Do you ever wonder why your company’s electricity bills are high? An energy-intensive and ineffective lighting system may be one of the reasons for this. You can replace it easily with modern, eco-friendly and highly efficient LED lighting by Luxon. Reactive power generated by the devices can be another factor. What is reactive power, how to defend yourself against it and how it depletes your company’s budget? – you can find answers to these and other questions in the article below. We wish you pleasant reading!
What is reactive power?
Devices that are connected to the power grid consume active and reactive power. We express active power, that is useful power, in watts, using which we describe receivers, e.g. lighting luminaires, air conditioners and other devices. It is natural for these devices to generate reactive, inductive or capacitive power expressed in units called var. The receivers producing reactive power are those with capacitors or inductors in the input circuits. They include, for instance, power supplies. These devices modify the voltage waveform and sinusoidal current, which causes the phenomenon of leading or lagging current in relation to voltage as showed in the Fig. 1. Such a shift in the electrical nomenclature is defined by the tgφ coefficient or its derivatives (among other things, cosφ and Power Factor). The greater the delay, the greater the value of reactive power. The most desirable value of tgφ indicator is 0.
S – apparent power
Q – reactive power
P – active power
We have visualised reactive, active and apparent power using the power triangle (Fig. 2.). In this case, we defined the active power using the longer side. Then, the second one visualised is reactive, inductive or capacitive power. Reactive power Q to active power P ratio is defined using tgφ value.
Power output and reactive power in enterprises
Approximately 50% of reactive power in the entire energy infrastructure is generated by transformers, high voltage transmission lines and others. In order to reduce these losses, grid distributors optimise the voltage levels, regulate transmission transformers, and use capacitor banks and chokes. However, we need to bear in mind that when connecting to the grid such devices as, for example, asynchronous motors, induction furnaces, electric machines, as well as LED lighting, they generate reactive power of various values and character.
In the invoice for electric energy consumption, we can see the cost of introducing reactive, inductive or capacitive energy to the grid. This happens when we exceed the tgφ limit provided for in the contract with the distributor. In the case of inductive power, the most common value from which the fees are charged is 0.4. In turn, the fees for capacitive reactive power are added for each var of energy input into the grid.
The simplest way to find out how much excess reactive power our business generates is to analyse the bill from the electric energy supplier. In the expanded list, apart from the fees for distribution and active power, there are also fees for inductive and capacitive reactive power. After the invoice analysis, we can check whether and to what extent we generate charges related to reactive power. Another way is to connect a power quality analyser to each electrical device or to the main switchboard.
The most common method of compensation is to use expansion joints in the electric switchboard. They can also be mounted directly at specific devices generating reactive power but this solution is used less frequently. What expenses could it entail? Most of all, it depends on the nature of operations of the given enterprise. The analysis of invoices and appropriate measurements are the basis for estimating the costs of implementation or modernisation of reactive power compensation. It is worth noting that activities concerning compensation can significantly reduce the company’s annual expenses, and the return on such an investment may occur after 15 months.
Modernisation of lighting and reactive power
Older luminaires, due to the way of their starting and powering, generate inductive reactive power. In turn, LED luminaires, power supplies for computers, server rooms or inverter air conditioners that have impulse (direct current) converters, for instance, input capacitive reactive power to the installation. When we modernise lighting, e.g. fluorescent lamps for LED luminaires, we remove elements in the form of devices generating inductive power, and we install devices generating capacitive reactive power. In this case, the phenomenon of over-compensation may occur. What consequences can it have? The expenses related to the excessive level of capacitive reactive power will increase, which may lead to an extended return on investment concerning modernisation of LED lighting.
In this case, you need to remember that replacement of LED lighting is the first step towards measurable savings. The next one is the balancing of active and reactive power, and possible installation of equalizers or modification of the existing ones.
From theory to practice
The diagram below shows the dependence of the Power Factor as a function of load of power supply OSRAM OTi DALI 100/220-240/700 D LT2 IND L used in some versions of Luxon LED luminaires.
Please note, based on the chart (Chart 1), that the relationship between the Power Factor and the power supply load is not linear. With reduction of the luminaire’s active power, this factor decreases. However, this information is not unambiguous. Please note that in the case of 100W power, the Power Factor is approx. 0.985. The reactive power for these values is equal to 17.5 var. In turn, in the case of 30W, h=the factor decreases to 0.895, and reactive power to 14.9 var. Based on this example, we proved that the reactive power value is closely related to the Power Factor parameter and the active power of the power supply system.
This dependence is important for lighting control systems. In simple terms, a reduction in the Power Factor does not always increase the value of the actual reactive power, i.e. we do not bear the costs associated with it. Please remember that every modernisation of LED lighting will change the reactive energy balance in the enterprise.
To sum up…
Modernisation of lighting in an industrial plant with an energy-saving LED system can significantly reduce electricity consumption, which will allow for saving even 70% of costs, and will positively affect the comfort and working conditions in the facility. However, please remember that modern LED lighting, despite the undeniable benefits, often changes the reactive power balance. For this reason, we suggest carrying out an audit after the modernisation. On its basis, it will be possible to design a reactive power compensation system. Our specialists will help you at every stage of lighting modernisation and optimisation of reactive power. You can be sure of spectacular savings.