Table of Contents
Advertisement
CGCM-DLR Unit Operation
Chapter 3
Three OEL current levels, high, medium, and low are defined for online
operation as shown in
Figure
33. The high and medium current levels can be
maintained only for time periods you define. The generator can operate
continuously at or below the low OEL current level.
Figure 33 - Online Over-excitation Limiting
High
Current
Level
Medium
0.0...30 A dc
Current
High
Medium
Level
Low
Current
Current
CONTINUOUS
0.0... 20 A dc
Current
Time
Time
Level
0...120 seconds
0...10 seconds
0.0...15 A dc
TIME IN SECONDS
The CGCM-DLR unit also uses two counters, the reset counter and the time
limit counter. The counters are used to prevent excessive heating of the exciter
field that can be a result of repeated over-excitation. The time limit counter
monitors the duration of an over-excitation condition. The reset counter counts
backward from either the high OEL time setting or the sum of the high and
medium OEL times, depending on the value of the time limit counter.
If, during an OEL cycle, excitation current returns below the low current value,
the reset counter begins counting backwards from its present value. If it reaches
zero, the time limit counter is reset to zero and a new OEL cycle can then occur.
If the reset counter does not reach zero before the excitation current rises above
the low current value, the time limit counter begins counting where it stopped
when the excitation current last fell below the low current value. If the time limit
counter is greater than the programmed high OEL time, the excitation current is
limited to the medium current value. This limit prevents repeated cycling of the
exciter field at its highest possible current value.
When the excitation current exceeds the OEL limit, the OEL alarm tag
OEL_Active = 1. In FCR mode, the OEL limiting is not active although the tag
is set. This tag is in the Scheduled Read table. The OEL function meets
ANSI/IEEE C50.13.
Rockwell Automation Publication 1407-UM002B-EN-P - February 2019
57
Advertisement
Table of Contents
