7671 as Earth electrode – conductive part, which may be embedded in the soil or in a specific conductive medium, e.g. concrete or coke, in electrical contact with the Earth. Earth electrode resistance – the resistance of an earth electrode to Earth. In a TT system where a connection to earth is not provided by the supply authority, it is still necessary for an LV final circuit protective device to disconnect an earth fault within 0.2 s. In order to achieve this, suitable maximum earth fault loop impedance must be provided, as noted in Regulation 411.5.4 of BS 7671. It is generally not possible to comply with this Regulation using only an earth electrode earth return so a residual current device (RCD) is usually installed. Regulation 411.5.3 details the requirements for RCD performance and Table 41.5 provides values of the maximum earth fault loop impedance for different RCD-rated residual operating currents. It should be noted that the terms ‘resistance’ and ‘impedance’ are used rather interchangeably in earth fault loops – although they actually have different meanings – as most of the circuit is just resistance with inductive reactance only in the supply transformer and larger supply distribution cables. Contact with Earth can also be made through other metalwork extraneous-conductive parts associated with an electrical installation, such as structural steelwork, metal, water or gas supply pipes, or other buried metalwork. The effect of this other metalwork may be seen to reduce the overall earth electrode resistance, but it cannot be relied upon as an electrode as it could be removed or replaced at some future time. Regulation 542.2 of BS 7671 details what may be used as an earth electrode. An earth electrode may be in long-term contact with a corrosive environment and so allowance must be made for possible corrosion or the electrode made of material that can withstand corrosion. When a new earth electrode is installed the installer will know its construction and location and some details of the surrounding soil condition, but its earth resistance can only be determined by a test measurement. During a periodic inspection of an existing earth electrode, the situation is less certain as there are unlikely to be details of its construction or its buried location. In addition, it may well have corroded to some degree and the inspector will have no knowledge of the underlying soil conditions so the resistance can only be ascertained by measurement.
Electrical resistivity is the measurement of the specific resistance of a given material. It is expressed in ohm-meters and represents the resistance measured between two plates covering opposite sides of a 1 m cube. This soil resistivity test is commonly performed at raw land sites, during the design and planning of grounding systems specific to the tested site
Soil resistivity testing is the process of measuring a volume of soil to determine the conductivity of the soil. The resulting soil resistivity is expressed in ohm-meter or ohm-centimeterSoil resistivity testing is the single most critical factor in electrical grounding design. This is true when discussing simple electrical design, dedicated low-resistance grounding systems, or the far more complex issues involved in Ground Potential Rise Studies (GPR). Good soil models are the basis of all grounding designs and they are developed from accurate soil resistivity testing.
This test requires the user to place four equally spaced auxiliary probes into the earth to determine the actual soil resistance, traditionally in ohms-cm or ohm-m. This test must take place around the entire area to determine the soil value at all locations. This test is done at different spacing, 5 to 40 feet, to determine the resistance value at various depths. This knowledge will aid in the design and implementation of the correct ground system to meet the particular site requirements. Following are the steps are done in measuring soil resistivity:
4 test rods are evenly placed apart in a straight line and are hammered into the ground to be reviewed to a deepness of no greater than one by the twentieth of the distance between the neighboring rods.
An earth resistance tester is connected to these four stakes.
The DC test option on the tester is then selected and performed, and the resistance figure R is recorded.
The soil resistivity level r in ohms/cm is then found out using the formula
r = 2 ρaR
where: R = the resistance (in ohms), a = the separation of the test stakes, in meters.
The electrical device which can transfer electrical energy from one circuit to another circuit (without any connection) utilizing mutual induction between the windings, is called a transformer. It works on the principle of electromagnetic induction. The transformer consists of the primary winding and secondary winding. It is used to increase or decrease the voltage levels of a circuit. In the entire electrical distribution system, the transformer is the main part. If the transformer doesn’t work properly, then the entire distribution system may get damaged and there will be no chance of transferring electrical energy. The electrical circuit can get damaged due to mechanical failures, electrical damage, thermal damage, and winding deformity. So, the functioning of the transformer should be checked by using the transformer testing process to avoid failures. The transformer testing can be done to determine the specifications, and performance of an electrical transformer. To meet the specific design and specifications, transformer testing should be done during the manufacturing process.
Types of Transformer Testing
To reduce electrical failures, mechanical failures, winding deformation, thermal failures, and insulation breakdowns of a transformer, transformer testing should be done. The transformer testing can be done in different types. They are,
- Routine tests
- Type tests
- Special tests
- Pre-commissioning tests
- Periodic or condition monitoring tests
- Emergency tests.