PCE Instruments Power Quality Analyzer
The measurement of power and power quality includes the basic parameters of voltage, current, watts (kW, VA, VAR) or the basic parameters of energy (kVAh, VARh, kWh). When evaluating the power utilized in a system, there are many options when choosing what to measure and whether recording of the power system is required. Based on your individual goals, purpose and problems, you may desire to measure Power, Power Quality, Power Logging, Energy Management, Event Recording, Transients, Sags, Swells, or Waveforms. Many parameters must be considered when looking at power and power quality including AC or DC voltage, AC or DC current, watts, kW, VA, VAR, PF, THD, Harmonics, or energy including kVAh, VARh and kWh. In addition to effectively performing basic tasks like measuring voltage, current, and power (wattage), power instrumentation varies considerably and you may consider ease of use, portability, and flexibility as well as capturing waveforms, event and parameter data logging and recording parameters. Each instrument may vary on capability, but the application and solution desired will dictate which instrumentation will be perfect for the application. There are many parameters needed to resolve most power issues and problems in commercial, industrial, and residential settings. The first consideration is always the wiring system in question.
Wiring Systems
The following configurations are some of the most common wiring systems used for measurement of power and power quality with additional wiring configurations available in specific instruments, including a three phase four wire Delta and others.
Single Phase Three Wire
This is the most common residential service in North America. Line 1 to neutral and Line 2 to neutral are used to power 120 volt lighting and plug loads. Line 1 to Line 2 is used to power 240 volt single phase loads such as a water heater, electric range, or air conditioner.
Three Phase Four Wire Wye
The most common commercial building electric service in North America is 120/208 volt wye, which is used to power 120 volt plug loads, lighting, and smaller HVAC systems. In larger facilities the voltage is 277/480 volt and used to power single phase 277 volt lighting and larger HVAC loads. In western Canada 347/600V is common.
Three Phase Three Wire Delta
Used primarily in industrial facilities to provide power for three-phase motor loads, and in utility power distribution applications. Nominal service voltages of 240, 400, 480, 600, and higher are typical.
The second consideration is the system itself and the type of Voltage and Current in the system. The following formulas are utilized for DC and AC circuits.
Power Measurement Formulas
For all DC Circuits and Resistive loads, P (power) is related to I (current) and V (voltage) and R (resistance) according to the following formula:
P = I2R = V2/R
For all AC circuits, including the source, inductive elements and capacitive elements, the formula used for defining power is shown as:
P = (½)VpIpcosθ = VrmsIrmscosθ
Where
Vp is the peak voltage,
Ip is the peak current,
Vrms is the rms voltage,
Irms is the rms in amperes, and
θ is the phase angle current and voltage.
In AC circuits, elements such as inductors and capacitors alter the direction of energy flow. The portion of power flow that, averaged over one cycle of the waveform, is known as “real power” (also referred to as active power). That portion of power flow due to stored energy is known as "reactive power”. In reality, most loads contain resistance, inductance, and capacitance, so both real and reactive power flows to the load. Apparent power is the vector sum of real and reactive power. Apparent power is the product of the root mean square of voltage and current and can be found displayed below in the Power Triangle.
Engineers, building managers, and consultants are concerned with apparent power, even though the current measured as reactive power does no work; it heats the system wiring, causing energy losses as well as possible heat and component failures. Energy and Power is costly. Wasting Power and Energy is not a goal for any user or owner of any system. Once problems are found, wiring systems, components and generation equipment must be sized properly to handle all the current produced.
The Power Triangle
These three types of power -- true, reactive, and apparent -- relate to one another in what is referred to as the power triangle. The relationship between real power, reactive power, and apparent power is shown below as vectors. P, Real power (true power, watts) is the horizontal vector and Q, reactive power (VAR) is the vertical vector. S, apparent power, (VA), is the hypotenuse of the right triangle below. The angle between the hypotenuse and the base of the triangle is Z, the impedance phase angle.
The sine waves below and the Phasor diagram display the relationship between the Voltage and Current in a typical measured system. Note that the current lags the Voltage by 90 degrees.
Voltage and Phasor Diagrams
![Voltage-Phasor-Diagram]()
Power Quality
Poor power quality can be extremely expensive since it increases energy costs. That may include excess power usage as well as being penalized for increasing poor power factor or higher peak demand utility charges that might not be necessary. Poor power quality takes its toll on equipment. This will increase the cost of maintenance and repairs. Replacement of premature failures of equipment as well as the cost of the diagnosis and replacement of this equipment can be extremely costly.
Although every user has a primary purpose in mind when checking and evaluating Power and Power Quality, the most common purpose is the measurement of how reliably and efficiently your systems operates under load. We usually begin to evaluate our systems response and use of electricity, but in utilizing power instrumentation, we may need to evaluate many parameters, including, but not limited to:
- Voltage, Current and Frequency Disturbances
- System Dips, Sags, Swells
- Harmonic Distortion
- Unbalances
- Transients
- Flicker
System problems are evaluated based on measuring the source and direction of the impending problem as well always measuring magnitude and direction. The timing of the problem is always important, whether one microsecond or one hour in length
Normal system analysis usually involves the measurement of voltage and frequency deviations. Most instrumentation will detail the range of measured values and the safety category capability of the instrumentation. Please use the link below to see the most recent advance in NFPA 70E.
Who sets the rules for electrical testing and safety?
Typical Applications for Power and Power Quality Measurement
- Verification of power distribution circuits
- Measurement and recording of power system quality (kW, VA, VAR)
- Energy metering (kVAh, VARh, kWh)
- In plant troubleshooting of power distribution panels and individual machinery
- Monitor pad mount transformers
- Determine harmonic problems originating from source or load
- Monitor phase unbalances
- Determine transformer K-Factor
- Setup and troubleshoot variable frequency drives and UPS systems. Verify correct operation by measuring key power quality parameters
- Harmonics Measurements. Uncover harmonic issues that can damage or disrupt critical equipment
- Inrush capture. Check start-up current where spurious resets or nuisance circuit breaker tripping occurs
- Load studies. Verify electrical system capacity before adding loads
- Energy Audits
- Predictive Maintenance
- Long Term Intermittent Analysis
Harmonics Definitions and Measurements
Most concerns for any Power quality system evaluation will include the measurement of Harmonics. Harmonic Analysis involves the real time existence of waveform distortions. As a definition, harmonic frequencies are odd end even multiples of the 60Hz (hertz) first fundamental frequency. The second harmonic is at 120Hz, (twice the fundamental); the third harmonic is at 180Hz and so-on. When all the frequencies are summed, the result is the measured waveform. Any deviation from a pure sinusoidal (sine) waveform indicates the existence of harmonic components. Harmonics may exist in any short or long time sequence, but harmonics only cause damage when they exist for a significant amount of time.
One reason harmonics cause so much damage is that they generate excessive heat. Some of the problems that may be caused by excessive harmonics are:
- Equipment failure
- Overloading of Power Apparatus
- Overloading Systems
- Instrument and Component Lifespan
- Degradation of Power Quality
- Unreliable Operation of Equipment
- Data Loss in Digital Equipment
- Overheating of neutral conductors and connections
- Overheating and premature failure of supply transformers
- Failure of Power Factor-correcting capacitors
- Excessive electrical noise
- Power interruption causing tripping circuit breakers and blowing fuses
- Power loss (due to heat loss in cables)
- Building wire failure
- Failure of Electronic Equipment
- Interference
Although Current and Voltage Harmonics exist and both may be detrimental to the system, current harmonics tend to be less severe as they extend from their point of origin; however, Voltage harmonics have a tendency spread and can damaging at a greater distance from their origins.
Harmonic Distortion
Once the source of the harmonic distortion is found, the process of determining how to prevent it and control it may begin. Following is a listing of common sources of harmonics typically listed as Non-Linear Loads i.e.,
- Personal computers and other microprocessor-based devices
- Uninterruptible Power Supplies (UPS)
- Fluorescent lighting (especially newer electronic ballast types)
- Battery chargers
- Static power converters
- AC heating controls
- AC and DC motor controllers
- Rectifiers
- Power supplies used in electronic and office equipment
- Power electronics such as Variable Speed Drives
- SCR-controllers
- AC/DC static converters
- Arc furnaces
- Welders
- Saturated Transformers
One of the most troublesome harmonics usually is the third harmonic and its odd multiples of the third. This is referred to as the Triplen Harmonics (3
rd, 9
th, 15
th, 21
st, etc.). These harmonics seems to be the most dominant and always have the highest magnitude and cause the most damage since the currents are additive on the neutral. The fifth (5
th) and eleventh (11
th) harmonics are also cause for concern since they will attempt to drive a 3-phase motor in the opposite direction and will possibly cause nuisance tripping and overheating.
It is important to establish the system evaluation; the harmonics that may be prevalent, any transients, sags, or swells and then attempt to find a mitigation approach to reduce problem areas.
Sometimes it is not evident until testing is done and measurements are made that small equipment added in a system over time may be the very culprit in producing damaging harmonics.
Power Meters Glossary Power Quality Overview
Power Quality vs. Power Demand