Application - ABB RELION 620 Series Technical Manual

Section 4
Protection functions
4.2.3.5
284
Level detector
The measured ground voltage is compared to the set Pickup value. If the value exceeds the
set Pickup value, the level detector sends an enable signal to the timer.
Timer
Once activated, the timer activates the PICKUP output. The time characteristic is
according to DT. When the trip timer has reached the value set by Trip delay time, the
TRIP output is activated. If the fault disappears before the module trips, the reset timer is
activated. If the reset timer reaches the value set by Reset delay time, the trip timer resets
and the PICKUP output is deactivated.
The timer calculates the pickup duration value PICKUP_DUR, which indicates the ratio
of the pickup situation and the set trip time. The value is available in the monitored data
view.
Blocking logic
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting in 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
trip timer is frozen to the prevailing value, but the TRIP output is not deactivated when
blocking is activated. 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

59G is designed to be used for ground-fault protection in isolated neutral, resistance
grounded or reactance grounded systems. In compensated networks, the pickup of the
function can be used to control the switching device of the neutral resistor. The function
can also be used for the back-up protection of feeders for busbar protection when a more
dedicated busbar protection would not be justified.
In compensated and isolated neutral systems, the system neutral voltage, that is, the
ground voltage, increases in case of any fault connected to ground. Depending on the type
of the fault and the fault resistance, the ground voltage reaches different values. The
highest ground voltage, equal to the phase-to-ground voltage, is achieved for a single-
phase ground fault. The ground voltage increases approximately the same amount in the
whole system and does not provide any guidance in finding the faulty component.
1MAC504801-IB E
620 series ANSI
Technical Manual