Auto Sync vs Sync Check relay

[rockman7892]

Can someone please explain to me the difference between an Auto Sync relay and a Sync check relay in regards to a generator application? In looking at an SEL 700G relay it appears that the relay can provide both functions but I don't quote understand the difference between the two functions.

Does the auto synchronizer sense when the generator is in sync with the system that it is trying to sync with and control/close the respective breaker when synchronization is detected, while the Sync Check relay checks for synchronization between the generator and the source at all times and trips the respective breaker when this loss of synchronization is detected?

From what I've seen its a good idea to have these two functions located in separate relays in order to eliminate a single point of failure taking out both of these functions.

Does the Auto Synchronizer also control the speed of the generator or is the generator speed strictly controlled by the generator controller or governor control?

 

[davidbeach]

The auto synch drives the generator governor (frequency) and AVR (volts) into a synchronized match with the reference system. The synch check function verifies that that has in fact happened. While the 700G can do both, I wouldn't; let one of the pair do the auto synching and have the other one verify that everything really is where it should be prior to the close.

 

[crshears]

Expanding on what davidbeach said, auto-synch apparatus will needs include [a] a means of detecting the relative or differential phase rotation of the incoming source as compared to the running system [ is it fast or is it slow? ] so as to know whether to provide signals to the prime mover's governor to either raise or lower its speed setting in way of reducing the slip frequency to an acceptable amount, voltage matching circuitry, and [c] synchronizing breaker closing circuitry to close the breaker when the incoming machine and the running system are in phase plus or minus so many degrees, depending on the nature of the machine being synchronized.

Straight-up synchro-check relays don't have all that.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Hoxton]

Also in high voltage applications, where the synchronizing breaker is remote from the generator control panel, the check synchronizer relay should be in the switchgear, and the auto synchronizer should be in the control panel.

Benefit is that the control signals are kept within the control panel, and the check synchronizer operates both as a check on the auto synchronizer and on inadvertent wiring changes bypassing the auto synchronizer. Very expensive when it happens.

In my humble view, an auto synchronizer is not a relay, it is a control device.

 

[crshears]

I agree, Hoxton, which is why I chose to specifically use the terminology "auto-synch apparatus"; casts a wider net.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Hoxton]

Ah! So you did. Good way of differentiating.