CYG PRS-7367 - Application Scope; Settings; Under Voltage Load Shedding Protection 27; Overview

Protection Functions
94 PRS-7367
3.14.3 59N Application Scope
The 59N are used to accomplish a selective protection against the voltage and current unbalance
for each machine separately. The protection can be used to monitor the voltage unbalance of the
busbar.
The 59N can be applied as a backup protection or it can be used as an alarm. The latter can be
applied when it is not required to trip loads tolerating voltage unbalance better than the rotating
machines.
If there is a considerable degree of voltage unbalance in the network, the rotating machines
should not be connected to the network at all. This logic can be implemented by inhibiting the
closure of the circuit breaker if the 59N operation has started. This scheme also prevents
connecting the machine to the network if the phase sequence of the network is not correct.
3.14.4 59N Settings
Table 3.14-3 59N settings
No.
Name
Values(Range)
Unit
Step
Default
Description
1
59N_Vol_Str
0.00 -100.00
V
0.01
3
Negative sequence overvoltage start value
2
59N_Op_T
0.04 - 120.00
s
0.01
0.04
Operate delay time
3
59N_Ena
0-1
-
-
1
Operation Enable/Disable
3.15 Under Voltage Load Shedding Protection 27
3.15.1 27 Overview
The three-phase under voltage protection function is used to disconnect from the network devices,
for example electric motors, which are damaged when subjected to service under low voltage
conditions. It includes a settable value for the detection of under voltage either in a single phase,
two phases or three phases.