Как защитить трансформатор

What’s the most-important el-
ement of the Smart Grid? Most
North American electrical utilities
will testify that the grid will only be
as smart as the assets that are
providing it with power: that is the
transformer among other things.
Of course, the mainstream con-
versation happening about the
Smart Grid has very little to do with
these assets. Instead, most of the
discussion of the Smart Grid in
the United States centers on the
smart meters (internationally, most
utilities understand that smart me-
ters does not equal Smart Grid) as
the aging transformer fleet con-
tinues to operate and failure rates
increase.
This may be with good reason,
as educating the masses about
how the grid can work for them is
a crucial piece to making this tech-
nology a reality. But so is ensuring
that the grid’s infrastructure is ca-
pable of handling these «smarts».
Many things can go wrong be-
tween the generating station and
the end point i.e., the customer.
With that in mind, it’s fair to expect
condition-based monitoring to be-
come a bigger part of the Smart
Grid conversation because keep-
ing tabs on how assets such as
transformers are functioning is just
as important as understanding the

nuances of meters.

To that end, a recent small sampling of global electrical utilities in-
dicated that dissolved-gas analysis (DGA) is still considered very im-
portant when it comes to condition-based monitoring programs. This
is because DGA monitoring remains one of the most effective ways
to predict when transformers are about to experience problems. The
problem with this method, however, is that it doesn’t happen frequent-
ly enough. The same survey indicated that most respondents say they
sample oil used for DGA analysis twice a year at most and send these
samples to a laboratory for analysis.
And a lot can happen in between samples. Thirty percent of trans-
former failures are related to failures of load tap changers (LTCs).
Performing oil analysis is becoming more critical on LTCs, and many
times LTCs are only sampled annually. If LTCs are responsible for such
a high amount of transformer failures, one would think they deserve
online monitoring, or at least sample them quarterly.ins and outs of GDA monitoring
There are two types of DGA monitoring—manual and online. Logic
would say online monitoring should be more prevalent in this day and
age, given that online solutions are capable of providing more frequent
updates on how an asset is functioning. But several factors, most no-
tably cost, have prevented widespread adoption of online DGA moni-
tors. New cost effective advancements, however, are starting to make
online DGA monitors more widely attainable for transformers and
LTC fleets.
Online DGA monitoring is the most popular «online» instrumenta-
tion utilities put on their transformers and LTCs. This does not dimin-
ish the importance of manual laboratory samples but simply bridges
the gap between DGA analyses to capture an event as it evolves. The
rule of thumb is that once an online instrument shows indications of
a potential issue, you always reconfirm with a backup analysis. This
backup analysis is a manual DGA performed with a reputable laboratory.
BETTER DGA MONITORING
IN 22 STEPS
Regardless of the method, here are some general tips to help ensure
when DGA is performed, it is performed correctly with maximized ef-
fectiveness and reliability.preparation
1. CREATE A SIMPLE SAMPLING PLAN
This involves knowing all the fittings and tools related to the equip-
ment to be sampled. It’s also critical to ensure easy access to the sam-
pling point according to company regulations, and always be sure to
have a waste container to discard flushed oil. This also includes hav-
ing a schedule for when you are to perform samples on a regular predefined basis. Consideration should be given to abnormal events (such
as running a transformer for an extended period of time above its
nameplate rating). Or, after an extensive maintenance outage that in-
cluded a significant amount of work. These «trigger points» should be
well defined as well as what actions are to occur. Sample results should
also be readily available to those that need them.
2. PREPRINT THE DATA SHEET FOR SAMPLING
Preprint the data sheet for the equipment to be sampled, if known,
or to be filled on site. The necessary information includes 1) Equip-
ment type and manufacturer, 2) manufacturing date, 3) sampling
point, 4) date of sampling and 5) top-oil temperature.
Other pertinent information should be noted as well (if desired and
tracked), such as current load on the transformer, cooling configura-
tion and ambient temperature. You should also strive to sample at the
same time of day and season that differs greatly in various countries for
consistency if possible, thus removing another variable that may affect
the sample results.

 

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