Transformer Protection
Voltage relays can be applied to protect large transforme
rs from damage as a result of overexcitation.
The concern for transformer overvoltage may be minimized in many power system applications where
proper voltage control of the generating unit is provided. However, where a tap changing regulating
transformer is located between the generating source and the load, some form of voltage protection may
be required to supplement the tap changing control and to prevent equipment damage due to over, as
well as undervoltage resulting from a failure of the tap changing control. The BE1-27/59
Under/Overvoltage Relay is well suited for these applications.
Ground Fault Detection
In a three-phase, three-wire system, a single conducto
r may break or the insulation may deteriorate
resulting in a high resistance ground fault which may not be detected by the overcurrent relays. This
condition, however, may be sensed by an overvoltage relay connected to a grounded wye, broken delta
set of potential transformers (PT's) as illustrated in Figure 1-1 with this connection, and a sensitive relay
setting, an unbalanced voltage condition such as described above, can be quickly detected and isolated.
BE1-59
7
6
D2816-13
05-29-98
Figure 1-1. Ground Fault Detection
MODEL AND STYLE NUMBER
BE1-27, BE1-59, and BE1-27/59 electrical characteristics and operational features are defined by a
combination of letters and numbers that make up the style number. Model number BE1-27/59 designates
the relay as a Basler Electric Under/Overvoltage Protective Relay. The model number, together with the
style number, describes the options included in a specific device and appears on the front panel, draw-out
cradle, and inside the case assembly.
The style number identification chart for the BE1-27/59 relay is illustrated in Figure 1-2.
1-2 BE1-27/59 General Information 9170600990 Rev H
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