New approach to power quality monitoring

Keywords : power quality monitoring

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First, why should we care about the quality of power supply?

In the "single-phase" power supply environment of the office and home, there is always a desire for a continuous 220V power supply to power the equipment in the circuit. In fact, the voltage is constantly changing. To better understand the quality of power, you can use the car on the road as a metaphor: road quality affects the life of the car, and some effects are immediately seen (such as tire wear), but some effects will take some time to be revealed. Similarly, poor power quality will increase the power consumption of the equipment; increase the cost of quality assurance, increase downtime, and reduce equipment life. When the power supply indicator exceeds the limit, the voltage/harmonic monitor (such as the VPM of the Ideal Industrial Company's voltage/harmonic monitor 61-830) will promptly inform you of the specific information.

Second, why is the voltage abnormal?

In many cases, the “circuits” that are connected to the building are relatively flat, and the “road surface” becomes rugged due to the interaction between the devices. The change in voltage (so-called "circuit") can be seen in the figure below.

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For example, when you turn on the home air conditioner, the light will be dimmed because the load in the circuit is temporarily increased, which affects the voltage that maintains the brightness of the light. As shown in the figure above, the relationship between voltage and current in the circuit, the load current increases, and the voltage decreases in the corresponding period. Events like this can cause computer crashes, sensitive processing interrupts, data transfer errors, and many other issues.

Poor power quality can cause many problems that are difficult to diagnose and sometimes not. The impact of power quality varies with device sensitivity and its ability to adapt to voltage. Usually the equipment is designed to have a certain range of adaptation to the power supply. The problem is only noticed when the voltage is outside the design of the device, just as some cars are only suitable for driving on flat roads, while some cars are off-road. The voltage/harmonic monitor captures the event that caused the problem, allowing you to determine if the device problem is related to power performance and to verify that existing circuits can support the addition of sensitive equipment.

The current power fault location tool is either too simple or too complicated. Simple data logging devices typically periodically sample voltages and provide limited information. Event capture has the potential to affect your device, and important events may be missed. Complex power analyzers need to be set up and interpret recorded data, and are not designed for wall outlets. Since the appliance is directly connected to the wall outlet, this is the most important place to measure voltage.

Third, what is power quality?

Unless the distance from the substation is too far and is affected by too many factors, the power supply is usually clean when it is connected to the building. Conditions that affect the quality of the power supply often occur at the outlet. If you take an AC camera with an oscilloscope, you will find that the waveform is a sine wave, which is related to the principle of AC power generation. A smooth or intact sinusoidal waveform represents the quality of your AC power source. Loads, wires, and external factors can interfere with a smooth sinusoidal waveform, reducing the quality of power supply near the power inlet and downstream equipment. Voltage events and harmonics can cause a drop in power quality.

Also using the analogy of a moving car, it is like a car running on a "bumpy road" for a device operating in a circuit with a voltage event. In order to better understand the different forms of voltage events, we must first have a clear definition of them. Voltage events are described in terms of their size and duration. The so-called scale, that is: how serious the incident is; the duration, that is, how long the incident has existed.

Voltage dip (SAGS)

The instantaneous drop in voltage is called a dip. The reduction may be small (eg, 10% down) or last for a short period of time. The voltage drop lasts for more than 1 minute and is called “undervoltage”; for a complete power outage, it is called “interruption”. Voltage dips can be caused by heavy load starts, such as motors, heavy machinery, and even vacuum cleaners. The capacity of the power system and the impedance of the circuit all affect the scale of the voltage dip.

Voltage swell (SWELLS)

The voltage swell is exactly the opposite of the voltage dip. The voltage rises briefly for 0.5 second to 1 minute. This release of energy is caused by a sudden turn-off of the motor or heavy machinery. Voltage swells are less common than voltage dips but are more harmful. A sudden voltage rise of more than 1 minute is called "overvoltage." Sometimes, a voltage dip occurs when the load is turned on, and a voltage swell occurs immediately after the system is overcompensated.

Pulse (IMPULSES)

Very short, very high voltage swells or spikes are called pulses, and their scale may range from 2 times to several thousand volts of normal voltage, and durations range from less than microseconds to hundreds of microseconds or even seconds. The pulse is characterized by the superposition of extremely high voltage spikes on the normal voltage waveform. The pulse is due to the short-term release of energy accumulated in the inductor or capacitor in the power system.

Harmonic (HARMONICS)

Unlike the ups and downs of the road, the effects of harmonics are a series of repetitive small fluctuations, like driving on a shoulder. Harmonics present in the circuit can cause additional heat, interfere with communication lines, cause electronic devices to malfunction, and reduce power factor.

Non-linear loads, such as computers, copiers, and speed control devices, generate harmonics. These devices produce frequencies above 50 Hz in the circuit. A continuous "flat top" of the voltage waveform means that the power supply cannot provide the load with the voltage peaks required for its operation.

The more electronic devices are used, the more likely the voltage is to be disturbed. Harmonics affect traditional loads and wires, causing them to increase heat, false triggers, and noise from communication equipment.

The number of harmonics present is expressed as a percentage of Total Harmonic Distortion (THD). If the THD exceeds 5%, the cause should be investigated.

Voltage performance and power quality are equivalent. Knowing voltage dips, swells, pulses, and total harmonic content (%THD) can save you time and money.

3. What is the impact of voltage overrun?

Voltage dips Voltage Sags

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As shown in the figure above: A voltage changes for 7 consecutive days, and a short voltage drop occurs on the first day. You may ask, if the voltage is changing at any time, why is there no fault in the electrical equipment? The reason is that the voltage adaptation range of the electronic device is ±10% of the normal voltage. Moreover, the duration of the voltage change varies with the type of device. The first change in voltage does not necessarily damage the equipment, but if the voltage fluctuations are too long or voltage events occur frequently, beyond the tolerance of the equipment, the equipment will be damaged.

When the voltage does not meet the requirements of the equipment power supply specification, the equipment will become difficult to operate, overheat or cause the insulation performance to fail to meet the actual voltage change.

For example, the voltage adaptation range of a refrigerator is ±10% of the normal voltage. If the voltage dip shown in the above figure appears, the input voltage drop of the refrigerator is 108V (taking the North American 120V voltage standard as an example), the motor will generate heat and efficiency. reduce. Long-term or repeated voltage dips can reduce the life of the refrigerator motor, resulting in a variety of voltage drops, including excessive wire diameter, long lines, and excessive power equipment.

Voltage Swells

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The effect of a sudden voltage rise on the power system is different from the voltage dip, but the results are similar. As shown in the figure above: a circuit with several computers, repeated voltage swells. These recurring voltage spikes can cause hardware damage, crashes, and anomalies, which can be quickly eliminated if it is known to be caused by a power problem.

Harmonics

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As shown in the figure above: The switching power supply interferes with the AC waveform. The sinusoidal peak of the current has a subsidence. According to Ohm's law, the voltage is inversely proportional to the current. Once the current waveform becomes such a non-sinusoidal wave, the voltage waveform will also be affected. Devices that generate harmonics are also affected by harmonics. As mentioned above, if multiple devices are using electricity, a flat top will appear at the peak of the voltage waveform, and the rectified regulated power supply will not be able to output a stable DC power. In other words, harmonics can affect other loads in the line.

Fourth, who needs to use voltage / harmonic monitor

Equipment installation and maintenance personnel

Observe the voltage parameters through this instrument

equipment manufactory

For cost management

Check if the power supply of the installed equipment meets the operational requirements.

Property management

Manage and maintain power consumption costs and power outages;

Identify whether the equipment is faulty due to poor power quality;

Verify that there are hidden dangers in the power supply environment of expensive equipment;

Verify UPS power system performance

electrician

Improve work efficiency

Quickly locate the cause of power failure

Medical equipment maintenance personnel

Confirm device performance

Check the quality of sensitive power supply

Laboratory equipment / IT equipment management staff

View the quality of sensitive devices

Ordinary electricity consumer

View the power usage of the device after the energy meter

UPS maintenance staff

Assist users in obtaining electricity demand

The US company's newly introduced voltage/harmonic monitor 61-830 is a powerful fault location tool that detects voltage dips, swells, drifts, pulses and harmonics, whether internal or external. Yes, it can effectively measure the power quality problems that cause equipment failure, and can verify that the power supply meets the equipment operating requirements. No need to set up, no computer or special software assistance, voltage / harmonic monitor 61-830 can timely report the time, duration and severity of voltage events. All of this information can be read by browsing the menu. The Voltage/Harmonic Monitor 61-830 is your starting point for power quality analysis.

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