Reactor Protection - Siemens 7UT51 Instruction Manual

7UT51 v3
Figure 3.4 Parallel Transformers using Cross
3.2

Reactor Protection

The ground differential element of a model 7UT513
can protect a reactor in at least two different ways.
Figure 3.5 shows a reactor bank made up of three
single-phase reactors with CTs available at the
breaker and one CT available in the grounded neutral.
Because three ground-side CTs are not available on
the single-phase reactors, the 87 and 87HS elements
cannot be used. Instead, the overcurrent elements
(50,51) provide primary protection, with the 87N
element providing reactor ground-fault and turn-to-turn
protection with increased sensitivity. If the system
voltage is abnormally high, the reactors will draw
higher-than-rated current, so a thermal overload
element (49-1) can provide backup protection.
PRIM-2330C
-
Connected Overcurrent Backup Protection
Figure 3.5
Application Examples
Reactor Protection for Bank Comprised of
Single - Phase Units
3
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