Reactive power compensator: application of UKRM devices and electrical safety conditions

The reasons for losses in electrical circuits are the presence in them of inductance and capacities that generate reactive power. In this case, only a part of the total power - the active component - performs useful work. The reactive component is used to create magnetic fields, heat the wiring and increase the load on the network. To prevent losses in networks, reactive power compensators are installed.

Full power

In power grids, where there is only a resistive load - due to heating devices, electric lighting, current and voltage change with zero phase shift. All power is active there and goes to the load. When used in networks of inductors and capacities, a reactive component appears. It is characterized by a phase shift between voltage and current.

Phase displacement means that there are times when the voltage and current values ​​have different polarity, negative current with positive voltage and vice versa. During these periods, the power is not used to carry out useful work, but returns to the energy source. Apparent power consists of active and reactive components. The power factor (KM) is numerically equal to the cosine of the phase angle between current and voltage (cosφ). It expresses the ratio of active power to total power.

When the cosφ is low, the following factors appear:

• the cost of using electricity is increasing;
• the load on the transformers increases and their service life decreases;
• heat losses increase;
• there is a voltage drop due to the presence of a reactive component.

The presence of a reactive component is an unfavorable factor for the electrical network and therefore it is necessary to include compensators in the network.

Compensating devices

The type of compensating device depends on what kind of component occurs in the network. If there is an inductive load, reactive power compensation devices using capacitors are used. If there is a capacitive load, choke compensators are used. An inductor in electrical engineering is a type of inductor.

At enterprises, most often there is an induction load, which is associated with the presence of asynchronous motors, transformers, electric furnaces in the technological chains. Therefore, capacitor compensating devices for reactive power are used there.

The main purpose of capacitor reactive power compensation devices in electrical networks UKRM is maintaining the KM of the network at the standard level, reducing the flow of the reactive component, stabilizing voltage. At the place of installation of the UKRM the following compensation methods differ:

• Centralized compensation with installation of UKRM on the high voltage side of 6-10 kV. In this case, only the network sections located above the transformers are unloaded. Consumer installations remain unloaded.
• Installation of UKRM on low voltage buses of 0.4 kV. Unloading of transformers and networks located above is provided. This is also a type of centralized compensation. Consumer networks remain under reactive load.
• Group compensation when UKRMs are connected directly to 0.4 kV production buses. Only the networks leading to the individual consumers remain under reactive load.
• Individual compensation consists in connecting the UKRM directly to the installations consuming reactive power.

Capacitor units improve the conditions for energy use: they reduce the load current by 30-50%, increase the service life of electrical appliances, reduce heat losses, reduce line noise, reduce phase asymmetry, use higher harmonic filters, make networks more economical and reduce costs electricity.

When choosing a compensating device, the characteristics of the equipment, environmental conditions and the complexity of the control processes are taken into account. The following types of compensation are used in 6-10 kV networks:

• Unregulated - consists of several stages, which are switched manually in the absence of load currents.
• Automatic - carried out by automatic switching of steps, each consisting of three capacitors connected by a triangle.
• Dynamic - for rapidly changing loads, an electronic reactive component compensator is used.

Protection of UKRM

For the safe operation of compensatory installations, it is necessary to create protective equipment and interlocks in case of unforeseen situations. The following measures are envisaged:

• Interlocks protecting against contact with live parts.
• Built-in disconnector to prevent short-circuit current.
• Electrical protection against exceeding the standards for current, voltage, phase imbalance.
• Interlocks preventing incorrect switching on of UKRM switching devices.
• The use of a switch to de-energize the installation when the doors are opened.

It must be borne in mind that when the capacitors are disconnected, there is a dangerous residual voltage at their terminals. Full discharge through the discharge resistors occurs in a few minutes.

It is contraindicated to make full compensation, bringing the cosφ to unity. This can lead to overcompensation. KM should have values ​​no higher than 0.90-0.95. The power of the UKRM is determined for each section of the network, taking into account the load characteristics and the type of compensation.

The constantly growing volumes of electricity consumption force us to be more attentive to its conservation. Technological progress increases the demand for energy resources, and the possibilities of generation are limited. Therefore, energy saving technologies come to the fore, and expansion joints are one of the important ways to save.

The economic effect from the use of these installations is great. Already at the design stage, it is possible to lay down a reduced cable cross-section and save on their cost. And in the production process, there is a saving in the cost of using electricity, which in some regions reaches 50% of the total cost.