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Electrical Maintenance

Facets of the work include testing, fixing and replacing equipment in buildings owned by corporations, government entities and modern industrial plants. Electrical maintenance is performed on hardware, systems, controls and components of the equipment.

In order to perform electrical maintenance, technicians must know several key components of electrical equipment systems. Transformers, electrical machines, digital communications and fundamentals of electricity are all important aspects of electrical maintenance.

One essential ingredient is knowledge of the SANS 10142, the wiring code. In addition to familiarity with local Municipal regulations.

 



Electrical Maintenance : Test Instruments : Infra Red Thermal Imager Digital Multi Meters

 

Preventive maintenance is far more cost-effective and efficient than performing maintenance when failures occur.

Unplanned downtime caused by equipment failures costs manufacturers millions in revenue every year. In some industries, the labour costs alone associated with downtime are calculated by the second.

Preventive maintenance – measuring key indicators on critical equipment to discover impending failures and then scheduling maintenance before equipment failures and downtime – is far more cost-effective and efficient than waiting to perform maintenance when failures occur.

To implement a proactive maintenance program, it is important to know which equipment needs repair, as well as the root cause of impending failures. Using test tools to measure key indicators on critical equipment regularly helps our electricians at RSA Bardo Electrical Systems uncover the root causes of emerging failures.

Preventive maintenance with planned downtime enables maintenance managers to minimise the amount of time a facility is out of operation; make the best use of personnel, and to have the required spare parts on hand.

This article describes using the following test tools to make measurements, track equipment condition over time and to diagnose failure conditions:

  • Digital multimeters (DMMs).
  • Clamp meters.
  • Infrared thermometers.
  • Insulation resistance testers.
  • Thermal imagers.
  • Vibration testers.

Service Contracts can be drawn up with Commercial enterprises, which will include SLA's (Service Level Agreements) which indicates how often our company will come to site, to replace lamps, check the lux levels, do thermal infra red scans / reports. Report back on any urgent electrical work that needs to be done.

RSA Bardo Electrical Systems also does UPS Maintenance and Generator Services.

Facility Managers of Commercial Buildings please make contact with RSA Bardo Electrical Systems for more information

Regarding Factory Maintenance, lamp replacement on High Bays, is often undertaken on a Monthly Bases.

Distribution Boards are checked for Hot Spots with an Infra Red Camera, reported and then corrected.

Most maintenance can be done live, although these is a time, for example repairs to the Power Factor Correction panel that needs to be powered down. This type of work can be done after-hours and on weekends.

A full Method Statement would be issued, and all role players informed.

For further information, please email rob@bardo.co.za or call: 071 533 6466

Thermal Infra Red Imagers / Cameras

Thermal imagers discover abnormalities and weak points quickly and efficiently, making them ideal for production monitoring and many other applications. Materials and components undergo non-destructive testing under operating conditions, allowing problems to be discovered before a breakdown occurs or a fire risk develops

Current Carrying Capacity of Conductors

Conductors are an electrical term for cable and wire. By using Clamp Meters we can determine how stressed the conductor is under load conditions. We can also determine, if its a three phase installation, if the load is balanced.

Equipment Key Indicators Measurement Test Instrument
UPS / PDU Intermittent Tripping
Process Interrupts
RMS voltage, rms current, frequency (Hz), connection resistance, data log readings over time for anomalies IR, DMM, TI
Transformer Heat
Buzzing
Temperature, impedance at neutral ground bond, voltage balance, current balance, loose connections IR, DMM, CM, TI
Panels, Switch Boards Intermittent Tripping
Hot Circuit Breakers
Voltage balance, current balance, data log readings over time for anomalies, loose connections, temperature IR, DMM, CM, TI
Lighting Panels Flickering Lights
Buzzing
Voltage balance, current balance, data log readings over time for anomalies, loose connections, temperature IR, DMM, CM, TI

Insulation resistance to ground

Disconnect any electronic controls before testing cabling and motors as misapplication of high voltage test equipment can destroy them.

Conducting the following insulation resistance tests regularly on loads and connections can help detect imminent equipment failure:

  • Ground testing line and load circuits at the starter will identify the resistance to ground of the starter, line circuits to the disconnect and load lines to the motor and starter windings.
  • In terms of general thresholds, AC devices can operate safely at no less than two megohms to ground and DC devices can safely operate at no less than one megohm to ground.
  • When measuring the resistance of a 3-phase motor between the load legs of the starter, you should see high resistance and roughly equivalent measurements between phases.

Note: Insulation resistance to ground tests conducted with an insulation resistance tester require disconnecting the components or cabling to be tested from the power system. Remember to incorporate this requirement into planned downtime.

Temperature

Infrared thermometers are a low-cost monitoring option for quick, frequent measurements of specific components while equipment is operating. Use your knowledge of the equipment to identify key hot spots to track, compare those temperature readings to operational limits, and watch for upward trends.

For example, scan the bearing housings on motors, the switches in circuit breaker panels, and the wiring connections at all equipment. For the best measurements, get as close as is safely possible to your target, make sure you’re not measuring a reflective surface, and compensate for emissivity.

Thermal imaging

Thermal imaging tools play a key role as screening tools in a preventive maintenance program You can use them to measure and compare heat signatures quickly for each piece of equipment on an inspection route without disrupting operations. With a thermal imager, you can quickly survey a much larger area than an infrared thermometer, and see how the temperatures of different areas relate to each other.

If the temperature or thermal pattern is markedly different from previous readings, you can use other maintenance technologies such as vibration analysis, motor circuit analysis, airborne ultrasound, and lubricant analysis to assess the severity of the problem and the time needed to repair it.

Thermal imaging applications

  • Monitor and measure bearing temperatures and condition in large motors or other rotating equipment.
  • Identify “hot spots” or “cold spots” in electronic equipment.
  • Identify leaks and determine fluid levels in sealed vessels and tanks.
  • Find faulty insulation in process pipes or other insulated processes.
  • Find faulty connections in high power electrical circuits.
  • Locate overloaded circuit breakers in a power panel.
  • Identify fuses that are at or near their current rating capacity or that are installed improperly.
  • Identify problems in electrical switch gear.
  • Capture process temperature readings.
  • Perform other equipment-specific troubleshooting and diagnostics.

Resistance

Resistance measurements must be made with the circuit power off. Otherwise, the meter or circuit could be damaged. A digital multimeter can check the resistance across most connections. High resistance readings can signal degraded connections, which can cause reduced supply voltage, nuisance tripping and potential equipment failure.

  • High resolution DMMs can also measure the resistance across relay and circuit breaker contacts. Resistance goes up as the contacts degrade.
  • IR thermometers can also identify high resistance connections which show up as hot spots when compared to a good connection.

Most DMMs measure down to 0,1 ohm and some measure as high as 300 megohm. For accurate low resistance measurements, use the DMM’s REL function to eliminate test lead resistance.

DC and AC current

Loads may draw slightly higher current as they age. Measuring current regularly can help you track equipment reliability. Use either a clamp meter or a DMM combined with a current clamp to measure current.
Remember to move test leads back to their voltage-measuring connections before attempting a voltage measurement after measuring current with a DMM.

Voltage balance

A voltage imbalance greater than 2% can reduce equipment performance and cause premature failure. Use your DMM to check voltage between phases for voltage drops at the protection and switchgear delivering power from the utility and at high-priority equipment.

Voltage imbalance can be calculated with the following formulae:

fluke-eqn-1

fluke-eqn-2

Voltage drops across the circuit breakers and switches can also show up as imbalance at the motor and excess heat at the root trouble spot. Before you assume you’be found the cause, double-check with a thermometer.

Current balance

Current imbalance is another root cause of overheating in equipment. Use a clamp meter or an AC current clamp with your DMM to check the current draw on each of the three legs. To determine average current, sum the current from all three phases and divide by three. Then, calculate the percent imbalance by subtracting the actual on one leg from the average amps, then divide by the average amps and multiply by 100 (see Eqn.4). More than 10% current imbalance can be a problem.
fluke-eqn-3
fluke-eqn-4
Inrush current

If a motor isn’t performing correctly or if your circuit is tripping unexpectedly, check inrush current at startup with a clamp meter or a DMM designed to capture inrush current. Inrush current can reach up to twelve times the normal operating current – much higher than the circuit breaker rating – without tripping the breaker, as long as the circuit isn’t overloaded. Evaluating inrush current depends on comparisons of inrush measurements over time for that motor.

Data management

Capturing electrical, temperature and vibration data during normal operation and troubleshooting is an important aspect of preventive maintenance. The traditional approach involves jotting individual measurements down on a notebook and later, if ever, transferring the data onto clipboards, spreadsheets or into a computerised maintenance management system (CMMS). Then, measurements are compared to assess equipment health. Test tools with wireless capability such as those part of the Fluke Connect platform can capture baseline and troubleshooting data and use a smart-phone to transfer the data to the cloud. This wireless work flow eliminates transcription errors and saves time.

Stored securely in the cloud, the data can be compared, trended and analysed from anywhere. Such analysis helps identify degradation of equipment that might be early indications of failure. Maintenance can be planned before operations are impacted.

Safety and test tool rating requirements

Before you start using your digital multimeter (DMM) or other test tools for proactive maintenance, make sure you understand the limitations of your tool and the safety precautions that go along with it.

  • Choose a DMM rated for 1000 V CAT III/600 V CAT IV and a clamp meter rated for 600 V CAT III.
  • For DMMs, look for true-rms, resistance of 0,1 ohm or less, capacitance test to 9,9 microfarads, and frequency. If you’re tracking data over time, get a DMM with data/event logging abilities and fast min/max, sufficient memory, extended-life batteries, an optical port and software for downloading measurement results to your computer.
  • For typical industrial and commercial motors, choose an insulation resistance tester with a minimum of 500 V output and resistance measurements to several gigohms.
  • Determine how close you can stand safely to your equipment during temperature measurements and use that to determine what distance-to-spot ratio your infrared thermometer must support. A distance-to-spot size ratio of 50:1 allows accurate measurement within 2,4 m, depending on target object emissivity.
  • Consider wireless test tools that let you take measurements from a safe distance and monitor on a smartphone.
  • Ensure that the voltage rating on your test probes matches your test environment. Insulation resistance testing typically requires high voltage probes, as do some DMM tests.
  • If you must make live measurements in a 3-phase environment, wear the appropriate personal protective equipment (PPE), use the three-point test method and, if possible, keep one hand in your pocket to prevent current transfer.

For any further information contact Rob Bardo. Cell: 071 533 6466

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