Power Quality Problems and Solutions

There are 9 recognised power quality problems. Here we look at what they are and how we can protect against them.


Problem Description Solution

Power Problem 1. Blackout
1. Power Cut
A total loss of the utility supply. One of the most recognised power quality problems. Caused by circuit trips, blown fuses, road works, faults etc. Obviously anything electrical switches off. Solved with any UPS as long as battery lasts. Check for how long you need to operate on battery for and what inverter system is suitable for your load.

Power Problem 2. Voltage Sag
2. Voltage Sag
A short term (momentary) dip in the power supply. Caused by heavy equipment switching on, lightning, grid faults. Causes equipment resets, crashes, flickering of lights etc. Any UPS will solve this. Frequent sags may deplete battery to point of non protection however.

Power Problem 3. Voltage Spike
3. Voltage Spike
A short term (momentary) high voltage rise in the power supply. Can be the most damaging power quality problem. Caused by heavy equipment- particularly inductive device – switching off, lightning and grid faults. Can cause damage to electronic components. A surge suppressor helps with spikes and most UPS contain such devices. Large surges can damage the surge suppressor and UPS however. Consider transformer based products to protect against the worst.

Power Problem 4. Under Voltage
4. Under Voltage
A long term sag in the supply voltage. Caused by high demand on network / underrated supply or high impedance source during higher than normal power use. Causes equipment malfunction, circuit trips, unpredictable operation of devices. Also known as a brown out due to the effect on incandescent light bulbs. An offline UPS won’t cut it here, save until the batteries run out, you need a line interactive or an online UPS system. Alternatively a voltage regulation device.

Power Problem 5. Over Voltage
5. Over Voltage
A long term rise in the supply voltage bringing it over the supply limit. Caused by low demand on the network, particularly when close to a sub station that may have long loops. Can cause damage to connected equipment, circuit breaker trips, component overheating. Line interactive and online technologies are the only UPS technologies that can protect against this. A voltage regulator would also suffice.

Power Problem 6. Electrical Noise
6. High Frequency Noise
High frequency interference on the utility supply. Caused by other electronic equipment. Can cause unpredictable equipment operation, data errors, audible noise on AV equipment etc. Possibly higher end line interactive UPS will protect against this, specific power conditioning equipment or online double conversion technologies.

Power Problem #7. Frequency Variation
7. Frequency Variation
A variation of the normal 50Hz (or 60Hz) supply frequency. This cannot happen on the grid and so is usually only an issue when running from generators. Inductive AC loads such as motors, transformers, pumps will not function properly and may be damaged and overheat. Only online double conversion can help here. If the variation is large, only online UPS with frequency conversion mode will protect against this.

Power Problem 8. Switching Transients
8. Switching Transients
Fast acting but low energy pulses on the supply. Caused by electronic devices on the same network. Will degrade electronic components and can cause damage. Equipment malfunction likely. Possibly higher end line interactive UPS will protect against this, specific power conditioning equipment or online double conversion technologies.

Power Problem 9. Harmonic Distortion
9. Harmonic Distortion
A degree of distortion from a “pure sine wave”. Caused by non linear devices such as rectifiers, particularly if the supply impedance is relatively high. Particularly harmful to transformers and motors. Can cause circuit breaker trips and burn out in Neutral conductors in 3phase systems.


Only online UPS can protect against this.


Summary of Power Quality Problems and the Solutions

If we pigeon hole our UPS into their designations we have VIX Series, VIS Series, VFI Series and TX Series:

Power Issue VIX VIS VFI TX
1. Blackout
2. Sags
3. Spikes
4. Under Voltage
5. Over Voltage
6. Noise
7. Frequency
8. Transients
9. Harmonics


✗ Never ✗ Probably Not ✓ Probably ✓ Yes

Why Probably and Probably Not?

Take a Blackout – why is the VIX series a Probably? This is because when running on inverter to protect against the blackout, the VIX does not output a pure sine wave but rather a square wave. This is fine for some systems but not all.

For transients and noise, it depends on the level and mode. In general terms VI technology allows what’s on the input through to the output but there may be a degree of filtration on this which can help. However VFI technology works by converting AC to DC and then back to AC which will remove any noise or transients from the output. However, typically VFI technology has a common Neutral between input and output. This means any noise or transient that effect Neutral to Ground will pass through, generally unimpeded. This is not a cause for concern in the majority of cases, but where it is, the TX series will provide protection against this.