Basler Electric BE1-87T - Manual (Page 13)

9171300990 Rev V BE1-87T General Information 1-1
SECTION 1 • GENERAL INFORMATION
Introduction
These instructions provide information concerning the operation and installation of BE1-87T Transformer
Differential Relays. To accomplish this, the following is provided:
• Specifications
• Functional characteristics
• Mounting information
• Setting procedures and examples
WARNING!
To avoid personal injury or equipment damage, only qualified personnel should
perform the procedures presented in these instructions.
These instructions may be used in place of all earlier editions. For change information, see Section 8.
Description
BE1-87T Transformer Differential Relays provide primary protection for power transformers and are
available in either Single-Phase or Three-Phase configurations. The solid-state BE1-87T compares the
currents entering and leaving the protected transformer. If a fault is detected, the relay initiates a trip
signal to isolate the power transformer. This limits damage to the transformer and minimizes the impact on
the power system.
BE1-87T relays use three types of restraint:
NOTE FOR USERS OF SENSING INPUT TYPE F RELAYS
Users of BE1-87T relays with Sensing Input Type F (three-phases three inputs
per phase) will find Difference Data in Section 6 of this manual that describes
features specific to these relays. The three-phase, three inputs per phase
design, previously available as Sensing Input Type F, has been modified and
is now available as Sensing Input Type G. Due to differences in components
and output terminal connections, Type G relays are not compatible with earlier
versions of the BE1-87T with Sensing Input Type F. There are also differences
in the output connections as described in Section 6, Difference Data.
• Percentage of through-current
• Second harmonic
• Fifth harmonic
Selectivity in differential relaying is based on the ability to distinguish between internal and external faults.
This is achieved by comparing the currents into and out of a power transformer. Comparing these currents
often requires more than two inputs. For example:
• Power transformers may have a significant portion (greater than 10%) of the current flowing in a
third or tertiary winding.
• Power transformers can have multiple breakers for a given winding (e.g., ring bus or breaker-and-
a-half bus).
BE1-87T relays are available with up to five restraint inputs for the single-phase unit and up to three
restraint inputs per phase for the three-phase unit.