SEL-487E Data Sheet Schweitzer Engineering Laboratories, Inc.
22
Transformer Thermal Monitoring
Transformer thermal monitoring for mineral-oil immersed
transformers is a standard feature in the SEL-487E. Spec-
ify the SEL-487E to provide this capability for monitor-
ing and protection of a single three-phase transformer, as
well as for monitoring and protection of three independent
single-phase units. Use the thermal element to activate a
control action or issue a warning or alarm when your trans-
former overheats or is in danger of excessive insulation
aging or loss of life.
The thermal element operates in one of three modes, depend-
ing upon the presence or lack of measured temperature
inputs: 1) measured ambient and top-oil temperature inputs,
2) measured ambient temperature only, and 3) no mea-
sured temperature inputs. If the relay receives measured
ambient and top-oil temperatures, the thermal element
calculates hot-spot temperature. When the relay receives
a measurement of ambient temperature without top-oil
temperature, the thermal element calculates the top-oil
temperature and hot-spot temperature. In the absence of
any measured ambient or top-oil temperatures, the ther-
mal element uses a default ambient temperature setting
that you select and calculates the top-oil and hot-spot tem-
peratures. The relay uses hot-spot temperature as a basis
for calculating the insulation aging acceleration factor
(FAA) and loss-of-life quantities. Use the thermal element
to indicate alarm conditions and/or activate control actions
when one or more of the following exceed settable limits:
➤ Top-oil temperature
➤ Winding hot-spot temperature
➤ Insulation FAA
➤ Daily loss-of-life
➤ Total loss-of-life
Generate a thermal monitor report that indicates the pres-
ent thermal status of the transformer. Historical thermal
event reports and profile data are stored in the relay in
hourly format for the previous 24 hours and in daily for-
mat for the previous 31 days.
Through-Fault Event Monitor
A through fault is an overcurrent event external to the
differential protection zone. Though a through fault is
not an in-zone event, the currents required to feed this
external fault can cause great stress on the apparatus inside
the differential protection zone. Through-fault currents
can cause transformer winding displacement leading to
mechanical damage and increased transformer thermal
wear because of mechanical stress of insulation compo-
nents in the transformer. The SEL-487E through-fault
event monitor gathers current level, duration, and
date/time for each through fault. The monitor also calcu-
lates a I
2
t and cumulatively stores these data per phase.
The SEL-487E through-fault report also provides percent
of total through-fault accumulated according to the IEEE
Guide for Liquid-Immersed Transformer Through-Fault-
Current Duration, IEEE C57.109-1993. Use through-
fault event data to schedule proactive transformer bank
maintenance and help justify through-fault mitigation
efforts. Apply the accumulated I
2
t alarm capability of the
relay to indicate excess through-fault current over time.
Figure 26 Typical One-Line Diagram for Collecting Transformer Temperature Data
Top-Oil Temperature (RTD)
Ambient
Temperature
RTD
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