What is reverse power (motoring) of a generator
It is a condition when the alternator ( that is supposed to generate alternating current) draws power from the bus bar, which results in the alternator acting as a motor hence called reverse power or motoring of alternator.
Cause for motoring of generator
- It may occur when the prime mover is not having sufficient torque to keep the rotor running at the same frequency as the busbar grid.
- Stuck up fuel rack, irregular combustion.
- Closing the breaker when the incoming generator is rotating slower than running the generator (synchroscope running in an anticlockwise direction)
- A sudden drop in the shipload and improper load sharing
- Load sharing or excitation system if not functioning properly
The direction of alternator rotation when on reverse power
An alternator running on reverse power will continue to rotate in the same direction as the direction of torque on a motor is governed by Flemming left-hand rule
The direction of the force on a generator is governed by Flemming right-hand rule, in both these rules thumb shows the direction of torque hence the alternator running in reverse power will rotate in the same direction
The direction of the force on a generator is governed by Flemming right-hand rule, in both these rules thumb shows the direction of torque hence the alternator running in reverse power will rotate in the same direction
The electric risk of motoring
Electrically, the winding is not at risk of burning because the current due to reverse power is a fraction of the nominal current of the unit (which can draw large magnitudes of reactive current in some modes of operation).
Risks on the primer mover
Even if the prime mover trip due to mechanical faults like loss of lube oil pressure etc..... since the alternator is now rotating the prime mover it can result in catastrophic damages to the mechanical side of prime movers, such as the dry running of the main bearing
Safety
- To counter this problem a reverse power protection device is placed which releases or trip the breaker preventing motoring if reverse power occur
- A time delay of 5 seconds prevents power tripping due to surges at synchronizing
- reverse power setting is 2 to 6 % for turbine prime mover an 8 to 15% for diesel engine
To learn more on testing of reverse power trip click on the below link
I don't understand the 8-15% reverse power setting...what is that setting?
ReplyDeleteI believe alarm is set at 8 - 15 percent of the power output
DeleteThis is all done by the manufacturer and tested by the shipboard staff regularly
For example if the manufacture set the alarm at 8 percent and the genset is rated for 100kw then the alarm will be set at 8kw for a set time delay(5 seconds).
hello everyone
Deletethank you for this precious clarification.
i just wanted to ask if we have like 4 or 5 percent for more than 5 seconds on diesel generators is that a problem?
if the engine is working properly without any problems with oil pressure or coolant temperature
Best not to deviate from manufacturer manual and setting.
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How can we avoid motoring in Genset synchronizing?
ReplyDeletethe controllers must have protection methods to avoid damage but if you are asking how so it can be achieved by matching rhe rotation between the two gensets speed and angle.
DeleteOnce the PMS (Power Management System) detects motoring in generator, the reverse power relay in the circuit trips the breaker hence preventing that Genset from motoring.
DeleteThe genset should only be re-started only after troubleshooting and removing the faults.
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ReplyDeleteUnderstanding reverse power protection is crucial for ensuring the efficiency and safety of generators. This detailed explanation covers various scenarios, including protection against overspend and generator motoring, highlighting the importance of reverse power relays in preventing damage and optimizing performance. For advanced solutions like grid synchronization and seamless power switching, explore Force-V's Dexterous product. To learn more about Force-V and their innovative renewable energy solutions, visit their website.
ReplyDeleteUnderstanding reverse power protection is crucial for ensuring the efficiency and safety of generators. This detailed explanation covers various scenarios, including protection against overspend and generator motoring, highlighting the importance of reverse power relays in preventing damage and optimizing performance. For advanced solutions like grid synchronization and seamless power switching, explore Force-V's Dexterous product. To learn more about Force-V and their innovative renewable energy solutions, visit their website.
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