Reactive power compensation installations. Reactive power compensators. Reactive power compensation

All types of capacitor units for reactive power compensation are necessary to stabilize the operation of electrical networks and reduce possible energy losses. This equipment includes static capacitor banks (SCB). Each BSC consists of parallel-series connected cosine capacitors in the shape of a star or triangle. The battery is equipped with current-limiting reactors, which are needed to regulate the current when turned on. For protection, a head switch or voltage transformer is used.

Thanks to this process, it is possible to significantly reduce the load on:

• wires;
• switching equipment;
• transformers.

By reducing resistance waveform distortion, the end user's power quality and the service life of all equipment are improved. But where does the interference in the current supply come from, and where does the need for compensation arise?

General questions of theory

In all large electrical networks, two types of resistance arise:

1. active - for example, in incandescent lamps, electric heaters;
2. inductive – for electric motors, distribution transformers, welding equipment, fluorescent lamps.

The total power is generated taking into account these two loads. This dependence is shown in more detail in the picture below.

When the voltage becomes negative and the current becomes positive and vice versa, a phase shift occurs in the current. At this moment, power flows in the opposite direction towards the generator, although it should go to the load. In this case, electrical energy fluctuates from the load to the generator and back, instead of moving through the network. The power that occurs during this process is called reactive power. This power generates a magnetic field, which also puts additional stress on the force fields.

In order to establish the full power of the network, it is necessary to determine both components: active and reactive. The value is calculated based on the power factor, or coefficient, which is cosφ - the cosine of the angle that appears between the curves of the active and reactive components.

Active power is used to convert into thermal, mechanical and other useful forms of energy. Reactive is not suitable for use for these purposes, but without it the operation of transformers, generators and other equipment whose operation is based on the properties of the electromagnetic field is impossible. Electricity supply organizations supply only active loads, because reactance supplies:

• increase equipment power by reducing throughput;
• increase active losses;
• lead to a voltage drop due to the presence of a reactive component.

Features of installation of compensation equipment

It is most convenient to generate the reactive part directly from the consumer, otherwise the user will have to pay for electricity supplies twice. The first time is for the supply of the active part, and the second time – for the supply of the reactive part. In addition, such double supply will require additional equipment. To avoid this situation, capacitor reactive power compensation units are used.

Important! Installing reactive power compensation (RPC) does more than just save energy. At industrial enterprises in Russia, the energy saving potential is only 13-15% of total consumption.

The level of electricity consumed at an enterprise is constantly changing, that is, cosφ can increase or decrease. Thus, the higher the power factor, the higher the active component and vice versa. To regulate this process, capacitor units are required that can compensate for the reactive component.

The capacitors on which this compensation equipment is built keep the voltage value at a given level. The current in capacitors, as opposed to inductance, operates in a leading manner. Thus, capacitors act as phase-shifting equipment.

All capacitor installations for reactive power compensation are divided into regulated and unregulated. The main disadvantage of the latter is that with a significant change in load and power factor, overcompensation is possible. If there is a possibility of a significant increase in cosφ in the circuit, it is not recommended to use an unregulated PFC.

Regulated devices are capable of operating in a dynamic mode, monitoring and tracking readings for further analysis. The controller included in this equipment monitors and calculates several indicators right on site:

• level of reactive load in the external circuit;
• determines the existing power factor;
• compares the coefficient with the specified values.

If the obtained value differs from the standard, the regulator connects or disconnects certain capacitors included in the compensator installation. The use of this equipment makes it possible to fully control the level of electricity supply in enterprises with a large number of devices with different purposes. This is especially important if it is quite difficult to accurately track how the reactive component changes across the network. The general principle of compensation makes it possible not to install separate equipment for each device with a reactive component.

Efficiency of using capacitor units

Despite the fact that it is most convenient to compensate for the reactive component directly at the consumer, to improve the quality of supplied electricity, the first installations are used at substations. This makes it possible to relieve the network and already save 10 to 20% of energy. Therefore, at 0.4 kV substations, users are switched from overloaded phases to underloaded ones.

For non-industrial subscribers, it is almost impossible to qualitatively align the phases using only one capacitor unit. This is especially true for residential buildings with single-phase loads. Here, compensation is carried out at each phase and filters are additionally used, the capacity of which can be changed automatically.

The rated voltage of capacitor units can be very different. High-voltage equipment 6, 10, 35 kV is used at substations. Low-voltage devices 0.4-0.66 kV are used directly on loads. Due to their high speed, low-voltage devices can stabilize not only constant, but also intermittent reactive power.

In general, reactive power compensation consists of 2 stages:

1. Centralized quality monitoring (rough compensation) by phase equalization and current filtering at substations;
2. Individual compensation at industrial enterprises, their individual divisions, as well as at the level of small consumers - owners of apartments and private houses. During this work, the reactive power compensation device reduces energy losses by ensuring the current is sinusoidal.

Previously, the problems of energy saving among small consumers were practically not taken into account. It was believed that the reactive component affects only the operation of large enterprises that use induction furnaces, asynchronous motors, step-down transformers and other devices.

But recently, the amount of transformative and stabilizing equipment used in the social environment has increased significantly. Semiconductor converters worsen the shape of the current waveform, thereby negatively affecting the functioning of other devices. But so far, KRM devices are almost never used for private household consumers.

Video

Specialists and directors of enterprises are increasingly asking questions of energy saving. Many consumers want not only to be independent from external energy sources, but also to reduce the cost of energy consumption. Therefore, more and more enterprises are using compensators, which allow them to obtain more reliable and less resource-intensive distribution networks. In addition to static compensators, there are also dynamic devices. The former are used for reactive power in networks without dynamic load changes; supply voltage harmonics do not exceed 8%. The static compensator is a capacitor unit equipped with electromagnetic contactors. This type of compensator is available with manual and automatic operating modes. The maximum number of switchings of such a compensator is no more than 5000 per year. If you need a larger quantity, then you should buy a dynamic compensator. A similar device is used in networks with rapidly changing loads, in which the harmonics of the supply voltage do not exceed 8%. According to the principle of operation, such a compensator is a capacitor unit with a thyristor switch.

Based on the method of power factor control, compensators are divided into:

• Automatic devices. These compensators are used in facilities whose technology leads to frequent changes in power consumption. Their advantage is regulation that does not require personnel, which is carried out using a microprocessor controller. Additionally, the compensators are equipped with functions for monitoring and leveling the motor life of capacitors.
• Non-adjustable compensators. They are used at facilities where the load does not change for a long time or its change does not lead to a change in the power factor beyond the permissible limit. Such a compensator makes it possible to disconnect and connect steps manually;
• Mixed compensators. Designed to compensate for reactive power of permanently connected consumers, which is similar to the operation of automatic compensators.

In the typical version, to connect the compensator to the network, a switch-disconnector is used with a built-in interlock that prevents the device door from opening when the switch-disconnector is turned on. The compensator is characterized by a modular design principle, which allows you to gradually increase the rated power.

We offer a wide selection of compensators, so you can choose the right device and purchase it at an affordable price in Moscow.

Electrical equipment consumes energy during operation. In this case, total power consists of two components: active and reactive. Reactive power does not perform useful work, but introduces additional losses into the circuit. Therefore, they strive to reduce it, for which they come to various technical solutions for compensating reactive power in electrical networks. In this article we will look at what it is and why a compensating device is needed.

Definition

Total electrical power consists of active and reactive energy:

Here Q is reactive, P is active.

Reactive power occurs in magnetic and electric fields that are characteristic of inductive and capacitive loads when operating on alternating current circuits. When an active load is operating, the phases of voltage and current are the same and coincide. When an inductive load is connected, the voltage lags behind the current, and when a capacitive load is connected, it leads.

The cosine of the shift angle between these phases is called the power factor.

cosФ=P/S

P=S*cosФ

The cosine of the angle is always less than one, therefore the active power is always less than the total power. The reactive current flows in the opposite direction relative to the active one and prevents its passage. Since the wires carry full load current:

When developing power transmission line projects, it is necessary to take into account the consumption of active and reactive energy. If there is too much of the latter, then the cross-section of the lines will have to be increased, which leads to additional costs. That's why they fight it. Reactive power compensation reduces the load on networks and saves energy for industrial enterprises.

Where is it important to consider the cosine Phi

Let's figure out where and when reactive power compensation is needed. To do this, you need to analyze its sources.

An example of a basic reactive load are:

• electric motors, commutator and asynchronous, especially if in operating mode its load is small for a particular motor;
• electromechanical actuators (solenoids, valves, electromagnets);
• electromagnetic switching devices;
• transformers, especially at no-load.

The graph shows the change in cosФ of the electric motor when the load changes.

The basis of the electrical equipment of most industrial enterprises is an electric drive. Hence the high reactive power consumption. Private consumers do not pay for its consumption, but enterprises do. This causes additional costs, ranging from 10 to 30% or more of the total energy bill.

Types of compensators and their principle of operation

In order to reduce the reactant, reactive power compensation devices, the so-called, are used. UKRM. The following are most often used as a power compensator in practice:

• capacitor banks;
• synchronous motors.

Since the amount of reactive power can change over time, this means that compensators can be:

1. Unregulated - usually a capacitor bank without the ability to disconnect individual capacitors to change the capacitance.
2. Automatic – compensation levels change depending on the network condition.
3. Dynamic - compensate when the load quickly changes its character.

The circuit uses, depending on the amount of reactive energy, from one to a whole bank of capacitors, which can be introduced and removed from the circuit. Then the control can be:

• manual (circuit breakers);
• semi-automatic (push-button stations with contactors);
• uncontrolled, then they are connected directly to the load, turned on and off along with it.

Capacitor banks can be installed both at substations and directly near consumers, then the device is connected to their cables or power buses. In the latter case, they are usually calculated for individual compensation of the reactant of a specific motor or other device - often found on equipment in 0.4 kV electrical networks.

Centralized compensation is performed either at the boundary of the balance section of the networks or at the substation, and can be performed in 110 kV high-voltage networks. It is good because it unloads high-voltage lines, but the bad thing is that the 0.4 kV lines and the transformer itself are not unloaded. This method is cheaper than others. In this case, it is possible to centrally unload the low side of 0.4 kV, then the UKRM is connected to the busbars to which the secondary winding of the transformer is connected, and accordingly it is also unloaded.

There may also be a group compensation option. This is an intermediate type between centralized and individual.

Another way is compensation with synchronous motors, which can compensate for reactive power. Appears when the engine is running in overexcitation mode. This solution is used in networks of 6 kV and 10 kV, and is also found up to 1000V. The advantage of this method over installing capacitor banks is the ability to use a compensator to perform useful work (rotating powerful compressors and pumps, for example).

The graph shows the U-shaped characteristic of a synchronous motor, which reflects the dependence of the stator current on the field current. Below it you can see what cosine phi is equal to. When it is greater than zero, the motor is capacitive in nature, and when the cosine is less than zero, the load is capacitive and compensates for the reactive power of the rest of the inductive consumers.

Conclusion

Let us summarize by listing the main points about reactive energy compensation:

• Purpose – unloading power lines and electrical networks of enterprises. The device may include anti-resonance chokes to reduce the level.
• Individuals do not pay the bills for it, but businesses do.
• The compensator includes capacitor banks or synchronous machines are used for the same purposes.

Materials

BASIC TYPES

• Unregulated (constant power)

They consist only of fixed steps. Operating principle: the disconnector is switched on and off manually (in the absence of load current). Brands of manufactured units are KRM, KRM1, UKL, UKL56, UKL57.

Adjustable (automatic)

They consist only of adjustable steps. Operating principle: switching is carried out automatically by turning the steps on and off. In this case, the power and moment of switching on are automatically determined by the electronic unit. By regulating and increasing the value of the cos(φ) coefficient, SlavEnergo high-voltage capacitor units automatically compensate for the reactive power of the load in electrical networks with a voltage of 6.3 - 10.5 kV. The most common abbreviations for such installations are KRM, UKRM 6, UKRM 6.3, UKRM 10, UKRL, UKRL56, UKRL57.

• Semi-automatic

In order to reduce the cost of UKRM 10 kV and 6 kV reactive power compensation installations, while maintaining a high level of quality, SlavEnergo has developed semi-automatic reactive power compensators - a hybrid of the two above-mentioned types of UKRM. They contain both adjustable (automatic) stages and fixed (non-adjustable) stages. Such devices have become widespread due to the fact that almost always some part of the load in the high-voltage network is constantly present, 24/7. For this “fixed” part of the load, the corresponding capacitances of capacitor banks are selected, placed in unregulated cells of capacitor units. Such stages are 2-3 times cheaper compared to automatic stages of similar power, which in turn has a beneficial effect on the cost of the UKRM reactive power compensation device as a whole.

• Filter

Any of the above high-voltage installations (unregulated, adjustable, semi-automatic), if necessary, are equipped with protective chokes against harmonic distortion. You can find out more about such installations

Technical characteristics of the main high-voltage UKRM*

Name	Power,	Adjustment steps kvar		Dimensions**	(at U=6.3 kV)	(at U=10.5 kV)
		Fix.	Reg.
UKRM-6.3 (10.5)-150-50 (100r+50r)	150	1x100	1x50	2394 x 1800 x 770	13,75	8,25	480
UKRM-6.3 (10.5)-300-150 (150f+150r)	300	1x150	1x150	2394 x 1800 x 770	27,49	16,50	530
UKRM-6.3 (10.5)-450-150 (300f+150r)	450	1x300	1x150	2394 x 1800 x 770	41,24	24,74	550
UKRM-6.3 (10.5)-600-300 (300f+300r)	600	1x300	1x300	2394 x 1800 x 770	54,99	32,99	600
UKRM-10.5 (6.3)-900-450 (450f+450r)	900	1x450	1x450	2394 x 1800 x 770	82,48	49,49	600
UKRM-6.3 (10.5)-1350-450 (450f+2x450r)	1350	1x450	2x450	3344 x 1800 x 770	123,72	74,23	910
UKRM-6.3 (10.5)-2250-450 (3x450f+2x450r)	2250	3x450	2x450	4294 x 1800 x 770	206,20	123,72	1375
UKRM-6.3 (10.5)-3150-450 (3x450f+4x450r)	3150	3x450	4x450	6194 x 1800 x 770	288,68	173,21	1850

The main load in industrial electrical networks is asynchronous electric motors and distribution transformers. This inductive load during operation is a source of reactive electricity ( reactive power), which performs oscillatory movements between the load and the source (generator), is not associated with the performance of useful work, but is spent on creating electromagnetic fields and creates an additional load on the power supply lines. Therefore, the reactive power compensator is very important.

Reactive power is characterized by a delay (in inductive elements the phase current lags behind the voltage) between the phase sinusoids of the voltage and network current. The indicator of reactive power consumption is Power factor(KM), numerically equal to the cosine of the angle (φ) between current and voltage. The consumer's power consumption is defined as the ratio of the consumed active power to the total power actually taken from the network, i.e.: cos(f) = P/S. This coefficient is usually used to characterize the level of reactive power of engines, generators and the enterprise network as a whole. The closer the cos(f) value is to unity, the smaller the share of reactive power taken from the network.

Example: with cos(ph) = 1, to transmit 500 KW in an AC network of 400 V, a current of 722 A is required. To transmit the same active power with a coefficient cos(ph) = 0.6, the current value increases to 1203 A.

As a result:

• additional losses occur in conductors due to increased current;
• the capacity of the distribution network is reduced;
• The network voltage deviates from the nominal value (voltage drop due to an increase in the reactive component of the supply network current).

All of the above is the main reason that power supply companies require consumers to reduce the share of reactive power in the network. The solution to this problem is reactive power compensation– an important and necessary condition for the economical and reliable functioning of the enterprise’s power supply system. This function is performed, the main elements of which are capacitors.

Correct compensation allows you to:

• reduce overall energy costs;
• reduce the load on distribution network elements (supply lines, transformers and switchgears), thereby extending their service life;
• reduce thermal current losses and energy costs;
• reduce the influence of higher harmonics;
• achieve greater reliability and efficiency of distribution networks.

Moreover, in existing networks

• exclude the generation of reactive energy into the network during periods of minimum load;
• reduce the cost of repairing and updating the electrical equipment fleet;
• increase the capacity of the consumer's power supply system, which will allow connecting additional loads without increasing the cost of networks;
• provide information about the parameters and status of the network.

And in newly created networks - reduce the power of substations and the cross-section of cable lines, which will reduce their cost.

Why compensate for reactive power?

Reactive power and energy worsen the performance of the power system, that is, loading power plant generators with reactive currents increases fuel consumption; losses in supply networks and receivers increase; The voltage drop in the networks increases.

Reactive current additionally loads power lines, which leads to an increase in cross-sections of wires and cables and, accordingly, to an increase in capital costs for external and on-site networks.

Reactive power compensation is currently an important factor in solving the issue of energy saving in almost any enterprise.

According to estimates of domestic and leading foreign experts, the share of energy resources, and in particular electricity, accounts for about 30-40% of the cost of production. This is a strong enough argument for a manager to seriously approach the analysis and audit of energy consumption and the development of a method for reactive power compensation. Reactive power compensation is the key to solving the issue of energy saving.

Main consumers of reactive power:

• asynchronous electric motors, which consume 40% of the total power together with household and own needs;
• electric ovens 8%;
• converters 10%;
• transformers of all stages of transformation 35%;
• power lines 7%.

In electric machines, alternating magnetic flux is associated with windings. As a result, reactive emfs are induced in the windings when alternating current flows. causing a phase shift (fi) between voltage and current. This phase shift usually increases and cosine phi decreases at light loads. For example, if the cosine phi of AC motors at full load is 0.75-0.80, then at light load it will decrease to 0.20-0.40.

Lightly loaded transformers also have a low power factor (cosine phi). Therefore, if reactive power compensation is applied, the resulting cosine phi of the energy system will be low and the electrical load current, without reactive power compensation, will increase at the same active power consumed from the network. Accordingly, when reactive power is compensated (using automatic capacitor units KRM), the current consumed from the network is reduced, depending on cosine phi, by 30-50%, and heating of conductive wires and insulation aging are correspondingly reduced.

In addition, reactive power, along with active power, is taken into account by the electricity supplier, and therefore is subject to payment at current tariffs, and therefore constitutes a significant part of the electricity bill.

The most effective and efficient way to reduce the reactive power consumed from the network is the use of reactive power compensation units (capacitor units).

The use of capacitor units for reactive power compensation allows you to:

• unload power supply lines, transformers and switchgears;
• reduce energy costs
• when using a certain type of installation, reduce the level of higher harmonics;
• suppress network interference, reduce phase unbalance;
• make distribution networks more reliable and cost-effective.

longitudinal and transverse reactive power compensation