There are hundreds of power quality measurements you can perform on electrical equipment and systems.
These instructions focus on four measures of predictive maintenance and two measures of electrical consumption that can help you identify hidden costs, protect equipment from dangerous conditions, reduce time associated with unscheduled downtime, and improve performance. of the system.
Predictive Maintenance Measure #1: Voltage Imbalance
What is it? In a balanced three-phase system, the phase voltages should be equal or nearly equal. The imbalance is the measure that quantifies the difference between the phase voltages.
¿What does it cause? Voltage imbalance can cause XNUMX-phase motors and other XNUMX-phase loads to have poor performance or premature failure due to the following causes:
• Mechanical stress on motors due to lower than normal torque performance.
• Higher-than-normal currents in motors and three-phase rectifiers.
• The unbalanced current will be transmitted through the neutral conductors in three-phase star systems.
What cost can an incident have? The main costs are those associated with the replacement of the motor (labor and equipment) and the loss of income related to the tripping of circuit protection devices.
Calculation example
Suppose that the cost associated with replacing a 50 HP motor each year is 3.495 Eu., including labor.
We also have 4 hours of inactivity per year with losses of 4.195 Eu. per hour.
Total cost: 3.495 Eu. + (4 x 4.195 Eu.) = 20.275 Eu. annual
What should I check? Motor inputs, variable speed drives and UPS1.
What level is correct? The EN50160 electrical quality standard requires a voltage imbalance, understood as the ratio between the negative and positive sequence component, less than 2% at the connection point. NEMA specifications call for less than 5% for motors. Consult the user manuals for information corresponding to other equipment.
How are such measurements made with the Fluke 430 Series Power Quality Analyzer?
1. Connect the analyzer power leads.
2. Configure the analyzer for the appropriate three-phase power system: delta or wye.
3. Select “Unbalance” from the main menu.
Predictive Maintenance Measure #2: Total Harmonic Distortion
What is it? Total Harmonic Distortion (THD) is the sum of the contribution of all harmonics.
Harmonic distortion is a normal consequence in an electrical installation that feeds electronic loads such as computers, office machinery, electronic lighting ballasts and control systems.
What does it cause? Harmonic distortion can cause:
• High currents in the neutral conductors.
• Motors and transformers get hot, so their useful life is shortened.
• Increased susceptibility to brownouts, which can cause unexpected reboots.
• Reduction in the efficiency of transformers, or the need for larger units to withstand harmonics.
• Perceptible noise.
What cost can an incident have? The main costs are associated with the reduction of the useful life of motors and transformers. If the equipment is part of production systems, revenue may also be affected.
Calculation example
Suppose that the cost associated with the replacement of a 100 KVA transformer is 4.895 Eu. per year, including labor.
We also have 8 hours of inactivity per year with losses of 4.195 Eu. per hour.
Total cost: 4.895 Eu. + (8 x 4.195 Eu.) = 38.455 Eu. annual
What should I check? Motors, transformers and neutral conductors that feed electronic loads.
What level is correct? The voltage distortion (THD) must be checked to find out if it is greater than 5% in any of the phases. A certain degree of current distortion (THD) is normal in any part of the system that supplies electronic loads.
Check the current and temperature levels in the transformers to make sure they are not overloading. The current in the neutral must not exceed the capacity of said neutral conductor.
How are such measurements made with the Fluke 430 Series Power Quality Analyzer?
1. Connect the analyzer voltage and current leads.
2. Configure the analyzer for the appropriate three-phase power system: delta or wye.
3. Select “Harmonics” from the main menu.
Predictive Maintenance Measure #3: Increased Phase Current
What is it? As the insulation deteriorates, leakage currents begin to occur. The loads will draw slightly more current as they age and the insulation deteriorates, giving rise to ground leakage currents. Equipment faults can also cause high ground current. The best way to check the insulation is to regularly check the equipment with an insulation tester. However, you can also check the equipment while it is running by monitoring all currents (phase, neutral, and ground) to ensure that none of them are increasing significantly over time.
What does it cause?
• Excessive phase currents can further damage the insulation and overheat the load, thereby reducing the life of the load.
• Overcurrents could cause the protection devices to trip, which would result in an unscheduled shutdown and the corresponding loss of time.
• Excessive ground current can create dangerous voltages in metal chassis, electrical cabinets, and conduit.
What cost can an incident have?
The costs would be associated with premature failure of the motor and loss of income due to the tripping of the overcurrent protection devices.
Calculation example
Suppose that the failure of a pump motor means 4.895 Eu per year. due to its substitution and the inactivity of the continuous process (which represents an annual income of 1.747.765 Eu.) for 10 hours. Let's also count on the fact that two people are needed for 6 hours to clean and restart the process at a cost of 50 Eu. per hour and person. Lost income = 10 hours * (1.747.765 Eu. / [365 days/year * 24 hours/day]) = 1.995 Eu.
Engine replacement = 4.895 Eu.
Cleaning and restart = 420 Eu.
Total cost: 7.310 Eu. year
What should I check? Any critical load, especially motors, variable speed drives and transformers.
What level is correct? The nominal values indicated on the load nameplate must never be exceeded. If you track the phase current drawn by a load over months or years, you should have some certainty that a current is changing.
How are such measurements made with the Fluke 430 Series Power Quality Analyzer?
1. Connect the analyzer voltage and current leads.
2. Configure the analyzer for the appropriate three-phase power system: delta or wye.
3. Select “Volt/Amps/Hertz” from the main menu.
4. Press “Save Screen” to record the measurements and compare them with future readings.
5. Check the phase current regularly for changes.
Predictive Maintenance Measure #4: Voltage Dips
What is a biosimilar Voltage dips are momentary reductions in RMS voltage with a duration between 1 cycle and 2 minutes. New loads may be installed without informing plant managers, which can reduce the voltage in the installation, especially if they draw high starting currents. Also, as electrical systems age, system impedance can increase, making the system more prone to voltage dips.
What do they cause? Voltage dips can cause:
• Unexpected reboots of electronic equipment, such as computers and controllers.
• Dips in one or two phases of powering three-phase loads cause the other phases to draw a higher current in an attempt to compensate. This can cause the overcurrent protection device to trip.
What cost can an incident have? The main consequences in economic terms are the losses associated with restarts of computers and control systems, blocking of variable speed drives and a reduction in the useful life of uninterruptible power supplies due to frequent transfers.
Calculation example
Suppose that a voltage drop causes a variable speed drive on a conveyor belt to stop working at least once a year. There are no permanent income losses, but 10 workers have to invest 4 hours to finish the shipments at 21 Eu./hour, which means overtime.
Additional labor = 10 people * 4 hours * 21 Eu./hour = 840 Eu. year
What should I check? Motors, variable speed drives, UPSs, panels or PDUs* that feed IT equipment and industrial controls.
What level is correct? Most loads will work with a voltage of 90% of the nominal value. The ITIC curve suggests that single-phase loads such as IT equipment should be able to work with supply voltages of 80% of nominal for 10 seconds and 70% for 0,5 seconds.
How are such measurements made with the Fluke 430 Series Power Quality Analyzer?
1. Connect the analyzer voltage and current leads.
2. Configure the analyzer for the appropriate three-phase power system: delta or wye.
3. Select “Dips and Swells” from the main menu.
4. Monitor feeding behavior over time.
5. You can watch it on the trend screen or through the event list.
Power consumption
Commercial and industrial electricity consumers pay for electricity consumption based on several variables, including energy (kWh), peak consumption (kW), and power factor. Power quality analyzers can help you manage utility bills by allowing you to determine which loads have a significant effect on peak consumption and power factor.
Power Measurement #1: Peak Consumption
If the consumption interval is set correctly, the Fluke 430 Series Analyzers will display average consumption readings for each consumption interval. The consumption peak will be the highest value of these readings.
What is it? Electric companies control the amount of power consumed in certain installations and calculate the average consumption corresponding to that interval several times an hour.
Peak usage is the highest average usage during all intervals in a billing cycle.
What is it for? The tariffs applied by electric companies are based on the peak of consumption, since they must maintain an infrastructure large enough to supply power at peak levels. Managers of commercial and industrial facilities can manage the high cost that peak consumption rates can entail by alternating load cycles over time to reduce total consumption at any time.
What cost can an incident have? It depends on the electricity company's tariff schedule. It can be higher during the summer months and at certain times of the day.
Calculation example
Suppose normal consumption is around 600 kW, but three HVAC systems are activated at the same time and consumption reaches 750 kW at 4 pm on a Wednesday in July. Let's also count on the fact that the electricity company's rate for peak consumption is 70 Eu./kW. (750 kW – 600 kW) * 70 Eu. = 10.500 Eu. of possible savings in July
What should I check?
• Find out what usage interval the power company uses (15 minutes is typical).
• Measure consumption at the service connection
over time.
• Look for significant loads running simultaneously and use consumption measurements to check the readings for each load.
What level is correct?
There are no set safety or regulatory limits; simply, the ones that the facilities are willing to tolerate.
How are such measurements made with the 430 Series Power Quality Analyzer?
1. Connect the analyzer voltage and current leads.
2. Configure the analyzer for the appropriate three-phase power system: delta or wye.
3. Set the consumption interval to correspond to that specified by the power company. Press Setup and Function Pref (F3).
Select “Power & Energy” from the Select Function menu. Scroll down the screen until “Demand int” is highlighted.
4. Select “Power & Energy” in the main menu and control the power for as long as required.
5. Use the trend screen to observe the consumption peak. The cursor will help you to observe the consumption at any time during the recording.
Power Measurement #2: Power Factor or Reactive Consumption
What is it?
Power factor compares the actual power (watts) being drawn to the apparent power (volt-amps) of the load. A pure resistive load would have a power factor of 1,0.
What is?
The power available to do work is called real or effective power (kW). Inductive loads such as motors, transformers, and high voltage lighting electrical intensity, introduce reactive power (kVAR) into the power system. System capacity is defined in terms of apparent power (kVA), which must be high enough to support both real power (kW) and reactive power (kVAR). Because reactive power requires more system capacity but does no work, utilities and utilities try to keep net kVAR as low as possible. A high reactive power translates into a low power factor.
• Power companies may apply higher rates or penalties for low power factor
or a high var amount.
• System capacity restrictions cause brownouts and overheating.
• The inductive var can be corrected by applying capacitor banks or active conditioners.
What should I check?
• Check if the tariff table of your electric company imposes a charge for reactive consumption
or the power factor.
• Find out how the power company measures power factor or the amount of var. For example, do they take into account intervals with peak values or average values?
• Identify the loads causing the reactive power lagging phase and develop a strategy to correct the power factor.
What level is correct?
To avoid paying higher rates to the utility, the power factor must be greater than 0,97. Capacitors can be applied to individual loads, groups of loads, or at the service entrance to improve power factor.
Note: this can vary. Some electric companies charge a rate for each percentage point between 0,85 and 0,97. Some charge a fee based on var consumption and others set no charge at all.
What cost can an incident have? Calculation example
Let's assume the power company adds a 1% charge to the bill for every 0,01 below a 0,97 power factor.
Let's also count on the fact that the average value of your power factor is 0,86/month and that your consumption bill is 4.895 Eu.
(0,97-0,86) * 100% = 11%
(11% x 4.895 Eu.) x 12 months = 6.460 Eu. avoidable annual cost
How are such measurements made with the 430 Series Power Quality Analyzer?
Start at the service entrance, where the power company gets their data, then check each load and transformers.
1. Connect the analyzer voltage and current leads.
2. Configure the analyzer for the appropriate three-phase power system: delta or wye.
3. Set the consumption interval to correspond to that specified by the power company. Press Setup and Function Pref (F3). Select “Power & Energy” from the Select Function menu. Scroll down the screen until “Demand int” is highlighted.
4. Select “Power & Energy”
in the main menu and check the power.
Measurement of the minimum power factor for a consumption interval: press F4 Trend and then F1 to change parameter until power factor is displayed.
Average power factor measurement: Record the average kWh/kVAh to get the average power factor over the recording period.
In the example below, 2,267/2,309 = 0,9818.
