Application of the RVSS to replace wye-delta motor starting
Contents
1. Application Notes AP03902009E Effective July 2012 Application of the RVSS to replace wye delta motor starting ELN Powering Business Worldwide Replacing a wye delta motor starter with an RVSS soft starter Application The wye delta method of motor starting has been established for many years It is today still a viable and reliable method of motor starting Replacing a wye delta starter with a reduced voltage solid state soft starter RVSS brings new features and benefits to an existing application allowing the system to benefit from new controls and protections Overview A wye delta starter generally consists of several contactors with mechanical and electrical inter locks and a timing system In its simplest form a timer is used to control the length of time the motor is first started using the wye winding contactors of a six lead motor and then switched to rewire the motor using the delta winding contactors The start time is selected based on experience and or observation of how much time the motor takes to reach synchronous speed Another function of the timer is to control the transition time between releasing the start con tactor and energizing the run contactor An open or closed transition method may be employed A separate timer may also be used for this purpose There are several variations of this procedure but the process is that of timed control of contactors to start and run the motor Th2. e tried and true functionality of the wye delta starter is offset somewhat by the requirement of external functions such as contactor control overload protection and interface timing to name a few In some cases such as in older systems the motor is no longer able to reach synchronous speed on the wye windings due to electrical and mechanical deterioration of components in the system and the constant reduced torque This leads to electrical and mechanical stress on the system during the transition Additionally this starting system does not offer protection against hazards that may develop during operation such as jam conditions and line faults including phase loss line voltage issues and motor deceleration control during the stop sequence to name only a few Replacing the wye delta starting system with an RVSS is a straightforward process In most cases locating the soft starter in the enclosure is simple as several contactors that are now unnecessary will be removed External overload devices may also be removed as the S811 has built in over load protection If so desired the contactors may be retained as an isolation contactor for the soft starter or used to switch power factor correction capacitors if installed in the system Figure 1 Wye Connection Start Figure 2 Delta Connection Run Figures 1 and 2 depict a basic configuration for a wye delta starting system An Isolation contactor controls con
3. t result in a successful motor start Please refer to the values of locked rotor amps LRA and locked rotor torque LRT in Example 1 Example 1 200 hp motor with 1327 LRA at 460V Locked Rotor Torque 957 lb ft Wye configuration 33 percent of full voltage LRA 435A gt 307 b ft torque Delta configuration 435A 102 lb ft torque insufficient to start motor Delta configuration 435A x 3 754A 307 b ft torque When converting a wye delta system to an RVSS the cables from the RVSS to the motor are doubled paralleled as the motor is at least a six lead motor Cable sizing is normally adequate to meet the demands of the delta configuration start Remember that while the delta starting current is higher the connections have doubled the conductors Ensure that the cables are of approximately equal length Verify that protection devices such as breakers and fuses are sized appropriately for the higher starting currents In some cases higher fuse and or breaker rating may be required Consult the soft starter product documentation for additional details in adjusting operating parameters Supporting documentation Reference Number MN03900001E 811 User Manual Additional Help In the event that additional help is needed please contact the Technical Resource Center at 1 877 ETN CARE Option 2 Sub Option 2 Eaton Is a registered trademark of Eaton Corporation All other trademarks are propert
4. t to approximate the same initial torque as would be developed with a wye delta system starting in the wye configuration However due to the rate of phase voltage increase during the start ramp time of the RVSS motor torque is also increas ing trom increased phase voltage and torque increases relative to Eaton Corporation Electrical Sector 1111 Superior Avenue Cleveland OH 44114 USA Eaton com 2012 Eaton Corporation All Rights Reserved Printed in USA Publication No APO3902009E Z12538 July 2012 ETN Powering Business Worldwide Application of the RVSS to replace Wye Delta motor starting the motor torque curve The net result is quicker motor acceleration and significantly reduced start ramp time when compared to the wye configuration timer setting In the event that this increased motor acceleration poses an issue for the application the accelera tion rate may be modified by the use of the current limit function of the RVSS Initial torque settings of higher values may be used to achieve the desired start ramp characteristics Start current Due to the difference of phase voltages when com paring wye and delta windings it is known that to achieve the same torque developed with a delta configuration as would be with a wye configuration the delta configuration current increases by a factor of three Attempts to limit delta configuration currents to similar values of wye configuration currents typically will no
5. tacts 1 2 and 3 the start or shorting contactor controls contacts 4 5 and 6 and a run contactor controls contacts 7 8 and 9 If the system Is a closed transition a transition contactor with inline resistors to control current inrush is also required not shown Application Notes AP03902009E Effective July 2012 When converting to a reduced voltage soft starter these contactors will be eliminated and removed from the enclosure The isolation contactor contacts 1 2 and 3 may be retained The run contactor that is removed during the conversion may also be retained and rewired as an external bypass contactor for emergency use not shown Two soft starter wiring configurations are possible with the six lead motor Line connected In Figure 3 leads are connected in pairs as shown The cables will be connected in parallel between the soft starter and the motor Ensure that these cables are of the same approximate length to avoid excessive current imbalance between the motor leads when the motor is wired in the delta configuration Inside the delta In Figure 4 this method as shown may allow utilizing a smaller soft starter for a given size motor when compared to being line connected 3 Phase L2 AC Line Voltage Figure 3 Line Connected Supply L1S L2S L3S Figure 4 Inside the Delta Connected Current and torque The reduced voltage soft starter RVSS initial torque parameter may be adjusted to 30 percen
6. y of their respective owners
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