Did you know that the problem of low power factor in the electrical installation – which can lead to fines from the energy concessionary, can be solved with the installation of power factor controllers?
Look at your electric bill. If it shows excess reactive consumption, this is a sign that there is a problem with the power factor. The further this consumption deviates from the legal value, the higher the fine imposed by the energy provider.
This is where power factor controllers come in, to help you correct this flaw in the electrical installation. Before presenting the types of power factor controllers, it is necessary to understand what power factor is.
What is power factor?
Power factor (PF) is a measure of how much of the electrical power consumed is being converted into useful work. The minimum allowed power factor on the energy bill, according to National Electrical Energy Agency (ANEEL)is 0.92. If the value is below this, the utility can charge a fine, as mentioned above.
The main causes of low power factor are discharge lamps (fluorescent, mercury vapor, sodium vapor, and metal vapor) with low power factor reactors (without capacitor), transformers at no load or low load, and induction motors (motors most commonly used in industry).
What a power factor controller is and how it works
Power factor controllers measure the voltage and current of the load continuously, calculating their values through mathematical algorithms in order to obtain TRUE RMS values. Calculated in this way, the power factor considers the harmonic content of the current and voltage, resulting in more accurate measurements.
Optionally, the power factor can be obtained via the serial interface of the power electronic recorder (REP) user output. In this case, there is no harmonic calculation.
As needed, that is, whenever the inductive power factor falls below the setpoint, the controllers activate one or more capacitor banks, thus providing an efficient correction.
The controllers have several features whose purpose is to protect your investment in capacitor banks. Among them is the rest time, that is, the time programmed to prevent a capacitor bank from being turned on again right after it is turned off, which could damage the capacitor and would certainly decrease the life of the contactors (which connect the capacitors to the power grid).
In the same way, every time the power factor exceeds the programmed switch-off point, by switching off inductive loads that were being compensated, the controller deactivates one or more capacitor banks, until the power factor exceeds the programmed switch-off point.
Another important feature is the disconnection of the capacitor banks when the grid voltage reaches high values, avoiding overvoltages of long duration, or when the harmonic content of the current and voltage is too high, which can cause resonances in the installation and damage the capacitors.
Example of a power factor controller
The controllers ST8200C controllers have several features whose purpose is to protect your investment in capacitor banks. Among them is the rest time, that is, the time programmed to prevent a capacitor bank from being turned on again right after it is turned off, which could damage the capacitor and would certainly decrease the life of the contactors (which connect the capacitors to the power grid).
Electrical Wiring Diagrams
The following figures show the connection schemes of the ST8200C controllers.
ST8200C phase-neutral connections
ST8200C phase-to-phase connections
NOTE: The current transformer (CT) must be positioned immediately after the power source (substation, transformer or switchboard) to measure the current coming from the loads and capacitor cells. Avoid having the CT signal wiring pass through the same conduits as the contactor control. Power is supplied via the auxiliary input.
ST8200C connections with user interface connection
Important notes on power factor controller installation
- The current transformer (CT) must be positioned just after the power source (substation, transformer or switchboard) to measure the current coming from the loads and capacitor cells, and its wiring diameter must not be less than 2.5 mm2.
- When the voltage measurement connection is between two phases, these must be different from the phase where you are monitoring the current through the CT. In turn, the TC should be connected to the controller’s TC1 and TC2 inputs.
- When the voltage measurement connection is between phase and neutral, the CT should be on the phase used and connected to the controller’s TC1 and TC2 inputs.
- Each contactor drive must be protected with an individual fuse.
- The voltage and current measurement wiring (CT) must be in conduits separated from the contactor control by a distance of at least 10 cm. The wiring should also not pass through the power cable ducts, where the current from the capacitors will flow.
- A specific CT must be placed for current measurement (always in the xxx/5A transformation ratio). If a measuring instrument already exists, the current measurement can take advantage of the instrument’s CT, provided that the CT signal is always connected in series with the controller. The CT terminals can be grounded.
- Be careful about the supply voltage and the way the contactors are connected. The common wire of the contactors must be different from the one used for powering the controller. Remember that the maximum voltage/current for each drive output is 250VAC/5A.
- When the optional REP interface is used, without connection to CTs and grid voltage, the electrical measurements of these two parameters will be reset to zero.
- Voltage must be applied to the measurement input for both the voltage and the current parameters to be displayed in the electrical measurements menu. Otherwise, these two parameters will be reset to zero.
Power factor controller front panel
LEDs 1 to 16 indicate when the respective capacitor bank is being driven.
- OK Equipment on
- ST Lit, indicates an active alarm
- RX Indicates serial channel receiving data
- TX Indicates serial channel transmitting data
Active power, also known as real or useful power, is the power that performs useful work on a given load. This load, in turn, can be lighting or any other device that converts electrical energy into some other form of useful energy. This means that the active power is responsible for generating light, motion, heat, etc. The unit of measurement of active power is Watt (W). Depending on the situation, this could be the Kilowatt (kW).
Apparent power refers to the total power that a given source is capable of providing to a system. This consists of the vectorial sum of the active power and the reactive power. Its unit of measurement is the Volt Ampere (VA) or kilo Volt Ampere (kVA). In the context of electricity trading, the apparent power is all the power made available by the energy supplier to a given property.
Apparent power is defined as the total power that a given source is capable of providing. Its unit of measurement is the Volt Ampere (VA). In this sense, the relationship between apparent power and active power is called power factor. That is, it establishes the relationship between the amount of energy supplied by the source and the amount of energy that is actually transformed into work. When a power factor is high it means that a large part of the energy coming into the installation is transformed into work. When it is low it means that only a small portion of the energy received is converted into work. This means that the greater the amount of active power, the higher the power factor.
The power factor
The power factor represents the ratio of apparent power to active power. This means that the power factor represents the relationship between the amount of energy that was delivered by the source and the amount of energy that was actually transformed into work, that is, that was used in the property in question. On a scale of zero to one, the higher the power factor of a load, the greater its active power, that is, the power converted into work. Conversely, the lower a power factor is, the lower its active power and therefore the higher its reactive power (that which does no effective work).
Power factor correction
The objective of power factor correction is to gain efficiency, besides avoiding mismatches between voltage and current, not allowing equipment to operate with maladjusted loads and without effective production.
It is known that low power factor occurs when too much reactive power is consumed in relation to active power. The reactive power can be neutralized by a capacitive load, so the safest way to effectively correct the power factor and compensate for existing inductive loads is to install a capacitor bank.
In some cases, such as in very capacitive systems like transmission lines, an inductor bank is used to compensate for the capacitive effect.
Inductive loads produce a forward current in relation to the voltage. Capacitive loads produce a delay of the current with respect to the voltage. The capacitor bank and the inductor bank act by compensating the lag between the voltage and the current, basically “opposing” the inductive loads.
Causes of low power factor
Often the condition and maintenance of equipment can lead to a low power factor. Taking industry as an example, a series of precautions must be taken, in addition to considering situations that can be identified and corrected.
Take a look at some of the factors that are the major causes of low power factor in enterprises!
- Low power motors acting together
- Equipment working without load
- Energy oversizing
- Defective or very old equipment
- Lighting using ballasts for lamps
- Use of welding machines
- Heat treatment apparatus
That is why it is important that the power factor stays within limits, considering the existing inductive load values. Thus, the proper sizing of the capacitor bank is necessary to have the best use of electrical energy.
Correcting the power factor in companies brings several advantages, see some of them in the list below.
- Reduction of electric energy consumption
- Increased useful life of facilities and equipment
- Reduction of heat generated in equipment
- Reduction of reactive current
- Avoid unnecessary maintenance on equipment
- No need to change conductor sections for larger gauge ones
- No need to change the transformer for a higher capacity one
What is a Power Factor Controller and why use it in industry – https://sultech.com.br/2018/06/20/saiba-o-que-sao-controladores-de-fator-de-potencia/