Field of the invention

The present invention relates to a star delta starter and more particularly relates to a star delta starter with improved and cost effective power contactors.

Background and prior art of the invention

Generally, three phase motors up to 10 H.P. are started with directly on line method but when high power rating three phase electric motors above 10 H.P. are commenced in that way, initially they employ six times more current (starting current) than they driven normally and it may cause disturbance in voltage supply line due to maximum inrush current. So, to reduce high starting current (inrush current), high power ratings electric motors are required to start at reduced voltage initially and then allowed to have full supply voltage when they come up to a speed of nearly equal to its full normal speed.

Plenty of star delta starters are available for starting high rating three phase electric motor at reduced voltage. While starting the motor, initially the motor windings are connected in star configuration to reduce the voltage. This in fact reduces the torque by a factor of three. After predefined period of time, when motor reaches to its full normal speed, motor windings are connected in delta configuration. For this determination and for magnetically operating the motor windings in star and delta configurations, a set of three conventional electric air - break power contactors of same configurations are being employed in conventional star-delta starter. However, such conventional star-delta starters require quit structural, circuitry and monetary improvements on the constituents of its electromagnetic air break type power contactors to design a simple and economically improved star delta starter for starting high power rating three phase electric motors.

A conventional star delta starter for starting a three phase star delta motor comprises three pole power contactors for supplying three phase power to star position and delta position, a timer control with a logic circuit for controlling AC power supply switching operation for star position and delta position and for adjusting a time delay of switching over from star connection to delta connection, an overload relay for

l protecting motor from overload, a start and stop push buttons to perform starting and stopping operation of star delta starter.

Fig. 1 shows an isometric view of an existing three pole power contactor (P) used in conventional star delta starters. For the construction of each main, star and delta contactors of the conventional star delta starter, said three pole power contactor having similar constructional and functional constituents is widely used.

Referred to Fig. 1, the conventional three pole power contactor (P) is formed of a top cover (1), a middle housing (2) and a base (3). The middle housing (2) and base (3) are covered by the top cover (1). A set of at least three spring operated moving bridges (5) is transversely arranged on the centre of the middle housing (2) in such a way that each of said moving bridges (5) carries a respective moving contact carrier at its top surface at a height "h" from the middle housing (2) so as to have at least three moving contact carriers (H). Each of said moving contact carriers (H) has two terminal ends and on to each bottom end of which a moving contact is secured so as to have a pair of moving contacts Gl and G2 as directed in Fig. 2. The base (3) consists of a coil wounded magnet arrangement (9) along with a common magnetic coil connection (9') and which is disposed below the middle housing (2) for the operation of each of the moving bridge (5). The base (3) also consists of an auxiliary (10) to supply a timer controlled auxiliary power supply to the magnetic coil connection (9') to energize the magnets of said magnet arrangement (9) during the operation of the power contactor (P). The auxiliary (10) is also used to connect control wirings of the conventional timer control and logic circuits with the power contactor (P) to logically control the vertical motion of the moving bridge (5) during the operation of the power contactor (P).

Also, a set of at least three fixed contact carriers, each holding a fixed contact at one end and a fixed terminal on the other end, is disposed on either sides of the moving bridge (5) so as to form a set of three fixed contacts (D) and a set of three fixed terminals (T) on either side of the moving bridge (5) and a set of three fixed contacts (D) and a set of three fixed terminals (T) on other lateral side of the moving bridge (5). The connection between each of the fixed contacts (D) and its respective moving contact is normally opened in "OFF" position of the star delta starter.

Referred to Fig. 3, a wiring diagram for three pole main, star and delta power contactors used in conventional star delta starter fitted with a three phase electric motor is shown. The main contactor has three moving contact carriers HI, H2 and H3 and six fixed contacts Dl, D2, D3, D4, D5 and D6, each of which adapted to locate at each end of each of said moving contact carriers. The delta contactor has three moving contact carriers H4, H5 and H6 and six fixed contacts D7, D8, D9, D10, Dll and D12, each of which adapted to locate at each end of each of said moving contact carriers of the delta contactor. Also, the star contactor has three moving contact carriers H7, H8 and H9 and six fixed contacts D13, D14, D15, D16, D17 and D18, each of which adapted to locate at each end of each of said moving contact carriers of the star contactor.

Before connecting the three phase motor winding terminals, the fixed contacts D10, Dll and D12 are connected with the fixed contacts D18, D17 and D16 respectively to form connecting terminals CI, C2 and C3 as directed in Fig. 3. Also, the fixed contacts D7, D8 and D9 are connected with fixed contacts Dl, D2 and D3 respectively to form connecting terminals C4, C5 and C6. Each of the three fixed contacts D13, D14 and D15 of the star contactor are short circuited with other remaining two fixed contacts so that the fixed contacts D13, D14 and D15 are electrically interlocked with each other.

Now, the primary motor winding terminals Ul, VI and Wl are connected to the fixed contacts D4, D5 and D6 respectively through a overload relay (11) and whereas, the secondary motor winding terminals U2, V2 and W2 are electrically connected to the terminals C3, CI and C2 respectively. The main three phase AC power supply lines LI, L2 and L3 are connected to the terminals C4, C5 and C6 respectively. Here, the connections are shown to be made at fixed contacts (D). However, in fact the connections are employed at the fixed terminals (T) corresponding to each of the fixed contacts rather than directly at the fixed contacts.

Once, the electrical connections are completed in the aforesaid manner, in the "OFF" state of star delta starter, all the fixed contacts corresponding to the main, star and delta contactors are normally open with respect to their corresponding moving contact carriers. When the start push button of star delta starter is pressed, the magnets corresponding to the coil wounded magnetic coil connection (9') of the star and main contactor is energized through the timer control auxiliary power supply to actuate their corresponding spring operated moving bridges (5) to move downwardly. This downward motion of the spring operated moving bridges (5) enable to make normally opened contacts Dl, D2, D3 and D4, D5, D6 of main contactor as well as D13, D14, D15 and D16, D17, D18 of star contactor to electrically contact with its respective moving contacts of the moving contact carriers to establish a closed star circuit connection as directed in Fig.4. Hence, the three phase motor is started in a star position. After a preset time interval, the magnets corresponding to the star contactor is de-energized by means of timer control operation to disconnect all the fixed contacts of the star contactor from its respective moving contacts by bringing the spring operated moving bridges (5) of star contactor in its original position. Simultaneously, the magnets corresponding to the delta contactor is energized through the timer control auxiliary power supply to actuate the spring operated moving bridges (5) of the delta contactor to move downwardly. This downward motion of the spring operated moving bridges (5) enable to make normally opened contacts D7, D8, D9 and D10, Dll, D12 of delta contactor to electrically contact with its respective moving contacts of the moving contact carriers to establish a closed delta circuit connection as directed in Fig. 5. Hence, the three phase motor is started in a delta position and runs at full rated speed.

When the stop push button is pressed, the original "OFF" state of the star delta starter is reached through the timer control operation. The logic control circuit of the timer maintains smooth and automatic functioning for starting the three phase motor through the star delta starter.

A disadvantage associated with such knpwn star delta starter is that they are either expensive to manufacture or are susceptible to complex erroneous wiring connections when it is being fitted with the three phase motor due to the fact that the power contactors used in such star delta starter employs a quite redundant number of silver contacts for the construction of the moving and fixed contacts. Hence, star delta starter employing improved power contactors of simple form and having comparatively less number of fixed and moving silver contacts is needed to overcome the aforesaid disadvantages.

Object of the invention

The main object of the present invention is to provide a star-delta starter having simple, compact and highly economic power contactors.

Yet another object of this present invention is to provide power contactors for the star delta starter which has a considerably less number of fixed and moving silver contacts.

Further object of the present invention is to provide a star delta starter having a less maintenance cost and less foundation cost power contactors. Summary of the Invention

The present invention relates to an improved star delta starter for starting a three phase star delta motor comprises improved power contactors configured to have a pair of three pole delta and main contactors, and a single pole star contactor for supplying AC power to star position and delta position, a timer control with a logic circuit for controlling AC power supply switching operation for star position and delta position and for adjusting a time delay of switching over from star connection to delta connection, an overload relay for protecting motor from overload, and start and stop push buttons to perform starting and stopping operation of star delta starter.

Detailed description of the drawings

A more complete understanding of operation and construction of present invention may be obtained b reference to the following detailed description when taken in conjunction with accompanying drawings wherein:

Fig. 1 depicts isometric view of an existing three pole power contactor used in conventional star delta starter.

Fig. 2 shows a schematic side view of three pole power contactor depicted in Fig. 1.

Fig. 3 depicts a wiring diagram for conventional three pole main, star and delta power contactors of star delta starter fitted with a three phase electric motor.

Fig. 4 depicts a wiring diagram for star poison of star-delta starter illustrated in Fig. 3.

Fig. 5 depicts a wiring diagram for delta position of star-delta starter illustrated in Fig. 3.

Fig. 6 depicts an isometric view of main, star and delta contactor according to present invention.

Fig. 7 depicts an isometric internal view of main or delta contactor according to the present invention.

Fig. 8 shows top and side view of moving contact carrier depicted in Fig. Fig. 9 shows schematic side view of main or delta contactor depicted in Fig. 10 depicts an isometric internal view of star contactor according to the present invention.

Fig. 11 depicts wiring diagram of the three phase electric motor fitted with main, star and delta power contactors of the "OFF" state star delta starter employed in the present invention.

Fig. 12 depicts the arrangement and circuit connection of main, star and delta contactor in ON (star) position according to present invention.

Fig. 13 depicts wiring diagram of the three phase electric motor fitted with main, star and delta power contactors of the star positioned star delta starter employed in the present invention.

Fig. 14 depicts the arrangement and circuit connection of main, star and delta contactor in delta position according to present invention.

Fig. 15 depicts wiring diagram of the three phase electric motor fitted with main, star and delta power contactors of the delta positioned star delta starter employed in the present invention.

Detailed description of the invention

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and arrangement of parts illustrated in the accompany drawings. The invention is capable of other embodiments, as depicted in different figures as described above and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation.

Referred to Fig.6, improved power contactors used in a modified star delta starter of the present invention is shown. The power contactor parts of the presently modified star delta starter employs an improved three pole main contactor (A), an improved three pole delta contactor (B) of similar configuration as that of main contactor (A), and a novel single pole star contactor (C) rather to have a conventional three pole configuration. The other parts of presently modified star delta start such as a timer control with a logic circuit, an overload relay, and start and stop push buttons are operated in a conventional manner. The improved three pole main or delta contactor mainly consists of a top cover ( ), a middle housing (2') and a base (3') having an AC or DC operated coil wounded magnet arrangement (9") as directed in Fig. 7. The top cover ( ) and base (3') has been positioned, structured and functioned in a conventional manner as described earlier.

Referred to Fig. 7, the modified middle housing (2') of the present three pole main or delta contactor includes a set of at least three spring operated moving bridges (5') being arranged transversely on the centre of said middle housing (2') in such a way that each of said moving bridges (5') carries a respective moving contact carrier at its top surface at a height "h" from the middle housing (2') so as to have at least three moving contact carriers (Η'). At one lateral side of the moving bridges (5'), a set of at least three fixed contact carriers, each holding a fixed contact on one end and a fixed terminal on other end, is disposed so as to form a set of three fixed contacts (D') and a set of three fixed terminal (Τ') corresponding to said set of three fixed contacts (D'), as directed in Fig. 7. While at the other lateral side of the moving bridges (5'), a set of at least three fixed contact carriers, each holding a moving contact stopper on one end and a fixed terminal on other end, is disposed so as to form a set of three moving contact stopper (12) and a set of three fixed terminals (Τ') corresponding to said moving contact stoppers (12). This in fact reduces a number conventional silver contacts employed at one end of each of the three fixed contact carriers of the main or delta contactor. Thereby, while manufacturing the fixed contact carriers of main or delta contactor of the present invention, three silver contacts, in comparison to the each set of fixed contact carriers of conventional main or delta contactor, is saved.

Each of said moving contact carriers (Η') has two terminal ends and one of said two terminal ends holds a moving contact (G') corresponding to each of the fixed contacts (D') at its bottom end, as directed in Fig. 8. While the other terminal end of the moving contact carriers (Η') is connected with respect to its corresponding fixed contact carrier by means of a flexible terminal link (13), as directed in Fig. 7 and which in fact reduces employing a conventional silver contact at one of each bottom ends of three moving contact carriers (Η') of the main or delta contactor. Thereby, while manufacturing the moving contact carriers of main or delta contactor of the present invention, three silver contacts, in comparison to the moving contact carriers of conventional main or delta contactor, is saved.

Hence, considering the above facts and while considering both main and delta contactors of the present invention, twelve silver contacts (six for main contactor and six for delta contactor) have been reduced in comparison to the conventional main and delta contactors.

The Fig. 9 shows that, in each delta or main contactor, below the proximity of one of the bottom end of the moving contact carriers (Η') holding a moving contact (G'), one of said fixed contacts (D') is secured and whereas, below the proximity of the other bottom end of the moving contact carriers (Η'), one of said moving contact stoppers (12) is secured so as to have a distance between each of the contact stopper and the respective end of moving contact carrier is same as that of the distance between each of the fixed contacts (D') and the respective end of the moving contact carrier holding the moving contact (G');

Referred to Fig. 10, a novel compact single pole star contactor (C) for the star delta starter used in the present invention is shown. It is also formed of a top cover (1"), a middle housing (2") and a base (3"), and said top cover, middle housing and the base of the single pole star contactor (C) are assembled in a conventional manner except that the size and number of constituent parts used for fabricating said top cover, middle housing and the base are taken care of while manufacturing the compact single pole star contactor (C). For an instance, On to the centre of the middle housing (2"), a spring operated moving bridge (5") is mounted by carrying a moving contact carrier (H") at its top surface at a height "h" from the middle housing (2"). Each of said moving contact carriers (H") has two terminal ends and each of said two terminal ends holds a moving contact (G") as in a conventional manner. At either lateral side of the moving bridges (5"), a fixed contact carrier holding a fixed contact on one end and a fixed terminal on other end, is disposed so as to form a pair of fixed contacts (D") and a pair of fixed terminals (T") as directed in Fig. 10.

Below the proximity of each of the bottom end of the moving contact carrier (H") holding a moving contact (G"), each of said fixed contacts (D") is secured so as to have a distance between each of the fixed contacts (D") and the respective end of the moving contact carrier holding the moving contact (G") remains same. Also at one end of the upper surface of the moving contact carrier (H"), a moving contact terminal (14) is provided to receive external wiring connection while a three phase motor is fitted with star delta starter. Hence, this single pole form of star contactor entirely reduces two fixed contact carriers as well as two moving contact carriers and which in fact reduces eight silver contacts, in comparison to the conventional three pole star contactor. Hence, the presently modified power contactors of star delta starter as a whole reduces twenty (12+8) silver contacts in comparison to the power contactors used in the conventional star delta starter. This enables to achieve an improved and cost effective form power contactors used in the presently modified star delta starter.

Referred to Fig. 11, a wiring diagram for the main, star and delta power contactors of the present invention fitted with a three phase motor is shown. The main contactor has three moving contact carriers HI', H2', H3', three fixed contacts Dl', D2', D3', and three fixed terminals Τ , T2' and T3'. The delta contactor has three moving contact carriers H4', H5', H6', three fixed contacts D4', D5', D6', and three fixed terminals Τ4', T5' and T6'. Also, the star contactor has a single moving contact carrier H7' holding the moving contact terminal (14) along with a pair of fixed contacts D7", D8".

Before connecting the three phase motor winding terminals, the fixed contacts D4', D6' are connected with the fixed contacts D7", D8" respectively and whereas, the fixed contact D5' is connected with the moving contact terminal (14) of the start contactor (C) so as to form connecting terminals CI', C2' and C3' as directed in Fig. 11. Also, the fixed terminals Τ , Τ2', T3' of the main contactor (A) are connected with fixed terminals Τ4', Τ5', Τ6' of the delta contactor (B) so as to form connecting terminals C4', C5' and C6' as directed in Fig. 11. Now, the primary motor winding terminals Ul, VI and Wl are connected to the fixed contacts Dl', D2' and D3' respectively through a overload relay (11) and whereas, the secondary motor winding terminals U2, V2 and W2 are electrically connected to the C3', CI' and C2' respectively. The main three phase AC power supply lines LI, L2 and L3 are connected to the connecting terminals C4', C5' and C6' respectively. Here, the connections are shown to be made at fixed contacts (D') and (D"). However, in fact the connections are employed at the fixed terminals ( ) and (T") corresponding to each of the fixed contacts rather than directly at the fixed contacts.

Once, the electrical connections are completed in the aforesaid manner, in the "OFF" state of star delta starter, all the fixed contacts corresponding to the main, star and delta contactors are normally open with respect to their corresponding moving contact carriers. When the start push button of the star delta starter of the present invention is pressed, the magnets corresponding to the coil wounded magnetic coil connection (9') of the star and main contactor is energized through the timer controlled auxiliary power supply to actuate their corresponding spring operated moving bridges (5') to move downwardly, as directed in Fig. 12. This downward motion of the spring operated moving bridges (5') enable to make normally opened contacts Dl', 2', D3' of the main contactor (A) as well as D7", D8" of the star contactor to electrically connect with its respective moving contacts of the moving contact carriers to establish a closed star circuit connection as directed in Fig. 13. Hence, the three phase motor is started in a star position.

After a preset time interval, the magnets corresponding to the star contactor (C) is de-energized by means of timer control operation to disconnect the fixed contacts of the star contactor (C) from its respective moving contacts by bringing the spring operated moving bridges (5') of the star contactor in its original position. Simultaneously, the magnets corresponding to the delta contactor (B) is energized through the timer controlled auxiliary power supply to actuate the spring operated moving bridges (5') of the delta contactor (B) to move downwardly, as directed in Fig. 14. This downward motion of the spring operated moving bridges (5') enable to make normally opened contacts D4', D5', D6' of the delta contactor (B) to electrically connect with its respective moving contacts of the moving contact carriers to establish a closed delta circuit connection as directed in Fig. 15. Hence, the three phase motor is started in a delta position and runs at full rated speed.

When the stop push button is pressed back, the original "OFF" state of the star delta starter is reached by the timer control operation. The logic control circuit of the timer maintains smooth and automatic functioning for starting the three phase motor through the star delta starter.

Although the preferred embodiment has been described in detail, it should be understood that various changes, substitution and alteration can be made therein without departing from the sprit and scope of invention as defined by the appended claims.