Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

Photocoupler

The soft starter has more and more applications with the advantages of small volume, adjustable torque, small smooth start shock and soft stop function. It has a tendency to replace the traditional auto-decompression, star-angle and other starters. . Since the soft starter is a newly developed starter device in recent years, there are still no guidelines and procedures for design, installation, commissioning and use. We also encountered some practical technical problems in the installation and commissioning of the soft starter. For example: the selection of different start load soft starters, the combination of soft start surge current and overcurrent protection settings, the relationship between soft start device capacity and transformer capacity.
1. Introduction to Soft Starter At present, the common soft starters on the market mainly include electronic, magnetic control and automatic liquid resistance. The electronic type has a majority of thyristor voltage regulation. In a sense, the frequency converter is also a soft starter, and it is a starter that can really achieve soft start, but the cost is higher.
The thyristor type soft starter is three sets of thyristors connected in series between the power supply and the motor in parallel, and the AC voltage is controlled by the microcomputer control to trigger the conduction angle. Thyristor type soft starters are available in ramp voltage type, snap-on plus ramp voltage type and current limiting type.
Ei8 o0 j?2 X! E The magnetically controlled soft starter is a soft starter constructed by a three-phase saturable reactor connected in series between the power supply and the motor. At startup, the excitation current of the magnetic amplifier control winding is adjusted by the word control board, and the reactance value of the saturation reactor is changed to adjust the starting voltage drop to realize the soft start of the motor. C5 b" a4 gf/ f0 n5 l9 C! I
Regardless of the thyristor type soft starter, the magnetically controlled soft starter can only adjust the output voltage when starting, and achieve the voltage drop at the control start and limit the starting current. Generally, the soft starter can't adjust the power frequency, and it can't start the motor from the zero frequency zero voltage like the inverter to achieve the impactless start. In fact, the soft starter must generate a certain inrush current when starting the device; the voltage and current curves of the ramp voltage type control soft starter are shown in Figure 1. When the thyristor soft starter is started with the ramp voltage, the soft starter should start to output an initial voltage (the initial voltage can be adjusted between 80 and 280V), so that the motor can generate enough initial torque to overcome the static friction of the mechanical equipment. Turn, the starting current is Is. Under the control of the microcomputer, continue to increase the output voltage to accelerate the motor. When the soft starter output voltage is close to the rated voltage, the motor has reached the rated speed and Is is reduced to the load current In. At the end of the start-up time t1, the soft starter outputs the rated voltage and sends a bypass signal to close the bypass contactor, the soft starter stops the output voltage, and the motor goes into normal operation. The soft start initial torque can be adjusted for the initial voltage and start time, and the starting current is controlled within 2~4.5 times of the rated motor current. ; ~
Low-voltage soft starter parking modes mainly include free parking, soft parking, and brake parking. Conventional motor parking is often used for free parking, but there are many applications. Free parking can cause great problems. For example, high-rise building pump systems, using free parking, will have a huge “water hammer” effect, which will damage pipelines and pumps. The use of soft parking eliminates this anti-inertial shock caused by free parking. When the parking time t2 issues a parking command, the motor terminal voltage drops slowly from Un. When the voltage drops, the motor current will have a small current impact, and then the motor current will drop with the voltage drop until the motor stops.
2, low voltage soft starter should pay attention to the problem ~ / S0 X8 B
2.1 Low-voltage soft start cabinet electrical wiring and component arrangement General low-voltage soft start cabinet electrical wiring shown in Figure 2. The electrical components in the cabinet are arranged in the order shown in the figure, so that the main wiring is short and does not cross, which facilitates the connection of the copper bars. The soft starter is installed on the right side of the contactor and is not affected by the heat of other components. The distance between the soft starter and the side wall of the control cabinet and other components is ≥100mm, which is convenient for the soft starter to dissipate heat.
2.2 In addition to technology, performance, and price comparison, soft starter selection should also consider the specific conditions such as the grid capacity of the equipment site, the light load of the equipment, and the frequency of startup. . {& a$ U" xx" O
For the pump type, the light load device is lighter, and the soft starter can be selected with simple function, low price and convenient operation. This type of equipment can meet the needs of the motor based on the rated power of the motor, using a soft starter with the same capacity as the sample. For large wind turbines, crushers and other equipment with relatively heavy starting loads, soft starters with more start-up functions, limited flow start functions, and complete protection should be used. Especially for large power equipment (200KW or more), it is best to use the start function to compare the full performance soft starter.
2.3 Isolators and fuses Select the isolating appliances in the soft-start cabinet, either the isolating switch or the molded-shell circuit breaker with isolation function. The low-power soft start cabinet should use the isolating switch fuse combination knife fuse switch. Not only does it provide protection against isolation, but it also reduces engineering costs. The rated current of the isolating switch is greater than the rated current of the motor to meet the operational requirements.
The thyristor surge Joule integral (I2t) value in the soft starter is limited. The use of a circuit breaker as a short circuit protection device cannot effectively protect the thyristor components. It is recommended to use a fast-acting fuse as a short-circuit protection device. Fast-acting fuses can be selected with aR or NGT type semiconductor protection fuses. The selection of the quick-blow fuse generally does not require the breaking capacity verification. The rated breaking capacity of the aR fuse is 50KA, and the breaking capacity of the NGT fast-acting fuse is 120KA, which can meet the needs of general power distribution engineering. In addition, the fuse also has a limited current function, and the protection of the thyristor is more reliable than the circuit breaker.
The principle of the rated current of the quick-blow fuse is that the device will not blow when it starts, and it must be reliably blown when the minimum short-circuit current occurs at the equipment installation. The specific load can be used to determine the load characteristics of the equipment and the starting current of the motor. Check the fuse manufacturer's fuse-current characteristic curve, I2t value and thyristor I2t value for calculation and selection. In the absence of the above information, the following empirical formula can also be used to calculate the selection:
Ifn≥(1.8~2.0)*Ie(A). j
Ifn—Fast fuse rated current (A)3
Ie—motor rated current (A)
2.4 Bypass contactor selection When the motor is rated at the end of the soft start, the AC contactor can be selected according to the rated current of the motor. It should be noted that when the cabinet is wired, the soft starter and the contactor are connected in phase, and the wrong phase sequence is not connected.
2.5 Overload protection device selection Soft start device Overload protection device should use thermal overload relay with overload protection, phase failure protection and temperature compensation function. When the specific selection, the motor operating current thermal component should be set within the current range. It is easy to overload the equipment during work, so that the rated current of the motor is close to the lower limit of the current range of the thermal element.
2.6 Transformer load capacity and protection setting value verification In addition to paying attention to the above requirements when selecting the soft start device, it is also necessary to pay attention to the load capacity of the equipment power supply transformer. Before the transformer is almost full, the soft start device should be carefully selected. In particular, when adding a relatively large power device, it is necessary to check the load capacity and protection setting value of the verification transformer. After adding the soft start device, the transformer secondary circuit breaker short circuit short delay release setting value Ir2 is: Ir2 ≥ 1.1 (IL+1.35*K*Ie) Type A: IL—load current A during normal operation of the transformer; K—newly increase the ratio of starting current of the soft start device to the rated current of the motor (see Table 1); Ie—newly increase the rated current of the motor A. It is calculated that Ir2 should be smaller than the actual short-circuit and short-delay release setting of the secondary circuit breaker of the transformer; otherwise, when the newly added equipment is started, the secondary circuit breaker of the transformer should be tripped. The soft starter selection failed.
Table 1 Typical equipment soft start effect and starting current reference value Application machine type selection function Execution function Start current (%) Start time (seconds) Centrifugal pump standard start to reduce impact, eliminate water hammer 3005~15!
Screw compressor standard start to reduce impact and extend mechanical life 3003~203
Centrifugal compressor standard start to reduce impact and extend mechanical life 35010~40$T
Piston compressor standard start to reduce impact and extend mechanical life 3505-10
$ c) i, V# V: g0 r/ V Conveyor conveyor standard + kick start smooth, reduce impact 3003-104
Fan standard start to reduce impact and extend mechanical life 30010~40
The standard start of the mixer reduces the starting current 3505~20
Milling machine heavy load start to reduce starting current 4505~60
3, typical application industrial control 365 forum - CV / _1 J / ] + t! y5 ? 9 s
Example: A new 250KW circulating pump is added to a second heat source plant in a city. Two sets of two standby units are used. The transformer capacity is 1250kVA, 10/0.4kV. In order to reduce the motor starting current and avoid excessive investment, our users require soft. Launcher. The load is a pump type, which starts very frequently, and adopts the SS2-250 soft starter with better cost performance. The isolating switch adopts HD17-630/3, the fuse adopts NT4-1250A, the bypass contactor adopts CJ29-500/3, and the thermal relay adopts JRS2-630/3. It has been running normally for two years and is able to meet user requirements very well.

4. Adjustment and commissioning The soft start control cabinet should be carefully checked after installation. Check the wiring according to the design drawings for correct wiring and reliable connection. Electronic devices such as thyristors are not allowed to be tested for insulation resistance. The thyristor insulation in soft starters can only be checked with a digital multimeter high impedance. When the new soft starter (in the cold state), the measured resistance value between each group of thyristor input and output terminals should be about 1.3MΩ, and the relative measurement resistance value should indicate infinity when the phase is not connected (the phase is not connected to the control loop). After the check is confirmed, the soft starter output is connected to a small power motor and set the technical parameters such as start mode, initial voltage, start time and down time. The motor and cable insulation must be checked with a 500V insulation resistance tester before the motor is connected to the soft starter. The insulation resistance complies with the relevant regulations before the motor is connected to the soft starter output for the start-up test. Before the first soft start, the machine should be powered by the manpower to check whether the machine has a “plug” phenomenon, and then the equipment start test and adjust the start parameters, then it can be delivered.
In short, the soft starter can adjust the starting torque, the equipment start-up time is short, the soft stop function, the component less maintenance, the ability to complete the difficult equipment start, the better performance of the motor start control equipment, should be promoted and applied.