Table of Contents
Advertisement
Frequency Functions
Due to its various frequency functions, the device is very flexible. That makes it suitable for a wide range of
applications where frequency supervision is an important criterion.
In the Device Planning menu, the User can decide how to use each of the six frequency elements.
f[1] to f[6] can be assigned as:
81U – Underfrequency;
•
81O – Overfrequency;
•
81R – Rate of Change of Frequency (df/dt);
•
81UR – Underfrequency and Rate of Change of Frequency (df/dt);
•
81OR – Overfrequency and Rate of Change of Frequency (df/dt);
•
81UΔR – Underfrequency and DF/DT (absolute frequency change per definite time interval);
•
81OΔR – Overfrequency and DF/DT (absolute frequency change per definite time interval); and
•
78V – Vector Surge.
•
81U – Underfrequency
This protection element provides a pickup threshold and a tripping delay. If the frequency falls below the set pickup
threshold, an alarm will be issued instantaneously. If the frequency remains under the set pickup threshold until the
tripping delay has elapsed, a tripping command will be issued.
With this setting, the frequency element protects electrical generators, loads, or electrical operating equipment in
general against underfrequency.
81O – Overfrequency
This protection element provides a pickup threshold and a tripping delay. If the frequency exceeds the set pickup
threshold, an alarm will be issued instantaneously. If the frequency remains above the set pickup threshold until the
tripping delay has elapsed, a tripping command will be issued.
With this setting, the frequency element protects electrical generators, loads, or electrical operating equipment in
general against overfrequency.
Working Principle
The frequency element supervises the three phase voltages » VA« , » VB« and » VC« . If all of the three phase voltages
are below 15% Vn, the frequency calculation is blocked. According to the frequency supervision mode set in the
Device Planning (81U or 81O), the evaluated phase voltages are compared to the set pickup threshold for over- or
under-frequency. If in any of the phases, the frequency exceeds or falls below the set pickup threshold and if there are
no blocking commands for the frequency element, an alarm is issued instantaneously and the tripping delay timer is
started. When the frequency still exceeds or is below the set pickup threshold after the tripping delay timer has
elapsed, a tripping command will be issued.
EMR-4000
(Please refer to the block diagram on next page.)
www.eaton.com
IM02602009E
622
Advertisement
Table of Contents
