Bus Coupler Scheme in 6.6 KV Breakers

I only can explain what happens in bus transfer for induction motors. I hope it was helpful. Induction motors are capable of developing transient current and torque considerably when they are subjected to momentary loss of power and reclosing on the same power supply. This can occur either during a bus transfer or during a fault-induced interruption. The magnitude of this transient torque could cause considerable damage to the motor or driven equipment. Slow transfer or reclosing can be used for motor protection. A remanent under voltage protection ANSI 27R on busbar (setting <25%Un) will gurantee the voltage drops below a certain value and we don't have harmful reacceleration at the moment of reclosing or bus transfer.

You can find more in the following source by simple google searching:

Cahier Technique Schneider Electric Co.

Automatic transfering of power supplies in HV and LV networks.

ECT161, G. Thomasset

1. "Slow change over" and "fast change over" imply an open transition (the contacts from the normal source open before the contacts from the alternate source close). An open transition always results in interruption of service to the load. Slow and fast refer to the time after loss of the normal source before transfer occurs. Depending on the nature of the load, you may need to wait until motors spin down (see post #1 by Abbas) , or you may need rapid restoration of power (hospitals, for example).
2. "Live bus" and "dead bus" synchronization imply a closed transition. That is, the contacts from the alternate source close before the contacts from the normal source open. If both sources are energized, closed transition can have disastrous consequences unless the phase rotation, frequency and voltage of the sources are matched.
1. Dead bus synchronization means that the normal source is deenergized before the alternate source connects.
2. Live bus synchronization means that the two sources will be matched in voltage, frequency and phase rotation, then connected together to allow transfer of the load from one source to the other without loss of power to the load. This requires a sync. check relay to verify the match.
3. The NO VOLT relay is used in both 1 & 2 above.
1. In an open transition, the NO VOLT relay initiates the transfer when it senses a loss of voltage on the normal source.
2. In a closed transition, the NO VOLT relay will bypass the sync. check relay to allow a dead bus transfer upon loss of the normal source. If the relay senses voltage, it will block the alternate source contact closure unless the sync. check relay verifies matching voltage and frequency.

Hi..

Can anyone advise me how to do "syn-check" and what equipment is necessary for this job. Many Thanks.

Hello pwr2thepeople:

Probably a very delayed response to your post !

An open transition need not always result in interruption of service to the load. If the bus is supported for instance by the back emf of the motors on it, then there would be no real interruption in the supported process, although there would be a dead bus time during which the bus will spin-down. A supervised fast transfer can do this job quite effectively and we use it for power plants and process industries all the time. Do visit us at www.aartechsolonics.com or email me at amitraje@aartechsolonics.com and I would be happy to share more info on this.

Amit.