90KW motor, harmonics are a bit big, how to match the compensation capacitor and reactor

Simple reactive power to prevent the capacitor from harmonic amplification resistance, use 7% reactor for more than 5 times, use 14% reactor for more than 3 times, use how big capacitance to know how much reactive power there is, and the reactive power is different for different working modes of the motor. At the same time, if you want to filter harmonics, you need to use no filter (filter capacitor + detuning reactor), and the harmonic amount of these two parameters can be calculated before you know the harmonic quantity. If possible, use APF.

Frequency conversion motor, series one or reactance rate reactor, the rated voltage of the motor should be, otherwise it can not be matched!

Is it inverter dragging? If it is a frequency conversion drag, when choosing a reactor, you need to consider four aspects:

First, the rated output voltage of the inverter; For example, 220V, 400V, etc.;

Second, the carrier frequency of the inverter, if the carrier frequency is higher than 20kHz, it is necessary to customize a special inverter output reactor, because the general reactor is designed for this carrier frequency band;

Third, the length of the connecting wire between the inverter and the motor. Most people in the industry believe that if the length of the connecting wire between the inverter and the motor is long, the impact of the line voltage drop on the motor is required.

Fourth, it is the brand of the inverter, the domestic inverter generally matches the inverter output reactor with the voltage drop, and the imported inverter generally matches the inverter output reactor with the reactance rate.

A damping reactor (i.e., a series reactor) is installed in the capacitor circuit, and the capacitor circuit is put into operation to suppress the inrush current. At the same time, it forms a harmonic circuit together with the capacitor bank to play the role of filtering each harmonic.

Reactors can be connected in series or parallel with capacitors to limit higher harmonics in the grid. The operating voltage can be adjusted by adjusting the number of shunt reactors.

When the neutral point of the reactor is used through the small reactance grounding device, the small reactor can also be used to compensate the interphase and phase-to-ground capacitance of the line, so as to accelerate the automatic extinguishing of the latent power supply current, which is convenient for adoption.

The electrical equipment of the power system will produce reactive power when used, and it is usually inductive, which will reduce the capacity use efficiency of the power supply, which can be improved by increasing the capacitance appropriately in the system.

PrincipleIn AC circuits, the phase characteristics of the voltage and current of resistors, inductors and capacitors are that in pure resistive circuits, the current and voltage are in the same phase; In the pure capacitor circuit, the current leads the voltage by 90°; In a pure inductive circuit, the current lag voltage is 90°. From the perspective of power supply, the ideal load is that p is equal to s and the power factor cos is 1.

At this time, the utilization rate of the power supply equipment is the highest. In practice, this is not possible, and it is only possible to assume that the loads in the system are all resistive. The nature of most of the electrical load equipment in the circuit is inductive, which causes the total current lag voltage of the system, so that in the power factor triangle, the reactive power Q side increases, the power factor decreases, and the efficiency of the power supply equipment decreases.

Nowadays, the capacitor cabinet generally does not add reactors, because the reactor and the capacitor are easy to resonate in series, and the peak of resonance is not good for the equipment.

In order to avoid resonance at high voltages, reactors must be connected in series, either in new construction or retrofitting.

The reactor added to 1% is used to suppress the capacitor closing inrush current, the % reactor is added to suppress the arc suppression harmonics, and the excess capacitance capacity after filtering is used to compensate.

If the harmonics generated by your equipment are very large, the compensation capacitor must be connected in series, otherwise the compensation capacitor will be easily damaged due to the increase of current; If there is no shock load and no large-scale converter equipment, the reactor can also be used.

The function of series reactance at the front end of the capacitor is to prevent series and parallel resonance between the capacitor and the power system, resulting in the harmonic being amplified, and the capacitor being damaged by overcurrent, and secondly, the series reactor can also play a role in limiting the inrush current. For example, 1% of the reactor only suppresses the inrush current at the moment of capacitor closing; The 6% reactor is to suppress the 5th harmonic and above.

There are two types of reactors: current-limiting reactance and harmonic reactance. In the past, current-limiting reactance + ordinary contactors were used, but now there are contactors that specialize in switching capacitors, and current-limiting reactance is generally no longer needed; When the harmonics in the system are large, the harmonic reactance should be increased, and the capacitor should be detuned capacitor to form a static compensation and harmonic filtering device.

In general, in order to reduce the response time, the use of dynamic compensation and detuning devices should now be considered. When there are many harmonic components in the load (such as with electric welding machine, electric furnace, etc.), a filter reactor must be added, and the filter reactor should match the harmonic times in the system (such as the main harmonic matching 6% reactance). And at this time, the rated voltage of the power capacitor should be selected one level higher.

There are two purposes for installing a reactor in the capacitance compensation cabinet: 1Limit the inrush current when the capacitor is put in. 2.In systems where a large number of harmonic currents are present, string reactors can avoid resonant amplification of harmonic currents, i.e., so-called detuning capacitors.

The design temperature standard for power capacitors is 45, and more than 45 has a great impact on the capacitors. In the case of a lot of dust and static electricity, the selection of capacitors is more demanding. In this environment, the operating life of general products is short, so when selecting a power capacitor, you should consider using a special power capacitor that is anti-dust and anti-static.

Unstable current has fatal damage to capacitors, so it is recommended that some enterprises with driving, lifting equipment or frequently started equipment should use special power capacitors with impact resistance.

The 15kw motor, in the working state of rated load, needs about 7 8kvar of reactive power.

If reactive power compensation is carried out, in order to prevent overcompensation, it can be made up to 6kvar.

This refers to essentially complete compensation.

But this is dangerous: when the motor is out of power and out of service, due to the discharge of the capacitor, the motor will self-excite and damage the insulation of the motor.

If you want to fully compensate, when the motor is out of power and out of operation, you should disconnect the capacitor first, and then disconnect the motor.

Generally, the local compensation of the motor is to compensate for the no-load reactive power of the motor: the no-load reactive power is generally 20 30% of the motor power.

That is, the 15kw motor compensates about 3kvar.

At this time, there is no need to worry about the self-excitation of the motor.

Three-phase four-wire to three-phase five-wire, in fact, the three-phase four-wire PEN line, in the need for the five-wire system to be repeatedly grounded, and then the PEN line is divided into PE line and N line, at this time the N line is regarded as a charged body, no longer grounded; PE wire is a dedicated grounding protection wire.

Three-phase four-wire to three-phase five-wire does require a ground wire. I guess the distribution cabinet and the ground are directly welded together, otherwise it shouldn't be wired like this.

If the distribution cabinet really does not have a grounding wire, when the equipment leaks, the distribution cabinet will be electrified. However, the magnitude of the voltage has to be calculated according to the configuration of the site.

The local compensation of the motor is to compensate for the no-load reactive power of the motor: the no-load reactive power is generally 20 30% of the motor power.

That is, the 15kw motor compensates about 3kvar.

The grounding is not standardized, and the correct one should be that there is a wire connected to the grounding body on the distribution cabinet.

If it is directly connected to the distribution cabinet, and the distribution cabinet is not connected to the grounding body, the equipment leaks, and the distribution cabinet will also be electrified, which is very dangerous.

There are several main considerations for choosing reactive power compensation:

Because the power grid is not clean, especially when there are many frequency conversion equipment, the harmonic problem is serious, so the capacitor string reactor is generally used for reactive power compensation. to prevent harmonic amplification and ensure the safety of capacitors.

1. The selection of tuning frequency, the tuning frequency is determined by the impedance ratio of the reactor and the capacitor, generally speaking, to prevent the 5th harmonic, the reactor can be selected 6%.

2. Capacitor withstand voltage = system voltage + reactor voltage rise + harmonic voltage.

All three are indispensable.

3. Reactor withstand current = system current + harmonic current.

qc = desired power factor - current power factor) * motor power: your 15kw motor 2 poles should be compensated 5 to 6kvar 4 stage should be compensated 6 to 76kvar

The actual value should be a little higher!

Based on the efficiency of the transformer, the transformer of 630kva can load 504kw, and when the power factor is increased to 10,000 kW, the capacitance compensation amount per kW is 1,000 yuan, and the total capacitance is required

504 thousand short).

If the power factor is increased, the load power of the transformer can be increased.

Power capacitors have a capacity of 450V and so on, generally in the capacitance compensation panel main switch using isolation switch, each capacitor with an empty opening, the empty capacity is slightly greater than the rated current of the capacitor.

The role of the reactor has two points: 1Elimination of subharmonic 2Protect capacitors and extend capacitor life. There are no parameters, we can't do anything, first understand your capacity or load power From the perspective of economic benefits, look at the optional or not, in the power, capacity, current is small to a certain value can not be installed reactance, but the capacity is large or the voltage and current are large such capacitors ** will be very expensive, you do not spend a little money to buy a reactance, not only can protect the capacitor, but also extend the life of the capacitor for about 5 years! At this time, it must be a good deal.

How to design the reactor if installed, magnetic flux density, core size, window area, winding material, number of turns......These are all related to the reactance.

If there is filtering, there is also a consideration of frequency selection or full-band aluminum foil ......Design and selection of relational reactors.

It depends on whether the system you need to compensate is clean, that is, whether there is a harmonic device, if the harmonic content of the system is within the national standard, you can not add the reactor! If it is understood that the system has a large harmonic content, the reactor with the corresponding reactance rate is matched in the true harmonic.

If you need a better electricity environment, the reactor is still better, now many devices will produce harmonics, and there is a problem that even if your own equipment does not produce many harmonics, but if you have a large harmonic source nearby, it will be easy to string to your side!

Yes, now electronic equipment is widely used, harmonics are everywhere, or it is better to add a reactor.

Now I don't add it, and I directly replace the fuse with a small empty opening.

1. Low-voltage capacitance compensation cabinet.

1.Overview: Most of the load types in the power system are inductive loads, and the widespread use of power electronics by power consumers makes the power factor of the grid low. The lower power factor reduces the utilization rate of the equipment, increases the investment in power supply, damages the voltage quality, reduces the service life of the equipment, and greatly increases the line loss. In order to improve the energy waste caused by the low power factor of the grid and these factors that are unfavorable to power supply production, the power factor of the grid must be effectively improved.

Obviously, it is unreasonable and often impossible for all of this reactive power to be supplied by generators and transmitted over long distances. The reasonable way is to generate reactive power where reactive power is needed, that is, to increase reactive power compensation equipment and devices.

2.Composition: Generally speaking, the low-voltage capacitance compensation cabinet is composed of cabinet shells, busbars, circuit breakers, isolation switches, thermal relays, contactors, lightning arresters, capacitors, reactors, primary and secondary wires, terminal strips, power factor automatic compensation control devices, disk instruments, etc.

3.Rationale:

In the actual power system, most of the load is asynchronous motors. Its equivalent circuit can be regarded as a series circuit of resistance and inductance, and its phase difference between voltage and current is large, and the power factor is low. After the capacitor is connected in parallel, the current of the capacitor will cancel out a part of the inductor current, so that the inductor current will be reduced, the total current will be reduced, the phase difference between voltage and current will be reduced, and the power factor will be increased.

2. Whether the low-voltage capacitor compensation cabinet needs to be recharged.

1.The role of the reactor:

The role of a reactor is twofold:

1) Elimination of subharmonics.

2) Protect the capacitor and prolong the life of the capacitor.

2.Whether the low-voltage capacitance compensation cabinet needs a reactor.

First of all, understand the capacity or load power of the equipment, from the perspective of economic benefits, consider the optional or not to install the reactor, in the power, capacity, current is small to a certain value can not install the reactor, but the capacity is large or the voltage, current needs to install the reactor.

Install reactors or harmonic suppression equipment such as filters on the power supply of the capacitance compensation cabinet. Otherwise, harmonics may cause problems such as capacitor bursting.

At present, there are two main ways to eliminate harmonics in the power system:

One is an active filter, also known as an active filter, whose main principle is to cancel out the harmonics in the system by generating harmonic currents of equal magnitude in the opposite direction of the harmonics. Its filter effect is wide, but the cost is high.

The other is the passive filter, also known as the passive filter, the main principle of which is to connect the capacitor with the filter reactor in series to form a low-impedance loop at the harmonic frequency, which is used to absorb the harmonics of the frequency, so as to achieve the function of reducing the harmonics of the system. However, its filter range is narrow, and it can only filter out harmonics of a single order.

The passive filter is what you call the compensation method of the capacitor.