CVE, CVE-1, CVE-2 and CVE-3 synchro-verifier relays are used to check the voltages on both sides of a breaker to see that they are approximately the same in magnitude and phase. These relays are not automatic synchronizers and should not be used as such.
The CVE type relays supervise the automatic or manual closing of a circuit breaker.
The CVE-1 has the CVE unit and is additionally equipped with line and bus voltage sensing, telephone type relays.
The CVE-2 relay is comprised of three telephone type relays and two over and under voltage toggle-type relays in addition to CVE unit and is used for selective initiation of reclosures.
The CVE-3 relay also has the CVE unit. A telephone relay is added for the purpose of sealing-in the CVE contacts once they have closed.