The 2T105 time delay relay is particularly suitable for use in protection & control schemes where precision time delays are required.
A typical use is for providing a definite time delay in circuit breaker failure protection. For example: The transformer multi-trip relays energize the 2T105 timer & if the circuit breaker (CB) fails to clear the fault within the pre-set (0.6s) the timer times out & operates a multi-trip relay. This in turn trips all CB’s on the section of the busbar connected to the CB, which has failed to trip.
Replacement of induction disc timing elements with solid-state relays can result in a loss of grading & reduced functionality due to the different reset characteristics. For example, the inherent slow reset time of induction disc relays provide an advantage in sensitive overcurrent schemes where pecking faults could go undetected due to the timer being instantaneously reset each time the current momentarily falls bellow the start setting. The 2T105 may be specified with a number of reset functions to avoid this problem & to suit specific protection applications.
Alstom: MVTT14, MVTT15
Reyrolle: DDB1, DDB5, DDB7, DDB11, DDB12