90% of the total break of the motors area unit in the main because of overloading caused by unbalanced voltage conditions or section failure. This fault remains unseen by standard bimetallic overload relays and wishes a negative sequence element of voltage or current sensing single phasing preventer. They trip the motor starter if it goes on the far side the set level of voltage or current.
GELCO current and voltage sensing SPP offers protection up to motor terminals and does not allow
conditions. The negative sequence current sensing is the best principle for single phasing protection.
Components Parts needed
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- Single Phasing: If anyone phase is removed, the unit will trip the motor
- Voltage sensing SPP: It gives protection at sensing points only. It senses negative sequence component of the voltage and protects the
motor against phase failure, unbalanced supply and reverse phase sequence of voltage.
- Current sensing SPP: It gives protection up to motor terminals. It senses negative sequence component of current and protects the motor against phase failure, reverses phase sequence and unbalanced supply of the current (> 50% of rated maximum current)
- Reverse phasing: When phase sequence is reversed, the motor rotates in reverse direction. This condition is not desirable to run the motor, so the unit will trip the motor. Unbalanced supply
- current and voltage:
The unit gives protection against unbalance voltage or current. If voltage unbalance is higher then 45+/- 5V, unit trips. If the current in any tow phase differs by 50% (10 A) of rated maximum current (20 A in case of 8-20 A unit) it trips motor.
- Low/High voltage cut-off: It senses supply voltage and protects the motor against too high or too low voltage conditions.
- Overload: It senses average current going to the motor and protects the motor against overload (overcurrent). Overload setting is to be set at 120% of the full load current.
- Dry run: When motor operates without load (i.e. water pump without water), the condition is considered as dry-run. Prodless dry-run setting is to be set depending upon no-load urrent of the motor else it may cause the missed tripping of the motor.
Phase preventer are used in industries are having following advantages:-
- They use to protect the motors and electrical systems in case of one/ two-phase failure in a three-phase power system i.e. they can protect the system from single phasing.
- They protect the system in case phase sequence gets changed and phase sequence protects the system so that motors could not start operating in reverse direction.
- They also protect the system when the voltage level falls below a particular level. Phase preventer is also named as single phase preventer.
Installation of Phase preventer in electrical systems
Terminals for Three phase supply
- Terminals for auxiliary supply
- NO/ NC contact for interlocking
Connections for the relay as below:-
There are few additional settings provided on Phase preventer are:-
- Under voltage setting: Do the Under Voltage setting to minimum
- Under voltage delay settings: Keep the Under Voltage Delay to minimum
- Unbalanced Voltage Settings: Keep percentage Unbalanced to maximum
Under Voltage Trip purpose setting
To protect instrumentality from beneath voltage it’s continuously suggested to stay beneath voltage setting to as minimum as attainable. If you don’t understand the settings then change the under-voltage setting knob till LED starts glowing red. currently Slowly change the knob to set in such some way that relay starts glowing inexperienced. currently, at that setting, it’ll be ensured that voltages are beneath acceptable limits.
Under Voltage Delay Settings
The delay set during this setting is that the most time that beneath voltage will exist in the system before inflicting tripping of motor or machine. Settings may be tired such some way that if the setting is completed too low then it should cause nativity tripping within the system. If the setting is completed too high then it should cause injury to motor or machine and purpose of installation to get defeated.
Voltage Unbalance setting
Voltage unbalance is another setting provided on the relay. In any system, most allowable unbalanced voltage isn’t specified. however it usually acceptable to the level of (+-) five-hitter relying upon allowable limits specified on motor or machine terminal plate.
In each system, there’ll not be dead balanced voltage in the system. therefore Unbalanced voltage setting to be done consequently, too low settings can cause unwanted interruptions and too high settings can cause injury to the motor or machine.
Another way of doing the setting is to 1st change the knob for unbalanced voltage setting till relay starts glowing red, afterward currently slowly change the knob in such some way that LED starts glowing inexperienced.
As per NEMA wear Unbalanced Voltage= (Maximum Deviation from Average voltage/ Average Voltage)X one hundred
Where average voltage= (L1+L2+L3)/100
After doing all settings relay LED was glowing inexperienced.