As a product research and development engineer, self-learning electrical control and automation do not allow the start-up of three different pacers. The industrial field, however, is absolutely taboo for direct full-voltage start-up of a sudden bursting power of up to 5-8 times the rated current, not only to bring down grid voltage, lined up other equipment, but also to accelerate the aging of electrical circuits, shock mechanical transmission structures and, lightly, to jump and burn hardware。
In order to avert the shock of large currents, pressure relief has become a demand, while the star triangle (y-) has been activated as the most commonly used pressure-relief programme for small and medium-sized electric generators, with its low-cost, simple-wire, and durable-spectrum features, as well as as a point of actual knowledge for entry-level electrical control. The article uses ground-to-ground thinking to explain the principles, connections, processes and operational attention of the star triangle, and to help you quickly get through this practical skill。
First understand the core: the distinction between star and triangle
The essence of a star-triangular activation is the use of an electric circuit around the current difference between the two wires, which is activated by the pressure-down stream and then switched to full-pressure operation. There are three separate circuits within the three-segregation power sets marked u1-u2, v1-v2, w1-w2, all of which are drawn out at the end of the line in order to facilitate switching。
The star-shaped method is the short-linking of the tails of the three groups of contour u2, v2, w2 and the first end of the three-phase power supply. Under this method, the circuit is subject to only 220 v of the phase voltage, the wire current is equal to the phase current, the activated current voltage reaches one third of the direct activation and the impact is significantly reduced, but the corresponding kickback is only one third of the direct activation。
The triangle method is to connect the tails of the rounding group sequentially, form a closed ring and then reconnect the power, which directly withstands the full pressure of 380 v, which is three times as high as the current, capable of yielding a rated rotation to meet normal load operation requirements. This is also the dominant method for the normal operation of electric power。
There is a power boundary that is commonly used in the project: small power machines below average 7. 5 kw, with a sufficient grid capacity, can be activated directly by a triangle at full pressure; small and medium-sized power units of 7. 5kw-75kw, which must be activated by a star-triangular decompression; and larger power machines over 75kw, which do not apply to a star-triangular launch, in exchange for programmes such as a coupling transformer or a soft starter. Remember this divide, you don't step on the pit when you choose and design。
A simple summary of the core logic of the star triangle: the first star-to-star approach to low-speed relief is activated, and when the turn-off is up, the current stabilizes, then the triangle is fully pressured, taking into account the safety and operational performance of start-up。
Ii. Star-tribe-starting circuits and running processes
The star triangle activates the main circuits and controls the circuits, which are the most common devices on the site, without special accessories and at low cost. These are the core components: air switches, main contacts, star contacts, triangle contacts, time relays, heat relays, and start buttons and signal lights。
The main circuit is responsible for power supply and switching, and the control of the circuit is responsible for logical control, and most importantly for electrical interlocking — it is absolutely essential that the star and triangle contacts do not be inhaled at the same time, or else they will be directly short-circuited. Time relays are the core of the automatic switch, setting the time delay and automatically cutting through the star triangle at point, without manual intervention。
The entire start-up process is clear: when the main contact and the star contact presses the start-up button, the main contact is inhaled, the electric is in a star-relief state and the speed is slowly rising; the time relay is in general 3 to 10 seconds (based on a slight change in the power of the electric power, a smaller power, a longer power), when the turn-off is close to a nominal value, the stream is back, the satellite contact is closed, the triangle is closed; and the final generator keeps the triangle fully under pressure and the stop button is broken. It is normal to switch a light current shock in a moment, and there will be no security problems as long as the locks are in place。
Iii. Strengths and disadvantages, application of scenes and pits
The advantages of a star triangle are real: hardware costs are low and can be connected to any few contacts relays; connection debugging is not complicated and new hands can be connected to drawings; failure points are low, maintenance is simple and the industrial environment is durable. However, it is also clear that its short plate is small and can only be activated with empty or light loads, that the heavy load is not moving at all, and that it is limited by 75 kw power and is not hard to use。
The corresponding applicable scenario is also clear: wind, water pumps, air presses, transmission belts of this type of space-borne/light-loaded start-up equipment, medium-sized and small three-step power units within 75 kw, with the highest cost-effectiveness using a star triangle. Devices such as cranes, shredders, crushers that require a reload-starter, or large power generators, are not chosen for the star triangle, and are vulnerable to failure and even damage。
In actual exercise, there are a number of common malfunctions: the power is not activated, most of which are power, button contact is poor, or the logic of interlocking is wrong; the switch-off is likely to be too short, the turn speed is not cut or the interlock is not working; the electric is acoustic, checking whether the side ends of the bypass group are backsliding or not; and the contact bonding is usually small in the selected stream or is too frequently activated。
The debugging is done bearing in mind a few details: the time delay is determined by the speed-stabilization of the electrical flow backsliding; the main contact and the triangle contacter are rated by the electric engine, and the star contactor can drop one; the connection must be separated from the end of the circuit group, provided that the interlocking is protected, the power is cut prior to the connection, and the empty tester is free to carry the load。
The star triangle, which appears to be the basis for electrical control technology, covers the core knowledge points of electrical properties, circuit logic, protection design and is well suited as an introduction to self-learning electrical automation. It does not have complex algorithms and high-end accessories, but it solves practical problems by simply switching, particularly in line with the practical thinking of industrial control。
For our research and development engineers, using the trans-star triangle can not only fix the design and commissioning of conventional power start-ups, but also build basic thinking about electrical control, follow-up software start-up, frequency modulation, plc automated control. If further optimization is to be achieved, traditional relay controls could be replaced by plc, which would make the start logic more flexible and stable。
