Application - ABB 615 series Technical Manual

1MAC059074-MB A
4.8.1.5
615 series ANSI
Technical Manual
The Timer calculates the PICKUP_DUR value which indicates the percentage of the time
elapsed since the activation of the PICKUP output with respect to Trip delay time. The
value is available in the Monitored data.
The DISABLE input can be used to coordinate the correct operation during the generator
start-up situation. By activating the DISABLE signal, both the PICKUP and TRIP
outputs are blocked. Once the DISABLE signal is deactivated, the Timer remains blocked
for an additional time duration as set through the setting Disable time.
Blocking logic
There are three operation modes in the blocking functionality. The operation modes are
controlled by the BLOCK input and the global setting Configuration/System/Blocking
mode which selects the blocking mode. The BLOCK input can be controlled by a binary
input, a horizontal communication input or an internal signal of the protection relay's
program. The influence of the BLOCK signal activation is preselected with the global
setting Blocking mode.
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode, the
operation timer is frozen to the prevailing value. In the "Block all" mode, the whole
function is blocked and the timers are reset. In the "Block TRIP output" mode, the function
operates normally but the TRIP output is not activated.

Application

The task of a generator in a power plant is to convert mechanical energy into electrical
energy. Sometimes the mechanical power from the prime mover may decrease so much
that it does not cover the internal losses. The task of an underpower protection is to protect
the generator from very low power output conditions.
Steam turbines become easily overheated if the steam flow becomes too low or if the
steam ceases to flow through the turbine. Hydro turbine of the Kaplan type may be
damaged due to the fact that the turbine blade surfs on the water and sets up axial pressure
on the bearing. Diesel engines may be damaged due to insufficient lubrication.
If the generator size is very large, it is uneconomical to continue running it with low
generated power. In the reverse power condition, large generators draw a considerable
amount of power from the rest of the system to feed their internal losses. Hence, it is
desirable to disconnect the generator in such situations.
In case of the parallel-connected generators, for example, the load of one generator may
be so low that it is better to disconnect it and let the remaining generators feed the network.
Where a low value of power setting is required, for example less than 2%,
the correction parameters should be used to compensate for the measuring
Section 4
Protection functions
721