Find Answers to all your power related questions, in our comprehensive FAQ below.
Alternating Current (AC) :This is the current drawn from the utility.
Direct Current (DC) : This is the current drawn from the battery.
Utility : This is the power from the service provider. In South Africa this is Eskom. In Tanzania this is Tanesco.
Power Factor (Pf): This is the ratio of apparent power to true power. Apparent power is VA and true power is watts.
Apparent power (VA) x Pf = True Power (watts)
Voltage Surge: This is when the utility rises by more than 10% for a short period of time (a few cycles)
Voltage Sag: This is when the utility decreases by more than 10% for a short period of time (a few cycles)
Transients (Spikes): These are rapid increases in voltage for a very short duration. Typically in excess of 400 volts (on a single phase 220 volt supply) for times of below 2 micro seconds.
Radio Frequency Interference (RFI): This is an electromagnetic signal that can disrupt electronic equipment.
Harmonics : A frequency that is a multiple of the fundamental frequency (50Hz in South Africa and Tanzania) eg 100Hz is the second harmonic.
Sine Wave : This is the voltage wave form generated by the utility supplier.
Quasi Sine Wave : . This is the output wave form of many Line Interactive UPS’s.
Crest Factor : This is the ratio of the peak value to the RMS value of a waveform. It is used to state the instantaneous overload that a UPS can accept.
Root Mean Square (RMS) : This value of voltage of current is 0.707 of the peak value of the wave form.
Peak : This is the maximum value that the sine wave reaches.
Prime Power : This is the maximum power that a genset can provide to run continuously.
Standby Power: This value is 10% higher than prime power. Gensets can normally run for 6-8 hours at this rating.
Photo Voltaic (PV) : This is the correct terminology for a solar panel.
Three Phase: Three individual voltage sine waves are produced simultaneously by the utility service provider 120 degrees apart.
Single Phase: The voltage between one of the phase voltages mentioned above and neutral.
Input to output voltage isolation: The input voltage and output voltage are not the same. (The input voltage is from the utility and the output voltage is from the inverter.)
A Cycle: This is the time taken for one Sine wave to be produced. In South Africa and Tanzania, this time is 20 mili seconds. 50 of these cycles occur in one second.
Many people believe that the only function of a UPS is to provide power in the event of a utility (power) failure. Power outages, even when load shedding is implemented, are not daily occurrences. Dips, surges, spikes and harmonics (dirty power) most certainly are. These unseen power disturbances can cause as many if not more problems than power failures.
In the case of microprocessor based equipment, both hardware (equipment) failure as well as software (data corruption) failure are as a direct result of these unseen disturbances. A UPS, especially an online UPS will resolve the majority of these problems.
To use a UPS does not require expertise in operation, But it is required that user is aware that there must be a utility electricity supply.
A UPS can be categorised into 3 main types:
OFFLINE OR STAND BY UPS
This is the most basic type of UPS and is used in areas where the utility power is fairly stable with the occasional outage (power failure). This UPS comprises of a battery charger, a battery and an inverter that has a square wave output. Utility mains feeds the load (computer etc.) directly until a power failure occurs. When a power failure occurs, the UPS inverter then switches on and produces a square wave output to feed the load.
LINE INERACTIVE UPS
This is a more sophisticated offline UPS. Some line interactive UPS have a sine wave output. In addition to the battery charger, battery and the inverter, this type of UPS has a built-in regulator to stabilise power fluctuations. It does not however, provide good regulation that certain electronic equipment requires, nor does it provide good input to output voltage isolation.
Unlike the 2 types of UPS above, the inverter of this UPS is always running and feeding the load. The output of the inverter is a sine wave. The utility mains feeds the battery which keeps the batteries charged and the inverter running. In the event of an outage, the inverter keeps running, being powered by the batteries. The regulation of this type of UPS is excellent and the output is isolated from the UPS input. This is the ideal type of UPS to provide power to critical electronic equipment.
The online UPS is ideal for environments where electrical isolation is necessary or for equipment that is very sensitive to power fluctuations. When city power sags, outages and other anomalies are frequent, online UPS provides advantages to sensitive IT equipment, backup generator, etc. The basic technology of the online UPS is the same as offline or line-interactive UPS. But it costs more due to the integration of rectifier and inverter into the UPS. Basically in an online UPS, the batteries are always connected to the inverter, so no power transfer switches are necessary. The rectifier also drives the inverter. When there is a blackout, the rectifier simply drops out of the circuit and the batteries keep the power steady and unchanged. When power restores, the rectifier resumes carrying most of the load and begins to charge the batteries. The main advantage of the online UPS is its ability to provide an electrical firewall between the incoming city power and sensitive electronic equipment. While the standby and line-interactive UPS merely filter the city power. The online UPS also provides a layer of insulation from power quality problems. It allows control of output voltage and frequency of input voltage and frequency.
An Automatic Voltage Regulator (AVR) is a device that can accept large voltage fluctuations (150 volts to 290 volts) and supply voltage to equipment that is within acceptable voltage tolerance parameters (190 volts to 242 volts) or better. It is important to note that an AVR does not provide backup in the event of a power failure.
There are many places in this world with bad electricity power supply conditions, many people are still experiencing constant surges and sags in voltage. Voltage Fluctuation is one of the main cause to the damage of home appliances. Every appliance has a certain input voltage range, if the input voltage drops below or surges higher that this range, it caused a definitely damage in the electricity. In some cases, the appliances just stop working. The Automatic Voltage Regulator is designed to solve such problems, it is designed to have a generally wider input voltage range than normally electrical appliances, and it boost up or suppress the input low and high voltage to the acceptable range.
AVR are mainly categorized into two types:
- Relay controlled tap changing type
- Servo Motor Type
The difference between Relay type and Servo Motor Type is that the Relay type responds more quickly than the Servo motor type. However, the Servo Motor regulates the output voltage more precisely: up to 3% tolerance in precision versus the 10% tolerance in the relay type.
An inverter is essentially a device that changes direct current (DC), which is current drawn from a battery to alternating current (AC) that is similar to the current that is drawn from the utility. Some inverters have built-in battery chargers and are plugged into the utility. Other inverters have solar panel (PV) inputs, whereby the batteries of the inverter are charged by solar power. There are also hybrid inverters that do both the above. Alpha Power supplies inverters that cater for all the above battery charging variations.
The Inverters can be categorized by wave form into:
Step wave inverter
Instead of the sine wave delivered by an electric utility, this inverter produces a square wave. Because current is a switched, or turned on and off, the generated current had very abrupt changes and over time looks like a wave with square corners
Modified Waveform inverter:
The shortcomings of the square-wave inverter become most evident when you try to use it to run a motor. Ac induction motors draw a substantial current surge on startup. They really prefer sine-waves to square-waves and may overheat on the latter. AC induction motors also store energy during a portion of each cycle, which will create problems if not returned to the battery or otherwise controlled.
Pure sine wave inverter
A few true sine wave inverters have appeared on the market, This kind of inverter will run motors cooler and may offer less interference with radio and TV. However, they are inherently more complex and less efficient, so they may not be justified in many installations.
It can also be categorized by application into:
- Isolation inverter (which is supposed to be used in a isolated place which have no AC power supply. The inverter simply convert the DC voltage sourced from the battery or solar panels to the AC voltage).
- Grid inverter( The inverter not only convert the DC voltage to AC, it also distribute the AC power into the utility power grid, meanwhile, the inverter can get the AC power from the grid to charge the batteries. It is more common that in this application, the inverter is being installed with a solar panel system nowadays).